Hi Pete,
Thank you for the reply. The elements were pre-drilled so I assembled the
antenna per the factory setting. The assembled antenna had its resonant
frequency at 7.030mhz which is what the factory recommended. I didn't perform
any changes on element lengths.
The performance test was done on SSB so yes the reflector is way too long to do
it's job properly. But I still expected more performance than what I
observed. The SWR at 7.160 was 2.50 as compared to an SWR of 1.60 on 7.030.
Although I don't do a lot of CW I left the resonant frequency on the CW portion
since I don't want a reversed pattern on the CW portion when I do work there.
I think that's why F12 recommended a resonant frequency of 7.03mhz as opposed
to a higher frequency somewhere between the CW and phone portions of the band.
I will do some testing on the CW portion and with a long-haul DX. I just
wished the performance could be better in the phone portion where I do most of
my operating.
Copying W2IRT as he also has a D240.
73,
Jonathan W6GX
Hi Jonathan - something is likely wrong, but you would need to make a number of
other tests to be sure, because arrival angles of signals vary. It is
conceivable that your DX station was arriving at an angle where the antenna's
F/B ratio is much less than the quoted peak. If it is an assembly issue, then
maybe you used the driven element dimensions on the reflector N6BT's Array of
Light makes a very interesting point about yagis - (I'll try to paraphrase)
that the driven element's role is to inject RF into the array, while the
parasitic element's length determines the directivity. Tune your radio too far
above the optimum frequency, and a reflector won't do its job very well. Tune
too far below and the length of the reflector will turn it into a director. I
was having a lot of trouble getting my F12 EF-240S to work well. At Tom's
suggestion, I think, I set up my MFJ-259B antenna analyzer with coax to a short
antenna some 300 feet from my yagi.
Tuning the analyzer with the antenna pointed away from this signal source, I
could very clearly see both phenomena described above. The antenna reversed at
7.1 MHz, making it clear that my reflector was much too short. Moving the
shorting bars quickly moved the "flipping point" comfortably below 7 MHz, and
put the best F/B ratio in the middle of the CW segment where I wanted it.
73, Pete N4ZR
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000
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