Batboard

Ok, here's a question for all you radio technophiles (i.e. electronic magicians), does the volume (speaker) voltage output on the MT1000 change as the recieved signal gets stronger or weaker?

I ask because I have a rigged repeater using 2 of the MT1000 internals, and I have noticed when a station goes out of range that the repeater drops the transmition (i.e. dekey's). The way the system is setup, in order to key the transmitter when a signal is incoming, I use a 5V/1A Micro-Relay (because from local tests the volume (speaker) output pin on the internal front panel connector seems to put out about 4V).

The whole setup seems to work fine when a station is in close proximity to the reciever radio. (These radios are 30 ft. up in the air by the way, in an attic.)

It appears you have tapped the wrong location on the board for relay activation.

The signal strength of the receiver is tied to the ALC and this is not the proper place to get a +5 volt signal from, and neither is the discriminator.

You can check various levels of voltage when the monitor button is depressed and see what the voltage levels rise to, but also note that there is a severe chance of loading as well, and you can bring down the levels with improper tapping of points on the back of the radio.

If you can only obtain a low level voltage to activate a tiny relay, then you should consider building a voltage amplifier using a darlington transistor as the added second stage will usually provide the gain necessary to drive a relay.

But make certain you will not be loading down the tap-off point first.

Then take the audio from the discriminator and feed it into the speech amp of the transmitter, probably in place of the miocrophone to make use of the preemphasis and to maintain proper audio shaping as well.

The deemphasis will be handled by the receiver so there should be no need to 'fiddle' with this section.

Active high to drive the darlington transistor, and activate the T/R relay for transmitter keying as well as feeding discriminator levels to the speech amp of the transmitter as well.

Of course a complete realignment will be required, especially the transmitter as you do not want the mic level to overdeviate the transmitter, or IMD products will be generated.

I suspect this is all high band gear you are running, as many F.Ds that I know of are located here, but you could be using UHF as well, and if this is the case, I have a really sweet and simple solution to your troubles.

My solution can also be used on VHF as well...

Well, you see that's the thing, the reciever outputs +4V from the speaker out when a remote station is transmitting (In close proximity to the reciever. Mind you by close proximity I mean maybe about ~ 10 - 20 yards.). This +4V output is enough to drive the relay to switch and key the transmitter.

However, the problem I'm having is (I'm just checking all my bases here), that apparently, when the remote station moves outside of the reciever proximity, the reciever must apparently, be putting out less voltage over the speaker out. Does this make sense?

-- EDIT --
I forgot to mention, I'm running VHF with a center of 155mhz.

That 4V you are measuring is probably not from the speaker as all audio is AC in nature, but the microphone does use that 4V for power due to the mic. being an electret condenser type which requires this voltage for power, and this is what I suspect you are seeing.

If the receiver ALC is operating, then there would be a corresponding drop in levels as the station moves away from the receiver as the power density is far greater in the near field than in the far field, so the level/s would be less as well.

I've taken measurements in the past of Genesis radios and have always had a tough time finding spots to tap from as many would load down the circuits and cause erratic behavior, plus the fact that many of the I.F and R.F paths are housed within the radio and not accessible from the back which makes it more of a problem(HT600 used for this test).

I'll take a peek in the service manual and try to find out more information on this topic as well.

Since you managed to pique my interest, I'll have to dig into this a little deeper I suppose!

Thank you for any assistance. Also thanks for taking a deeper look for me .

It sounds to me like you've rigged up some sort of system to key the transmitter based on received audio. Ordinarily the transmitter is keyed by a carrier operated relay. This is activated by either a carrier or the correct PL tone, not by audio from the speaker.

Either I'm not understanding correctly or . . .

Good luck.

With the MT1000, the speaker only opens on correct PL. Hence the hook up in that fashion.