High SWR after amp install

[Dx717]

Hello all, I hope I’ve posted this question in the correct area.
I’m running a Stryker 447hpc2 set at 1 watt dead key, Stryker SR-a10 single antenna thru rg8X coax. My SWR was at 1.2.
A few weeks ago I added a new 2 pill amp with 9’ of 8X coax jumper. With the amp connected but OFF (meter between radio and amp) I key mike and still show 1.2 SWR.
I turn amp ON and key mike it will jump to 3.8 SWR. So I’ve never used the amp since I installed it. All power leads are connected directly to battery with additional ground straps on each component chassis
My question is I’m not sure what to do or try to lower the SWR so I can use this setup?

 

[TheRealPorkchop]

Meter between the radio and amp, you’re reading the input tune of the amp with it powered on. Amp off and the relay is bypassing the amp so to speak.

 

[543_Dallas]

Yep, youre looking at the input match. It should be low. A quick and dirty fix for it can be to find a different length cowaxe jumper that makes it play nice. Without some tests there is no easy answer as to why this is happening.

I'm curious what the swr between the amp and antenna is. You could have a bad input match or parasitic oscillation. A scope is the best tool to see oscillation but If you have an average and pep reading watt meter that will help. Put the meter between the amp and antenna. If the swr goes through the roof with the amp on (don't forget to recalibrate)try this. Turn the mic gain down and measure your AM carrier power on pep and then average. They should be equal but if there not the amp is oscillating.

Different coax lengths can also be a work around for an amp with an oscillation problem. 6 or 12 feet of rg8x seem to work more often than not.

 

[Tallman]

Hello all, I hope I’ve posted this question in the correct area.
I’m running a Stryker 447hpc2 set at 1 watt dead key, Stryker SR-a10 single antenna thru rg8X coax. My SWR was at 1.2.
A few weeks ago I added a new 2 pill amp with 9’ of 8X coax jumper. With the amp connected but OFF (meter between radio and amp) I key mike and still show 1.2 SWR.
I turn amp ON and key mike it will jump to 3.8 SWR. So I’ve never used the amp since I installed it. All power leads are connected directly to battery with additional ground straps on each component chassis
My question is I’m not sure what to do or try to lower the SWR so I can use this setup?

What type of amp? Some have a compensation network for input tuning.

 

[dave457]

Probably the amp is not tuned correctly

 

[338_MtRushmore]

Probably not your problem, but excessive voltage can do that too.

 

[nomadradio]

IIRC that radio is capable of around 70 Watt peaks.

A 2-transistor amplifier will probably be overwhelmed with that drive level.

Sounds like you need a bigger amplifier or a smaller radio.

73

 

[midnight special]

harmonics gives false readings,,,,,,,,

 

[sp5it]

Poorly designed/manufactured amp.
Mike

 

[Shadetree Mechanic]

The input might be tuned for 10 meters. This is the only legal way to make it. Some modifications to the amp input will be needed. As mentioned earlier, a longer piece of coax coiled up between the radio and amp might help.

 

[SHACKMASTER SAM]

The amp has an input impedance problem or is oscillating. Using various lengths of coax is simply using coax as a conjugate matcher but does not solve the root problem. You need to find the root cause of the problem. But unless you are good at working on amps (more than turning screws or pots), you need to look for a good tech. I have had amps that had bad input matches and I used a cheap matchbox between the amp and radio to temporarily solve the problem. But that should only be used as a temporary fix, not a permanent solution. You could be doing damage to either the radio or amp running them in a mis-matched condition. Good luck!

 

[TheRealPorkchop]

The amp has an input impedance problem or is oscillating. Using various lengths of coax is simply using coax as a conjugate matcher but does not solve the root problem. You need to find the root cause of the problem. But unless you are good at working on amps (more than turning screws or pots), you need to look for a good tech. I have had amps that had bad input matches and I used a cheap matchbox between the amp and radio to temporarily solve the problem. But that should only be used as a temporary fix, not a permanent solution. You could be doing damage to either the radio or amp running them in a mis-matched condition. Good luck!

Shack Master - I like that name.

 

[Rwb]

Lot better name ,shack master than mr golden screwdriver