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Re: [TowerTalk] F12 Delta 240 performance observation

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Subject: Re: [TowerTalk] F12 Delta 240 performance observation
From: SPWoo <>
Reply-to: SPWoo <>
Date: Wed, 19 Sep 2012 07:39:15 -0700 (PDT)
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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.

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
The Reverse Beacon Network at, blog at,
spots at, port 7000 and, port 7000

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