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Sunday, June 9, 2019

Quality Issues In Modern Portable Radios

My luck with buying modern portables and pocket radios has not been the best. They often have problems right out of the box or develop them within months or the first year of operation. By modern portables, I'm talking about the last 20 years or so, at least since the year 2000.

In the narrative below are $905 dollars of radios I have bought in the last ten years and the problems I have had with them. This points to continued quality control issues and poor materials in today's cheap (and not so cheap) consumer radios coming out of Asia.

What's a radio nut to do? I doubt things are going to change any time soon. You either put up with it or leave the hobby.

MY EXPERIENCES

Kaito KA1103 $80

After a year an occasional processor glitch would cause tuning to become erratic, skipping every other channel. The only fix was pulling the batteries and letting the radio sit overnight. Reset did not cure problem.

Radio was also highly sensitive to static. Wipe your hand the wrong way across the display face and the processor would lock up.

Eton E1 $400

At about the one year point the radio and display would go dead intermittently due to apparent processor problem. Problem remained intermittent and was never resolved.

Rubberized coating got sticky and attracted grime after about a year. I used alcohol to remove the rubberized coating but the plastic underneath didn't fare well in some areas, bleaching the grey color out.

Another ding for this radio was the poor quality display for such an expensive radio.

Tecsun PL-380 $45

After a year many of the Tecsun's notoriously hard-to-press buttons started to fail to make contact making it impossible to set frequency or control radio settings. Some buttons now are unusable.

Mechanical tuning encoder is sub-par and cheap. When tuning slowly in one direction, frequency will jump intermittently to a channel in opposite direction.

Eton Traveler 3 $45

The weak orange-on-black display is unreadable in outside daylight. Overall contrast has gotten even worse over time.

Mechanical tuning encoder is sub-par and cheap. When tuning slowly in one direction, frequency will jump intermittently to a channel in opposite direction. Again. The problem is is particularly bad on this radio.

CCrane Skywave $80

Mechanical tuning encoder is sub-par and cheap. When tuning slowly in one direction, frequency will jump intermittently to a channel in opposite direction. Again.

Sangean ATS-909X $205

AGC problems started after about a month. Radio eventually went dead at two months. Sent in to Sangean for repair. Two way shipping costs were $26. Radio now works great. Good job Sangean. I was sweating this, as the 909X is a particularly expensive portable.

Panasonic RF-562DD $50

Tuning glitch occasionally occurs at a certain spot on the dial where the radio suddenly goes dead. It seemed to be a misplaced litz wire contacting one of the I.F. cans. After moving the wire the problem disappeared, I thought. It has since re-ocurred occasionally. Maybe a battery contact issue caused by flexing of the case by the tight dial mechanism? Or a bad leaf in the tuning capacitor? Still unknown. Luckily it's only very intermittent.

SUMMARY

Manufacturers: WAKE UP! Use better materials. Up your quality control game. Charge a little more if you have to. Sell me a radio that will work a year from purchase.

Will I keep buying Asian radios? Probably.

If you feel like adding your experiences to the comments section, please do.

Monday, March 25, 2019

The DXer's Light Source

Not a radio but something you might need if you DX at night. The Thrunite Ti3 V2 Keychain Flashlight.

I do a lot of my DXing in the wee hours of the night. With the warm weather of Arizona year-round, most of that is done outside too. Many of the modern digital portable radios have dial lights, but even these don't have lighted buttons. The older portable radios didn't generally have dial lights at all. The nighttime DXer needs a way to illuminate their radio for tuning and settings changes.

Bulky flashlights are out. Who needs 'em. They take up too much room and are too heavy. Penlights were traditionally cheap and fell apart quickly and didn't give much light in any event. And the bulbs constantly failed. Maglites had that weird little bulb that you could never find.

About a year ago I came across a review touting the Thrunite Ti3 V2 Keychain Flashlight. It's tiny and smaller than the palm of your hand. It's also LED, so no bulb to burn out. It takes a single AAA battery. It has three light intensities. And it will light up your backyard on the highest setting. The lower two settings are perfect for radio work in the dark. I bought one.

This guy has a great review of this unit on his backpacking site: backpackinglight.com

There is no cheap Harbor Freight click switch to fail on this light. It works by rotating the barrel to switch the light on. Twist once - dim. Twist twice - medium intensity. Twist three times - high intensity. And a secret setting not documented - twist six times in quick succession and the light flashes on and off in a strobe fashion.

This is the coolest, best penlight I've ever owned, so much so that I've since bought several for Christmas and birthday gifts. It is rock solid machined aluminum and built like a tank. It's priced right at about $14. You will love it and use it daily if you are a nighttime DXer sitting in the dark.

You can see it on Amazon right here:

See it on Amazon

I don't normally push products on this site, but I can't help it on this one. It's the perfect item for the nighttime DXer.







Friday, March 15, 2019

Review Of The Panasonic RF-562DD Receiver

Partly based on Jay Allen's positive review on his Radio Jay Allen web site, and also because it's analog and not DSP-based, I ordered this radio. One of my favorite older radios I no longer have was the Panasonic RF-565, similar in size. It was an good performer. Additionally, the RF-562DD has that sharp retro look from the early 1960s. It's reputed to be pretty hot. Let's see how it stacks up.

This a 3-band radio - MW, FM, and shortwave. The Panasonic RF-562DD claims to be the "new" RF-562D. I can find no obvious differences between it and the RF-562D. It could possibly be engineering changes. The radio seems to be manufactured for a foreign audience, that is, foreign to the western hemisphere.

The radio was purchased from Amazon. Price $48.99. If you order one, be sure to have them repackage it in a second box. The radio itself is packaged in a bare-bones shirt-cardboard type box as shown in the picture below. I know of one gentleman who ordered it and it was shipped in this box. He was surprised it survived the trip. Secondly, you don't want the general public knowing what's inside your shipment.

RF-562DD What's in the box - showing radio in leather case

I'm not sure when this radio was introduced. I've seen references to it as early as 2011. The radio is an analog design, and uses a monolithic CD2003GP IC chip for virtually all superhet stages, similar to the earlier Sony radios like the SRF-59 and ICF-S10MK2. The CD2003GP is an excellent single chip AM/FM radio requiring very few external components. The IC has all the building blocks required for a desirable AM/FM receiver.

QUALITY AND ERGONOMICS

The large, side-to-side slide rule dial extending across the top of the radio only tunes 530 - 1605 KHz on the mediumwave band, so North American buyers beware. I was able to get to 1660 KHz on my unit. The face has a sort of a magnifier bar over it to enlarge the frequency readout, a nice touch. It also has a retro "Log" scale, 0-10, another nice touch. Lacking is a dial light. The FM band covers 88 - 108 MHz. The single shortwave band covers 4.75 - 18 MHz.

The radio is bare bones, black and silver, and all plastic. It's size is 210 x 120 x 65 mm (8.25 in x 4.75 in x 2 in). Panasonic has included a nice faux leather case which fits snugly to the radio. It reminds you of the first transistor radios of the 1950s and 1960s which all came with leather cases allowing their controls to be accessed through cutouts in the cases.

The external antenna is a single telescoping whip at 32 inches long. It does not swivel. The whip is used for FM and shortwave reception.

The radio takes two "D" cell batteries and they will last nearly forever, especially if the radio is used with earphones. Panasonic claims upwards of 280 hours in AM mode. It does not come with an AC-mains power source. You can supply your own if you have a 3.6 VDC wall wart @ 300 ma, positive center pin. Also supplied is a vinyl carrying strap which can be affixed to the top of the radio. There are no other accessories besides the case and carrying strap. There is no manual, though with such a simple radio as this you surely don't need one.

The front-facing speaker is 8 cm (3.15 in) in size. Power output is 800 mw, more than adequate for room-filling volume. Only two controls protrude through the case on the front - a tuning dial and a switched volume control which also powers the radio on. At the back is a 3-position slide switch which selects the band. On the right side of the radio are the 3.6 VDC input jack and a monaural mini earphone connector. If you use stereo earphones or earbuds, you will need to purchase a monaural to stereo adapter. Radio Shack, oh how we miss you.

I will register two dings at the outset, one for the lack of dial light, and one for the monaural earphone jack, even though FM does not receive in stereo. Virtually all earphone and earbuds today are stereo and have stereo connectors. It would have been a simple matter to use a stereo jack and wire the channels in parallel to avoid the use of an adapter. The lack of dial light requires you to carry a small penlight with you if the radio is used in the dark.

Primarily I'm a mediumwave DXer, so we will cover mediumwave observations with this radio in this article. A few comments on its FM and shortwave capabilities are at the end of the article.

Panasonic RF-562DD - sans leather case

SENSITIVITY

The radio comes with a nice 140 mm (5.5 inch) ferrite rod antenna for mediumwave. This is a superhetrodyne, so there are a couple of coil windings on the ferrite. AM I.F. frequency is 455 KHz. FM I.F. frequency is 10.7 MHz. Sensitivity of the RF-562DD is nothing short of amazing for its size and mediocre build quality. I've done both skywave and daytime sensitivity tests from western Arizona, comparing signal strengths with various radios I own. Using a 5-star ranking system, this is where I'd place it among my selected receivers.

Sensitivity Breakdown

Panasonic RF-2200    5.0 *****
CCRadio EP Pro       4.5 **** 1/2
Panasonic RF-562DD   4.0 ****
Sangean ATS-909X     3.5 *** 1/2
Tecsun PL-880        3.0 ***
Tecsun PL-600        3.0 ***
Sony ICF-S10MK2      2.5 ** 1/2
Sony SRF-59          2.0 **

Despite reports of low sensitivity of the Sangean ATS-909X, mine was hot right out of the box, and was my best performer until the Panasonic RF-2200 and CCRadio EP Pro were acquired. Now the RF-562DD bests the '909X by just a little.

RF-562DD circuit board showing ferrite antenna

NULLING ABILITY

The RF-562DD has good nulling ability, better than many. Nulls are sharp and well defined. Very helpful for skywave DXing.

A difficult station to receive here at night is Phoenix's KFYI-550, using 1 KW at a distance of 130 miles. The groundwave signal is weak and of course the skywave at this distance is almost non-existent. Other low-level marginal signals, notably Colorado's low power nighttime KRAI-550 at only 500 watts best it. I sometimes don't even hear KFYI on the CCRadio EP Pro. I can hear KFYI with the RF-562DD, albeit weakly. I believe the difference here is the better nulling ability. I'm able to bring down KRAI-550 at Craig, Colorado just enough for Phoenix to surface. It is equal to or slightly better than the EP Pro in its nulling ability and that makes all the difference.

Nulling Breakdown

Panasonic RF-2200    5.0 *****
Panasonic RF-562DD   4.0 ****
CCRadio EP Pro       3.5 *** 1/2
Tecsun PL-600        3.0 ***
Tecsun PL-880        3.0 ***
Sangean ATS-909X     3.0 ***
Sony SRF-59          2.5 ** 1/2
Sony ICF-S10MK2      2.0 **

SELECTIVITY

Slightly above average. Better than the Sony ultralights mentioned, but not as good as the bigger portables. The radio's extreme sensitivity appears to be about maxed out for this chip, close to the overload point. I have coupled the radio to an 18 inch passive loop and it couples extremely well. If coupled too closely to this loop the RF-562DD can be easily overloaded by nighttime skywave signals. This is not all bad in the case of this radio. Loose coupling works best, and since it responds well at various coupling distances it is often better than the DSP units which are notoriously bad-couplers.

Selectivity Breakdown

Panasonic RF-2200    4.5 **** 1/2 (2 bandwidths)
Sangean ATS-909X     4.0 ****     (2 x I.F. DSP filtering)
CCRadio EP Pro       3.5 *** 1/2  (2 DSP filters)
Tecsun PL-880        3.5 *** 1/2  (4 DSP filters, surprisingly low)
Tecsun PL-600        3.5 *** 1/2  (2 bandwidths)
Panasonic RF-562DD   3.0 ***      (1 bandwidth)
Sony SRF-59          2.5 ** 1/2   (1 bandwidth)
Sony ICF-S10MK2      1.5 * 1/2    (1 bandwidth)

TUNING

Tuning is rather sharp and requires a deft touch, particularly above 1000 KHz. The dial has a bit of tightness to it, possibly because it's new, and isn't silky smooth like the analog dial of the CCRadio EP Pro. There's a slight amount of backlash but that's easily gotten used to, and expected. It's a joy to tune through a signal's peak again with the analog tuning. Tuning is easier below 1000 KHz as the stations are more well separated. Remember that analog tuning tunes in a roughly logarithmic scale, wider at the lower end and scrunching the band closer together at the higher end. This makes stations quite close together above 1000 KHz. In that area it takes a finer touch with this radio, and is a bit challenging with the stiff dial.

Dial accuracy is fairly accurate on this radio, better than the CCRadio EP Pro, but as with most analogs (the RF-2200 is certainly an exception here!) it can be difficult to know exactly to which channel you are tuned to. Having a digital spotter radio nearby can be a big help, particularly in the daytime with fewer signals and bigger gaps between stations. At night, if you DX consistently like I do, you get to know the band almost like a fingerprint.

My particular unit had an intermittent tuning glitch at the lower end of the dial where the radio suddenly went dead of signals at about 600 KHz. Tapping the front of the radio or the tuning knob fixed it. It wasn't a power issue because I could still hear low level hiss through the speaker or earphones. I initially suspected a bad tuning capacitor or broken circuit board path. After opening the case, it turned out to be a misplaced litz wire contacting one of the I.F. cans. After moving the wire the problem disappeared. This points to continued quality control issues in today's cheap (and not so cheap) consumer radios.

AGC

By my taste, this radio has great AGC characteristics, those being very fast attack and fast decay. I believe these are the best for DXing. They can be tiring to the ear over long listening periods, however, for weak signal work you need AGC which responds and relaxes quickly, revealing very weak background signals, buffeting, echo, and subtle but quick variations in strength and quality. Just one man's opinion.

Old timers will remember the receivers of many years ago having a switchable AGC system - slow, medium, fast, and off. The DXer often switched the AGC off and used the RF gain control to control signal strength. With the AGC off you heard everything, even extremely weak, on-channel signals mixed with the stronger ones. Fast AGC is the next best thing to the "off" mode. The RF-562DD has excellent fast AGC. Weak signals are apparent under very strong ones.

AUDIO

If you love treble you will love this radio. Many may find the audio rather harsh and tiring. I do, and I'm more tolerant than most. Yet the voice intelligibility is good - no mushy or muffled audio here like found in some radios, notably some Sonys (ICF-2010 can be this way) and the Sangean ATS-909X on the narrow bandwidth setting. I will agree that the audio section could use just a little more bass. I've noticed some occasional (but minimal) audio distortion on some signals, almost as if the audio section is starting to overload. This is usually straightened out by a tweak of the tuning dial. It is not RF overload.

SIGNAL SPURS AND IMAGES

I did a quick check and did not find any blatant signal spurs. No bleed-through images of mediumwave stations were detected on the shortwave bands. That's a good sign that the selectivity is adequate.

NOISE

The RF-562DD itself has a low noise floor which is good for DX and weak signal work. I found it more susceptible than average to digital noise and hash, however. Keep it away from wall warts, TVs, computers, and other appliances.

THE RF-562DD IN ACTUAL USE

Reception of KRLD-1080 out of Dallas, Texas at 1017 miles distant can be a little difficult on some receivers here in western Arizona due to nearby and adjacent-channel KNX-1070's IBOC sidebands. The Los Angeles, CA station is only 237 miles distant and transmits with 50 KW. Being so close, KNX doesn't fade down much and IBOC hash can be extremely strong on 1060 and 1080 KHz. Radios which make the grade here are the good nullers and those with extra I.F. bandwidth selectivity. The RF-562DD does a good job due to its good nulling ability. The Sangean ATS-909X does a good job due to its design employing DSP selectivity in the I.F. stage. The Tecsun PL-880 with its multiple DSP bandwidths is also a winner.

Another good indicator of DX ability here is the reception of Montana's KMON-560 at Great Falls (5 KW). Directionally, it is sandwiched between Denver's KLZ-560 (5 KW) and San Francisco's KSFO-560 (5 KW). Only about 90 degrees of aperture exists between these two. KMON is right up the middle to the north. KSFO's two tower pattern pushes to the southwest, and only delivers about 500 watts in my direction at a distance of 537 miles. KLZ in Denver at 667 miles does better and it's directional pattern pushes about 2400 watts towards me. Little KMON at 963 miles is a different story, however. It has a near-perfect cardioid pattern to the northeast and I am exactly in a deep notch at the back end. Only about 50 watts is pushed in my direction. This is a tough one to log. You must sit on this frequency for awhile and wait for San Francisco and Denver to deep fade. If you are lucky, and Montana's KMON is coincidentally at a good fade up, you might hear it. I have heard this station with the RF-562DD and the CCRadio EP Pro. I attribute this to sensitivity and superior nulling.

A receiver's selectivity is severely tested here on 650 KHz and 730 KHz due to the 50 KW blowtorch station pairs KFI-640 Los Angeles, CA / KTNN-660 Window Rock, AZ and KDWN-720 Las Vegas, NV / KCBS-740 San Francisco, CA. These are the top four strongest stations here at night. Reception on 650 KHz and 730 KHz is easily handled by the Panasonic RF-2200, the CCRadio EP Pro, and the Sangean ATS-909X. The RF-562DD manages, doing a little better than the ultralights. However, at extreme fade up of these blowtorch signals, some side splatter is evident on 650 KHz and 730 KHz. This is not unexpected on a radio in this price range.

FM

Though I'm not an FM DXer or FM aficionado, the FM section of the RF-562DD seems a little above average in sensitivity. I had some minor overload problems when tuning near the frequency of a local 100 watt FM station. I was within 1/2 mile of the station.

When tuning across the FM band, an annoying treble hiss on a station's audio becomes present as you tune off the station's center towards its edge.

Note that audio output to the headphone jack is not stereo.

SHORTWAVE

The single shortwave band (4.75 - 18 MHz) seems almost an afterthought on this radio. Performance is poor though sensitivity is not bad. Tuning is very delicate to say the least and almost impossible to land on a station. Practice helps. I wish Panasonic had left shortwave off and reduced the price of the radio by $20.

Don't buy this radio expecting great or easy shortwave reception. Consider a CCrane Skywave SSB, Tecsun PL-880, Sangean ATS-909X, or Tecsun PL-600 series instead.

SUMMATION

This radio is an nice mediumwave performer with great sensitivity, better than average selectivity and nulling ability. It could serve as your MW DX machine and even more if enhanced with a small passive loop (12-18 inches would be ideal).

Great AGC characteristics.

A nice retro look with faux leather case allowing access to the controls.

Easy on batteries but no AC adapter.

Audio might be considered harsh as it has overwhelming treble, reminding me of the original Tecsun PL-600's audio. The audio is not for everyone.

Tuning can be a little delicate, particularly on shortwave. Shortwave in general is poor. FM is adequate. Do not buy for shortwave.

Other minuses - no dial light and headphone jack is monaural only. Requires a mono to stereo adapter.

All plastic and somewhat cheap looking. I feel this radio is $20 over-priced, mainly because of the near useless shortwave inclusion.

Bottom line: It's not an Ultralight, but if you want an inexpensive mediumwave, analog DX radio that's more sensitive than the run of the mill DSP Ultralights, this could be your radio for a $50 bill. It is retro and has a good look about it. Beware of harsh audio.

Todderbert did a nice video review of this radio on his channel. Be sure to check it out and his other reviews.


The CD2003GP Monolithic AM/FM receiver chip

Tuesday, February 19, 2019

Notes On Mediumwave Loops And Wire Antennas

The following comments pertain to mediumwave reception.

I've constructed many loops here, both passive-tuned and hard wired for the DSP radios.

A question arose recently asking what is the equivalent air loop size to a 200mm (8 inch) length ferrite? Speaking from experience, I'll submit an educated guess and say the rough passive-tuned loop equivalent is an approximate square loop of 8-9 inches.

I've built smaller loops, on the order of 6 inches. They produce a signal strength about equivalent to the existing ferrite in a Tecsun PL-380, which is just shy of 4 inches long. The problem I've had with the really small loops of that size is that the nulling is pretty poor. The figure-8 pattern is not well-defined.

HARD-WIRED LOOPS

I have a hacked Tecsun PL-380 with the ferrite removed, and also an Eton Traveler 3 with the ferrite removed. I soldered wire leads in place and brought them out the tops of the radios for testing hard wired loops. I use micro-clips for all connections here for testing.

Two loops are currently in use here: an 8 inch and an 18 inch. Both are square loops, close-flat-wound with insulated telephone wire, about 24 gauge solid. The 8 inch has 26 turns and the 18 inch has 12 turns. If you wind a 12 inch loop, use 16 turns.

Both the 8 inch and 18 inch give good hard-wired results. Of course the 18 inch blows the doors off the 8 inch, and is the better nuller. You don't need a 5:1 step up transformer for impedance matching. Use the fully-wound loop. Inductance for both these loops is ballpark around 240 µH. I've found that is a good value to shoot for.

I will say, be careful if hard-wiring directly to the input of the DSP radios. They are very sensitive to static. I haven't blown one out yet, but I've come close. Any static or spike on the line when clipping to the chip will send it into desense for a few minutes, even if off. It eventually recovers, at least mine have so far.

At night, the PL-380 handles an 18 inch hard-wired loop pretty well without overloading. Not so much the Eton Traveler 3. Its sensitivity is a touch better than the PL-380, and otherwise will occasionally overload. A 12 inch loop might be a better bet for the Traveler 3. You shouldn't have any overload trouble with the 8 inch loop.

PASSIVE-TUNED LOOPS

Both 8 inch and 18 inch loops can be made passive and tuned with a 365 pF variable capacitor very nicely. The 18 inch ranges out nicely from 530-1700 KHz without further attention. The 8 inch only tunes to about 1430 KHz, so I jumper a clip wire across a few turns to get to 1700 KHz.

The advantage of the passive-tuned loop is that you can reduce the coupling by moving the loop a bit farther away from the radio, thus reducing the signal overload problem.

As others have stated, coupling a passive-tuned loop to a modern DSP chipped radio can be finicky because the radio gets de-tuned by the loop, then it re-tunes, then the loop is upset again. I have best results by coupling the passive loop off the end of the radio's ferrite. The tuning interaction is less. As so:

|
|
L
O
O  --RADIO FERRITE--
O
P
|
|

These DSP radios will start to overload much above 80 or 90 dBµ on the RSSI meter. Incidentally, the Eton Traveler 3 measures to 99 dBµ but the PL-380 only measures to 63 dBµ.

Remember, an RSSI reading of 34 dBµ is the equivalent of the old S-9 on vintage receivers us hams remember. 50 microvolts to the input = S-9. 34 dBµ also = 50 microvolts on these radios. A respectable signal. 80 dBµ is huge and it's not surprising this can cause overload.

Also, consider that the induced voltage in a loop increases linearly with the number of turns, the area of the loop, and the frequency. An 8 inch loop has nearly twice the voltage output as a 6 inch loop. Area 64/36 = 1.77 times the output. An 18 inch loop has more than twice the voltage output of a 12 inch loop. Area 324/144 = 2.25 times the output.

Here's a curious tuning tip that may not be apparent at first. It requires two DSP radios. Hard-wire a square loop to the first DSP radio (ferrite removed). This DSP radio tunes the loop in place of a 365 pF variable capacitor if you don't have a spare, sort of a "digitally tuned passive loop". Couple this loop inductively to the second, unmodified DSP radio like you normally would. Now you can accurately tune the passive loop by reading the frequency on the first DSP radio. Overkill, yes. But an interesting hack.

Bottom line on building a very small loop - 8 inches would be a minimal size for any appreciable gain.

FURTHER THOUGHTS ON HARD-WIRED vs. PASSIVE-TUNED LOOPS

I was all-in for awhile with the hard-wired loop, connected directly to the DSP's front end. The DSP chip tunes the coil just like the ferrite. What more could you want?

The problem here, again, is potential overload. These little DSP radios are not bullet-proof like the table-tops of the old days. An 18 inch or larger hard-wired loop produces massive un-tuned signal to the front end of the radio across the entire mediumwave band. The key word here is "un-tuned". You are relying solely on the DSP's existing circuitry to differentiate massive signals across a wide range of spectrum. Hard-wired loops above a certain size invite overload. We seem to crossover into this territory above the 12 inch range.

Hard-wired loops are great in quiet locations, especially for long distance daytime DX. Nighttime is a different story, as signal strengths can equal urban levels even without the loop-assist. You must find a way to incorporate selectivity to reject or lessen that which you are not interested in.

To summarize, using a passive tuned-loop and coupling inductively gives you two additional important advantages over the hard-wired loop:

1. A double-tuned front end. A tuned-loop has selectivity itself and its passband will essentially only present that large signal on the channel to which it is tuned.

2. The ability to decouple the loop from the radio by moving it farther away is sort of a poor man's RF gain control. If the radio is still overloading, move the loop away a bit.

An additional option to the passive-tuned loop is the successful FSL or Ferrite Sleeve Loop antenna. It is compact. If tuned with a variable capacitor, it will reject off-channel signals, lessening front-end overload as it serves as a double-tuned front end again. And it is directional of course. The C.Crane Twin Coil 200mm ferrite has similar qualities, a double-wound ferrite loop with a signal peaking ability.

ABOUT LOOPS AND NULLING

This applies not only to open air loops but to ferrite loopsticks as well. Rotating the loop off the station "peak" varies the induced signal voltage according to the trigonometric sine of the angle away from the peak. At 30 degrees off peak you have reduced the signal pickup by half the voltage (50%). At 45 degrees, 70% reduction. At 60 degrees, 86% reduction. At 90 degrees, theoretically 100% reduction, or zero signal. Now, we all know that 100% reduction is generally not theoretically obtainable, but sharp loops do come close.


The image above depicts the signal pickup for various angles of the signal arrival in relation to the side of the ferrite loopstick. Note that at only 30 degrees off the zero null the signal has increased to 50% of its full value. Passive box-type loops react exactly the opposite. Full signal occurs end-on to the loop instead of broadside.

Closed loops have magnetic pickup by nature. They receive the magnetic component of the passing wave. The magnetic component of a mediumwave station's signal is horizontal and parallel to the ground. Its electrical component is in the vertical plane. This is why when you rotate a radio's ferrite loopstick towards vertical the signal level drops to near zero.

WINDING FERRITE RODS AND BARS

Paul S., in Connecticut, who participates in the UltralighDX group, has some great tips on winding the ferrite coil:

The older and later 'pocket radio' designs were both made with a mix of price and quality. Older designs had weaker transistors/tubes and needed a high quality ferrite coil winding. A pocket model of the 60's had better transistors and could be made physically smaller, the circuit would compensate for the smaller ferrite rod.

Nonetheless, both designs are not optimum, as the most recent studies have shown. I refer to Ben Tounge's (of Blonder-Tounge Radio/TV) Article #29 at his namesakes website. I also note that there were mathematical errors in popularly published catalogs of ferrite material.

So what is a near optimum design one might ask?

1.) Keep the ferrite bar at least 10 times its diameter for nulling properties.

2.) Try to keep the coil winding between 1/2 and 1/3 of the ferrite bar length.

3.) Space the coil winding 3x the wire diameter (in typical designs its usually 2x the diameter). For example #30 gauge wire of 0.01" diameter is wound at 0.03" instead of the typical 0.02". This removes some "proximity effect" especially when many turns are involved.

4.) The wire diameter itself has to be minimized to reduce the "Skin Effect". This seems counter-intuitive because thin wire has more resistance per foot (meter). But, that's DC resistance... we are looking to reduce AC (AM radio signal) resistance. Such AC resistance gets larger when very little current flows in the center of the wire: the smaller diameter wire "saturates" the wire better, with more AM radio signal current flowing in the center of the wire.

5.) Because of #3 and #4 above, a single wire of small gauge (say #30 or better yet #32) can be wound upon the ferrite bar. However, the best choice is still Litz wire based upon #46 gauge strands. Its more expensive, and you do get what you pay for. I will also say that one would be surprised at how good a single #32 wire (0.008") spaced at 0.024" is.

6.) Using a single wire, one can wind directly on the ferrite bar (most of this 'magnet wire' is insulated), but most prefer using a layer of heat-shrink tubing over the ferrite bar.

So, in recap, the older radios got the wide spacing right, and the newer ones got the small gauge wire right, but neither got both right. One thing not mentioned in most commercial radio designs is the actual inductance of this ferrite bar antenna. I do know that some designs are intentionally high up to 700µH for Sony's in the 60's-70's. Modern DSP designs need 350-500uH, and can use short bar lengths (re: small wire diameter).

Regards,

Paul S. in CT

Thanks for the tips, Paul.

WIRE ANTENNAS

Loops in general are directional and have many advantages over simple wire antennas, should you have a radio which you can attach a wire antenna to. The non-DSP Sangean ATS-909X, the C.Crane EP Radio Pro, and Tecsun PL-880 are three which allow direct connection of wire antennas.

I find directly-connected (or inductively-coupled) horizontal short wire antennas for either DSP or non-DSP radios to be somewhat useless on the mediumwave band. Note, I am talking about SHORT wire antennas. Longer wires, and the longer the better, are preferred to the short variety. By longer, we are talking 200 feet or better. By short, I generally mean about 50 feet or less.

The Beverage antenna or "wave antenna" is a very long wire receiving antenna mainly used in the low frequency and medium frequency radio bands, invented by Harold H. Beverage in 1921. It's routinely run about six feet off the ground and may or may not be terminated at the far end with a resistor directly to ground. It has massive signal gathering ability and is also somewhat directional. A variety of Beverage, the BOG antenna (Beverage On Ground) has the same attributes going for it, laid directly on the ground. Neither are generally tuned, but can be. Beverage antennas work best if their length approaches a full wave or greater.

Another option is the flag or otherwise large-sized, single wire rectangular loop antenna. It may be 20 ft. tall by 50 feet long or larger. It is directional, and characteristically very quiet as loops are. It can be tuned as well. It has excellent performance.

THE VERTICAL ANTENNA

Lastly, a different option than the rest is the vertical antenna, an antenna poo-pooed by many but one which I've had many successes throughout a 55 year radio hobby. As a ham, over my active years I used verticals on the HF bands to work stations world-wide using only flea power at times. Using a simple vertical, I have worked long-path propagation from Denver to Sweden over the Pacific and Indian Oceans using CW (Morse) for example, a distance of some 19,000 miles. Their low angle take off is exceptional. But what about mediumwave?

Believe it or not, they are also useful for mediumwave reception. After all, the vertical is used by mediumwave stations to transmit!

The key to the vertical in all situations is matching it properly through a balun transformer of some kind. This will enable maximum signal (voltage) transfer to the receiver. It doesn't have to be tuned, just matched. I use a 25 ft. vertical here, matched through an RF Systems Magnetic balun, essentially a 9:1 transformer. 50 feet of coax is run from the RF Systems balun to the inside of the house. Coupling to the receiver is done inductively. Wind 15-20 turns of insulated wire around a 4 inch ferrite bar and connect to the coax, one side to center and one side to ground. Position the 4 inch ferrite near the radio's internal ferrite. The resultant increase in signal pickup is astounding.

A 25 foot vertical seems short for the mediumwaves, but its signal output is as good or better than a 48 inch passive-tuned loop. If there is a drawback it's that it is omni-directional versus the passive loop. However this can be advantageous for certain types of bandscanning. Park on a frequency for several hours while you are doing something else and you will hear the fade up and down of several stations. You will get to know the relative signal strengths of each over the long term listening period.

Also going for it is its same-plane alignment to the transmitted signal (vertical). The short horizontal wire antenna is 90 degrees to the mediumwave signal's polarization plane and perhaps even 180 degrees end-on or 90 degrees broadside to the station as well. A 20 dB or greater difference in signal strength can be realized in the vertical over the horizontal wire antenna. 20 dB is an increase of more than three times the signal pickup voltage.

Note that groundwave reception, even over extreme distances during daytime hours, is virtually in the vertical plane at all times. Nighttime skywave varies, but hardly less than 30 degrees off of vertical even at extreme distances. You can prove this yourself using your portable radio with internal ferrite loop antenna. At night, tune to a medium to strong distant station. Tilt the radio from horizontal towards vertical and the signal will be reduced dramatically as you approach the 45 degree point. The effect will be less-pronounced for stations closer than about 300 miles which have a higher angle arrival.

Much mediumwave fun can be had through experimenting with different antennas. Give it a try.

Friday, January 18, 2019

2019 US-Canadian Mediumwave Pattern Reference Is Here

The 2019 US-Canadian Mediumwave Pattern Reference for all stations is now available. Find the download link at upper right. Remember, the links change each time a new set is uploaded. Always look to this RADIO-TIMETRAVELLER site for the current link. Download is 52 MB.

DOWNLOAD LINKS

Media Fire link here.

Mirror link here.

If you download from the Media Fire link, be sure to click the DOWNLOAD button.


The Media Fire site is ad-supported and has several ad links on the page and will also issue an ad pop-under.

The other link at the upper right of this page is to Tomas Hood's NW7US site. It is ad-free. Thank you Tomas for mirroring this download. Both downloads are the same.

INSTALLING

The maps are HTML-based, so no regular install is necessary. Simply unzip the downloaded file and click on the individual map file to run. The map will open up in your web browser. They are self-contained, with image icons embedded right into the code. You must have an internet connection to view the maps.

IMPROVEMENTS FOR 2019

1. The previous 2016 map version became crippled due to Google's new precondition for all Google Map usage now requiring a user key. I have applied for and received the requested key. It allows a fixed amount of map-usage bandwidth. All maps should now display fully.

Note: Google may throttle map-usage bandwidth based on excessive use. Whether this will happen is unknown at this time.

2. Skywave signal maps have been totally recoded for 2019. Many months of coding and testing were involved. Predicted signal levels are calculated in accordance with current ITU methods of recent years (1999 onward). The following new parametrics are now additionally considered in the skywave calculation:

   * Hourly transitional loss variance from sunset to sunrise.
   * Seasonal gain or loss, January - December.
   * Diurnal enhancement at the sunrise and sunset period.
   * Winter daytime skywave enhancement (only on maps created for times during the day).
   * Daily seasonal nighttime skywave enhancement.
   * Take off angle variances for stations at relatively close distances (experimental).

3. Colored plot (yellow) introduced for groundwave 0.1 mV/m level.

4. Small changes made to the map's title bar heading.

5. Unlimited, Daytime, and Critical Hours plots are at the 1.0 and 0.1 mV/m levels. Skywave this year is set at the 0.15 mV/m level. In all cases except for the nighttime graveyard stations, levels have been chosen to minimize pattern overlap and to more closely follow those which might be helpful to the mediumwave DXer.

ABOUT THE MAPS

Included is a complete set of GoogleMap-based, HTML-driven maps which show the most current pattern plots of all licensed US and Canadian mediumwave broadcast stations from 530 - 1700 KHz. The set includes all frequencies for the indicated services: Unlimited, Daytime, Nighttime, and Critical Hours. Individual maps are grouped by channel frequency: 540, 550, 560, .. 1700 KHz, etc. Data for the plots in this offering is based on the current FCC and Industry Canada databases available at the time of its creation (January 16, 2019).

The daytime map series, in two parts, shows expected groundwave coverage patterns for Unlimited and Daytime (part 1), and Critical Hours (part 2) operations. Daytime signal patterns represent groundwave coverage at two levels, out to the 1.0 and 0.1 millivolts per meter contours. The choice of these levels is made in order to more closely match those which might be helpful to the mediumwave DXer. Note that daytime reception of signals out beyond the depicted 0.1 mV/m pattern is very possible, and in fact likely for the DXer. The contour line represents a signal strength at the station's extreme fringe distance, a level usually received on a sensitive portable radio with a low ambient local-noise level. I have chosen this signal level to give a good representation of what can be received by most DXers during sunlight hours.

The nighttime map series shows expected skywave coverage patterns for Unlimited and Nighttime operations. Nighttime signal patterns represent the standard SS+6 (sunset plus 6 hours, or approximately midnight Central Standard Time), 50% signal probability at 0.15 millivolts per meter. Note also that nighttime reception of signals out beyond the depicted pattern is very possible, and in fact quite likely for a skywave signal. The maps represent a signal strength between distant and fringe, a level generally easily received at night on most portable radios. I have chosen this signal level to give a good representation of what should be fairly easily received by most DXers on an average evening. The nighttime signal probability of 50% means that the signal will be received at this level approximately 50% of the time at Central Standard Time.

HOW THEY ARE PRODUCED

Using the actual FCC database files, Radio Data MW will auto-generate an interactive HTML pattern map, showing the pattern plots for all stations included at the discretion of the user. A complete set of mediumwave pattern maps can be generated in about five hours of processing time. Processing time has increased by nearly two hours in 2019 due to enhanced skywave calculations and other upgrades.

For daytime signal maps, Radio Data MW generates a real pattern plot based on transmitter power, antenna array efficiency and directivity, ground conductivity and ground dielectric constant of the path to the receiver. Increased conductivity of water paths over the Great Lakes are also accounted for. It display actual (but approximate of course) signal level boundaries for Local, Distant, Fringe, Extreme mV/m levels, or any custom mV/m level chosen by the user.

For skywave signal maps, predicted signal levels are calculated in accordance with current ITU methods of recent years (1999 onward). A number of parametrics are now analyzed and accounted for in the calculation, namely diurnal and seasonal changes, and daily sunrise and sunset enhancements to the signal. The process is rather complicated.

The online Google Maps API is used to generate and plot each station on a map of the US. An accurate flag pin is placed at each transmitter location, and in satellite view may be zoomed in to see the actual transmitter site. Map flags are color-coded to indicate Unlimited (light red), Daytime (yellow), Nighttime (black), and Critical Hours (grey) services. Each flag has a tooltip-type note, and when hovered over with the mouse will display a note on the station.

A pattern plot for each station is generated and displayed. Each pattern can be calculated using standard formulas used by the FCC or ITU to compute the base values at one kilometer, and field strength formulas at distance based on the works of many people over the years. See Field Strength Calculations: A History and Field Strength Calculator One, previously posted on RADIO-TIMETRAVELLER. See the RADIO-TIMETRAVELLER blog at: http://radio-timetraveller.blogspot.com/

An accurate ray path can be drawn from all transmitters to a user-specified receiving location by inputting latitude-longitude coordinates on the heading bar at the top of the map. Super-imposed on the pattern plots, the ray paths show the listener where he or she falls on each station's pattern, a handy guide to knowing where you stand.

Individual station plots can be turned on or off by a checkbox. Click the station flag and you will see the option in a pop-up balloon. Check or uncheck the box, then click the ReDraw button. The entire plot set can also be turned on or off by buttons at the top of the map.

Included in each station's flag tooltip are FCC facility ID, engineering (application) ID, and distance of the station from the home latitude-longitude. Of interest to the DXer, by setting the home location latitude-longitude to your location and redrawing the map, each flag tooltip will have the distance from your location to the station.

SPECIAL NOTE ON SKYWAVE PLOTS

The skywave calculation has been totally overhauled and enhanced to more reflect actual signal expectations across the U.S. at night. The fact of life is that pattern overlay occurs on many frequencies. Simply select the plots you want to analyze. Check the No Plots checkbox then ReDraw to turn off all plots. Click any station flag and check the box to plot that station then ReDraw.

You will occasionally see a skywave plot which looks much smaller than surrounding plots. This is a case where the station's skywave signal did not meet the mV/m threshold (0.15 mV/m). The groundwave plot level is substituted in this case. The station does in fact have a skywave component, however small, it will be measurably less than the 0.15 mV/m level (very weak). It may be receivable!

The darker line defining the outer edge of the skywave plot shows the location of the 0.15 mV/m signal point at all compass points. Note that skywave signal strength does not decrease linearly with distance from the station. From the station outward, the signal strength will generally increase to a point usually 200-400 kilometers distant where it will peak, then decrease somewhat linearly from there.

Also note that the atmospheric background noise level on the mediumwave band is generally considered to be approximately 36 dBu (dBu in this case = dBµV/m), equivalent to 0.063 mV/m. Signals below that level will not be heard unless they fade up above the noise. A gain or directional antenna can be used to increase signal strength while limiting or even reducing the overall atmospheric background noise level.

Image below is an example of the 1370 KHz daytime ground contour map.

Hope you enjoy.

Daytime Ground Contour Map 1370 KHz

Friday, January 11, 2019

The KKOB-770 Synchronous Operation In Santa Fe

Returning back to Arizona from Denver after Thanksgiving, I decided to stay in Santa Fe, New Mexico. This was a perfect opportunity to check out the status of the KKOB-770 synchronous transmitter site in Santa Fe.

KKOB-770, as most of you know, is Albuquerque's 50 KW blowtorch outlet, "The Talk Monster". A single tower does duty during the daylight hours. At night, a second tower is switched on, the signal covering most of the western U.S. with a westerly-facing cardioid pattern. The nighttime notch at the base of the cardioid falls over Santa Fe.

KKOB maintains a 230 watt synchronized transmitter just one mile west-northwest of downtown Santa Fe, adjacent to the John Griego Vietnam Veterans Memorial Park. A single tower is visible just a couple of hundred yards or so from the parking lot of the park. The tower is a 231 ft. (70 meter) high affair, with an effective height of 65 electrical degrees.

The purpose of this operation is to fill in KKOB's nighttime pattern in the Santa Fe area. Santa Fe is 56 airline miles from Albuquerque.

Driving past the location at mid-afternoon about 2 PM, it was evident that the tower was transmitting during the daytime hours. Driving along the road past the park's parking lot, and closest to the tower at about 200 yards, I had the car radio tuned to 770 KHz. Weird signal fluttering occured for several hundred yards along the road as the Santa Fe and Albuquerque signals combined. For several seconds, the phasing of the two signals completely nulled, resulting in no signal at all.

It was a strange listening experience, as Albuquerque's KKOB-770, at 50KW, normally puts out a respectable signal to this area in the daytime.

The following synchronous operations are authorized through FCC license in the U.S. The FCC terms them as "Experimental":
Call          Frequency     Power     Location
---------     ---------     -----     -----------------
(D)WI2XAC      740.000       500      Ponce, PR
(N)WI2XAC      740.000       100      Ponce, PR
(U)KKOB        770.000       230      Santa Fe, NM
(D)KM2XVL     1220.000       170      Huntsville, TX
(N)KM2XVL     1220.000        11      Huntsville, TX
(U)WBZT       1230.000       800      Pompano Beach, FL
(U)KCOH       1230.000       410      Houston, TX
(U)KDTD       1340.000       200      Kansas City, KS

D = DAYTINE, N = NIGHTTIME, U = UNLIMITED
I've been wanting to check out this operation for awhile.

Click image for a larger version.

KKOB-770 Santa Fe. 230 watts synchronous operation.

KKOB-770 Santa Fe. 230 watts synchronous operation.

KKOB-770 Albuquerque. 50,000 watts. Single tower daytime, both towers at night.