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Re: AO-40 Update 2001-07-20



On Wednesday 25 July 2001 17:14, Vince Fiscus, KB7ADL wrote:

> A dish might be the way to go then. I was hoping for something small
> that would be easy to mount beside the other antennas on the boom.
> Your Drake doesn't have a pre-amp in it does it?

Not in the sense that you're thinking. Stock Drakes start off with 24dB 
gain. A tweak to the matching coil of the first (RF) amp stage yields 
another 3dB; I think that's what's done in the Millicom version. 

I also have David's kit of parts that (in the hands of someone who 
knows what they're doing--perhaps not me!) will take a cherry vanilla 
stock Drake (which I also have standing by) to 38dB and <2dB NF.  

 see http://www.g0mrf.freeserve.co.uk/filter.htm

David also has a new modification that replaces that same first stage 
with a PHEMNT. See  http://www.g0mrf.freeserve.co.uk/drakephemt.htm

We're promised gain/NF numbers for that approach when he gets back from 
Surrey. (Prseumably not with the Fringe On Top). 

David also points out to you:

>It may be OK when we're all on the other transponder (S1) with it's 
>extra 9dB gain dish antenna. But at the moment 16T is just too small.

I really do have to agree with G0MRF that what I'm running now is 
marginal at best with the current AO-40 configuration. But with a 
number of QSOs in my log, and a dismal antenna geometry for DX (tripod 
standing in the shadow of my house to an elevation of about 45deg 
elevation on azimuths of 90-140 degrees), I'm planning to hold off on 
enhancements for now, in anticipation of two developments:

 1- Finding a new job and
 2- AO-40 final commissioning

Only when the bird reaches its final configuration can we judge what's 
really going to be required for normal operation. At that point I can 
elect to modify my second Drake, or build a dish antenna for bigger 
ears (and accept a requirement for higher pointing accuracy). 

Or if I find work sooner, I can add a low-noise preamp in front of the 
converter and solve the problem (with money) that way. 

Once I'm happy with the performance of my S-band receive system, I can 
consider a roof or tower mount for the whole rotor system, and gain 
access to the bird when it's well-positioned for DX to the eastern 
hemisphere.

 73 de Maggie K3XS 
  

-- 
-----/___.   _)   Margaret Stephanie Leber    / "The art of progress  /
----/(, /|  /| http://voicenet.com/~maggie   / consists of preserving/
---/   / | / |  _   _   _    `  _AOPA 925383/ order amid change and /
--/ ) /  |/  |_(_(_(_/_(_/__(__(/_  FN20hd / change amid order."   /
-/ (_/   '  K3XS  .-/ .-/    ARRL 39280   /___ --A.N.Whitehead ___/
/____ICQ 7161096_(_/_(_/__AMSAT 32844____/ <maggie@voicenet.com>

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