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1991-12-22
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3KB
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56 lines
SUBJECT: Log Periodic Dipole Array - Part Three
Since the first couple of postings about this antenna, I have
watch the SWR readings and made notes of some of the propagation
features of the antenna.
The antenna's orginal design came from an older ARRL Antenna book
and the ARRL Handbook (87). Evidently the design has been around since
dirt was invented.
To date, the SWR has had minor changes, some for the better and
some worse. There are no SWR readings above 1.8:1 and that is one feature
that has not changed. Most of the other changes, in SWR, have had little
or no impact on the operation. These changes may be the result of
temperature changes as we have had readings in the forties here on occation.
Front to Back notes: The LPDA does not have the FB ratio that
a good yagi does towards the bottom of its range, but at high end, the LPDA
runs rings around the yagi.
Reception: I've run yagis here for years and I can honestly
say that the LPDA 'hears' better due to the capture area of the antenna.
Transmission: With the low SWR across the HF Band, the LPDA works
well with or without a tuner. Since I operate MARS Phone Patching for the
USAF, I have had numerous oportunities to query operators in South America
and the US. All report that the signal is as good as the three element
monoband yagi I used before. These operations take place above the
20m band but below the 17m band. When operations take place on
bands above 20m, the LPDA shows improvement in gain.
Weathering: The LPDA has been subjected to wind gusts of 50 mph
plus with no ill effects. The LPDA is however a great haven for the
many birds we have here in Florida. I believe they have a Bar & Grill
up there. At one time, there were no less than 63 birds on the antenna.
After a quick carrier, there were zero. Lucky for them, they do not
roost up there at night. My phone patching output is the legal limit.
Overall, the LPDA is the antenna for me. The design was the
hardest and even that can be done with a handheld calcuator and the
text in the handbook. Previous postings provide the reader with
all the precut values needed for operation from 13.5 to 29.5. The
22-ft boom is about the same size as a 20m monobander. If you can
put up a 20m monoband yagi, then you can put up a LPDA. No traps,
coils, or power limitation except the balun.
-------------------------------------------------
To Everyone on HAM_TECH (and you too Jim) ;-), have
a Safe and Happy Holiday Season.
- Wayne Sarosi, KB4YLY / AFA2GN