STRANGE RADIO HAPPENINGS - FREQUANCIES

[Switch Kit]

cybernet board - 02A PLL - radio is like new condition , problem , holds about half the frequncies on the radio OK , the other half are just blank on the freq counter with no power shown , if I use the VCO I can get the other half of the frequancies but I then lose the other half ? either way , power is more so on the lower side on either half of the frequancies that I can get, any ideas on what this might be ? Could it be the PLL ? thanks

 

[loosecannon]

VCO cant cover the range.
needs to be broadbanded.
if you have access to old "secret cb" books; they had lots of mods for the PLL02A SSB models.
maybe one about broadbanding in there. who knows. i'll look in mine if i get a chance.

you might try tuning it with the mic keyed, and go VERY slowly.
you might find a sweet spot where all channels are covered, or just a few on the edges are not. you might just have to get it "perfect". LOL just kidding!!!

when the VCO is "out of lock", there will be no RF power output.
best of luck with it,
loosecannon

 

[Switch Kit]

This is AM only model , couldn't find the "sweat" spot as you mentioned . My question was , could it have anything to do with the PLL ? I have many 02a chips , been kind of busy and was going to give it shot for all it was worth when I had the time. Thanks for the input LC

 

[HootyAl]

Hey switchkit, just a thought..but if your gonna replace the chip you might want to consider installing an ic socket..they're cheap as dirt and sure do make reinstalling a breeze!! No fear of damage from heat or static..usually pick em up at rat shack.Just count the number of pins and give them a call (let your fingers do the walkin) Hooty

 

[Crusher]

I think you may have to add a varactor diode to the VCO circuit. It has been a long while since I played with radios now mainly amp stuff. I'll look in my Thomas publishing books or the screwdrivers experts guide. Lou has some good stuff in that book if I remember right.

 

[loosecannon]

i looked at some old secret cb books, and even way back in the 80's, it seems they knew this chassis would only cover about 150 channels.
the solution i found was to add a second VCO block tuned to either the lower or higher freqs. using a relay.
seems like alot of work to me.

i did find a suggestion on the defpom site.
not sure if its for your particular chassis, but it looks like it should work.
here's a link to the page. the broadbanding stuff is just past halfway down the page.
there is a diagram.
http://www.radiomods.co.nz/addon_pll02amanual.html

good luck,
loosecannon

 

[Switch Kit]

changed the pll and it is still doing the same thing , varactor diode could be my next move. These radios are pretty cut and dry , they are 30 year old 40 channel radios that have met the test of time , every now and then I come across one that is very strange, but most of them always still work as they should, there are easy fixes and some will have you scratching your forhead for awhile , and if that should last for very long ? they will usually become a parts radio and or a shelf trophy. Thanks for all the replys on this one.