Odd CB antenna problem

[chris142]

I have a 150w linear under my passenger seat(I want to make sure that the Jeep behind me can hear me ).

I bought a 5ft K40 antenna. It's very stiff so it wont bang against my roof and drive me banannas.

Now when I key the mic the Linear wont unkey. It keeps transmitting and it's transmit light stays on.

My match is almost too good to be true with this antenna. Match is 1.2 on all 40, dude at the truckstop CB van was suprized too.

I went back to the flexable antenna that bangs on my roof and the linear works normal now. Match is 1.3 on 1 and 1.6 on 40 so it's good too.

How can the longer antenna have an effect on the linear? Weird RF output or something?

When the long antenna is on and the linear is "stuck" transmitting I can unplug the coax and it will stop transmitting and the light will go out. Does not matter if I unplug the input or the output.

[blackZZR]

I am wondering what kind of meter you are using to get the Standing Wave Ratio, is it a single needle or a double needle unit? Single needle units are usually not very good units and can give false readings. Sounds like you have a imbalance that is feeding back and keeping the linear on and transmitting.

I will try to put this in words you do not need advance training in radio theory

now a little about SWR, it is always represented in a x to 1 even though the ratio could be 1 to x. in other words it is never represented in a negative even though it could be. What a SWR reading represents is a imbalance in the ohms reading at the connection point of the coax and the antennae, we are using 50 ohm as our designed antennae feed ohm reading, so we use a coax that is rated at 50 ohms.

ok so if the coax side has the most ohm, or the antennae side does, it always is represented x to 1
with a single needle meter you cannot see which side has the higher resistance
.
Taking a reading without the linear in there and see what the SWR is. get a good match and then add the linear and see what happens, also if the linear has 2 power settings try the lower setting. You see what happens is that as power going down the coax increases so does the ohms on the line,(the ohms rating of a line is affected by the conductor size and the amount of separation they have, power on the line increases so does the ohms reading) so you could be using getting the imbalance that way, Oh did I tell you to get a 2 needle SWR meter, that way you can see better what is going on. Now if the feed back is what we would think is a would make it look like a 1 to x then you are still needing to tune that antennae till it looks like a x to 1, you can tell this with a 2 needle meter. with a single needle meter then it always will show the reading in a forward way. Now once the ohms are matched and the Standing wave is decreased on the coax side then the linear will turn off by itself.

PS. do not even try to key up that unit without the antennae installed or a dummy load on that puppy or you can get seriously injured or blow that linear up. Always have it a complete system. And you are aware running a CB with more than 5 watts is highly illegal. (sorry I had to include that to protect my license) Anyway hope this helped as not knowing how SWR works, or having the proper meter you can be just pissing in the wind. Your SWR meter needs to be tuned to the frequency range you are testing and should be a 2 needle unit, one showing forward and one showing return reading to get a good tuning, using any single needle unit only can get you close, but on a 5 watt system like any CB without a linear that is good enough. Why most guys have single needle is they are cheap, why most guys with double needle units can not properly tune with them is they have no clue about SWR theory and could not tell you what it is or what is affected.

Now I could have put that in other terms such as SWR isif that is a negative then it is a dead short, if it is a 0 then it is a balance and if it is a positive then it is an open circuit so you can see why the linear is not turning off if that is a negative, it keeps feeding back and holding open even though your key is off.

[chris142]

Thanks for the input. The guy at the CB shop has a electronic box that he hooks to your coax and pushes a button. After a few seconds it computes your match and shows it on a screen. I think that it will also print it on a piece of paper too.

I'm assuming that it's accurate, he's got it on the correct frequency and that he knows how to use it.

I have a cheap one from Radio shack. A 1 needle one that reads high. If it says that my match is 1.5 the one the CB store has will read 1.3 or 1.2.

I've heard that you should only use coax in 18ft/1/2 wave lengths. That makes no sense to me. The inner conductor is inside of the outer shield so IMO coax length shouldn't matter.

Lots of beliefs about this.

My jumper from the amp to my antenna is 6ft. Maybe I do need a 18ft piece of coax and I'm wrong about coax length?

I know about the 5w......I thought it was 4w limit on 11m. CB has started to take off here and you can't be heard w/o power.I like to talk skip too. I got a contact yesterday afternoon out of NW Arkansas.

I was joking about using power on our trips I know that 1w is plenty with my setup to be able to talk to a few jeeps on a trail plus somebody might have a pacemaker

I will ck the match with the amp on though. Thx.

[chris142]

I'm looking for a SWR meter with 2 meters in it.

Will something like this work?

http://cgi.ebay.com/1pc-SZ-70-Panel-...item20b050cd23

[blackZZR]

coax length has noting to do with it. the match point of the antennae, where the coax and hooks to the antennae is where you need to match ohms, Ohms of the antennae to ohms of the coax. Now what I think you have is negative SWR, how can you tell if the SWR is positive or negative with either a digital SWR meter, or a single needle SWR meter. Ever get a antennae and you are trying to match it and it seems you cannot get it to do anything? That is because you are fighting SWR in reverse. You shorten the antennae and it gets worse.
That is because SWR is always written as positive. with a 2 needle SWR meter the needle are on opposite sides of the dial, where they meet is your SWR, you can see which side of the system needs to be tuned. Go to Ham Radio Outlet and get a 2 meter SWR meter with 2 needles, it will cover the frequency range you are working with, should be between 35 to 50 dollars.
Anyway, you can go out and do whatever you want with the coax length, but the only thing they are rated at is Db per 100 feet and ohms, all yours should be 50 ohm as you get a good match without the linear hooked up and even with it hooked up.
From a theory standpoint, what I think your problem is, the linear is turned on by the keying of the mike and stays on till voltage is removed, with a negative SWR the standing wave on the coax looks like a dead short, so the linear never sees a no voltage situation and stays powered up. This is caused by mutual inductance in the amplifier circuit (coil) so as long as there is a return on the coax the linear is getting back feed to the transformer and that causes enough power to be generated to keep the linear powered up.
I hope you can understand what I am saying. it takes a bit of electrical theory and transformer theory to see it clearly, but the Linear is just a huge transformer, with one coil inside another (a transformer) as long as the secondary coil is powered by the Negative SWR (dead short) them it will induce enough current to back feed the control circuit of the Linear causing it to remain on. The only way to get that to stop is tune the match point to a zero or positive SWR ratio.

[blackZZR]

I'm looking for a SWR meter with 2 meters in it.

Will something like this work?

http://cgi.ebay.com/1pc-SZ-70-Panel-...item20b050cd23

bingo but your linear will fry that one, it only hamdles 10 watts

[chris142]

Ya that makes sense. I'm off to order a SWR meter. Thanks. I'll report my findings when I get it.

[chris142]

bingo

The add does not say what frequency it covers.

[chris142]

Kool . I know what I'm looking for now though.

[chris142]

This one cover my frequency and does 1k on 144m.

Wonder what it does on 11m?

http://cgi.ebay.com/DAIWA-CN-101L-CR...item439f798c98

[blackZZR]

This one cover my frequency and does 1k on 144m.

Wonder what it does on 11m?

http://cgi.ebay.com/DAIWA-CN-101L-CR...item439f798c98

divide 300 by frequency in mhz and get very close to the meter you are in

[chris142]

Well it's fixed. I went to the CB van/store looking for a good swr meter. The guy felt my Coax and found a "bump" under the cover. Must be a damaged spot in the shield under the rubber cover.

Replaced that piece of coax and it's all better. Still need to get me a good meter though.

[blackZZR]

So, what is the reading top to bottom channels now?

[chris142]

According to the meter @ the CB shop..1.2-1 on ch1 and 1.6-1 on ch40.

My cheap meter shows very close to that. Stilll need to get the 2 needle meter though.

[blackZZR]

I would think the damaged Coax was why the ohm match was where it was. now with a good line you are getting a better match.
I use a 2 needle unit I bought primarily for VHf ham radios that covers the CB frequency range. However it will not meet the 400 watt linear I have, so I have no idea what the match is at that range. Kinda similar of your 200 watt linear, The impedance match is effected by voltage but the formula is not on my brain, however I am sure it will be fine with your match.