[amsat-bb] Re: New Lindy's QRV
kl7uw at acsalaska.net
Tue Feb 9 11:08:01 PST 2010
At 05:23 AM 2/9/2010, Bill Dzurilla wrote:
>I would be suspicious of the construction. I can get a few minutes
>of good copy from AO-51 on a high pass with just a rubber duck on an
>HT. If you do get a preamp, the run between the antenna and the
>preamp is critical, so if possible keep it short and use good
>coax. Ed seems to be having success with 4' of RG-58U, but
>generally the use of any RG-58U at 70cm is not a good idea.
Agreed in general, but if you look at the antenna it requires small
diameter coax. Loss at 450-MHz for RG-58 is around 9-10 dB (I didn't
look it up so used the loss for RG-223). So for 4/100 feet the loss
is 0.4 dB. This adds to the preamp 0.7 dB NF so it is not optimum,
but a lot better than the typical 432 ham receiver that is, at best,
6 dB NF. My FT-847 with internal preamp on is 12 dB NF, so reduction
to 1.1 dB is a good improvement. The cable length is for convenience
and could be made shorter.
Using better coax from the preamp to the shack would also be
better. I used 60-feet of RG-58, because I am "cheap". yet, it
seems to be working pretty good.
When I get the connections completed on my tracking array, I can
compare it with my 0.5 dB NF preamp and 436CP42. The latter is lower
to the ground so may encounter some ground clutter limiting tracking
to zero elevation. Let you all know when I get it QRV. When I had
it roof -mounted at the old qth, I could track AO-27 down to a few degrees.
>Here's a quick summary of my results with various antennas:
>* HT and rubber duck or other antenna mounted directly on the HT -
>success only at high elevations
>* HT and Arrow or Elk antenna, no preamp - success from horizon to
>horizon, if no trees or other obstructions
>* base rig and dual band omnidirectional ground plane, no preamp,
>40' of RG-213U - success on most birds only when elevation is above
>* base rig and dual band omnidirectional ground plane, ARR preamp,
>40' of RG-213U - success on most birds when elevation is above 15 degrees
So far, with the Lindy+4 feet RG-58+preamp I am seeing good signals
to and a little below 10-degrees.
>* base rig and Elk antenna on 12' pole at 15 degrees fixed
>elevation, azimuth rotation with old TV antenna rotor, ARR preamp,
>70' coax run (my current setup) - full success from horizon to
>horizon on all birds, except in directions where blocked by trees or roof.
>The Elk is $135 shipped and the used rotor was $25, and this combo
>is by far the most effective I have used. My community has antenna
>restrictions, but so far no one has complained about the little 2'
>long Elk. The Elk could be replaced with a homebrew Cheap Yagi or
>tape measure yagi, which can be built for $10.
>I am not aware of anyone who is able to work the sats at low
>elevations with any type of omnidirectional antenna, even with the
>best preamp. You can have plenty of fun working the birds at higher
>elevations, but you will be able to work more passes and better DX
>(e.g., Europe on AO-7) if you can catch them at lower elevations.
That is why my Lindy is set up only for the typ. mode VU FM birds. I
will use the better directional antennas for the linear birds (when I
get them connected).
>73, Bill NZ5N
73, Ed - KL7UW, WD2XSH/45
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
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