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Re: Re: Helix antennas,



SSB Electronics (in QST and on Web) sells a model 2000 for 2m and a similar 
model for 70cm. They are EXCELLENT.

...hasan, N0AN
----- Original Message ----- 
From: "Zachary Schrempp" <ke7eyq@gmail.com>
To: <k5oe@aol.com>
Cc: <amsat-bb@amsat.org>
Sent: Sunday, May 14, 2006 4:39 PM
Subject: Re: [amsat-bb] Re: Helix antennas,


> For those of you using preamps, which kinds do you find to be the best
> bang for the buck on 144 and 435 MHz, and where do you usually
> purchase them...or do you homebrew them?
>
> Zach KE7EYQ
>
> On 5/14/06, k5oe@aol.com <k5oe@aol.com> wrote:
>> Zach,
>>
>> > Thank you all for your input. It is nice to have so many helpful
>> > people give antenna advice.
>>
>> One of the things AMSAT members are best known for is giving people 
>> advice :-)  Seriously, Steve's reference to Kent's Cheap Yagi is a good 
>> choice for the current fleet of LEO's.  They are easy to build and tune 
>> and have the simplicity of a linear design.  Any pair of Yagi's in the 
>> 3-5 elements range are more than good enough for all the LEOs.  Adding at 
>> least a 70 cm preamp (at the antenna) is always the best money you will 
>> spend.
>>
>> Save the helix effort for 1.2 GHz and up:  I no longer have the page on 
>> web, but I built and used a 70 cm helix based on the AF9Y design (I used 
>> an aluminum pan for the reflector :-)) and found it fine for transmit, 
>> but not a good receive antenna for that band.  The reason?  By it's 
>> nature the helix is very widebanded (thank you Dr. Kraus), a real 
>> convenience when building a transmit antenna, but not so good for receive 
>> selectivity.  I found the wideband UHF noise allowed into the receiver 
>> (amplified by a wideband UHF preamp) to greatly degrade receive 
>> perfomance.
>>
>> Many people enjoyed success with helices on AO-40, including me, but that 
>> was a few years ago now and things have changed considerably since then. 
>> The explosion of WiFi sources very near the 2.1 GHz band may very well 
>> have changed the spectrum profile enough to make a helix+preamp unusable 
>> in any densely poplulated area below 15 or 20 degrees elevation.  For 
>> S-band downlink on P3E and Eagle, I would suggest a narrow-banded 
>> antenna/feed such as a patch or Yagi is a better choice.  For uplink on 
>> 70 cm or L-band, a helix is still a great choice.  FWIW, I employed a 
>> pair of concentric helixes for L/S on a 4' dish for about 6 months and 
>> they worked fine.  I replaced the helices with the dual patch feed now 
>> shown on the web page and was much happier with that arrangement (better 
>> s/n, the real difference).
>>
>> 73,
>> Jerry, M0MOE
>> ----
>> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>> Not an AMSAT member? Join now to support the amateur satellite program!
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>>
>
>
> -- 
> Zachary Schrempp, KE7EYQ
> AMSAT #36023
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
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