[amsat-bb] Re: Fw: ELK or ARROW

[Bruce Robertson]

I had a great time experimenting with homebrew handheld dual-band
antennas for satellite work before I bought an arrow antenna. It is
important to note that, as in so many applications, higher antenna
gain is not necessarily better. Think of it as a narrower flashlight
beam: are you sure you can point the beam directly at the bird? If you
lose track of it, how easy will it be to find it again? Moreover, a
longer boom means a heavier antenna, and it is amazing how heavy a
handheld antenna becomes after 10 minutes!

So I'd say that it is just important in our discussions of antenna
gain to discuss pattern. If the handheld satellite antenna's gain is
improved by making a pencil-thin front lobe and some side lobes,
that's really no good: you'll be too frustrated trying to find the
bird.

There are, however, some aspects of the entire receiving system that
we can improve. This diplexer number is a bit alarming. I expect it is
possible to do better.

Another trick commonly used on home stations is to put a preamp at the
antenna output. The low-noise preamp improves the overall noise figure
of the system, and compensates for the 'down-stream' losses if put
before them, i.e., at the antenna.

As it happens, I've been thinking about how it might be possible to
super-charge an arrow antenna with a 435 preamp. I have a small ARR
switching preamp handy, but it needs 12v. Some sort of AA battery pack
with a charge-pump circuit might do the trick of small enough. Will
the added weight on my wrist be worth the improved reception on 435?
Only experimentation will tell.

73, Bruce
VE9QRP

On Sun, Dec 28, 2008 at 3:22 PM, Bob K0NR (email list) <list at k0nr.com> wrote:
> amsat-bb-request at amsat.org wrote:
>> It seems improving the 2.4 dB of insertion loss of the diplexer would be a
>> better strategy (although not necessarily easy in the space available) than
>> attempting to modify what is very mechanically sound antenna.
>>
>> 73,
>> Joe kk0sd
>>
>>
>
>    I am surprised that the duplexer/diplexer (take your pick) has that
>    much loss.
>    Has anyone verified this via a direct measurement (such as via a
>    network analyzer)?
>
>    Bob K0NR
>
>
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