900 MHZ Spectra drops DPL

[dmurman]

I have two 900 mhz D37 Spectas that exibit the same problem. While transmitting the DLP will drop, then return. This has been confirmed by montoring on another radio with DPL enabled and watching the S-meter. The power does not drop. This happens intermittently. I have replace the drawer unit, cable, mic, control head and power cable. Only item I have not replaced is the antenna. The vehicle is a Ford Escape and the unit is mounted in the back. The power cable runs directly to the battery. The antenna is perminentally mounted on the roof towards the rear and to the center. I am suspecting that the problem may be RF getting into the radio causing the DLP to drop. Has any one else experienced this type of problem with the Spectra? I am going to lower the power to see if it is an RF issue.



David
WA4ECM

[Will]

Does your antenna have the required counterpoise? If too close to any edge you can have RF radiated back into the radio.

[dmurman]

I would take a picture but there is plenty of metal around the antenna. I swapped a different antenna, shorty in an inclosure so I'll see what happens on the way home if there is anyone on the repeater. Thanks for your reply.

[dmurman]

I changed the antenna and lowered the power. Still have the DPL dropping out intermittently. I set it on the bench and it does not exibit the problem. Going to scope out the power leads and check the transmitted signal with the spectrum analyzer.

[Will]

Is this a Ham or commercial frequency radio? Some of the so-called Ham mods do funny things to DPL modulation.

[dmurman]

Motorola Spectra is a commercial radio. Works fine on the bench and I used the second Motorola Spectra in the shack. Both trunk units.

[t95mwp]

Look at RF board for 10mf close to the R633 and make sure that resistor is properly soldered and replace that cap and all other ones.

[dmurman]

Well the problem was with the mic. Remembering that the mic controlled the receive PL/DPL when hung up I changed the mic and the problem is now gone. Looked inside the mic and I noticed that the red wire had been pinched and that the wire from the metal backing to the circuit board was not the same wire that Motorola would have used. Not sure what else was done to the mic. When I get time I'll see what in the mic would have caused the issue with the DPL dropping out on transmit.
Thanks to all that responded.