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Re: Pre-amps



Michael,
Here are things to consider:
The higher Galictic noise on 2 Meters.
Terestial signals that can overload the preamp if your station is in a 
metropoliton aera.
 Modern radios have low noise receivers and additional gain can make 
recption worse if the amplifier gain overloads your receiver.
Ground noise, ( objects that are at ground temperature, [300 deg K=3dB]  ) 
seen by antennas that have trees or buildings in the path will increase 
system noise.
 A good front to back ratio on receive antennas helps reduce ground noise. 
If your system is working well you should see a reduction in noise as the 
elevation increases from 0 degrees. Adding a quality preamp your station in 
a rural area away from strong signals, with a lossy feed line, and a older 
receiver can make a considerable improvment in reception. In a metropoliton 
seting, the preamp could be a prescription for poor recption.

Art , KC6UQH

 ----- Original Message ----- 
From: "Michael Tondee" <mat_62@netcommander.com>
Cc: <amsat-bb@amsat.org>
Sent: Saturday, June 17, 2006 7:38 PM
Subject: Re: [amsat-bb] Pre-amps


> Bruce,
> I'm glad to have come upon this post as I was going to try and go the 
> Ramsey kit route for a two meter preamp as well. I was going to use the RF 
> switch and mount the whole thing in a weatherproof enclosure at the mast. 
> Guess I'll have to rethink that.
> I love my ARR 70cm mast mount preamp but unfortunately  I can't afford the 
> same on the two meter side right now so I'll have to come up with another 
> solution.
> On a side note related to preamps, my TS-2000 doesn't have 13.8 VDC at the 
> coax jack for preamp power so I use a bias tee. Should this be powered by 
> a separate supply from the rig or does it matter? I'm using my  DC supply 
> I use for my rig and have wondered if this was acceptable.
> 73,
> Michael, W4HIJ
>
> Bruce Robertson wrote:
>> 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
>> VE9QRP
> ----
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