Radio receiver pre-amp device

[Josh]

My questions here typically go unanswered for some reason, regardless, here it goes.

On my GM300 I was able to install one of those nice hamtronics.com pre-amps directly inside the radio while retaining the transmit ability of the radio without damage- by design of the GM300 I was able to do this becuase there were separate RX and TX lines running to the RF board and the TX/RX relay located somewhere in the PA module.

At any rate, I've got a CDM1250 now and want to do something similar, of course being smaller, there's no room for the amp internally and simply mounting it directly in-line with the co-ax isn't an option.

Then I recalled those amplification devices that are typically for ham HTs that amplify both the inbound and outbound signals, but I don't know exactly what they're called. Did Motorola make something like this for VHF hi-band- something tubable?

Or, does someone have the schematics to the CDM radio such that I can located sections of the logic/rf board where I can solder in some RG174 or something and get the pre-amp setup just outside the radio?

Help is requested and help received appreciated.

-Josh

[kc7gr]

<snip>

Then I recalled those amplification devices that are typically for ham HTs that amplify both the inbound and outbound signals, but I don't know exactly what they're called. Did Motorola make something like this for VHF hi-band- something tubable?

Nothing of that nature that I'm aware of was ever made by Motorola. The most likely reason, to my mind, is that portable power output in excess of 5-6 watts poses some serious problems in terms of battery capacity (for lasting a typical 8-hour shift), as well as concerns about RF exposure safety.

Can't help with the schematics. Perhaps someone else will.

Happy hunting.

[Al]

Josh,
Sorry to answer your question with a question, but what do you hope to gain by adding a receive preamp to an otherwise properly designed receiver? Motorola's designs in their current receiver front ends almost always use low noise bipolar or FET devices. The devices are chosen to allow best noise figure with optimum overload and intermod performance. Unless you are very careful in your selection and use of any RX preamp, you will almost certainly destroy the intermod and overload characteristics of the receiver.

[Will]

Josh,

There are a line of outboard Power amps that have a FET preamp in them. They switch by sensing RF. Mostly made for the Ham market. Mirage, is one mfgr. that comes to mind. These external amps are NOT type accepted in comercial service.

[Josh]

Josh,

There are a line of outboard Power amps that have a FET preamp in them. They switch by sensing RF. Mostly made for the Ham market. Mirage, is one mfgr. that comes to mind. These external amps are NOT type accepted in comercial service.

I don't need an RF sensing amp that will amplify the transmitted signal.

I'm either A) Looking to add a preamp internally or B) adding a preamp externally with an RF sensing device so my radio's wattage doesn't pass through and destroy the amp

My reason for adding it is simple. I want to hear more. I've added an amp to my GM300 and by golly it makes a world of difference. 16db amplification per the specs. Yes, I am aware that it'll drop the selectivity but intermod isn't much of an issue around here anymore since the cops all went 800- their extensive use of 110w spectras on VHF a few years back brought me hell- but back then I was using scanners...

Regardless, I will check into mirage, and if I have to remove the 2meter amplifier I will, just so I can get the signals I want amplified, amplified. (BTW, I RX 160Mhz, the only TX'ing I do is on the ham band, but don't need a preamp for the ham band)

-Josh

[Cowthief]

Hello.

There were little preamps that you could put inline with your talkie antenna.
The things looked a little funny, a black box your antenna sits on, but the things work.

[indigo]

Josh:

Believe it or not I have had tremendous results amp'ing 160-161 with a rat-schack inline active amp I had laying around here. I can advise the M/N etc. if you or anyone else needs to know. It's a wide banded though, from what I can recall, but when I'm scanning RR's the results are impressive. I had initially tried this RS inline on some scanners and of course it just about blew out the front ends of the consumer garbage (i.e. Bearcat / Realistic, even overloaded a Vertex VX150 with intermod etc.), but with /\/\ units it's impressive. This is with using an experimental all copper elevated roof-mounted ground plane I built on my bench one lazy weekend.

These scanners have since been disposed of in lieu of the /\/\ gear to listen/scan with when they're not in use otherwise. Gotta love
/\/\ gear i.e. (MT1000) for use as a scanner - they're sensitive and tight as, well, as mother-/\/\ intended...

[scottm]

AR2 also makes a switched preamp. Check here http://www.advancedreceiver.com/page6.html

Scott

[Josh]

AR2 also makes a switched preamp. Check here http://www.advancedreceiver.com/page6.html

Scott

I don't know why, but I no longer receive ANY reply notification from batlabs any more and it's getting me pissed...but that's another story.

I found the resolution to my problems.

I bought another Hamtronics pre-amp, which should be here tomorrow and through eBay, discovered a kit by ramsey electronics that switches RF via relay....up to 100watts. I bought it and it came in the mail today. All I have to do is assemble it.

So, I think I've got a good solution....just hope all goes well!

-Josh

[KC8NIY]

Josh,

I'm really curious how that works out for you. Please post your results if/when you have time. Thanks!