SWR before linear

[BC Coyote]

Yes, there were a few guys doing it right and building proper amps back in the day and some even into recent years. Unfortunately those high quality amps make up only a tiny percentage of all the CB amps out there. For every Magnum or high-end Cobra there are a thousand P.O.S. amps with no filtering, no bias, and terrible build quality.
So while I agree with everything you say, I pretty much stand by my statement...

 

[BayouRadioAmplifier]

so do you have the AM or SSB button pushed in.?

if your amp still matches the schematic.

measure input SWR with one or both pushed in.

this changes the RF input network. I have a customer's TS DX-250
that I posted here about, and I keep both AM and SSB switches
pushed in, and the input match is good. so that I drive it with a 3.8 watt carrier.
just have the SSB delay.

on these amps that I keep for myself, I change the input
network resistors and remove that switching. use coax cable.
make it right. for about 4 watts carrier drive.
add a bias circuit if there is none.

 

[fourstringburn]

Ok, experts! Situation: president richard 10/11 meter has a swr of 1.0 to antenna capable of 500watts. The monent I put dx350 inline. SWR between radio and linear is 2.6-3.0. SWR between linear and antenna is 1.3

Of course internet is full of answers. Most say the Swr between radio and linear is not important as long as it’s not like 10.

If that is the case, is there anything I can do to get it down other then adding coax which is just a mask. Or just not worry about it

I did notice the connectors on linear are a bit oxidized from age, I was going to clean those up thinking it may be messing with a good solid ground. And yes the linear is grounded to multiple scrubbed and cleaned seat post bolts

Thanks yall

One thing I forgot to mention about the above advice I posted is that isn't really a fix for an impedance input mismatch but rather a way to mask the problem so your radio sees a better SWR.

 

[jpachla]

SWR rise when amp is ON or OFF?

Swr 1.0 with amp off. Just checked

 

[sp5it]

Swr 1.0 with amp off. Just checked

So it is shitty amp with bad tuned input circuit. Output probably too. Junk amp.
Mike

 

[jpachla]

So it is shitty amp with bad tuned input circuit. Output probably too. Junk amp.
Mike

Ok, so will a qualified tech be able to remedy this?

 

[sp5it]

Rebuilding amp? That Texas Star you have was designed by complete idiot with zero RF circuits knowledge.
Get better amp and get rid of that crap.
Mike

 

[BayouRadioAmplifier]

Rebuilding amp? That Texas Star you have was designed by complete idiot with zero RF circuits knowledge.
Get better amp and get rid of that crap.
Mike

.

ha ha ha. yes! I agree so much. True. true.

the way the 27 MHz RF wiring is done. all them input switches for
LOW MED HIGH the "v" variable models. all is bad.
all is wrong. so messed up....

I can't believe what I see.

for example, them RM Italy "linear" amps. (no bias circuit)
so not linear.

but the amps I keep for myself. I make them right.

"Mr. Mike" from Poland, you tell the truth.

 

[dave457]

They are techs on this site that should be able to fix it

 

[jpachla]

Ordered new lmr240uf for patch cable to linear. The current cable has crappy ends. See if this helps the issue, as I wiggled cord swr was bouncing all around

 

[nomadradio]

as I wiggled cord swr was bouncing all around

A strong hint as to the culprit I'd say.

73

 

[BC Coyote]

Ordered new lmr240uf for patch cable to linear. The current cable has crappy ends. See if this helps the issue, as I wiggled cord swr was bouncing all around

Never thought I'd see a 26 post thread come out of loose cable!

Especially when I nailed the problem in post #2 a mere 30 minutes after the original post......

 

[9C1Driver]

lol yup post number 10.

 

[nomadradio]

People skip soldering the coax braid on their coax jumpers. And for good reason. It's tough to get it hot enough to properly solder the braid to the connector, and not just to itself. But it makes the service life of that jumper short. The braid oxidizes and makes poor contact with the metal body of the plug. Not a problem until you put real fire to it and then "poof".

73

 

[doffo]

People skip soldering the coax braid on their coax jumpers. And for good reason. It's tough to get it hot enough to properly solder the braid to the connector, and not just to itself. But it makes the service life of that jumper short. The braid oxidizes and makes poor contact with the metal body of the plug. Not a problem until you put real fire to it and then "poof".

73

I read that wrong I think... One better solder the coax braid right?!?!