Quick question. Can I use it as it is with it on with the low SWR or may I be looking for trouble. Now I'm afraid of a possible fire.
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SWR high when amplifier is off
- Thread starter Capt Crunch
- Start date
If your antenna SWR is below 2:1 it is usable. If you are running power it is still usable.
When you tune the antenna's SWR you are tuning to a FREQUENCY not a power level.
The SWR going into the amp is affected by more than just the antenna. Capacitors can be shorted or opened, inductors can do the same. If it is part of the input circuit of the amplifier impedance can show high SWR.
If you can take the amp out of the circuit and go straight to the radio check your SWR then. If you have an antenna analyzer check it that way.
There are lot of possibilities, If you have installed the system properly and the power wires are fused the likelihood of fire are lessened.
OK Thanks. I was just wondering because of that RL1 thing you described.
So I just tried the dummy load as per OldTech03 I have(15W Radio Shack). SWR was 1.4 on 20 with the amp off. I popped the amp on for a sec and it was showing 1.2 SWR.
Yes its all wired correctly.
I had to order the barrel connector cause no one has around me. It will be here Friday, they say.
I am thinking it may be the amp as when I tried adjusting the predator to drop from the high SWR nothing happened, and I moved the whip all the in and all out and in the middle and SWR did not move. I tried the others as posted and they all went up with the amp off only less SWR than the predator which I thought it might be because that's all metal.
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IT may indicate a burned relay contact or coax jumper to rear connector.
Why do I say that?
When you run hot amps - e.g. little to no fan cooling - that coax sleeve and insulator is plastic and will soften.
IT may not perforate - but it will soften and then it tries to find a good equilibrium to rest once the heat is removed - that can make the coaxial aspect of equal distance throughout the length of jumper - in question. You may have a warped coaxial jumper from the heat produced in the amp.
So don't use the amp until you get a better idea of that impedance bump. For when the amp is on, that means the amp itself is absorbing the SWR reflection as in itself. But when the amp is off that relay bypasses the mess but still goes - re-routes - shorts both connectors to themselves - via that relay and the coax itself. So if the SWR issue is in the coax, or even the relay - the Amp is susceptible to self destruct from it, .DON'T USE THE AMP until you figure out your next step and fix it.
Ok thanks. Just waiting now for the barrel connector to check coax now.
Here's a pic of the inside of the amp. I know it's difficult to tell but was looking for anything visible. The amp always had fans on it but this past month I broke the fans and haven't had a chance to hook the new ones up. Probably used it several times but not really long talking. I know when it's time to stop lol. I guess the connector will be the next step to test antenna and coax.
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Ahh, So is was the one I was thinking about...
Heres a quick tip - KEEP AMP UNPLUGGED FROM POWER - but Reverse the connections - see if the SWR stays the same - Hook up ANT to XMT and XMT to ANT - the recheck SWR - DO NOT POWER THAT AMP DURING THIS TEST.
This is more of a check of which one -
Set SWR on meter to FWD setting...
IF the SWR FWD is the same, then the coax may have been damaged so you simply need to replace jumpers.
IF SWR changes - then more than likely the relay may be more at fault than the coax. Burnt contacts.
The aspects of distance to the connectors is what I'm looking for - if one of the coax jumpers is bad, it's position in the line will affect the FWD reading - not necessarily the overall SWR - it can still be the same - but the ASPECT of the impedance bump affects the CLAIBRATION "FWD" setting too...(Because the coax and the antenna AFTER then look as a complex load affecting the impedance bump like a coaxial balun)
Just some thoughts...
Heres a quick tip - KEEP AMP UNPLUGGED FROM POWER - but Reverse the connections - see if the SWR stays the same - Hook up ANT to XMT and XMT to ANT - the recheck SWR - DO NOT POWER THAT AMP DURING THIS TEST.
This is more of a check of which one -
Set SWR on meter to FWD setting...
IF the SWR FWD is the same, then the coax may have been damaged so you simply need to replace jumpers.
IF SWR changes - then more than likely the relay may be more at fault than the coax. Burnt contacts.
The aspects of distance to the connectors is what I'm looking for - if one of the coax jumpers is bad, it's position in the line will affect the FWD reading - not necessarily the overall SWR - it can still be the same - but the ASPECT of the impedance bump affects the CLAIBRATION "FWD" setting too...(Because the coax and the antenna AFTER then look as a complex load affecting the impedance bump like a coaxial balun)
Just some thoughts...
Will give it a try thank you. May take a day or two my radio doesn't have FWD and hooking a meter to the line is a bit of a pain. May be stretching it but any good if I hooked the meter where the amp goes?
OK, so I tried hooking the meter where the amp goes. Pretty sure I found the connector may be loose from the connector to the antenna coax. The other jumper I had was new and this one is older. Maybe should have changed both. Going to check the connector now. I can change the swr turning the coax which I know it shouldn't be turning all the way around.
Not sure this was the problem, cause, or what totally. I rewired the connector and its still the same only now the SWR dropped a little from 3 to 2 with it off and with it on it now drops lower to 1:1. The normal SWR for the antenna I used Skipshooter and predator 5ft was 1.3ish matched on 1 and 40.
I'm going to wait for the barrel connector and start from the beginning and match antennas if needed for that setup and go from there.
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OK. Taking a step back now. Really bothering me, lol. I am a stickler for my stuff working right. I put the meter where the amp should be and tested it again just now with a matched antenna I know did 1:3 matched and a hair less on 20. It is that at the radio now and at the meter where the amp should be it is a hair above the 1:3 line. Also while on I heard base stations that I know their receive reading and that's fine. I then just now also hooked the coax back up to the amp and the SWR is just before the 2 when the amp is off and 1:1 when its on. Receive signals were the same when the amp was on or off. I also tried all the buttons on the amp and it stayed at 1:1. All SWR swing downwards when I talk, if that means anything. Receive amp works fine. So I am thinking amp problem now pretty much for sure. Sks. Going to wait for barrel connector and see what happens then.
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Here is why I'm thinking what I posted above...
The above is a portion of a T/Star Schematic - courtesy of CB Tricks - the Switch Side.
Note S2 - C3 - C44...
Now I had someone a long time ago say, why not check the terminals? Wouldn't the relay short out the antenna to XTMR? Well, yeah, but it is not a dead short - it's a RF short but not a physical DC derived Short.
S2 switch - routes from Relay - thru itself - back to Relay Pin 5 to 8 will be shorted in OFF state. But not the outputs.
So 6 and 9 are in the center - 5 to 8 are on the "coil side" or closer to the center. IT would be little harder to check.
So let's look at layout...without the parts...
The above shows routing Green Relay 5 to 8 from SWITCH 2 RED TO SWITCH 1 Relay 7 and 10 (Power OFF)
So they would be the quickest way to check for DC short, but not bad RF routing (burned contacts or Cap failure)
So it's why I mentioned the SWR FWD trick, to determine if one side of the relay contacts are open it makes the rest of the system appear RF-bound as a mistuned cap.
The above is a portion of a T/Star Schematic - courtesy of CB Tricks - the Switch Side.
Note S2 - C3 - C44...
Now I had someone a long time ago say, why not check the terminals? Wouldn't the relay short out the antenna to XTMR? Well, yeah, but it is not a dead short - it's a RF short but not a physical DC derived Short.
S2 switch - routes from Relay - thru itself - back to Relay Pin 5 to 8 will be shorted in OFF state. But not the outputs.
So 6 and 9 are in the center - 5 to 8 are on the "coil side" or closer to the center. IT would be little harder to check.
So let's look at layout...without the parts...
The above shows routing Green Relay 5 to 8 from SWITCH 2 RED TO SWITCH 1 Relay 7 and 10 (Power OFF)
So they would be the quickest way to check for DC short, but not bad RF routing (burned contacts or Cap failure)
So it's why I mentioned the SWR FWD trick, to determine if one side of the relay contacts are open it makes the rest of the system appear RF-bound as a mistuned cap.
Hey there Capt. If you have your SWR meter after the radio and before the amp, IOW the swr meter between the radio and amp, when the amp is off and you read the SWR you are reading the SWR of the antenna, just as if the amp was not in line. As soon as you turn the amp on and you check your swr you are now reading the swr into the amplifier NOT THE ANTENNA. When your amp is on and your swr meter is before the amp you no longer can read the swr on the antenna. You can only read the antenna swr when the amp is OFF. If you move the swr meter after the amplifier you will ALWAYS read the antenna swr and it won't change. I think this is where you are getting confused.
Ok so I gave it a try and the FWD did not change when I switched the coax.