Motorola Desktop Repeater TX RF Feedback?

[wrds815]

Hello Everyone,

 

Hope all is well with you and your families.  As a side project I've been building a small personal/emergency repeater at my home for the last couple months.  Finally got the the right antenna and tuned to my repeater frequencies.  All using LMR400 cable, Ed Wong antenna and a cell wave duplexer tuned by a professional with readouts.  

 

I am using a CDR700 desktop system with two CDM750 radios using CPS R06.12.05 and a RICK

 

I also incorporated an Argent Data System ADS-SR1 for repeater ID and "remote" knock down. This was a little extra project that I got working with the RICKs accessory port.

 

Anyways to the issue...

 

Recently I noticed the repeater would get stuck in TX mode with a high pitch tone and this would happen randomly.  After checking CPS and swapping TX and RX radios, I am having the same issue.  Keep in mind I am still new to these radios.  This would happen if I used my HT or used the TX radio direct with a mic.

 

So I further tested the radios doing process of elimination, I turned off the RX radio and the issue when I TX stopped, however this is the weird part.  My RX radio is off via the front push in power control.  Even though I don't hear my voice on the TX radio, it somehow receiving my signal from my HT.  TX radio is programmed for TX only but somehow receiving and transmitting at the same time???  I see my RICK activate COR when I use my HT and I can hear myself on my other HT radio. I am TX on 467.6250 and RX 462.6250 on my HT.  My TX repeater radio only has 462.6250 programmed.

 

I swapped the radios again and same issue.  Is my RICK doing something weird? My ADS-SR1 is not connected and nothing on the accessory port.  Is the RX radio still on somehow even though its supposed to be off.  If I disconnect the RICK from the RX Accessory port the RICK shuts off as it receives power from it.   I am lost and would appreciate anyone's idea on this problem.  

 

Thanks so much for reading my post. 

 

Phil

[gortex2]

So some issues come to mind. First is get rid of the LMR400. 

 

How is your CDM programmed. TX radio should be programmed for 462.625 TX And RX. RX radio should be programmed for 467.625 TX and RX. You cannot program a radio for TX only so i assume something is amis on the CDM. with a mic on the CDM you should be able to TX to your HT with no issues, and then recieve you HT on the RX radio with all the RICK unplugged. The rick is pretty basic and the description you mention looks like programming.

 

Also where is antenna located ? away from equipment I assume ? 

[wrds815]

So some issues come to mind. First is get rid of the LMR400. 

 

How is your CDM programmed. TX radio should be programmed for 462.625 TX And RX. RX radio should be programmed for 467.625 TX and RX. You cannot program a radio for TX only so i assume something is amis on the CDM. with a mic on the CDM you should be able to TX to your HT with no issues, and then recieve you HT on the RX radio with all the RICK unplugged. The rick is pretty basic and the description you mention looks like programming.

 

Also where is antenna located ? away from equipment I assume ? 

 

Hi kb2ztx,

 

Thank you for your reply and input into this matter. Sorry I didn't get any notifications that you did. 

 

The radios are programmed with TX or RX only personality with the exact frequency for TX and RX as you had mentioned.  However, for the TX radio it does allow me to program both TX and RX but under the advanced tab in CPS. 6.12.05 it has a check off for TX only personality which is activated.  

 

I am able to TX direct from the CDM and receive on the RX radio without the RICK.  

 

The antenna is on my chimney on a 10' pole using an ED Fong Antenna.  However, there is approx 15' of CAT5e cable without any power running adjacent to the LMR.  Do you think this could be the issue? I have read mixed reviews on LMR. Do you suggest I use Heliax?

Thanks for you time.

 

Phil

[gortex2]

The CAT5 should not be causing your issues. What duplexer and cables are you using ? Did you buy the LMR premade ? Did you put a watt meter on it yet ? It really appears your are getting RF someplace it should not be.

[wrds815]

The CAT5 should not be causing your issues. What duplexer and cables are you using ? Did you buy the LMR premade ? Did you put a watt meter on it yet ? It really appears your are getting RF someplace it should not be.

 

I am using a recently tuned by a motorola dealer Cellwave 50watt duplexer.  LMR was premade at 50'.  I used a surecom meter and it the TX is 99%.  SWR 1.4. I am using all N connectors except for the short jumper coming from the radio duplexer.  It's all the original copper looking coax that came with the radios.  

 

There is a camera attached to the same pole as the antenna, thats where the cat5e cable comes into play.  Otherwise they are separated in the attic.  Power input is not even near the coax or cat5e.

[wrds815]

The CAT5 should not be causing your issues. What duplexer and cables are you using ? Did you buy the LMR premade ? Did you put a watt meter on it yet ? It really appears your are getting RF someplace it should not be.

 

So after further testing and hooking up another repeater.  Looks like its an antenna line problem.  I should take the antenna off and use a dummy load to test the feed line, and then remove the camera on the pole.