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Ranger 69ffb4

my2995dx

Active Member
Apr 2, 2005
294
74
38
lancaster pa
Question on this 69ffb4 when I have it hooked up to A99 I get higher swr on lower channels 1.8 now if I hook up my 98vhp or any other radio it's at a flat 1 would that be due to the amp section in this 69ffb4.
 

I would suspect that it is generating some harmonics. The harmonics are on a frequency that the antenna is not tuned to, and that part of the signal gets reflected at the antenna feed point. A low pass or band pass filter would fix this. If the amp section is being overdriven, that would cause it. Try reducing power to see if it helps.
 
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I would suspect that it is generating some harmonics. The harmonics are on a frequency that the antenna is not tuned to, and that part of the signal gets reflected at the antenna feed point. A low pass or band pass filter would fix this. If the amp section is being overdriven, that would cause it. Try reducing power to see if it helps.
Stays the same
 
Your radio may be suffering from an issue I have seen on 2 diferent rci69vhp. Mismatched mosfets in the driver or final section can cause oscillation which could explain the higher swr.
What are you using to measure the swr?
 
Dee 2000 swr/power meter also I have a analyzer mini 60 they both show 1.0 swr
When an amplifier or radio goes into oscilation it will output many other frequencies besides the 27mhz that your antenna is tuned for. Your antenna cannot radiate the rf that is outside of its resonance so all of that junk rf comes back as reflect/swr.

Because of the way the biasing works on the driver pair and final pair both mosfets in each section need to be matched for capacitance and vt or they will go into oscilation. I recomend replacing the driver and final pair with a set of Infineon Irz24n mosfets from digikey as I have received fakes when buying from ebay.
I have not seen this issue in a 69ffb4 but I have seen it in two 69vhp.
 
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When an amplifier or radio goes into oscilation it will output many other frequencies besides the 27mhz that your antenna is tuned for. Your antenna cannot radiate the rf that is outside of its resonance so all of that junk rf comes back as reflect/swr.

Because of the way the biasing works on the driver pair and final pair both mosfets in each section need to be matched for capacitance and vt or they will go into oscilation. I recomend replacing the driver and final pair with a set of Infineon Irz24n mosfets from digikey as I have received fakes when buying from ebay.
I have not seen this issue in a 69ffb4 but I have seen it in two 69vhp.
I'm going to check a few things here like my jumpers and.coax seems.Just a cobra 29 I have a 1.0 now if I put a 600 inline it also jumps up 2.5-3 so I want to check all coax I never had this problem before going to order new.driver and final also this is new to me
 
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Sometimes condensation in between sections of an aluminum antenna can cause swr spikes, I had this issue with my sigma venom until I used a stainless self taping screw to tie all of the sections together and the issue has not came back.
Also check the low pass filter coils in the cobra 29, If they are spread that is letting 54mhz through and when you amplify that you will get reflect. I had this Issue in a 2517 that a previous tech had spread the coils in. When I would run it into a 4pill it would make my swr rise to 3 to 1. After collapsing the coils no more high swr with the amp on.
 
Sometimes condensation in between sections of an aluminum antenna can cause swr spikes, I had this issue with my sigma venom until I used a stainless self taping screw to tie all of the sections together and the issue has not came back.
Also check the low pass filter coils in the cobra 29, If they are spread that is letting 54mhz through and when you amplify that you will get reflect. I had this Issue in a 2517 that a previous tech had spread the coils in. When I would run it into a 4pill it would make my swr rise to 3 to 1. After collapsing the coils no more high swr with the amp on.
I'll check that I also have a new pres Richard I forgot about I'm going to put that on and check it to see what I get
 
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Back in the day of when I was tweaking and cleaning up radios - one of the many things I used to see was improperly set MOSFET bias.

That high SWR, right there - is an indication of the MOSFET in with either the Driver, Final or both - are set too high and sending down the strip, everything - and putting it into that amp board.

The quickest way to fry those piggy boards was to try and raise power for swing to levels they want to see - by adjusting the Bias of the output of the Radio - into that amp.

You can tell that by just running the radio on your 40~50 amp power supply and look at the amount of current it was taking in. Turn on the amp and see 50% increase - well, to some they think it's fine, to others, no - more like 25% amperage increase makes better sense than to set the amp to Dead key what you think (by your meter not the ones they made the claims on. So if your meter seems stingy - the results of this test is on you) the wattage should be.

Put your hand on it and see if you wind up with Grill marks...if you feel it's getting hot, then you've got a problem further up the amps' chain, being the very top of what this post is about. Turn down the bias so they (your MOSFET's) don't stay on so long they spit out harmonics and throw it at the amp's input.

The amp is not filtered guys, the filtering for much of that output is in the Radios' strip on the radio board - ok?

High SWR on that radio - when all the other indications from all your other more-trusted equipment shows good, then the Canary in the Coal mine is trapped in the amps own mess at the radio - trust your instincts on this. If all other radios work on this system, then the new piece is the POS - fix it.

This is coming from a guy that had to replace, resoldered and reset a lot of Galaxy MOSFET radios just because of the Black n Decker Golden Powered High-Torque Miracle Mayhem tool they called a battery-powered screwdriver with interchangeable bits...
 
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