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Adding preamp to MSF5000

The General forum is where users can discuss any topic regarding Motorola communications equipment - hardware, software, etc. There are also several focused forums on this board, so please take the time to ensure that your questions doesn't fall into one of those categories before posting here!

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Adding preamp to MSF5000

Postby KENL » Fri Sep 19, 2003 12:31 pm

Anybody have ideas on the best way to add a receiver preamp to an internally duplexed UHF MSF 5000.

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Postby xmo » Fri Sep 19, 2003 3:50 pm

Not a viable project, I'm afraid.

The MSF receiver front end filter selectivity is part of the duplex filtering and the existing preamp is integral within that casting.

Even if there were a place to add another preamp, the UHF MSF5000 internal duplex filtering has barely enough isolation to operate without desense as it is.

Your only realistic option would be to use an external duplexer with sufficient selectivity and rejection to allow you to install a preamp in the receive leg after the duplexer and ahead of the station rx preselector.

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Postby Charlied » Fri Sep 19, 2003 5:35 pm

And don't forget to hook the domeflotcher up to the thingamajig and by pass the hickamadodger.

Don't worry about it. It's technical jargon... :wink:

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Postby bernie » Fri Sep 19, 2003 8:41 pm

My two bits worth:
You can not hear below the noise level of the site.
Your sensitivity should be approx.3 uv -117DBm or so. 12DB SINAD
Amplifiers are very potent medicine.
There certainly are applications where you might install an amplifier, however I have seen many systems improved by removing un necessary amplifiers.
I have a hand out that I use in training classes that I would be glad to share with you.
There is a procedure for determining exactly how much gain you need.
It is in the hand out.
Aloha, Bernie

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Postby MSS-Dave » Sun Sep 21, 2003 7:52 pm

Here's another vote in the DON'T category. Most MSF's I've worked on will give 12dB SINAD at about .15uV tuned per the manual. Internal duplexed units are a pain to tune but work well when right. External preamps will cause desense in the RX if the gain is too high. Even 1-2 dB can be too much in high noise sites. You have more flexability in seperate TX/RX connectors because you can add filtering as needed to the RX chain or a better duplexer externally.


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