Repeater/Simplex trasmitter question

[FMROB]

Here is another stupid custom application I want to run past the masses.

Have a customer who has a two three site voted system with one quantar. They want repeater fire ground so people can listen from a distance while operating direct on the input side of the repeater. So in other words, operate point to point on the portable radios on the input of the repeater. This allows the dispatch to have a big ear, fire ground ops to remain simplex, and its repeater.. Great.

Now IF the dispatch needs to acknowedge and emergency transmission (not happening often) he will be talking on the repeater output (not good).

So I need to have this system operate in repeater mode, however when the console keys up the quantar will TX on lets say CH2 (input channel of repeater). Im thinking of using a TX/RX releay off the rear of the quantar to disconnect the duplexer and connect ther transmitter to the antenna directly upon CH2 key up.

Issues:

1) its going through as JPS voter (I think it supports non standard key tones)??

2) The quantar is TRC from the JPS. How would you operate the TRRX relay?

Im fried, please help..


Thanks, Rob

[Bill_G]

Don't mess with switching the duplexer in and out. Have them put simplex repeaters in their command vehicles. The crew can work a simplex TAC channel on scene, but it will be repeated to dispatch through the commander. Dispatch will hear everything. If dispatch needs to talk on the main channel, they can. When the incident is done, the BC turns off the repeater.

[FMROB]

Bill,

I got what your saying, but I don't think that I can pull that off. They have all the infrastructure working now, but the dispatcher has to now change channels on a control station radio to reply on fire ground. This is obviously a much lower height antenna and poor way of doing this, thus the work around at the actual repeater.

[MassFD]

Raise the control station antenna and let the dispatcher use that as his normal means of talking over the repeater via the TRC. Lets say the Quantar has a 20 W output, if the dispatcher has a 20W control station that has the same antenna height as the Quantar when he talks on the control station he will be at 20W on the input and the output.

Not the way we do it, we still have GM-300s on FG repeat and when the dispatcher keys he is keying both the TX and the RX radio at the same time. Both TXers are combined by the duplexer and TX from the same antenna. Most likely not FCC approved but either is portable to portable communication on a repeater input freq.

Thats the only 2 ways I know how to do it.

[Bill_G]

That would work. Moving TRC over from the voter to a control station with an antenna at or near elevation with the repeater antenna would have a similar footprint even 6db down. Dispatch would participate in the system like every other user, and they would not have to change "channels" on the desktop to talk to an incident on the input freq. It would be transparent for dispatch.

What dispatch would lose is the full duplex audio with the voter, but only if they are using four wire. With a control station, they are automatically half duplex and could not receive field units while they were transmitting. You don't want to split the phone lines between the voter and the control station because you'll set up a feedback loop in their headsets as their mic returns to their earpiece. Dispatch would also lose supervision over the repeater, but that might be a big issue.

Overdriving the rcvr input with the power from a control station isn't a big deal. Quantars were designed for harsh rf environments including busy sites with towers that look like porcupines. If you give some horizontal separation of even 10ft, you've helped protect the rcvr from overload. For certain you've overcome the issue of dispatch supervisory control.

I think you have a winner Rob. Push this option with the customer.

[FMROB]

Kevin,

Thanks what I am looking to do, but with the quantar. I guess I could use a different FT like 1750 to TX on channel 2, which I could program the input into the quantar. The problem is that the duplexer will be way out of tune. I will be squeezing 473.xxxx through the the port which will be tuned for 470.xxxx. I am utilizing a 526 EMR/RFS duplexer. As far as moving or installing any new antennas, thats a no go. It is a north shore department and HQs is in the low spot, so TX out of HQ is marginal at best. I can't add any more antenna real estate at the tower site. I am stuck with the one antenna and quantar. The other issue is the JPS voter and FT selection.

Thanks, Rob

[MassFD]

Yea, the Quantar creates a problem there.

I would not try to Xmit 473 out of the Quantar as the duplexer tuning on the Xmit side is tuned to pass 470 and notch 473 the VSWR mismatch may just shut down the TX, if not any 473 that did get past the notch and to the antenna port would also have a direct path to thru the RX can and wipe out the front end of the receiver.

Your original idea of taking the duplexer out of the path with a coax relay could work but I would worry about what happens if the relay does not switch, could wipe out the receiver.

When we get rid of the GM300's and CDM repeaters we are going to go with the high power control station. I have the tower space and the antenna and feedline are aready in place.

Wish I had something else to offer, will keep thinking.

[FMROB]

Ok, So here is my other idea. Co Locate with the quantar a stand alone CDM + tone remote radio wired in line with the TX wire line for the Quantar. From the PTT line of the tone remote activate the coaxial realy to simply switch over and interrupt the antenna line of the duplexer of the quantar setup. I might be able to accomplish this with a differnet key tone like 1850. I don't see any backfeed to the quantar as the relay would prevent this. Thoughts??

This is bulky and not as clean as I would like it to be, but I am albit puzzled by this

[MassFD]

I think that could work but I see a problem.

I know the Quantar is on a voter, The receivers will hear the CDM on the input and attempt to key the Quantar via the TX wireline thay share, if the Quantar does key it will not have an antenna as the CDM is using it. The same will also happen if the Quantar has in cabinet repeat, local receiver is going to hear the CDM and try to localy repeate it with no antenna connected.

[FMROB]

Yes, good catch. I geuss I cold also use the tone remote PTT line to power TX Inhibit on the quantar? I remember a pin in the rear for that function. I will have to look at the manual to see.?

I wish there was an easier way of doing this

[MassFD]

The TX inhibit would work but you will still have a problem shareing the TX wireline. When the CDM Xmits on the input the remore receivers will hear it and the voter will attempt to key the Quantar using the shared TX wireline.
Now you have 2 devices (console for the CDM and Voter for Quantar) generating tones on the same wireline. You need a seperate wireline for the CDM.