I am really new at electronics projects. I am trying to build a repeater out of two mobile VHF radios and I'm not sure how to solve a problem I am having:

My main problem is with the radio that I want to transmit. It does not have VOX mode on it and I'm not sure how to get the first radio to trigger the second radio to transmit. Is there a simple way to do this or do I actually need a radio with VOX capability?

Thanks in advance for any and all help I may receive!

-David.

dspurg7310 wrote:
I am really new at electronics projects. I am trying to build a
repeater out of two mobile VHF radios and I'm not sure how to solve a
problem I am having:

My main problem is with the radio that I want to transmit. It does not
have VOX mode on it and I'm not sure how to get the first radio to
trigger the second radio to transmit. Is there a simple way to do this
or do I actually need a radio with VOX capability?

Thanks in advance for any and all help I may receive!

-David.

Surf over to the Repeater Builder page at
http://www.repeater-builder.com/products// They have lots of info on
repeaters and some of the problems associated with convertting a mobile unit
to repeater service.
Be sure to look at the technical info page at
http://www.repeater-builder.com/rbti...tml#main-index. It has lots of
links to other sites that might come in handy.
--
David
dgminala at mediacombb dot net

dspurg7310 wrote:

I am really new at electronics projects. I am trying to build a repeater
out of two mobile VHF radios and I'm not sure how to solve a problem I
am having:

My main problem is with the radio that I want to transmit. It does not
have VOX mode on it and I'm not sure how to get the first radio to
trigger the second radio to transmit. Is there a simple way to do this
or do I actually need a radio with VOX capability?

You need to build a circuit that connects the Squelch signal from your
receiving radio to the PTT input of the transmitting radio.
This could be as simple as a transistor and a resistor, it could add
some timer(s) and tone generator(s), or it could be a complicated circuit
with a microcontroller.
It all depends on how you want the repeater to behave.

Rob wrote:
dspurg7310 wrote:
I am really new at electronics projects. I am trying to build a repeater
out of two mobile VHF radios and I'm not sure how to solve a problem I
am having:

My main problem is with the radio that I want to transmit. It does not
have VOX mode on it and I'm not sure how to get the first radio to
trigger the second radio to transmit. Is there a simple way to do this
or do I actually need a radio with VOX capability?

You need to build a circuit that connects the Squelch signal from your
receiving radio to the PTT input of the transmitting radio.
This could be as simple as a transistor and a resistor, it could add
some timer(s) and tone generator(s), or it could be a complicated circuit
with a microcontroller.
It all depends on how you want the repeater to behave.

Ah, brings back memories! Permit me a few words of bandwidth.

I built our club's repeater in the 70s. WR4ARO, iirc. Don't recall
much but it was a Motorola Sensicon (A?) receiver strip and an RCA
transmitter strip. It wasn't quite as simple as tagging off the squelch
to key the xmtr, although that could work functionally. I built a COR
(Carrier Operated Relay) circuit from a 73 Magazine article.

The gist of it is that you need some 'hang-time' with a repeater to deal
with mobile drop outs, and you need to be able to sub in the callsign ID
at intervals and deal with timers and such to allow the thing to shut
off transmitting in the case of noise or a deadman on the mike.

Much easier these days since rptr circuits are more commonplace and
well-designed.


Think outside of the VOX box.

GL,
Bill

Bill M wrote:
Rob wrote:
dspurg7310 wrote:
I am really new at electronics projects. I am trying to build a repeater
out of two mobile VHF radios and I'm not sure how to solve a problem I
am having:

My main problem is with the radio that I want to transmit. It does not
have VOX mode on it and I'm not sure how to get the first radio to
trigger the second radio to transmit. Is there a simple way to do this
or do I actually need a radio with VOX capability?

You need to build a circuit that connects the Squelch signal from your
receiving radio to the PTT input of the transmitting radio.
This could be as simple as a transistor and a resistor, it could add
some timer(s) and tone generator(s), or it could be a complicated circuit
with a microcontroller.
It all depends on how you want the repeater to behave.

Ah, brings back memories! Permit me a few words of bandwidth.

I built our club's repeater in the 70s. WR4ARO, iirc. Don't recall
much but it was a Motorola Sensicon (A?) receiver strip and an RCA
transmitter strip. It wasn't quite as simple as tagging off the squelch
to key the xmtr, although that could work functionally. I built a COR
(Carrier Operated Relay) circuit from a 73 Magazine article.

The gist of it is that you need some 'hang-time' with a repeater to deal
with mobile drop outs, and you need to be able to sub in the callsign ID
at intervals and deal with timers and such to allow the thing to shut
off transmitting in the case of noise or a deadman on the mike.

That is why I wrote about timer(s) and tone generator(s). There are many
things you can add... In the 70s/80s people built very complicated
electronic circuits, but today it is normally done with a microcontroller
and software. Of course this can mean very complicated software...

On Apr 23, 5:51 pm, Bill M wrote:
Rob wrote:
dspurg7310 wrote:
I am really new at electronics projects. I am trying to build a repeater
out of two mobile VHF radios and I'm not sure how to solve a problem I
am having:

My main problem is with the radio that I want to transmit. It does not
have VOX mode on it and I'm not sure how to get the first radio to
trigger the second radio to transmit. Is there a simple way to do this
or do I actually need a radio with VOX capability?

You need to build a circuit that connects the Squelch signal from your
receiving radio to the PTT input of the transmitting radio.
This could be as simple as a transistor and a resistor, it could add
some timer(s) and tone generator(s), or it could be a complicated circuit
with a microcontroller.
It all depends on how you want the repeater to behave.

Ah, brings back memories! Permit me a few words of bandwidth.

I built our club's repeater in the 70s. WR4ARO, iirc. Don't recall
much but it was a Motorola Sensicon (A?) receiver strip and an RCA
transmitter strip. It wasn't quite as simple as tagging off the squelch
to key the xmtr, although that could work functionally. I built a COR
(Carrier Operated Relay) circuit from a 73 Magazine article.

The gist of it is that you need some 'hang-time' with a repeater to deal
with mobile drop outs, and you need to be able to sub in the callsign ID
at intervals and deal with timers and such to allow the thing to shut
off transmitting in the case of noise or a deadman on the mike.

Much easier these days since rptr circuits are more commonplace and
well-designed.

Think outside of the VOX box.

GL,
Bill

Hey OM:
VOX is easy. Take the 8 ohm speaker output, with a step up line
transformer, match the speaker output to the mike input.
Take a 1N914 rectify the audio from the mike input, unfiltered, to the
high capacitance input of a power FET. Put a 50K pot across the gate
to ground so you can adjust the "hang time". Use the FET to drive the
PTT.
Squelch the the receive radio, so now you gots VOX to the
transmitter.
Soon as the receive radio unsquelches it keys the transmit.

The caveat here is: if you interfere with a co-ordinated repeater, you
going to have to work it out, you might end up on the losing end of
that, because you can't become co-ordinated by a State co-ordinating
counsel.

73 OM
de n8zu

Wow, thanks everyone! That's a lot of information to go through! lol Being that I am so new to this though, I was hoping maybe someone would have a simple way to make this work and have a diagram and instructions on how to accomplish this task the easiest but most effective way. Keep in mind, I am new, so lots of detail would be great! As I learn more about electronics and circuits, I will keep a lot of this information you have given me as reference and hopefully learn a lot! Thanks again!

-David.

"dspurg7310" wrote in message
...

Wow, thanks everyone! That's a lot of information to go through! lol
Being that I am so new to this though, I was hoping maybe someone would
have a simple way to make this work and have a diagram and instructions
on how to accomplish this task the easiest but most effective way. Keep
in mind, I am new, so lots of detail would be great! As I learn more
about electronics and circuits, I will keep a lot of this information
you have given me as reference and hopefully learn a lot! Thanks
again!

-David.


Basic repeater controllers are cheap these days.
I'm using a CAT-1000 on my 2 meter machine.
The biggest problem you will need to overcome
is receiver desens when the transmitter is keyed.

Unfortunately that takes a lot of horizontal real
estate to obtain satisfactory isolation between the RX and TX
antennas. The best way is to use a good quality duplexer on a
single antenna, but now your talking about a major expense.

Pete

I really need to clean out the old posts from my local cache...