President McKinley- Noise blanker

[ForestRunner98]

Hey WWDX!!

Is there a way to adjust the noise blanker in these radios?? Never worked like it should on AM or SSB. I couldn’t find anything in the manual or online. I figured it’s something that’s in a chip and can’t be adjusted.

Thank you all!!!
Bill

 

[nomadradio]

Can't remember which circuit board that one has in it. If it's a PC-385, you feed 25 MHz into the receiver, and peak L1 and L2. If either or both is way off peak, you'll need to turn down the signal level as you go, to keep the peak response sharp. Excess signal will flatten the peak when turning a slug.

Got used to using a noise-pulse generator and tweaking for minimum noise on SSB.

And if it's a different pc board, I'll have to track down Sams CB-219 at work when I get there this week. Most Uniden CB radios have at least one tuning slug in the noise blanker.

73

 

[ForestRunner98]

Thanks Nomad!! I didn’t want to go around turning stuff willy nilly. Funny that it’s not in the service manual.

 

[nomadradio]

Looked at Sams CB-219 today. Looks like the same circuit board as a President/Uniden Washington (5-pin mike). Can't remember Uniden's "PC" number for that one. PC-385, maybe?

The Sams says to apply a pulse source to the radio, along with a weak steady receive signal, and put your 'scope onto the test point. Tune L1 and L2 for max pulse amplitude.

I built a pulse generator decades ago just for radios like this. Has a variable output level. We just tweak the slugs in L1 and L2 for most effective blanking in sideband receive. Don't use AM, since this will place the AM-only ANL circuit into the receiver audio. Makes the function of the blanker harder to hear.

But that's what prompted me to build the pulse generator, was an alignment procedure that said to apply pulses to the radio's antenna input.

My earlier reference to 25 MHz was for the 1978 and earlier radios. They used a totally different blanker circuit than the radios that use the MB8719/8734 PLL chip.

73

 

[ForestRunner98]

Sounds good Nomad!! Would have been easier with one can but 2 is better than 4-5!!

Thank you again!!