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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 15th Oct 2017, 9:51 pm   #1
sheriff076
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Default Microwave Modules MML 144/30LS

Hello,

I've picked up the above 2m amplifier from Hornsea radio rally this afternoon, with a view to use this with an FT-817 radio (clearly, 2m band only on transmit).

I was hoping to get some help, given I can't ask the manufacturer, anything would be welcomed. I've found a manual online which gives basic instructions to connect it all together and its from a time where dual band rigs were largely un-heard of.

So thats the background out of the way, here are my questions and I'm assuming it works (not tested at this moment, job for later in the week).

Would any harm come to such an amplifier if the bypass switch was enabled and I was operating on the 70cm band. (currently I use my FT-817 with a dual band white stick on the roof). Does the bypass give a truly straight through operation, or does it use some of the circuitry (which would be damaged from 70cm operation)

Would the pre-amp function work on the 70cm receive side, or is there band pass filtering to only pre-amp 2m band?

This amplifier has an Off, FM and SSB selection switch, can I use CW mode with the amp on say SSB? are there any issues to look out for?

I don't know anyone with such an amp, hence hoping someone on hear might be able to help me understand any 'watch outs'


Regards,


Steve G7TAO
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Old 16th Oct 2017, 12:37 am   #2
Terry_VK5TM
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Default Re: Microwave Modules MML 144/30LS

To answer your questions in order:

As long as both the PA and pre-amp are turned off, it can be left connected. You can then use 70cm.

The pre-amp is tuned input, so no, it won't work on 70cm.

I'm not sure I would be trying CW through this unit, it wasn't designed for that mode. Somebody with more experience of this unit would be in a better position to say if it would work.

Terry VK5TM
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Old 16th Oct 2017, 6:53 am   #3
Radio Wrangler
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Default Re: Microwave Modules MML 144/30LS

With the switching in bypass mode, you'll find that the relays used and the circuit layout will be good enough for 2m, but may give a fair bit of loss and a poor match on 70cm. As you said, it pre-dates dual-band radios and the designer will have been thinking of 2m only.

The preamp has tuned circuits in its input to protect it from overload from out of bad signals like pagers. In the 70cm band it will give you a lot of loss and not gain.

If the preamp is in the bypass path and you transmit on 70cm, with the amplifier in bypass mode, you could be transmitting into the output of the preamp.

It's safest to stick with just what it was intended to do and connect your antennae directly to the FT817 when using any other band.

With an SSB/FM switched mode amplifier, the bias conditions are changed. SSB is set for lower efficiency, higher linearity. FM doesn't need good linearity, so the bias will change to something more like class-C to put the efficiency up. CW should work best with FM mode provided the rf detecting auto change-over doesn't set the relays clattering. A solid transmit/receive connection or control may be needed.

David
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Old 16th Oct 2017, 2:06 pm   #4
Martin G7MRV
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Default Re: Microwave Modules MML 144/30LS

Quote:
Originally Posted by sheriff076 View Post
I don't know anyone with such an amp, hence hoping someone on hear might be able to help me understand any 'watch outs'
Other than me, of course

As others have already said, both PA and Pre-amp OFF for 70cm use. And FM mode most likely best for CW. I find mine when driven from the FT-290mk1 on High (2W), works best on the 1W i/p setting!
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Old 16th Oct 2017, 3:51 pm   #5
G6Tanuki
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Default Re: Microwave Modules MML 144/30LS

They were popular in the late-70s/early-80s as a way to give the then-ubiquitous portables like the Trio TR2200G, Icom IC202, Mizuho SB2-M, Totsuko TR2100M and Yaesu FT290 a bit more 'oomph' - typically people would have the amplifier fitted in their car and couple their portable-radio to it for mobile operations.

As others have mentioned, it was built before dual-band 2/70 radios were a thing: as such it won't amplify [either on transmit or receive] on 70cm. Similarly, the switching circuitry is likely to be lossy if used in 'passthrough' mode on 70cm.

Better to take it out of the chain entirely when operating on 70.

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Old 16th Oct 2017, 7:42 pm   #6
sheriff076
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Default Re: Microwave Modules MML 144/30LS

Quote:
Originally Posted by Martin G7MRV View Post
Other than me, of course
Hi Martin, I didn't know you had this in your stable. I'll be sure to pick your brains on this subject as and when.
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Old 16th Oct 2017, 7:44 pm   #7
sheriff076
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Default Re: Microwave Modules MML 144/30LS

Thanks to all of you for your contributions. Its been helpful to firm up my understanding of the way its likely to work if i had 70cm on rig. Looking forward to seeing if it works next.
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