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High SWR with amp

Discussion in 'CB Antennas' started by Supspt454, Jan 25, 2020.

  1. M0GVZ

    M0GVZ Sr. Member

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    That's actually a good thing, it eliminates the RF grounding of the antenna because if that had been the issue you'd have noticed the SWR changing when you changed the length of the coax. I can guarantee you it will not be the antenna itself. They'll easily handle anything reasonable you can throw at them and you'd melt the RG58 before you killed the antenna.

    As loosecannon has implied you need to use an external SWR meter between the amp and antenna to check the SWR is still Ok there. If it is then the culprit is the input matching circuit tuning on the amp.


     
    2NC995 likes this.

  2. Tokin

    Tokin 42Zero Tampa

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    Bad match sosmewhere. Possibly a bad jumper/pl259/connector if you didnt previously have issues with the amp. Make a list and start knocking them off one by one till you find it.
     
    RT431 likes this.
  3. Redbeard U812

    Redbeard U812 WDX-1030 / U812 South Texas

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    Turn that variable pwr way down or you're gonna pop something. If you are putting more than prescribed into the amp gonna have blue smoke. Like LC asked, why run a 955 into a HD? My 497 would swing over 135w . I looked into running an amp with the 497 but it wasn't cost effective, would only cause problems.
     
    RT431 and Woody-202 like this.
  4. Supspt454

    Supspt454 Member

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    Radio DK 1/2 watt with VR all the way down. Swings to 70ish. Again, I didn’t want this radio maxed out. I had the high drive built for this radio with intentions on keeping everything happy and cool. I’ve changed coax lengths between radio and amp, and amp and antenna, every way you can think of. I’ve checked swr with an inline meter both before and after amp, all with diff lengths coax. It took all day. I’ve checked impedance on every jumper, every ground, every center conductor in the system. I’ve check antenna ground and even added a temporary ground to the antenna just to see what happened. Nothing I have done has changed anything. EXCEPT... (this is where it gets weird). Assuming the radio swr meter is a way to see a rise or fall in reflectivity back into the radio, which is spiking up and causing my radio to go into swr protect mode, when I leave my property and get a quarter mile down the road, everything works as it should. I tested this by driving to town this morning and just happened to try it having spent all day messing with it yesterday. Radio swr never got over 1.5 when I was away from my property. The closer I got back to my place the swr rose back and when I pulled in the driveway it went back into swr protect mode. I’ve got some very strange happenings going on here. Maybe this is where they are filming “Stranger Things” season 4???
     
  5. Supspt454

    Supspt454 Member

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    This only takes place when the amp is powered on. When it’s off, everything works as it should. Turn it on and goes crazy unless I drive away from my house. Oh and by the way, when I get down the road, it doesn’t matter if I’m in transit or stopped. It just works.. get close to my house again and, we’ll, ive explained that already. ‍♂️
     
    Tallman likes this.
  6. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    The amp is not the problem. Why are you testing close to a house? When I setup and test I am in a big parking lot away from the light poles and power lines.
     
    #21 Tallman, Jan 26, 2020
    Last edited: Jan 26, 2020
  7. Redbeard U812

    Redbeard U812 WDX-1030 / U812 South Texas

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    I'm just one for hard mounts, better grounding. But that is real strange, close proximity to homestead and hi swr. Guess your radio is like my dogs, at home they act up, but in truck they behave. Dogs love trucks, guessing your radio likes truck rides too? :D
     
    Woody-202 likes this.
  8. SIX-SHOOTER

    SIX-SHOOTER Sr. Member

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    I'm guessing the amplifier does not have a tuned input?

    SIX-SHOOTER
     
  9. loosecannon

    loosecannon Sr. Member

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    sounds like you've got it all figured out.
    just don't key up in the driveway and you're all good.
    LC
     
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  10. Supspt454

    Supspt454 Member

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    Nah. It was just a teaser. It started again on another drive. Back to square one.
     
  11. loosecannon

    loosecannon Sr. Member

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    ok try something for me.

    set the deadkey of the stryker at 2 watts, and check the SWR into the amp (amp on of course) using the built in meter on the stryker.

    what is that SWR?
    is it better or worse than it was when you had the deadkey set at 1/2 a watt?

    if it improved, try messing with the deadkey, setting it for 1 watt, 3 watts, maybe even 4 if the SWR still seems to be going down when increasing power.

    let us know the actual numbers you note at each power level.
    LC
     
    AudioShockwav and Tokin like this.
  12. Tokin

    Tokin 42Zero Tampa

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    Thinking the same thing LC. That amp may not like such a low dk. Typically you want a dk of 1w or more.
    I say make a list of everything it can be and start checking them off one by one till you find the solution.
     
  13. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Hmmm...

    Never did say the Texas Star Amp - was it on the SSB delay or not?

    Why - well when you run low power into an Amp - that's one thing - you can adjust D/K for that to obtain enough "keydown" and keep it down - but if you run a swinger radio and then expect a low-SWR on all ranges of power - that is not the best way to run it.

    That's an issue of Class - when in SSB MODE it's more of an AB amp - loose term...

    When you run the swing into a Class C - when you get choppy results on a low DK that is TOO LOW for that amp to work right.

    So the "Swing Thing" - either you limit it (not so much) and tune DK up higher for bottom limit results (Hold relay in) - or try running more into the SSB delay mode (heck disconnect it and run a direct key to that mess if you have to just to keep SSB mode without the annoying delay) So your low Dead Key can keep working the amp without running into a Full on to partially cut off state due to it (D/K).

    I'm thinking your amps SWR problem is due to how the input network is handling signal weaker than it should be...Relay chatter or swamped input tune(d) stuff...
     
    #28 Handy Andy, Jan 27, 2020
    Last edited: Jan 27, 2020
  14. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    I read further into your posts and I caught this...
    HoldThisCoax.jpg

    That is a good way to look at this - "Stranger Things" ...

    I think we may have answered the question when you said you started to drive away...

    That usually indicates the Alternator is now putting out enough current into the system to top off the battery and offset the voltage drop that amp starts to draw down using the system...

    It affects your deadkey as well as voltage drop - a simple drive under load, wham - the alternator kicks in to offset it.

    So the "drive away" and then the slowing down of the vehicle to your neighborhood ...
    ItGetsalittlerougho.jpg
    Seems to tell me you issue is you need more RF power from radio - D/K to amp related.

    So that means Amp and Radio - check and see...are votlages ok? I mean seriously - tap the + of the radios own power lead with the DVM RED, and the + of the Amps power lead using your BLACK (negative), leave the DVM in in VOLT setting 20v to try and then less to obtain more SENSITIVE readings, and key the stuff - if you get more that 2 volts showing on the meter that is your DIFFERENCE between the Radios' Power Feed potential and the Amps Power Feed Potential - if one drops more than the other - 2 volts or more - you need to fix that drop.

    Can you bump up D/K in Radio to offset the SWR - as a test to see if SWR improves faster...

    If the higher DK seem to make your SWR better as in, to "stop shutting down your equipment" - that goes back to the voltage drop the amp has - on itself, because it uses a relay and buttons to route RF as well as power the pills. So if the amp "stutters" as you key up your radio - naturally the SWR will jump - it's not foolproof.

    A little extra AWG wire onto a better route of wiring to that amp can help a lot in this case...

    You may have to go under the hood of that amp and look for ways to make it more sensitive to input. That may mean removing the RF sense and using direct key to make the relay kick. I'm thinking the amp either by inherited design, or tuning done to it, is not catching all the RF the radio is sending to it, thru it's (amps own) input network - simply because of the heavy class C bias. Tends to force clipping of the signal until it's strong enough to force conduction. You may not have a choice here. Either bump up the DK and run a little more limiter or the amp needs to little more work on the input side to make it more want to amplify on low RF signal - else with heavy class C amps, you really have to push a watt or more to get the amp to at least be linear and amplify what it sees.

    This is not a diagnostic, but then - if the relay is old, that can have an effect on your stuff.
     
  15. Supspt454

    Supspt454 Member

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    Thanks for all the replies folks. Sorry it’s been a couple days to reply. Still fighting this flu bug. Anyhow, before I had ever posted anything I was checking the amp with various levels of VP DK. Up to around 4-5 watts and as low as it would go at around a half a watt or so. Nothing really seemed to change anything. DVOM readings at an idle are around 14.8 and when radio is being used during TX it only drops to 14.4. This is measured on a FLIR CM85 DVOM. Amp is on its way back to the manufacture for testing and or tweaking. Also I’ll be hard mounting an antenna soon through the roof. I might have to have a couple drinks before I actually start to drill though.
     
    Redbeard U812 likes this.

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