I built a LoG antenna last year and evaluated it. Most of the claims
for the performance of this antenna are in error. I posted the summary
of performance here:
http://forums.qrz.com/index.php?threads/easy-as-falling-off-a-log.617550/
I will copy that message below, so you don't have to go to the link and
find it:
I built a 15 ft on a side LoG back in April when there were signals on
160 for measurement purposes. The results were as expected. Here is the
summary.
1. Measured gain: 160 = -44 dBi, 80 = -35 dBi, 40 = -19 dBi (by
comparison to a reference antenna of known gain)
Those numbers agree closely with EZNEC values.
2. Without a preamp on 80 cannot copy any signals that are less than S9.
On 160 cannot copy any signals that are less than S9+20. On 40 cannot
copy any signals that are less than S7. (S meter is on TS-990S. Your S
meter may be calibrated differently.) I have a preamp to make up the
gain difference, but since there are claims that a preamp is usually not
needed, I did that test.
3. No directivity was measured. All directions approximately the same
gain. This is in agreement with EZNEC. Measurements of low angle signals
on 160 was difficult because most of those signals were below the noise
floor of the LoG. Was able to copy some big gun EU stations on 80.
4. S/N performance was very poor. 80 was the worst band and 160 was the
best. On 80 my 80 meter inverted L (transmit antenna) beats it by 0 to
10 dB S/N. A BOG beats it by about 6 to 10 dB S/N. On 160 my 160
inverted L beats it by about 3 dB. A BOG is about 12 dB better than the
LoG on 160. The LoG S/N is significantly worse than my transmit antennas
and much worse than a BOG.
5. Was unable to measure any effect of common mode feedline currents.
Same pattern and gain with or without feedline choke and feedline grounding.
6. LOG shows good response to very high angle signals. Unfortunately
that's not what you need it to do. It would work well for very close
stations but close stations are usually so strong that you don't need a
receiving antenna.
7. All testing was done when there were no thunderstorms close. Since
the antenna has very good response to high angle signals, the S/N should
be much worse (compared to other options) if storms are close.
All of this data is in agreement with known information about how
receiving antennas work. That's the reason the results were as expected.
When the noise source is atmospheric noise, you can't improve the S/N by
using an omnidirectional antenna. S/N is improved by having an antenna
with maximum gain in the direction of the station and minimum gain in
all other directions. That's the way all commonly used receiving
antennas work. If you have a single man-made noise source, an antenna
that nulls that direction may improve S/N, but generally won't have much
affect on atmospheric noise.
Jerry, K4SAV
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