Pro-83 issue with close call on VHF-HI

[grem467]

a buddy of mine pointed something wierd out to me, and has been confirmed so far on 2 different scanners... on VHF-HI, in close call mode, if the signal is too strong, the radio wont detect it. It wont pick up a 50w mobile from inside the car, but has no problem detecting it @ 10w.. if a 1w portable is too close to it, it also wont detect it till the transmitter is moved away.

Make note that this does NOT happen on VHF-lo, UHF or 800, as i can have it on top of my 50w spectra, and have my 5w portable touching the dang thing and it locks every time.. seems to be an anomaly with VHF-HI as it can lock on to a 5w CB sitting next to the antenna. I am unable to determine if this affects air band or not, as i do not have an air-band transmitter to test with.

Im wondering if they made VHF-HI so sensitive that a strong signal overloads it, odd that it doesnt do it on any other band ive tested though.

 

[johnvassel]

I suspect that the close proximity creates too many 'hits' on the radio, and somehow increases dramatically the point at which it will unsquelch and find a signal.
Is it really a flaw? How often are we 1 foot from the 'unknown' transmitter?

john

 

[grem467]

well on a portable i will agree, but the fact that it wouldnt pick up a 50 / 25 watt signal till it was some distance away was the main point.

also the fact that it doesnt do it on any other of the close call bands.

 

[johnvassel]

well on a portable i will agree, but the fact that it wouldnt pick up a 50 / 25 watt signal till it was some distance away was the main point.

also the fact that it doesnt do it on any other of the close call bands.

I'll try and duplicate your results when I get in my truck tomorrow.
But, testing my 83 on the day I got it, 50w vhf and 35 uhf (and less) I never noticed it 'not' picking up a signal.


john

 

[The_Inspector]

Perhaps the scanner has an AGC (automatic gain control circuit) in it and is active in strong RF fields. This would be a good thing as it is a safety feature, keeping the scanner's "front-end" semiconductors from blowing from overload...Just a hunch.