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Re: ao-40 antennas



Al:

I did a bulk purchase of the Philips-Tech dishes here in
Maryland, so several of us are running them.

Specifically, I run the stock feed assembly with the RG213
fed into a DEM preamp-downconverter combo. My noise floor
with this setup is about 3 S-units on the FT-847. I also
tried the DEM preamp/TransSystem 3733 combo. This gives me a
5+ S-unit noise floor. That was too much for me so I went
back to the DEM preamp/converter. The 3733 is now on the
output of a small 13 turn helix that I'm also testing.

Don, W4VQA, covered his BBQ dish with copper strips soldered
together. He still is running the stock feed assembly into a
DEM preamp/TransSystem 3733. He did a better job on his 3733
Murata filter mod than I did, so his noise floor is several
dB lower than mine. And his receive setup is much different
- A sideband converter into a Collins 32S1 receiver. He
believes the copper does enhance the receive signal. It also
allows us to try a helix feed assembly instead of the linear
yagi that's in the Philips now. More to follow on that.

My thoughts on this are: the RG213 may contribute to a small
loss of signal at 2401, but it shouldn't adversely affect
the noise floor, and with a preamp, that loss is more than
compensated for. If you want to optimize the antenna, cover
it with copper, or aluminum window screen or some other
suitable RF reflector, and use a 2 or 3 turn helix as a
feed. You should gain several more dB from the circular
feed.

Good luck.

73,
Art N3OY


Al Lawler wrote:
> 
>   I'm using the Phillips-tech 24dbi(Linear) bbq dish
> with a DEM preamp and a drake 'easy-mod' converter
> with great success.  I can definately hear as well
> as the vast majority of people on the birds (and quite
> obviously better than many.).
> 
>   My only concerns about the dish are:
> 
>   1)  The feed pigtail has about 3 feet of RG-213 (terminating
>       in an N connector), which obviously has a
>       negative effect on the ultimate noise figure.
> 
>       (I've been thinking about trying to just
>       cut off the unnecessary cable, but am not
>       convinced that the cable loss I'd save would
>       offset the losses of a hand-soldered n connector,
>       and unfortunately, the feed itself is sealed
>       in plastic making it impossible to mount the
>       preamp without at least some pigtail.)
> 
>   2)   I STILL don't hear as well as the people using
>        1-meter circular dishes.  This was apparent last night
>        as my s1 sqint ingle got up to 15 degrees or so,
>        and I was struggling to listen in on QSO's where
>        both parties obviously heard each other just
>        fine, despite similarly poor squint angles.)
> 
>        I've caught myself on one or 2 occasions
>        accidently cq'ing on top of a very weak QSO.
>        (There is a LOT of activity on ao-40 at very low
>        signal levels.)
> 
>   IN short, the phillips dish is a quite good antenna,
>   and my setup is as good as (or better) than most ao-40
>   users, but there are many people down by the noise-floor
>   who are hearing substantially better than me.
> 
>   -al
>   WB1BQE
> 
>   FT736r
> 
>   2x9 el cushcraft (dummy-load) yagi uplink
>   Phillips spg-36 bbq dish -> DEM 13ulna -> drake
> 
> 
> Richard Donner wrote:
> >
> > Would people like to comment on the following antenna links for ao-40
> > antennas for 2.4 ghz
> >
> > http://www.hyperlinktech.com/html/products/antennas_2400.html
> > http://www.hamtv.com/pdf.files/Cat4.pdf
> > http://www.hamtv.com/cat97.html
> > http://www.phillips-tech.com/main.asp?page=page6.asp
> > http://www.ssbusa.com/ao40dishes.html
> > http://www.downeastmicrowave.com/Antennas.htm
> >
> >
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