cobra 148 gtl pc-412GC I found a resistor from ground to R176,L34,C137 and r255 i'd like to know what is that for? radio it does only two watts IDK if the resistor is 150 ohms or 1500 ohms. Thats a new project to restore this radio.
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what is this ?
- Thread starter Robalo
- Start date
Is VR10 still in place? It looks like the pins are in the through holes in the board where those three wires are. It looks like they tried a variable power mod but left the original VR on the board.
It looks like an ANT WARN (SWR) mod, The original pot may have burnt up or they wanted to mess with the SWR side and so they dropped power thru this resistor to lessen the SWR SENSE limit an ANT Warn light from flashing or staying on...
I've seen them do this and I had to use similar for people wanting to use the 148 and Grants' to drive a High-Drive amp. The ANT light always blinked and sometimes stayed on - if the radio has ST or need to set SWR CAL inside the radio to view SWR direct - they did the "ANT Warn" light mod so they didn't see it winking at them when they modulated.
I've seen them do this and I had to use similar for people wanting to use the 148 and Grants' to drive a High-Drive amp. The ANT light always blinked and sometimes stayed on - if the radio has ST or need to set SWR CAL inside the radio to view SWR direct - they did the "ANT Warn" light mod so they didn't see it winking at them when they modulated.
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Ok got it radio with low key 2 to 3 watts am and 8 to 10 ssb it don’t do more and that ready for amp nice. Thank you all of you
It does not do more that two watts dk . And I never see that resistor before and I was wonder what kind off mod was.
Must be VR10 (AM Power) - versus VR12(SWR)...???
Although I don't think that is right to think it's VR 10 - the location of the Resistor (It's 150 ohms Brown-Green-Brown) By location it is VR 12 - towards the Rear Panel.
Heres a better "grab" showing coax connector and photos original orientation...
Which tends to lean towards someone setting up the radio for an AMP that had SWR issues - so they "drained off" the Reflective power AFTER the Sense pot...which to me is JMHO but he did ask "What is This?" and listed TWO questions - one it's value, the other the possible purpose...
They lowered the DK to 2 watts, but when you "Swing" into an AMP - you can generate a reflection back (by appearance or admittance) thru it's network - so the SWR ANT WARN light can start to blink, or if the amp has power settings, the higher power settings versus the lower ones - tend to have more "touchy" reflection issues,
This RF problem can cause a squeal in the Mic audio and or - even make the ANT light stay lit thru the keyup. So even though it's turned down - the SWR climbs because of the delicate balance the High Power setting is doing to the Radios' own network. And if the Amp is really off kilter, the SWR on any power level the AMP can switch to, can make any radio with an SWR sense circuit listening in to the Reflection side - would tend to turn off the radios TX side preventing further damage - it thinks can happen.
So to prevent that - we (Techs like us) step in and make the mess work in such a way that the radio can survive - yet provide a lot of conversation around the worktable from the stories the rest of us have about similar stuff...
SIGH...
Heres a better "grab" showing coax connector and photos original orientation...
Which tends to lean towards someone setting up the radio for an AMP that had SWR issues - so they "drained off" the Reflective power AFTER the Sense pot...which to me is JMHO but he did ask "What is This?" and listed TWO questions - one it's value, the other the possible purpose...
They lowered the DK to 2 watts, but when you "Swing" into an AMP - you can generate a reflection back (by appearance or admittance) thru it's network - so the SWR ANT WARN light can start to blink, or if the amp has power settings, the higher power settings versus the lower ones - tend to have more "touchy" reflection issues,
This RF problem can cause a squeal in the Mic audio and or - even make the ANT light stay lit thru the keyup. So even though it's turned down - the SWR climbs because of the delicate balance the High Power setting is doing to the Radios' own network. And if the Amp is really off kilter, the SWR on any power level the AMP can switch to, can make any radio with an SWR sense circuit listening in to the Reflection side - would tend to turn off the radios TX side preventing further damage - it thinks can happen.
So to prevent that - we (Techs like us) step in and make the mess work in such a way that the radio can survive - yet provide a lot of conversation around the worktable from the stories the rest of us have about similar stuff...
SIGH...
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