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Adding preamp to MSF5000

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KENL
Posts: 15
Joined: Tue May 21, 2002 4:08 pm

Adding preamp to MSF5000

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

Hi,
Anybody have ideas on the best way to add a receiver preamp to an internally duplexed UHF MSF 5000.
Thanks,
Ken K2ATT

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xmo
Moderator
Posts: 2547
Joined: Fri Oct 12, 2001 4:00 pm

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.

Charlied
Posts: 80
Joined: Mon Feb 10, 2003 1:15 pm
What radios do you own?: MTS2000

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:

bernie
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Joined: Wed Nov 07, 2001 4:00 pm

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

My two bits worth:
Dont.
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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MSS-Dave
Posts: 770
Joined: Mon Jun 30, 2003 6:02 pm
What radios do you own?: XTL5K, NX300, PD782, Spark Gap

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.

Dave


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