Kenwood TK-3180 seems to exhibit fencing on scan receptions

[K7HUT]

Same station listened to while not in scan, and the audio is constant.
When that station interrupts a scan, the 3 seconds of audio is usually choppy like a picket fencing type of behaviour.
Fades out and back in about like a 2Hz volume modulation or something like that.
Again, I can turn off scan, go to that station, and it's constant audio as one would expect.

Any ideas? Bad unit? Just got it off ebay.

p.s. have an TK-8180 in the truck that doesn't do that, fwiw.

 

[mmckenna]

It's not doing priority scan, is it?

 

[K7HUT]

Thanks mmckenna.

There is a Priority 1 Channel config'd, with tx and rx tones. AC Control is off, so I would not expect any interruptions from the Priority Channel, which is quiet this time of the night (our club repeater). The Scan Type is set to Single.

I would note that the green receive LED (carrier indicator) is blinking in concert with the audio fluttering of a channel receiving audio during Scan. The duty cycle of the LED/audio is like 80% on, 20% off, something like that. This is happening even with very strong channel signal reception. Strange.

 

[mmckenna]

Even if there is no traffic, it's going to bounce back and check.

Set your "look back time" to something longer. Sounds like you have it set to the default 0.50s

 

[K7HUT]

I see. Yes the lookback time (A) is set to 0.50 seconds. That is just about how long the audio is on for the channel that interrupts the Scan, before it goes off (maybe reverting back to the Priority Channel 1, interrupting the current channel for a moment to check on the Priority channel), and then back.

I'll try to set the Lookback A timer to like 3 seconds, and Lookback B to like 4 seconds.

Thanks for that tip!

 

[K7HUT]

Yup that resolves and explains the issue.

Found another thread that also explained it well:

TK-250 Pulsing Priority Scan

I have a TK-250G radio that has some problems when using priority scan. I have the radio set so that the selected channel is always priority. When I'm scanning, if there's traffic on a channel other than the selected (priority) channel, the traffic comes in pulsing. The audio pulses and the...

forums.radioreference.com

I guess my 8180 has a much smaller 'audio hole' than this handheld 3180 and I never noticed it. I would have thought by the part number that the chipsets inside were the same and that the 3180 would/could use the same settings as the 8180. My 8180 I think has all the default settings of 0.5 and 2.0 seconds for Lookback A and B timers but I never hear this hole before.

Thanks again Mcckenna.

 

[K7HUT]

Just to wrap it up, I adjusted the Look Back programming on my 8180, and yes, I now notice that the 'audio hole' created by looking back to the Priority Channel is much smaller on the mobile 8180 unit, vs the handheld 3180, and hence I never noticed it.

 

[DeoVindice]

I experienced the same issue with an NX-200. I'm not using priority scan anymore but might try it again with a longer lookback time.

 

[K7HUT]

I belong to a GMRS club where there are important nets to follow along during the daytime on one channel, so I like to have priority scan working for that channel, despite being in another zone scanning.

It's funny, just making the look back timer longer doesn't change the 'audio hole' length of time, but it sure seems to mask the annoyance of the interruption quite a bit.

 

[KK6ZTE]

It's funny, just making the look back timer longer doesn't change the 'audio hole' length of time, but it sure seems to mask the annoyance of the interruption quite a bit.

Why would it change the length of the audio hole? It still requires a certain amount of time to determine if there is traffic and if that traffic matches the decode conditions (PL/DPL/optional signalling)

 

[K7HUT]

I only repeat that notion from another thread I linked above, and it makes sense. A superior RF chain in a better quality radio architecture could make that 'certain amount of time' less, and a less well implemented DSP demod and matching filters, etc., could take more time. Check out the other thread, the poster explained it very clearly.