swr

[shadow]

hi everyone, newbie here,

ok, its a bit of a broad question, so please ask whatever u like.
i have a cb in my car, with a 1.5 metre whip antenna, ive made a radial ground plane to help the signal out, my swr readings are a bit high, ive adjusted my way, so it reads about 1.1 on fwd, and 1.5 on rev.
i have a magnetic mount on the roof of my car.

questions:
should my fwd when i set be in the red at "set, then on rev it should drop to about 1.1-1.5

how big should the radials be on the ground plane

is it worth putting a round wire from the mag mount to the chassis of the car

will ferrite beads help if i put on the antenna coaxial cable, i have on the power leads.
thats all for now, any help would be appreciated

thanks

 

[W5LZ]

shadow,
I have a feeling I'm not understanding you as well as I should. Any chances of a picture of your antenna? Or just describe your antenna in more detail?
- 'Doc

 

[shadow]

Thunderpole Trucker SS | Mobile CB Radio Antenna | THUNDERPOLE
like this one, has 1000w instead of 3

 

[loosecannon]

first of all, you dont need that ground radial thingy. those are just advertising hyped junk.

try testing without it and see what happens.

the other thing im thinking of has to do with how you are measuring your SWR.

what kind of SWR meter are you using (post a link to a pic if you can), and do you know how to properly calibrate this meter?

later,
LC

 

[W5LZ]

shadow,
The link you posted shows a common type of base loaded mobile antenna. I would think it should work about as well as any other of the same overall length.
The 'groundplane' portion of this antenna when used with a mag-mount is furnished by capacitance -through- that mag-mount to the metal (vehicle body) the mag-mount is placed on. The braid of the feed line is capacitively coupled to the metal the mag sits on. You do not have to provide a 'groundplane'. Or, if more 'groundplane' is required, it would be furnished by extending the vehicle's metal body in some way. (Several ways of doing that.)
If you are speaking of one of the gadgets typically sold that clamp/connect to the vertical portion of the antenna, and is called a 'groundplane', it isn't a 'groundplane' in any sense of the word, doesn't 'do' the same thing at all. (What 'loosecannon' is referring to.)
A word about antenna advertising. If you see "comes pre-tuned", it only means in a very general way, as in maybe for a particular band, but never for any particular portion of that band. How can any manufacturer tune an antenna if they have no idea where/how the thing is going to be mounted? If 'they' got to a 2:1, I'd have to say 'they' got pretty close, which certainly doesn't mean it's close enough. The end user still has to tune the antenna for it's particular environment.
SWR meters. I would suggest reading the manual for that meter's use (I hope you got one!). Very basically, it has to be calibrated before the readins have any meaning, are accurate to any extent. From what you described, it's placed in Forward, radio keyed, adjust 'Cal' knob till needle points to the calibration mark on the meter's scale. Un-key the radio, switch for SWR or Reverse, key radio again to read the SWR. There are several different ways meters can be calibrated, not all of them are the same, so that's why they send instructions with them. (No, I don't think you are an idiot, you just aren't familiar with the procedure yet.)
Good luck with it.
- 'Doc


(All things considered, what can you say about people who drive on the wrong side of the road anyway? )

 

[shadow]

thanks for the input guys, was wondering bout the ground plane thing, i'll remove it. swr meter was set as u described, well is now, a mate gave me the meter and put it on for me, so i tried it the other way round, adjusted fwd to the set or cal point, switched to ref, and bingo, 1.1, max im getting on all 40 channels is 1.2, so thats pretty good.
spoke to a guy today 20 miles away, almost crystal clear at both ends, so thats not bad, only prob i have now is if i turn on my HID headlights, they whack a huge amount of interference through the cb, so i'll have to ferrite them i think, unless there is a better way, cd player also causes a minor crackle. cb is wired to battery, with ferrite beads on power cable.
the swr meter is a midland swr-25, i thought i had to attatch antenna to left side, wasnt, its the right, like a moonraker one.
also, i have a mini mag mount, 3.5 inches, would the 5.5 been better, or would running a wire from the bottom of the mount to the chassis help???

 

[W5LZ]

"or would running a wire from the bottom of the mount to the chassis help???"

Not really. If it does, then something isn't 'right' with that mag-mount and/or the antenna tuning.
The size of the magnet/mag-mount has two purposes. The important one is that it is strong enough to hold the thing on the vehicle, and makes it removable. The other is it acts as one 'plate' of a capacitor, so the bigger the area of that magnet the bigger then capacitor, the better 'connection' with the 'other half' of the antenna, the vehicle body. Don't put too much importance on that 'size'/area thingy, there' are just too many variables in that. If the magnet is large enough to hold the antenna on the vehicle, it's probably going to be big enough for the other. The best solution is to just drill a hole and be done with it! Which sort of defeats the mag-mounts purpose, huh? Oh well. Big difference between 'best' and 'convenient'.
- 'Doc

 

[Beetle]

Your HID headlights might be more of a problem than you realize. You have two spark gap transmitters shining light on the road and blasting RF energy from DC to daylight. Have fun!