Dumb question re SWR tuning

[gwhayduke]

I've got a cobra 29 ltd that I'm trying to install in my truck. The Cobra radio has an SWR meeter built-in. You take an SWR reading by setting a switch to the "swr" position, keying the microphone, then reading the meter.

What would cause the SWR meter to peg all the way over to the right without anything connected to the antenna input? I know this would happen if I had a short in my antenna line somewhere, but what would cause that without anything connected to the antenna input?

[WA6IGJ]

OK

First, save some time and try your manual... if you don't have one the following is general information for SWR testing.

Most 'manual' SWR meters (not the dual meter types) require you to transmit and then 'calibrate' your SWR meter to read 100% in the 'FORWARD' mode.

Now there must be some way to set your SWR meter to read 'REVERSE'. The lower this indication the better because it represents power that didn't make it to the antenna and got 'reflected' back to your transmitter.

It's important to note if you are using a external or standard SWR Meter - a coax jumper is used between your meter and your transmitter... that jumper CHANGES your actual SWR! This especially true for VHF and UHF frequencies. Your best bet is to use a male-to-male (PL-259 to PL-259) connector to get the meter as close to the transmitter as possible!

And by the way, you *NEVER* want to transmit without a decent load on your transmitter! Where is all that power going to go?

Hope this helps

[N_Jay]

Both a short and an open are both (theoretically) infinitive SWR, meaning all power sent out is reflected back.

[va3hub]

Originally Posted by gwhayduke

I've got a cobra 29 ltd that I'm trying to install in my truck. The Cobra radio has an SWR meeter built-in. You take an SWR reading by setting a switch to the "swr" position, keying the microphone, then reading the meter.

What would cause the SWR meter to peg all the way over to the right without anything connected to the antenna input? I know this would happen if I had a short in my antenna line somewhere, but what would cause that without anything connected to the antenna input?

The same that would happen to your truck motor if you over revved it without a load.
Now instead of thinking mechanical,think electronics and such,treat your SWR meter like your Trucks RPM gauge,
Try to keep your SWR reading at 1.1 or 1.5..........anything over 2.5 your starting to look for smoke,not good.
Don't key up without a load,you will fry your CB like you would over revving your motor,but faster.....way faster...lol.

Hope this Helps.

[canav844]

First, NEVER KEY WITHOUT AN ANTENNA ATTACHED!!!! It will fry your radio and turn it into a big brick. (takes all the output power that sends your signal miles and pumps it all straight back into the radio itself because it has nothing to radiate it outward, away from the radio.

Setup your antenna,
then flip the switch to CAL,
with door closed, key the mic and
turn the calibration knob (on the talkback knob for my 29LTD chrome) to the calibration mark,
then flip the switch to SWR and
key the mic to get what your SWR reading is.

Anything under 2 and the antenna needs adjusting before you can do any regular transmit, but I'd tinker with it until you're under 1.5

[BNSFrailfan]

Originally Posted by canav844

First, NEVER KEY WITHOUT AN ANTENNA ATTACHED!!!! It will fry your radio and turn it into a big brick. (takes all the output power that sends your signal miles and pumps it all straight back into the radio itself because it has nothing to radiate it outward, away from the radio.

Setup your antenna,
then flip the switch to CAL,
with door closed, key the mic and
turn the calibration knob (on the talkback knob for my 29LTD chrome) to the calibration mark,
then flip the switch to SWR and
key the mic to get what your SWR reading is.

Anything under 2 and the antenna needs adjusting before you can do any regular transmit, but I'd tinker with it until you're under 1.5

First start on Channel 40 then switch to Channel 1 for SWR. That's what I was told. Been doing that for well over 15 years now.