[TowerTalk] Actual LP Performance vs Tribanders

[Pete Smith]

At 03:44 AM 6/26/2004, Peter Sundberg wrote:
>So f/b on groundwave is important and so far, from what I have seen the
>results are pretty close to what the software model tells you. But again,
>in precise numbers you can't say it is exactly -19db or -21db but you can
>sure tell -8db from -18 db.


My recent experience leads me to agree, Peter.  After adjusting the 
reflector on my shortened 2-element 40-meter yagi, I could not hear any 
front-to-back while listening to skywave signals in the CW band.  As a 
check, I transmitted on it while turning the antenna, as a friend about 5 
km away listened.  At each heading, he would tell me how much to adjust my 
output power to return to a given S-meter reading.  Converting the 
resulting power ratios to dB told me that at 7005, the antenna was slightly 
reversed; at 7050 it was bidirectional, at 7150 it had about 10 dB 
front-to-back ratio, and that F/B had diminished to about 6 dB at 
7250.  Nulls off the side were about 20 dB deep.

I understand that anything near the antenna can and will affect groundwave 
field strength, but since the only variables in this test were the pointing 
of the antenna and the frequency, this result seems to be a pretty good 
indication that the reflector is tuned too high.  I wouldn't swear by the 
absolute field strength values, but relatively speaking they make 
sense.  This is too bad, because it will not be easy to correct the 
reflector tuning.


73, Pete N4ZR
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