As the headline says, I noticed my RCI 69ffb4 SWRs shoot way up, pinging the meter when I turn the RF power (dk) all the way down. When turned all the way up, they drop to the 1.3 area. I asked a cb "tech" why that was, and he said he never heard of this. Anyone have an answer, or even an educated guess?
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SWRs increase as RF power turned down
- Thread starter Slowpoke
- Start date
Shadetree Mechanic
Delaware Base Station 808
I have seen amplifiers do this. The cure involves increasing the negative feedback of the output transistors to keep them from oscillating.
All of my amps do this, 1.5 SWR with DK set @1 swinging the rest, but they drop back to normal as soon as I modulate to 1.1 SWR. I've never worried about it as I don't hold a DK for more than a second or two. My DX500V is the worst at 1.8 then dropping to 1.2 on modulation. As for the "cause" I have to go with Shadetree because I honestly don't know.
Would that be considered "reverse swing?" I've seen that on yt vids. They usually correct it. My concern is, if I go low dk, the swr pings the high end. On max dk (not sure, but I thinks max is set at 25%, or 112w) low at maybe 25w, I have to check, it lowers to now, after more tweaking the quad wound tip, 1.15-1.3.
Reverse or backwards swing is referring to the output power....usually from too high of a DK, too much drive into the amp, a poorly tuned radio or amp, assuming the antenna is resonant.
Right, the modulation. The vids I watched show the modulation swing backwards, until corrected. I thought that's what you were referring to. My mistake.
Has your rig been worked on? If so, has it always done this or just started? What antenna and coax are you using?
Turn the modulation on the radio all the way down and then drop the power and see if it still does it.
I'm wondering if you're getting feedback somewhere when the dead key is dropped.
I'm wondering if you're getting feedback somewhere when the dead key is dropped.
AmericanEagle575
Supporting Sr. Member WDX-1863
Does your Tech know you have an "auto SWR" board?
The SWR card, is the riser in the back - by the antenna connector jack.
Contains two pots, my info isn't current, but you might need the tech to simply redo the tune-up steps to see if he can fix the condition.
But...(isn't there always a condition - conjunction - Junction - What's your Function?)
There are two problems with "auto SWR" - you have to remember.
One main one is, you cannot turn it off. IT's always on - but you can switch the meter so you can watch something else.
Kinda like the older On-Air arial TV - when bored waiting for the Game to start - you could always...
This could be a while...
But the second one is even knowing the SWR - in order to MEASURE it, it needs a "carrier" to calibrate against - so if someone's done mods or let it do the "swing thing" - then that is why the SWR skyrockets. It' does not have enough forward power (needs carrier) to properly calibrate and display SWR - so it sees any wild swing with no carrier - as High SWR.
So, mods can cause the condition (extra overhead) allowing more audio-in thru causing - allowing more audio "presence" and can create a ultrasonic (EHAF Extremely High-Audio Frequency) squeal you can't hear but your audio chip will get extremely hot from it - THEN YOU KNOW, even a mal-aligned TX Mixer to Band-pass filter cans alignment gone wrong or even the Carrier Bal - botched Balanced Modulator adjustment - can push an IF signal into the TX strip causing the mis-calibration.
The SWR card, is the riser in the back - by the antenna connector jack.
Contains two pots, my info isn't current, but you might need the tech to simply redo the tune-up steps to see if he can fix the condition.
But...(isn't there always a condition - conjunction - Junction - What's your Function?)
There are two problems with "auto SWR" - you have to remember.
One main one is, you cannot turn it off. IT's always on - but you can switch the meter so you can watch something else.
Kinda like the older On-Air arial TV - when bored waiting for the Game to start - you could always...
This could be a while...
But the second one is even knowing the SWR - in order to MEASURE it, it needs a "carrier" to calibrate against - so if someone's done mods or let it do the "swing thing" - then that is why the SWR skyrockets. It' does not have enough forward power (needs carrier) to properly calibrate and display SWR - so it sees any wild swing with no carrier - as High SWR.
So, mods can cause the condition (extra overhead) allowing more audio-in thru causing - allowing more audio "presence" and can create a ultrasonic (EHAF Extremely High-Audio Frequency) squeal you can't hear but your audio chip will get extremely hot from it - THEN YOU KNOW, even a mal-aligned TX Mixer to Band-pass filter cans alignment gone wrong or even the Carrier Bal - botched Balanced Modulator adjustment - can push an IF signal into the TX strip causing the mis-calibration.
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It's a new RCI 69ffb4, a higher end Wilson coax, all ss mounts, connectors, procomm quad antenna, and extra ground straps.
- No one is chatting at the moment.