Hello richard- this is Patrick N2OEQ on long island. Sorry our contact on fo-29 was short. Try to keep your downlink frequency steady by adjusting your uplink frequency. It was a good contact nontheless.

I recently did a little homework before purchasing a Hamtronics recieve only preamp. Apparently, adding a preamp increases the dynamic range possibly introducing unwanted signals but then I thought, Hay!, wouldnt that make it easier with a 5khz seperated channelized FM radio? Not sure. Anyway, I seem to be doing OK with rated 18 Bb of gain which is close to the low setting of your mirage. Are you using seperate antennas, how far apart, and how long and what type of coax? Best thing I guess is to experiment. Calculate station gain subtracting and adding gains to help figure out your setting requirements.

I use for FM satellites; icom 229H @ 50 watts into short vertical for omni coverage, a homebrew 8 element UHF yagi-uda beam with preamp at antenna and 25 feet of 9913 coax to FT 8800 dual band rig. I tried using a diplexer before the preamp but better signals are had without the filter and good seperation of the antennas. I'm pretty new to this so the other techies should have a lot more for you.

Thanks for the contact, you sounded strong on fo-29, thanks & 73, pat n2oeq

On Sun, 20 Aug 2006, Richard Lawn wrote:

I'm about to mast mount a new Mirage 70cm preamp. It has a high/low setting. Any suggestions from the group as I'm sure many of you are using this preamp. Is the high setting too much gain? I got tired of forgetting I had the ARR preamp on an frying it by sending too much RF into it. 73 Rick W2JAZ

Richard Lawn, Dean College of Performing Arts University of the Arts 215-717-6125

---

Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

Hi Rick,

Here's a simple method for determining the proper amount of gain for a preamp. It does talk about preamps with continuously adjustable gain, but you should at least be able to get in the ballpark with your Mirage..... I've actually gone inside of some ARR's I've used and added a T pad to set the gain... YMMV.

73, Mike N1JEZ AMSAT #29649 "A closed mouth gathers no feet"

==== Here's a method that requires no test equipment at all. It comes from G4DGU, who designed all the original muTek transverters and outboard preamps to have adjustable gain. This method uses the sharp threshold effect of FM detectors at low S/N ratios, and it allows you to optimize the preamp/transverter gain for your local band noise conditions.

1. Turn the transverter/preamp gain well up.

2. Find a very weak but steady unmodulated carrier (off-air, not from a signal generator or a local birdie). Rotate the antenna until you can just detect the signal in FM mode.

3. Reduce the preamp/transverter gain until you hear the noise increase. The FM threshold is sensitive to a small fraction of a dB in S/N.

4. Increase the gain just a little,to the point where you can't hear the quieting improve much.

5. Switch back to a real DX mode.

Remember that every dB of unnecessary preamp/transverter gain will probably subtract almost 1dB from your system intermod intercept!

The penalty of adjusting the gain correctly is that you're living just above the "knee" where S/N will begin to deteriorate rapidly if something changes. It's worthwhile to repeat this test every few months - especially just before a contest.

73 from Ian G3SEK Editor, 'The VHF/UHF DX Book' 'In Practice' columnist for RadCom (RSGB)

----- Original Message ----- From: "Richard Lawn" [email protected] Subject: [amsat-bb] Mirage Preamp Setting

I'm about to mast mount a new Mirage 70cm preamp. It has a high/low setting. Any suggestions from the group as I'm sure many of you are using this preamp. Is the high setting too much gain? I got tired of forgetting I had the ARR preamp on an frying it by sending too much RF into it. 73 Rick W2JAZ

Richard Lawn, Dean College of Performing Arts University of the Arts 215-717-6125