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Re: Pre-amps

I've had some recent experience with 2m preamps that I thought I should add
to this thread. These are not reviews, just another straw in the wind.

Thinking that the NF of a 2m preamp is not as critical and being a
confident and experienced homebrewer, I decided to do the Ramsey kit with
the RF switch. I had two difficulties. The first was that the RF switch is
designed for FM use and, out of the box, chatters on SSB and CW
transmission. With the prompt help of the people at Ramsey, I altered the
delay circuit, but it never became satisfactory. Secondly, and only
speaking qualitatively, I didn't find the noise floor improved as a result
of this unit. I tried tuning its tuned circuit, but I never got it right. 

I then got a 2m preamp built into a second-hand 2m amp. The same problem as
before: I expected the beacon of VO-52 to 'pop up' a bit from the noise
when this was engaged. It just seemed that everything got louder. 

More recently, I bought a proper mast-mounted low noise preamp built by
ARR. This was a second-hand unit. It did the trick, lowering the noise
floor in a manner similar to the 70cm unit I have.

(The reader who has got this far might say, aha, but the mast-mounted unit
will inevitably be better than the in-shack model due to the line loss and
increased noise it causes. I don't believe this is the issue. I'm running
only 40' of 1/4" heliax to the 2m unit, and my 70cm preamp to which I'm
comparing is in-shack with a run that has a similar loss in its band.) 

Reluctanly, then, I recommend a high-performance unit at 2m as well as
70cm. I am quite pleased with ARR equipment. I would be interested if
others have had better luck with Ramsey RF switches, in part because I have
a second one in the treasure chest waiting for another project.

73, Bruce

Bruce Robertson, 
Dept. of Classics, Mount Allison University
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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