[amsat-bb] Re: Fw: ELK or ARROW
tim at timtapio.com
Mon Dec 29 01:13:04 PST 2008
Putting on a preamp worked wonders (I used a Hamtronics). I'd go in the
backyard with it and I put the Arrow on a tripod. It worked out well but I
did have desense problems. I finally went to separate antennas, put them on
an MFJ tripod and bought a rotor from Radio Shack. I pointed the antennas up
at a 30 degree elevation and had my best success this way.
The boom was regular schedule 40 pvc and had quite a bit of sag, the 2 meter
antenna was vertical and the 70 cm was horizontal. I then rearranged the
antennas to the opposite orientation (I don't remember what my justification
was) but I never did get a chance to compare them, life events made
operating take a back seat.
I still had desense issues so I finally tossed in a Comet diplexer that I
had in the box of goodies....(I don't have a "junk box".
I also had about a 10' run of RG-8x so system losses didn't amount to much.
Just my experience but I recommend use of a diplexer as a filter for the
receive....terminate the 2 meter side (I used an old Ethernet 50 ohm
Tim T K4SHF #35580
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Bruce Robertson
Sent: Sunday, December 28, 2008 10:41 PM
To: Bob K0NR (email list)
Cc: amsat-bb at amsat.org
Subject: [amsat-bb] Re: Fw: ELK or ARROW
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
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.
On Sun, Dec 28, 2008 at 3:22 PM, Bob K0NR (email list) <list at k0nr.com>
> 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
>> 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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