Icom IC-FR4000 Repeater issue

[Cowley639]

I'm having an issue with a Icom IC-FR4000 UHF repeater. We just installed this repeater to replace an aging Motorola Quantar. The repeater is installed in a building (antenna is 90ft AGL) with about 50ft of 1/2" hardline, a Comet CA-712EFC antenna, and an older Motorola Duplexer (not sure the model). The repeater is programmed on 464/469 repeater pair with a 141.3 PL tone.

This issue is; when a user key's up on the repeater, the repeater transmits just fine with good clean, clear audio. However when the user un-keys and the repeater tail takes over, occasionally the users radios receive static for a split second or two over the repeater tail (the tail is set to 2 seconds). Sometimes this happens, sometimes it doesn't. I've had users report this using both Motorola XTS, and Kenwood TK radios.

Is there any way to prevent this? Maybe something i've overlooked in the programming? Could I just shorten the repeater tail?

Any help would be greatly appreciated. Thank you!

 

[prcguy]

I would run a desense test to make sure the repeater and duplexer are playing nice together. I suspect a weak signal into the repeater would also be noisier with the transmitter on vs off. The Quantar is many times more repeater than the Icom considering quality and performance and it could be the Quantar receiver is a bit more immune to duplexer problems.

 

[Cowley639]

I don't have a way to test desense, plus I have limited knowledge on that front. Would a duplexer re-tune help? It's been six years since it's been tuned (which was when we initially installed the repeater).

 

[jeepsandradios]

Could be the repeater. ICOM UHF FR4000 units had issues with oscillating internally. I have 2 on a shelf that do it when it gets cold. Last one i sent back to ICOM lasted a year and now its happening again. I'll most likely replace it with a Quantar when the snow clears up.

 

[prcguy]

The most common cause of desense is a mistuned duplexer or one that does not have enough TX/RX isolation. Its best to test and tune them at the site as transportation to the site can detune a duplexer. I don't want to recommend tuning it unless you can do it at the site and if you have to pay someone to travel with equipment that's going to be expensive.

You might try a test like shutting off the repeater transmitter or capping it with a load then monitor very weak signals like hand helds at a distance using the speaker in the repeater. Then connect the transmitter back up and listen again at the repeater speaker to see if the weak signals are being interfered with when the repeater transmitter broadcasting. If not then your duplexer is less of a suspect.

If you are very careful you could take the repeater and duplexer and all associated cables to your radio guy and have it tested as a complete unit. They should test into a service monitor then into a test antenna and do a desense test under full duplex into the antenna. If they find a problem it can then be fixed in the shop but now you have to get it back to the repeater site without disturbing anything. This can also find other known problems as mentioned above. BTW, what does the duplexer look like, a series of four to six round or square cans about 4" in dia or a little flat pack thing about the size of a book?

You could also stick the Quantar back in and I would first do some testing with very weak stations then immediately connect the Quantar and repeat with the same radios at the same distance. If not PM me with a good price on the Quantar and I'll give it a good home.

I don't have a way to test desense, plus I have limited knowledge on that front. Would a duplexer re-tune help? It's been six years since it's been tuned (which was when we initially installed the repeater).

 

[12dbsinad]

1) make sure your repeater isn't unsquelched

2) Icom sometimes does not detect other brands reverse burst. This can cause a squelch clash when a user un-keys. Try changing from No-tone to Phase on tone burst setting and see if that helps. You may not solve it completely but the squelch burst should be fairly short, not go on for seconds at a time.

 

[Cowley639]

Going to have a friend of mine (who works for a radio shop) come to the site and look at everything this weekend, and possibly re-tune the duplexer on-site if needed. So hopefully that will help.

prcguy, check your PM

 

[said73us]

Hi
Tune the duplexer to both RX and TX frequencies ,IF not , you will fined high reflection during transmitting