High SWR

[Cocoabean]

So I recently installed a new Midland 1001z cheapy with a Cobra HG A1000 21" magnet mount antenna. I have the radio properly grounded, with a 2 foot coax going to my SWR meter, then 16 feet of coax to the antenna on the center of my roof. when I test channel 19, i get about 2.5-3 on my meter. Strangely enough, when i touch any of the coax or the microphone cable, the SWR drops dramatically, sometimes below 2. I've looked all over the internet and I understand that under 3 is barely acceptable and that under 1.5 is desired. I still have to tune the radio, but I think the initial SWR should still be lower than what I am getting. The cable touching issue also puzzles me, any help would be greatly appreciated!

[bookie]

the reason your SWR drops is your body absorbs some of your power. with less forward power they is less reflected power.

check the ground-plane of your antenna. your ground may not be very good. if its a mag mount the ground in the base may be old and broke. most old radio's had a ground post on the radio somewhere, you may want to run a good ground from a screw on the back of your radio case to a good known ground in your car.

always check your SWR with your car in an open area, in a low static area (well grounded).

nate

[Cocoabean]

I dont know how to really go about checking my ground place, its the top of a roof of a van. Also, the antenna is brand new.

[bookie]

new does not mean good. not sure about that antenna, give me a few and i'll find it and see how its made. in the mean time if you have another radio then try it and see if your SWR is better. same thing for the coax, antenna and a second ground source. its called the PLUCK-N-CHUCK method in the electronics field.

nate

[Cocoabean]

I dont have another radio, but ill try it on my friends setup if i can get him to come over, thanks btw.

[bookie]

what kind of jumper do you have? if its a crimp type then you may want to check it or go ahead and have it soldered. this is a cheap fix if it proves to be your problem. i've seen the cheap radio shack jumpers with crimp ends look good on multimeter when you check for resistance or continuity but then fail when they where put in-line. the reason was a poor ground, or the center pin was just barely touching the center copper wire of the coax.

hope something i say is helping you.

nate

[countryboy]

like they said. i would ground your cab to the frame, ground the radio, try differanat coax. and even try differant lenths of jumpers. make sure all coax conetors are tight. do not wad or coil up your excess coax.
[Please login or register to view this link]

[Circuit Breaker]

the reason your SWR drops is your body absorbs some of your power. with less forward power they is less reflected power.

Actually, that isn't true. If he re-calibrates the meter while he's touching the radio and checks the SWR again, it should be the same as it was.

[mopar2ya]

So I recently installed a new Midland 1001z cheapy with a Cobra HG A1000 21" magnet mount antenna. I have the radio properly grounded, with a 2 foot coax going to my SWR meter, then 16 feet of coax to the antenna on the center of my roof. when I test channel 19, i get about 2.5-3 on my meter. Strangely enough, when i touch any of the coax or the microphone cable, the SWR drops dramatically, sometimes below 2. I've looked all over the internet and I understand that under 3 is barely acceptable and that under 1.5 is desired. I still have to tune the radio, but I think the initial SWR should still be lower than what I am getting. The cable touching issue also puzzles me, any help would be greatly appreciated!

Bookie has been doing a pretty fair job of letting you know -what- your problem is. I am going to try and help you understand why.

The condition that you are experiencing is because there is RF that shouldn't be there, on the outside of the coax. (it should only be on the inside) As you have seen, it is also on your mic, SWR meter, and radio. The most common reason for this is a poor antenna image, or counter poise, or ground plane. All three of those things mean the same thing.

The way to think of virtually any antenna system is to compare it in your mind to a dipole. A dipole has two halves. One half is attached to the center conductor of your antenna connector, and the other half is attached to the shield or outside of your antenna connector. When RF current flows on the antenna, for it to work properly it needs to have the other half of the antenna like a dipole would have. This can be the other half of the dipole, a ground plane kit on a base antenna, your vehicle in a mobile antenna, or a ground radial system for a radio station. When the other half of the antenna isn't being -used- by your signal, the RF finds other places to go that it shouldn't be, as you have found out.

So, why is this happening to you?

My first guess would be a faulty or poorly designed antenna. This is almost certainly your problem, even though the antenna is new.
The next guess would be coax problems.
And finally, a faulty SWR meter.

While my assumption is that you have an antenna issue, any of the three things I mentioned could cause the RF to not -see- the other half of the antenna, and travel to all the places it shouldn't be.

Mopar

wan•na•boo (wah-nah-boo) Informal n. Derived of wan-na-bee 1. One who aspires to be a
Peakaboo. 2. One who imitates the behavior, customs, or dress of a Peakaboo. 3. A product
designed to imitate the qualities or characteristics of something built by a Peakaboo.
-.. --- -. - / ..-. --- .-. --. . - / - --- / -.. .-. .. -. -.- / -.-- --- ..- .-. / --- ...- .- .-.. - .. -. . / .-.-.- / .-.-.

[bookie]

yeah, what he said. lol

nate

[Cocoabean]

I guess it's probably just a cheap antenna, the coax is built into it. I ditched the meter and it helped cut down on the squeeling that my friend would get when i transmitted to him. I'm pretty sure it is NOT the ground plane as it is in the center of the roof of a VW bus, and its steel. Thanks to everyone who contributed though.

[mopar2ya]

I guess it's probably just a cheap antenna, the coax is built into it. I ditched the meter and it helped cut down on the squeeling that my friend would get when i transmitted to him. I'm pretty sure it is NOT the ground plane as it is in the center of the roof of a VW bus, and its steel. Thanks to everyone who contributed though.

It wouldn't matter if your antenna was attached to a piece of metal the size of a football field. If you are experiencing the issues that you are, the RF isn't using that piece of metal like it should. If it were me, I would either exchange the antenna, or, if that weren't a possibility, I would take it apart and make sure that the shield of the coax is connected to the magnet in some way.

Magnet mount antennas usually just have the shield pinched between whatever metal they use structurally and the magnet, or pinched between that metal and the plastic frame of the base. My bet is that either this connection is completely missing, or only partially there. Fix it and I bet your problem will go away, and system performance will drastically improve.

Mopar

[Cocoabean]

I guess it's probably just a cheap antenna, the coax is built into it. I ditched the meter and it helped cut down on the squeeling that my friend would get when i transmitted to him. I'm pretty sure it is NOT the ground plane as it is in the center of the roof of a VW bus, and its steel. Thanks to everyone who contributed though.

It wouldn't matter if your antenna was attached to a piece of metal the size of a football field. If you are experiencing the issues that you are, the RF isn't using that piece of metal like it should. If it were me, I would either exchange the antenna, or, if that weren't a possibility, I would take it apart and make sure that the shield of the coax is connected to the magnet in some way.

Magnet mount antennas usually just have the shield pinched between whatever metal they use structurally and the magnet, or pinched between that metal and the plastic frame of the base. My bet is that either this connection is completely missing, or only partially there. Fix it and I bet your problem will go away, and system performance will drastically improve.

Mopar

OK, so if the outer coax should be connected to the magnet, should the outer coax also have continuity with the ground of the car if i just had the antenna mounted and tested between the outer thread from the antenna wire and a known ground on the car? I can't really take the antenna apart, but I could probably return it.

[Cocoabean]

Update:

I exchanged my antenna for the same one to rule out defectivity. I set everything up, it still has the same problem with the SWR dropping upon touching the radio, mic wire, or antenna wire, but it sure seemed to be recieving a hell of a lot better. I was picking up signals loud and clear from Portland, Oregon. I'm about thirty miles north of Los Angeles.

[mopar2ya]

Well, if it is working for you, let it be I guess. The antenna is incredibly short (21") for CB use. I assume this is most of the problem. If it is sufficient for what you use it for, by all means, continue to use it. I would imagine a significant performance increase would be seen by upgrading to a taller antenna. If you like the magnet mount idea, the Wilson 1000 or 5000 is a nice choice. They are rather pricey though.

Good Luck,

Mopar

wan•na•boo (wah-nah-boo) Informal n. Derived of wan-na-bee 1. One who aspires to be a
Peakaboo. 2. One who imitates the behavior, customs, or dress of a Peakaboo. 3. A product
designed to imitate the qualities or characteristics of something built by a Peakaboo.
-.. --- -. - / ..-. --- .-. --. . - / - --- / -.. .-. .. -. -.- / -.-- --- ..- .-. / --- ...- .- .-.. - .. -. . / .-.-.- / .-.-.

[Cocoabean]

Ya I looked at the Wilson's, they're more than what my radio cost. I tried grounding the radio chassis to the body of my car, didn't seem to help at all...

[countryboy]

well got me maby someone here might figer it out . maby you can borrow a buddys antenna and try it. maby a differant type of antenna will help?

Just my thougts. thou...

[Cocoabean]

What if i just yank the whip out and put in something longer? Like will any long piece of metal work?

[mopar2ya]

That won't work. The loading coil in the base of that antenna is designed to work with a whip the length that the antenna originally came with. If you substitute a longer whip, it will be resonant at a much lower frequency than the CB band.

Mopar

wan•na•boo (wah-nah-boo) Informal n. Derived of wan-na-bee 1. One who aspires to be a
Peakaboo. 2. One who imitates the behavior, customs, or dress of a Peakaboo. 3. A product
designed to imitate the qualities or characteristics of something built by a Peakaboo.
-.. --- -. - / ..-. --- .-. --. . - / - --- / -.. .-. .. -. -.- / -.-- --- ..- .-. / --- ...- .- .-.. - .. -. . / .-.-.- / .-.-.

[Cocoabean]

OK, didn't think so. You've guys have been a great help, I've decided to go for a Wilson 1000. Ill update this when I get it.