Tuesday, February 24, 2015

The dBµ vs. dBu Mystery: Signal Strength vs. Field Strength?

We've just talked about Tecsun's use of the term dBµ (Greek letter µ 'mu') in a previous article. They use it as a measure of received signal strength on their DSP radios. But there is another dBu (lowercase 'u' this time), also a measurement of strength, and more commonly used. What's the difference?

We first need to identify dBu's cousin, millivolts per meter.

You may have seen the term mV/m, or millivolts per meter, used as a measurement of field strength. The common unit used in measuring E-field "strength" is volts per meter, or V/m. Volts per meter is a lot when we are dealing with small received signal levels, so millivolts per meter 'mV/m' (one-thousandth of a volt per meter) is usually used. We have all seen mV/m used in a receiver's sensitivity specs, or to represent a station's received field strength at a given distance. Defined, an electric field of 1 mV/m is an electrical potential difference of 1 millivolt existing between two points that are 1 meter apart, perhaps along a one meter length of wire or between two parallel planes placed in the path of a signal. Technically, a millivolt per meter (mV/m) is achieved if a voltage of 1 millivolt is applied between two infinite parallel planes spaced 1 meter apart.

dBu (yes, lowercase 'u'), in reality is another improper contraction - a shortened version of dBµV/m (there's that Greek letter µ 'mu' again). dBµV/m is commonly and usually written nowadays as dBu, using the lowercase letter 'u'. It is the term used worldwide by engineers and the FCC for measuring electric field strength of AM, FM, and TV broadcast stations at prescribed distances. dBu is directly related to mV/m (mV/m = 1000 times µV/m), and is the logarithmic representation of mV/m.

Graph depicting measured dBu levels for KOA-830 (1934)

Have a look at the 1934 graph above depicting various dBu levels for station KOA-830, Denver. Confusing things even more, in the old days dBµ was indeed used as the shortened version of dBµV/m, and not dBu. (note: KOA currently is allocated to 850 KHz).

It is interesting to see what the different dBu values represent in terms of field strength. Several levels are represented. I have converted the dBu values to millivolts per meter:

88 dBu: 25 mV/m (urban)
74 dBu: 5 mV/m (residential)
54 dBu: 0.5 mV/m (rural)
36 dBu: 0.06 mV/m (atmospheric noise level)

For propagation aficionados, some other interesting things are of note here, in terms of propagation of this 50 KW signal over the excellent ground conductivity of the mid-west:

1. The ionospheric signal (the skywave) is strongest in the 300-500 kilometer range.
2. At about 200 km distant, the skywave strength essentially matches the groundwave strength, at about 63 dBu (1.4 mV/m).
3. The skywave signal level rises above the atmospheric noise level at just 30 km distant.
4. The groundwave signal level doesn't drop below the atmospheric noise level (36 dBu) until about 550 km distant., a site most are familiar with, uses the following mV/m values to represent different reception zones:

2.5 mV/m (68 dBu, local, red line)
0.5 mV/m (54 dBu, distant, purple line)
0.15 mV/m (43.5 dBu, fringe, blue line)

They are essentially in agreement.

Confusion continues to exist between Tecsun's dBµ (their version of dBµV), and dBu. They are constantly confused as the same thing, though they are very different. Note, however, that dBµV is indeed indirectly related to mV/m, and dBu.

So let's define them again, concisely:

dBu (letter 'u') from (dBµV/m): the decibel (logarithmic) representation of electric field voltage above or below one microvolt per meter.

dBµ (mu 'µ') from (dBµV): the decibel (logarithmic) representation of voltage above or below one microvolt across a load.

All you have to do is remember two things:

1. dBu (letter 'u') is actually another name for dBµV/m, related to mV/m. It came into common use many years ago.

2. dBµ (mu 'µ') is somebody's shortening of dBµV. Tecsun re-coined this one.

Important! You cannot convert dBµV as shown on the DSP radios to mV/m or dBu! The values are not interchangeable. The difference is found in what is called Antenna Factor, or the ability (actually efficiency) of the antenna to convert the passing field to an electrical voltage which can then be received by the detection process. As each antenna is different, each will transfer a different signal voltage to a radio's input. Each antenna (a ferrite loopstick is an antenna) will have a different Antenna Factor.

It matters little whether (at reception time) the received signal is ultimately impressed on a ferrite bar or rod, or a long wire, or a bed spring, in that the receiver will take whatever tiny voltage induced and convert it into intelligible audio if it is strong enough. Remember, as stated before, the iron core ferrite rod is basically a signal concentrator. The longer the rod and thus the more iron ferrite, the more the concentration, and the greater signal voltage, at least to a point.

The FCC offers a conversion calculator to convert from mV/m to dBu and back.

If you'd like to figure it yourself, you can by using the following formula:

dBu = 20 * Log(mV/m * 1000)

To reverse the computation, converting dBu back to mV/m:

mV/m = 10 ^ (dBu / 20) / 1000

(Log is the common logarithm, or base 10).

How, then, do we go about measuring millivolts per meter, mV/m?

Millivolts per meter (mV/m) is a way of defining a station's expected (or measured) field strength at a receiving location. Field strength can be measured by a device specifically designed to measure the strength of the passing wave. Potomac Industries makes the model 4100, a device which measures field strength. It was the subject of a previous blog post. Formulas to calculate approximate field strength can also be used.

Potomac Industries 4100 measurement.

Please note that a mediumwave station's expected field strength at a receiving location depends on many factors. One is transmitter power. Two, the distance from the transmitter. Three, the ground conductivity variations along the path between the transmitter and receiver. Four, the frequency of the wave. There are other factors too.

I did some articles on signal measurements and ferrite antennas on my blog a couple of years ago. Maybe they will help with introducing some of this field strength material.

Field Strength Calculations (3 parts)

An Unassuming Antenna - The Ferrite Loopstick

Field Strength Calculations: A History

I hope this helps in identifyng the difference between dBµ and dBu.


Stephen said...

Hi Bill,

I wasn't sure which blog post to comment with these video clips on, so I randomly picked this one. :)

Recently I went to some monitor points for my local stations and recorded short video clips of reception on my PL-606 there.

The playlist:

In the FCC info, if you look at the applications list when doing an AM Query, some stations have their license posted. On some, there are monitoring points specified, where the field intensity at a certain distance and bearing should not exceed a certain level under certain conditions of operation. Also often there's a description of the spot, so when I went there I did what I could to be at the specified location.

Btw KCBQ uses MDCL, so I've learned with that station to use the unmodulated carrier level (the silence between sentences, as it's a talk station) to read the signal strength. (There were a few other monitor points specified that I didn't get to.) I was going to paste text from a couple examples of the monitor points specified in the license (the 0.63 mV/m night one and the 189 or whatever mV/m day one), but the license authorization isn't loading from the FCC's site.

As you and I have both observed, a particular field strength does not always translate to a particular indicated signal strength plus or minus X dB. Where I am, there's a small window where it seems the indicated signal is about 21 dB less than the actual signal, but it only works from about 60 dBu to 80 dBu or so, or something like that.

Also, a couple weeks or so ago, I put my PL-398bt (which has a busted loopstick or something) and PL-606 (fully functional) in the back window of my Civic, both tuned to 760-KFMB, trained my camera on them and recorded a video monitoring the signal strength.

I started out on the onramp from Santo Rd onto eastbound CA-52, got off at Mast Blvd then got right back on (pausing on the onramp by KFMB's center tower), then continued on 52 east, transitioning onto CA-67 north. A little while after getting on 67, somewhere around where it turned east, the battery ran out in the camera, but I was able to get a fairly good range of signal strengths. Being in KFMB's nighttime null to the east, the signal faded out on the PL-398bt. I should note that it was rush hour and 52 east is usually heavy that time of the morning, so I was going much slower than I normally might have otherwise gone.

You may notice the level on the 398bt continue to rise, while on the 606 it reaches like 88 or 89 then jumps down to 85, rises, jumps down, rises again, jumps down, until the 398 gets into the 40s or 50s or so. Then, after passing KFMB, the reverse happens. So with this video you can "see" how the PL-606 is continually desensing as you're getting closer to KFMB, then cranking it back up upon having passed the station.

73, Stephen

Stephen said...

Ok, now that I was able to load the stations' licenses from the FCC database, here's some info from a few of the monitor points I visited...


Night Operation:

102.5º - The measurement point is located on the median of Marguerite
Canyon Road near the intersection with willow Road in Lakeside,
102.5° -- 5.68 km -- 0.63 mV/m = 56 dBµV/m -- "24 - 33 dBµ"

Day Operation:

Direction of 148.5° true North. The measurement point is located on
the west side of El Monte Road adjacent to meter pedestal #13746.
148.5° -- 4.52 km -- 189.5 mV/m = 105.6 dBµV/m -- "84 - 86 dBµ"


Night Operation:

Direction of 93 True North. From transmitter drive turn left on
Braverman and proceed 0.25 mile, then turn left on Magnolia Avenue. Go
south on Magnolia to the intersection of Mission Gorge Road and
Woodside Avenue. Turn left to Woodside Avenue, proceed on Woodside to
Winter Gardens Blvd (approximately 2.7 miles) turn right on Winter
Gardens Blvd procee south to Lemon Crest Drive (approximately 0.5
mile). Turn left on Lemon Crest, turn left again on first Street,
Orage Crest Drive. Monitoring point is in street at first entrance to
apartment complex on east side. The distance to the point is 2.1 miles
from the array. The field intensity measured at this point should not
exceed 7.1 mV/m, nighttime.
93° -- 3.38 km -- 7.1 mV/m = 77 dBµV/m -- "51 - 53 dBµ"

Day Operation:

Direction of 102.5 True North. From transmitter site proceed through
the gate, turn left, and then proceed 0.25 miles west on Braverman to
the stop sign. Turn South on Magnolia and proceed 0.95 miles to the
intersection with Woodside. Turn left on Woodside and proceed
northeast 0.4 miles to the underpass at State Route 67. Proceed under
Route 67 and continue on Woodside for 2.15 miles to the intersection
with Winter Gardens Blvd. Turn right on Winter Gardens Blvd and
proceed south 0.65 miles to Rockcrest. Turn left on Rockcrest and
proceed 0.3 miles east to Single Oak. Turn right on Single Oak and
proceed 0.3 miles south. The measuring point is at the curb on the
right side of the road just before the road curves to the right. The
field intensity measured at this point should not exceed 61.3 mV/m,
102.5° -- 3.86 km -- 61.3 mV/m = 95.7 dBµV/m -- "74 dBµ"


Night Operation:

Direction of 143° true North. The measurement point is located on the
west side of the Park and Ride lot on the southeast corner of the
intersection of Blossom Lane and Lake Jennings Park Road.
143° -- 6.39 km -- 6.71 mV/m = 76.5 dBµV/m -- "52 - 53 dBµ"

Day Operation:

Direction of 102° true North. The measurement point is located
adjacent to the 2.5 mile marker sign on the east side of Wildcat Canyon
road, 1.46 mile (2.35 km) northeast of the intersection with Willow
102° -- 3.35 km -- 9.82 mV/m = 79.8 dBµV/m -- "49 - 51 dBµ"


Hi Stephen,

Thanks for the video and detailed station loggings with dBu levels. Very interesting. I've had similar results in measuring differences. I wish there was a simple way or formula to correlate the two - dBµV/m and Tecsun's dBµ, but there isn't as far as I have been able to determine. I would expect them to track somewhat together, but that doesn't seem to be the case. I think it has to do with AF, antenna factor, and frequency sensitivity differences at different ends of the band.

Will get a Tucson chart or two off to you before the end of the month. Have had the program torn apart again revamping some code. I actually discovered I have more to do on the multi-countour plots. More work for the summer when time. I need to add the abilty to mix and match levels between stations instead of doing the same plots for all stations. Also, on switchable plots (when and if I get that done) will need to be on a station basis and not an individual contour level basis. I can't easily switch off a single plot in HTML.



Stephen said...

Hi Bill,

The hoped-for sunset on the 28th at KUAZ test didn't happen due to scheduling conflicts (we were invited to dinner), but I was able to go to KUAZ early in the morning on the 30th. The recording setup didn't go as well as I had hoped, though, partly from time and partly from recording equipment limitations. I was able to record what happens on the PL-606 and the Eton Traveler III what happened to 1490 KFFN's signal when 1550 KUAZ powered up, but was unable to include the CC Pocket, Sony SRF-59, or Sangean PR-D15. Also the Traveler III's display is nearly impossible to read outdoors except if you position things just perfectly. Also I tried including the PL-380 by using the stereo mike on the Zoom H2n, putting it on one side and having it set at +/- 1 kHz bandwidth, but the PL-606 (on the other side and set to +/- 4 kHz bandwidth which it incorrectly shows as 6) drowned it out. I had the T3 directly connected via line-in, which replaced two of the H2n's 5 microphones. (The other 3 were used in mid-side form for the PL-606 and PL-380.)

Anyway, here's the video -

It starts with 6.5 seconds of 1490-KFFN on the PL-606 (and PL-380 if you can hear it). KUAZ is still off the air.
Then, 13.5 seconds of 1490 on the Traveler III, starting with repeating what was on the previous clip. About 10 seconds in, KUAZ powers up.
Next, 22 seconds of the PL-606, backing up to a few seconds before KUAZ came on. About 16 seconds of this is some sounds from the PL-380 while it shows various signal numbers, before it finally silences and settles on a "50/00" indicated signal.
Then, 16.5 seconds zoomed on the Traveler III, tuned to 1550 KUAZ, during some of which I'm tilting it to show the display better. (Note: I had trouble adjusting/tilting it earlier to show the signal on 1490, but I remember from being there I saw, with my own eyes, around low-mid 40s dBu on KFFN before KUAZ was on, then when KUAZ came on it dropped to around 00/00 to 03/00 or so.)
Then, another 31.5 seconds zoomed on the PL-606, at first showing the 50/00 desense, then tuning to KUAZ in time for a part-repeat of the traffic report's sponsor info, then the weather.
Finally, 13 seconds, zoomed out, with a mix of both versions of audio, tuned to 1550 KUAZ.

73, Stephen

Stephen said...

I'd like to find an ultralight radio (preferably vertical form factor to slip in my pocket and listen while doing other activities, unless it has a decent secure belt clip) that doesn't suffer from the demonstrated defect.

(Also I forgot to enable the email follow-up comments option.)

Stephen said...

Oh, and also, here are video clips of bandscans near Vail, AZ, and Gila Bend, AZ, on the PR-D15. Vail was done around 3pm on the 29th, and Gila Bend around 2pm on the 30th.

Btw how far east of Tucson have you heard KFI? I thought it was farther east than Vail, I wonder why I wasn't hearing it there, and why it was so weak in Gila Bend... otoh I think I did hear KALL in Gila Bend.


Hi Stephen,

Glad the trip went well. Well I have to say I'm not surprised all the radios went into extreme desense when KUAZ came on. I see the tower in the background. The input circuits were overwhelmed by that 50 KW signal. There isn't a radio made that can overcome that at that distance. Not even military spec radios.

I liked your band scan videos. I think you got a small signal out of KFI-640 there in Gila Bend. I can easily get them on the truck radio there. Not a big signal, but adequate. Seems like I have heard them out to about Benson or Wilcox. I have heard Denver's KOA-850 in eastern Arizona but they drop out just before the NM state line. I do believe I have heard KALL-700 in Douglas, down by the border about 2 in the afternoon. That's a long haul. All daytime stuff of course.

Am wrapping things up here. I'm putting the program in mothballs for awhile as of this week. I got a lot accomplished in the last 3 weeks. I'm down to the web plot switching thing. I won't spend a lot of time on that but will look into it. I can make whatever plots I want now anyway.

Will be heading north then east about April 16.

Thanks for the report!



Stephen said...

Hi Bill,

Aww, I was hoping that at least something out there would at least mitigate it somewhat. :/ I've had situations where I've been at my grandma's house 1/3 mile from a 50 kW and wanted to listen to a first or 2nd adjacent that radio-locator says I'm outside the fringe contour sometimes. And, even at my house where the strongest signal is only about 120-130 mV/m or so, it wreaks havoc in that part of the band. I think I'd be able to hear KDIS much better, for example, if KSDO and KCBQ didn't desense so much. Looking at the charts you made for me, for example, 570-KLAC comes in MUCH stronger than 1110-KDIS, in spite of only being 5 dB stronger and the low end of the band supposedly having worse sensitivity probably due to the small antennas with improperly optimized loopsticks/coils, and 970-KNWQ and 980-KFWB are even a little better than KDIS, despite being about 7 and 6 dB weaker respectively. Also 1280-KFRN (about 1 dB weaker than KDIS) is noticeably better, and even 1340-KCLU in spite of being 12 dB weaker is about comparable to KDIS in strength. Also 1450 KFSD is a lot *more* stronger than KDIS than the 2.5 dB difference in strength on paper would lead you to believe.

Ahh, I guess the PR-D15 isn't as good as your truck radio then. :/ I guess I need to keep looking if I want to find a portable in that size range that can get KFYI, KBLU, KTIE, KAVL, KWVE, KNBR, KALL, KDWN, KCBC, KAZM, KGO, KXNT, KRLA, KIHC, KPSI, KFIG, KIXW, KDUS, KFNX, KNWQ, KEIB, KERN, KPSF, KXO, KMZT, KLPZ, KKZZ, KFNY, KTYM, KSPA, KUNX, KNZR and others at midday with a listenable (not fringe strain-to-hear-it) signal. (I left off some other targets that have stronger co-channels (including mexicans you didn't list), but did include some that on current equipment I can hear as carriers or hints of audio but not good enough to listen to program content (including ones with first-adjacent much-stronger IBOC-spewing stations.) Also I think some stations changed calls since then, for example your list shows KKZZ on 1400 but I think it's now 1520.) I'd also like a pocket-sized portable that can get some of those stations, but I could give up the weaker ones due to the small antenna, although I'd like the antenna to be the best design it could be (proper winding inductance, coil design, good litz wire, decent ferrite material, etc) to maximize its capability given the size restraints.
Unless you see something else, I think my longest haul catch there was KALL in Gila Bend.

Ahh. Any idea when you might update the patterns downloads, or post some example of what's been accomplished so far? :) And if the mothballs haven't grown too much, do you have a way to make a southwest USA map shading the locations where no signal exceeds a certain threshold? For example I'm thinking 3.16 mV/m, 1 mV/m, 0.316 mV/m, 0.1 mV/m, 31.6 µV/m, 10 µV/m, primarily daytime groundwave. I'm wanting to plan another midday DXpedition. Ideally I'd find a place where NO signal is detectable at all on the PR-D15 (or at least my ultralight DSP radios) in the daytime, but I kinda doubt I'll find one within reasonable driving distance of El Cajon (leave in the morning after breakfast, get to the place, DX for a few hours, come home in time for dinner without going too far above the posted speed limit).

So you're taking a more northern route this time? Through Denver again, or any chance you might be going farther north? If the latter, I'd sure be interested in how far your truck radio hears stations like 540-CBK, 550-KFYR, 570-WNAX, among others, in the daytime. :)

Also, when I was in AZ, I was noticing & confirming a suspicion I've had that to me seems quite interesting. Apparently the ground conductivity in AZ is much better than in VA, in spite of the former being desert and the latter being more green or something. I remember some lower-power / higher-frequency stations going farther in AZ than in VA.

73, Stephen


Hi Stephen,

At the expense of being a little verbose, I'll answer here. Maybe there are others tuned into the conversation. I'll break this into a couple of parts as it exceeds the max for a comment.

KKZZ on 1400 vs. 1520... I show it currently as a silent station on 1400. I don't have a reference to it on 1520. Am using the FCC database as of 03-16-2015.

You asked:

Any idea when you might update the patterns downloads, or post some example of what's been accomplished so far?

The skywave maps have changed somewhat due to better formula tweaking, but mostly due to accurately calculating proper signal takeoff angles (angle above the horizon) for the distance spanned. I was surprised at the changes in shapes of some of the plots, particularly the multi-towered affairs. Signal take off angle caused me great problems the last three weeks. For example, locating the distant point where a skywave signal hits .25 mV/m is not easy. It's easy to calculate the signal strength at, let's say, a point at 800 km, but to do the reverse: calculate at what point (at each azimuth degree 0-359) the signal is at .25 mV/m is another story. I finally have it down. It is hugely CPU intensive to do many stations.

I may do a new run of maps before mid-summer. It would probably still be by frequency block: 540 KHz, 550 KHz, etc. Perhaps in the future it might be best to just plot each station on its own individual map to avoid the confusion of overlapping. Yes, I know, it would be great to switch on and off individual plots. That's something I will look at this summer - but if too complicated I won't put the time into it. I need to be done with the killer hours I am spending on this program. I probably have spent 150 hours on it in just the last four weeks. Yes, 150 hours. 8-12 hours per day at least for the last three weeks.

You asked:

Do you have a way to make a southwest USA map shading the locations where no signal exceeds a certain threshold?

Let me be clear that there is no gradient type shading. Not even sure that would be possible with Google Maps in this environment. They are simply semi-transparent plots which overlap here and there. Maps can be created showing the extent of, let's say, x number of stations at the 0.1 mV/m contour level. Depending on signal level chosen, there may be open spaces in between. Not likely there's much of the country which has signals devoid of 0.1 mV/m coming from somewhere. You have a little better luck at 1 mV/m. I plotted Kansas, for example at 1 mV/m. Probably less than 3% is free of signals at that level. 3.16 mV/m is more like it. Imagine California? The higher levels are a different story of course. I don't think I've ever been anywhere in the US where there is NO mediumwave signal detectable on the radio. Not sure where you'd go, certainly nowhere around the L.A. - San Diego area.

Automobile radios are usually pretty sensitive, and generally way more sensitive than pocket portables. I would venture to say my truck radio is even quite a bit more sensitive than my Sony 2010. I've added to my truck whip antenna a little extra length of stiff music wire (about 24 extra inches). This improves it even more without too much overloading unless I'm very near a transmitter. I've often thought of just buying an automobile radio and installing it in the house with a 12 volt power supply. They are noise magnets though, with the vertical antenna. But I also don't have any house, trailer, whatever that is free of buzzing noise. I hate it. That's why I DX mobile almost all the time, or drive into the desert in AZ, or farm country when in NY.

Thank for the trip report.





Okay on the signal strength anomalies. I notice them too in certain situations. I did a check on your KCLU-1340 and KDIS-1110. You do have a near 100% salt water path to KCLU. That may make the difference there. That and some low mountainous ground between you and KDIS. The 'simple' Norton groundwave field strength algorithms don't account for HAAT, or height above average terrain, but assume a smooth ground surface. That is a whole 'nother ballpark there, adjusting for mountains. Sea water conductivity (as well as ground conductivity) is accounted for, however.

Yes, Arizona seems to have great ground conductivity, north especially. I have a pipeline into KALL in Salt Lake, for example. All it takes is a small loop to hear them. 500+ miles there. I can also hear the 50 KW outlets in the San Francisco Bay area. You are right, the east coast is not so good. In Rochester, the nearby Great Lakes (Erie and Ontario) help a little. I can hear WJR-760 in Detroit (292 miles) across the length of Lake Erie. I have picked up Chicago's WBBM-790 (534 miles) using a massive loop and under extreme conditions. It's not easy on that side of the country.

Yes, I'm taking the northern route through Denver, then east. 540-CBK, 550-KFYR, 570-WNAX might be receivable in the Denver area, I never have tried them before. Likely on 540 you would hear that 5 KW outlet in Las Vegas, NM. If I can remember, I'll try listening for these.



Stephen said...

Hi Bill,

It's totally okay, I can easily get that way. I think sometimes I've had to take 3 or 4 posts to reply, and my last one just barely made it in under the wire.

Ahh, well maybe radio-locator isn't all that accurate then, cause shows it as "currently off the air" on 1520. They show KUNX as being on 1400, which was on 1520 and formerly on 1590 when KVTA was on 1520.

Ahh wow, I bet that seems hard. Lemme guess, sometimes you have different points where the signal is a given strength depending on the takeoff angle, etc?

Ahh, maybe just a few stations per map might work? Maybe in cases where stations don't overlap, or only overlap a little, you could put a few stations on the same map? Also one suggestion, if you split them among their own maps or something like that, would be to maybe have each frequency be in its own folder.

Also, if sometime you open it up for others to contribute to the project, I'd love to see Mexican and other countries' stations be able to be added. (I wonder if David Eduardo, who I see on a couple radio boards, knows of any good resources for Mexican station technical data...)

Hmmm.... maybe I need to raise my threshold for strongest signal acceptable for a DXpedition site? For example I was hoping that on a medium-sized portable the strongest signal would be fairly weak, and on a radio with terrible selectivity, it wouldn't hear its IBOC sidebands at all, for example. How hard would it be to locate places, preferably in San Diego county (but I guess I could expand to Imperial county, maybe parts of Orange, L.A., Ventura, Santa Barbara, Riverside, San Bernardino counties, maybe even western AZ or extreme southern NV but idk) that have the weakest daytime signals receivable there? Also there'd be the question of getting there, too. If it's private property or the middle of a wilderness it wouldn't work. I'm wanting to guess that somewhere near / southeast of Julian would be something like that in San Diego county. If I could find a place where I could get some of the stations you hear, like San Francisco, Salt Lake City, Denver, Albuquerque, etc, without San Diego, L.A., Inland Empire, Imperial Valley / Mexicali, Yuma, Palm Springs, etc. being too pesky, that'd be nice.

Ahh. :') Btw I've heard good things about the Pioneer Supertuner IIID radios. I'm thinking of getting one sometime to replace the stock radio+cassette in my Civic (cause I hardly ever use cassettes anymore). Although, I've been able to hear 840-KXNT at midday on it, something I can't do with other radios. At least I think - unless it's an image - selectivity leaves a lot to be desired on this radio, seeing that 1110-KDIS gets stomped on by 1130-KSDO any closer to their TX site than my house.

Oh, speaking of overloading, when I was at the KUAZ site, that was my mom's Honda Accord I drove to the site, and I had my radios sitting on top of the car. (It was too early for my parents to get up so dad let me borrow the car. My Civic didn't make the trip to AZ.) Anyway, I remember it being a bit noisy, but I was able to hear the 1490 (that was blocked on the portables) on the car radio when KUAZ was on.

Ahh, I've been tempted to use a car radio as a home radio, too. For example I've been wanting to get my paws on one of the Delco AM Stereo radios. Now, how to hook up a large outdoor loop antenna (like at least 6-10 foot diameter) & a rotator to it...

Stephen said...

I kinda thought HAAT was for FM & TV, but I guess it could affect AM too? Hey that reminds me. It's been a while, but I kinda remember being able to get some San Diego & Tijuana AM stations near the top of the mountains north of L.A. and San Bernardino (like near Tejon Pass, Cajon Pass, or Crestline, for example) that I couldn't hear in L.A. or San Bernardino area itself, or at least they're noticeably stronger up there than down below. Considering that sometimes I hear San Diego / Tijuana FMs up there that are more difficult below, and that I hear L.A. FMs (their transmitters on Mt. Wilson) in parts of San Diego sometimes ... could it be remotely possible that on the mountains I'm hearing the low-angle skywave signals from the San Diego AM stations, before they've reached the ionosphere?

Ahh. I think just an 8" loopstick was good enough to hear them in Gila Bend. I'm now wishing I'd also tried for them on the Traveler III, I almost wonder if I might have had at least a tiny little trace....

So WBBM changed frequency? That must explain why I haven't heard them recently, after only hearing them once several years ago. On 780 if I don't get splash from my local 760-KFMB, I get KKOH, and if I null that, KAZM pops in. As for 790, it's occupied mostly by KABC and XESU.

I think you might have a little better luck with the 500s in Kansas. :) What I'd especially think would be interesting would be to hear, at midday, a Canadian *AND* a Mexican station on the same frequency, at a strength at least like this - - that's 1390 XEKT and KLTX on the SRF-59 at Pacific Beach, CA. For example, I'm thinking 540 CBK and XEWA, or 800 CKLW and XEROK, bonus points for doing it near 810 WHB's transmitter. :)

73, Stephen

Stephen said...

Hi Bill,

Something I thought I should mention, regarding the idea of finding the weakest-signal area in San Diego county. For one thing, I'd prefer to stay near major highways, like CA-78 or CA-79, or maybe just off I-8 (although that's a bit far south, more on that in a bit) or county S-1 or S-2.

Also, when I guessed that near Julian would have the lowest incoming daytime signals, that takes into account Mexican stations, including but not limited to 5 kW 1390-XEKT in Tecate, 5 kW 990-XECL in Mexicali, 10 kW 1050-XED in Mexicali, among others. (Btw when I was in Borrego Springs in February, XED was actually slightly stronger than 970-KNWZ, and XECL was a little weaker. I think the 3rd runner-up or so was 1 kW 790-XESU.) I wonder if there could be some way to take them (and others that may affect it) into account...

73, Stephen


Hi Stephen,

Sorry about getting WBBM's frequency wrong (790 vs. 780). It's been 5 or 6 years since that reception. WBBM isn't a station that I normally have connection with on a regular basis. :-)

KKZZ - downloaded the latest FCC database. They do show as 1520 and silent. Eyes probably blurry here I guess. :-)) Too much code...

Yes, the skywave signal calculation to determine where a certain mV/m occurs is pretty intensive. It's recurring calculations at each degree of azimuth, sort of sneaking up on the final result.

I see HAAT being used in the most advanced groundwave calculations for mediumwave. The math is way beyond my ability. Up on a mountain you will be receiving a very small angle. It's probably less than you think. 2500 ft. elevation rise over 30 miles, let's say, is only an angle of 0.9 degrees above horizontal. Not noticeable in signal level from horizontal.

I'll see if I can make you a map of weakest signal area for your location. We'll see how it comes out, anyway.