Sidebar Sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.

Broadbanding Vintage 23 channel rigs....

S

sdmahr

Active Member
Dec 14, 2012
154
31
38
Recently I've been integrating DDS VFO's into vintage, (early-mid 70's), 23 channel SSB radios with great results. The last remaining issue I'd like to make "better" is to broadband the radio to operate in a "wider" bandwidth than they will now. (Pretty narrow operating range)

Currently receive and transmit are strong in a range of about .500. I center the tuning at 27.425 and I'm good from 27.1XX - 27.6XX range. I've read that one can jump the pins of some of the adjustable coils and widen the radios ability to perform over a wider range. What I haven't been able to find is exactly what tuning coils are the ones that need to be "jumped", (a.k.a. using ends of coil taps rather that the centers).

I'd like to try the "broadbanding" first on a Cobra 138A if anybody has any suggestions or knowledge on which tanks are the ones to jump for expanded operation. (Lower "Q")

Thanks
 

sdmahr said:
Recently I've been integrating DDS VFO's into vintage, (early-mid 70's), 23 channel SSB radios with great results. The last remaining issue I'd like to make "better" is to broadband the radio to operate in a "wider" bandwidth than they will now. (Pretty narrow operating range)

Currently receive and transmit are strong in a range of about .500. I center the tuning at 27.425 and I'm good from 27.1XX - 27.6XX range. I've read that one can jump the pins of some of the adjustable coils and widen the radios ability to perform over a wider range. What I haven't been able to find is exactly what tuning coils are the ones that need to be "jumped", (a.k.a. using ends of coil taps rather that the centers).

I'd like to try the "broadbanding" first on a Cobra 138A if anybody has any suggestions or knowledge on which tanks are the ones to jump for expanded operation. (Lower "Q")

Thanks
Click to expand...
Nobody remembers any broadband mods for these old chassis? Cobra 138A? Midland SSB? (Same chassis), SBE Console II's ? KRACO ?? Radio works great but a very narrow operating range I'd like to EXPAND as to not lose RX and TX so fast.

Thanks for any input you can provide. I've come up empty on the net..
 
  • Like
Reactions: crappykraco
sdmahr said:
Nobody remembers any broadband mods for these old chassis? Cobra 138A? Midland SSB? (Same chassis), SBE Console II's ? KRACO ?? Radio works great but a very narrow operating range I'd like to EXPAND as to not lose RX and TX so fast.

Thanks for any input you can provide. I've come up empty on the net..
Click to expand...


That's cool that you are using the DDS VFO's to make these rigs useful in the 21st century. Try increasing C162 from 1pF to 3-5pF. T22 upstream doesn't look like it can be broadbanded in the usual way. Be sure to report results. Also see the link below if you haven't already. 73 and have fun!
www.cbcintl.com/docs/Broadbanding.pdf
 

dxChat
Help Users
  • No one is chatting at the moment.
  • @ BJ radionut:
  • @ BJ radionut:
  • @ Wildcat27:
    Hello I have a old school 2950 receives great on all modes and transmits great on AM but no transmit on SSB. Does anyone have any idea?
  • @ BJ radionut:
  • @ ButtFuzz:
    Good evening from Sunny Salem! What’s shaking?


      Top Bottom
      Back