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XPR4550 UHF remote "hum on transmit 1-1.5 seconds"

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256QAM
Posts: 64
Joined: Fri Oct 14, 2011 3:29 pm

XPR4550 UHF remote "hum on transmit 1-1.5 seconds"

Postby 256QAM » Sat Jun 25, 2016 8:54 am

Dash mount radio worked great as a bench radio. Installed in vehicle, remoted with PMLN5404A kit and 5 meter cable. On analog wide band ham modes, awful hum/buzz on transmit for the first 1-1.5 seconds before it levels out to regular audio. Tried moving to a separate Astron power supply to bypass the vehicle electrical system with same results. Upgraded to latest 1.x mobile firmware, same result. Disabled MDC1200 signaling in mode, same issue. XTL5000 in same vehicle on VHF works flawlessly, tied to same electrical point. Removed GPS antenna, same result.

Remote kit problem maybe?

Was able to find a hint of this same problem a couple years back on the forum but not resolution post:

Code: Select all

Re: XPR5550/5350 Hum on Transmit
Unread postby WB4JGI » Mon Apr 09, 2012 10:44 am

I have that same problem on my 4550 mobile on a UHF ham frequency. The hum will begin when I press the PTT and will stay for around 1-1.5 seconds.
Maybe they'll release that update for the older model radios. I'd love to upgrade to a 5550 I just can't due to there not being a remote mount option for it yet.

256QAM
Posts: 64
Joined: Fri Oct 14, 2011 3:29 pm

Re: XPR4550 UHF remote "hum on transmit 1-1.5 seconds"

Postby 256QAM » Sat Jun 25, 2016 1:04 pm

Update -

Took the radio out of the vehicle entirely, converted back to dash mount, bench power supply and different antenna, same buzz on transmit.

256QAM
Posts: 64
Joined: Fri Oct 14, 2011 3:29 pm

Re: XPR4550 UHF remote "hum on transmit 1-1.5 seconds"

Postby 256QAM » Sat Jun 25, 2016 2:12 pm

Another update -

Placed radio in RF Test Mode and ran through the channels, with the hand mic, keys up perfectly with no audio distortions. Switched back in to the standard codeplug mode and still hearing the distortions. Reverted back to a codeplug from December and still has the big bold audio hum on key up. Disabled battery saver, no change. AGC not active in analog or digital.

256QAM
Posts: 64
Joined: Fri Oct 14, 2011 3:29 pm

Re: XPR4550 UHF remote "hum on transmit 1-1.5 seconds"

Postby 256QAM » Sun Jun 26, 2016 2:49 pm

Test day 3...

Pulled radio to PTT using rear accessory connector (Pin 17 PTT to Pin 16 Ground) and the noise is gone. Key up with hand mic and the buzz is back. Key back up with rear connector and the noise is gone. Remain keyed up with rear PTT and key up and mic, the buzz is present until the hand mic is unkeyed. Bad mic? Just want to confirm before I order a new one.


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