Ic f121s - PTT detect

[thesavo]

Is it possible to program an f121s to open or close a relay on PTT?
I want to use power another receiver and turn it off when PTT is closed. I plan to operate with a receiver near the radio and don't want to blow the receiver on transmit.


Would I use the horn output?

Icom cs-f100 pinout

anyone help me with a link to a place with the mic pinout on this model? Thanks Al

forums.radioreference.com

 

[mmckenna]

Doesn't appear that the circuit is there that you'd need.

the Horn circuit is for driving a horn when a radio call triggers the circuit.
There are radios that will do what you need, but the F121 was kind of a lower tier radio and probably wasn't designed to do this sort of stuff. There might be a place internal to the radio that you could connect to do what you want, but if it's not designed for end user access, the interface might be a challenge.

There are RF controlled relays that will do what you want. They'd go in line with the coax and trigger a relay to power down your RX, or disconnect the antenna.

Might be a good option to upgrade your radio, also.

 

[thesavo]

OK. That is also what I was thinking if there was no PTT out. So need to look for an rf relay?

 

[mmckenna]

OK. That is also what I was thinking if there was no PTT out. So need to look for an rf relay?

RF Relay that will cover the VHF band, or build one (not horribly hard), or find one of the many other radios on the used market that will give you a PTT output.

 

[mmckenna]

Here's an expensive option:

MFJ-1708B, RF SENSING, TR SWITCH

MFJ RF Sense Transmit/Reveive Switch Replaced the MFJ-1708 Switches your antenna from receiver to transmitter using a relay. Shorts your receiver to ground during transmit. Use RF sensing with adjustable delay or PTT line. Has selectable open/short mute. RF Sensing for radios that do not have a...

mfjenterprises.com

Personally, for that price, I'd source a used Motorola CDM-750 VHF off e-bay. The 20 pin connector on the rear has programmable function pins that should give you what you need.

 

[thesavo]

If I can get a cdm 750 with programming included, it may be worth the price.
Thanks for the name of the TR switch.
The next question would be, are there special considerations for connecting a voice keyer to a cdm750 ?

 

[mmckenna]

The rear 20 pin connector on the CDM would have everything you need to connect an external PTT as well as getting audio in/out of the radio:

HT750/1250/1550/PRO5150/7150/9150/GP320/340/360/380/ GP318/338/GP640/680/1280/CDM750/CDM1250/CDM1550,etc.

The audio in/out often requires some massaging to meet the requirements of your external device.

 

[jeepsandradios]

Where are your antenna's and what receiver are you using ? I run 4 radios in my F150 along with a scanner and never had an issue other than minimal desence of the scanner while transmitting.

 

[thesavo]

I have a quarter wave mag mount a few feet away. The radio can transmitted 50 watts. I wanted to use with another radio listening on other frequencies.
I am concerned about blowing the front end on the other receiver.

 

[FKimble]

That close it better be a good radio, otherwise it can still take out the front end!

Frank

 

[mmckenna]

Yeah, you'll desense the receiver at minimum, risk blowing the front end.

You need separation between the antennas, unless your goal is to break something.

 

[thesavo]

Yeah, you'll desense the receiver at minimum, risk blowing the front end.

You need separation between the antennas, unless your goal is to break something.

So should I forgo the switch and just have a different antenna a few wavelengths away.

 

[mmckenna]

I would.

 

[12dbsinad]

If the antenna's are 24+ inches apart you probably won't blow out the front end, but will certainly render the other radio useless during transmit from severe desense. Do you need to run the radio at full output power? if you can cut it back to 25w it certainly won't hurt anything.