Here is a chart of signal strength tests for 3 longwire lengths - 70 ft., 150 ft., and 240 ft., made Nov. 30, 2008 between 1200 and 1300 local time. In all cases, strength increased with incremental increase in wire length, except for 810 kHz, KGO. I'm sure this anomoly was due to band conditions at the exact time of monitoring.
KPLY, 630 kHz, Reno, NV was not receivable at all.
All stations monitored transmit below 1000 kHz. The 240 ft. longwire is resonant at approximately 1000 kHz at a quarter wave, the 150 ft. longwire approximately 1520 kHz. It is apparent that increasing wire length up to at least one quarter wave will always increase signal level. Two stations were not receivable at all (no signal apparent) until wire length was increased from 70 ft. to 150 ft., where they then became readable. It seems at least 150 ft. of wire is necessary for daytime DXing.
Signal strengths are indicated in S-units. See notes at bottom for symbol explanation. Eton E1, preamp off.
Strengths indicated as follows: 70ft---150ft---240ft
550 kHz KFYI Phoenix, AZ 6---8---9
560 kHz KBLU Yuma, AZ 5---**1---**1
580 kHz KSAZ Marana, AZ 1.5---4.5---6
590 kHz KSUB Cedar City, UT 1---1.5#---2.5#
600 kHz KOGO San Diego, CA 1.5---3.5---5
630 kHz KPLY Reno, NV 0---0---0
640 kHz KFI Los Angeles, CA 3.5---5.5---7
660 kHz KTNN Window Rock, AZ 0---$---3
680 kHz KNBR San Francisco, CA 3---3.5---5
700 kHz KALL N. Salt Lake City, UT 0---2#---4.5
720 kHz KDWN Las Vegas, NV 5---7---8
740 kHz KCBS San Francisco, CA 1.5---5.5---8.5
760 kHz KFMB San Diego, CA 1---3---4.5
770 kHz KKOB Albuquerque, NM 1---1---3
810 kHz KGO San Francisco, CA 3---2.5---4
830 kHz KFLT Tucson, AZ 3.5---6.5---9
930 kHz KAFF Flagstaff, AZ $---2---4
Symbols-
0 No signal apparent
$ Signal there, but not intelligble
# Signal there, poor intelligibility
Notes-
**1 Station was off the air at this time for some reason.
