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1/22/2020 12:12:56 PM
Posted: 7/31/2009 3:13:47 AM EST
I am setting up my CB radio in my car and the SWR readings on Channels 1 and 40 are very close to 2:1 (channel 1 is about 2.1:1 and channel 40 is about 1.9:1). Is this a problem? The reading on channel 20 is almost 1:1

Thanks,

Mike

Link Posted: 7/31/2009 4:35:56 AM EST
No problem...this is normal. You tune the antenna for the center of the freqs you plan on using, and the swr will rise the further away from that freq you get. 2.1:1 is not going to hurt anything

-Space
Link Posted: 7/31/2009 6:02:31 AM EST
What is your setup? What kind of antenna, and how is it mounted? Your match on 20 is very good, with 1 and 40 not bad, but with some more info, I bet we can get the match on 1 and 40 lower.

The match on my Wilson 5000 is flat on 20 (1.1:1) and no higher than 1.5:1 on the upper and lower ranges of frequencies of my radio. I have spent some time making sure everything is grounded/bonded and properly installed.
Link Posted: 7/31/2009 6:44:13 AM EST
yup,, that's kind of the goal, to match antenna to center of band. it looks like to me your anteanna has a narrow bandwidth. i dought if it was designed that way, so check ground, mounting location.
Link Posted: 7/31/2009 7:06:04 AM EST
Bandwidth of the antenna is pretty narrow. If you consistently use channels at one end or the other then you'll want to tune the antenna more toward that end.

Or get an antenna with wider bandwidth.
Link Posted: 7/31/2009 4:01:39 PM EST
The setup I have is a Firestik Firefly 3 foot antenna on a firestik hood channel mount, with a Uniden PRO520XL. This is mounted in a 2000 Ford Focus Sedan.

Well on the way home (before I read all of the replys to my original post) I went to an open field at the local elementary school and tested my SWR on channels 1 and 40 in 4 different kinds of conditions: 1) all windows open, engine off 2) all windows shut, engine off 3) all windows open, engine on 4) all windows shut, engine on.

The readings in conditions 3 & 4 were 2.2-2.1 in channels 1 and 40. In conditions 1 & 2 the readings were slightly lower, but I will be using the radio in conditions 3 & 4 90% of the time.

I also measured the readings on channel 20 in all of the above conditions and they were around 1.1:1.

Obviously this was a ton of testing load on the SWR meter and the radio, as I didn't get out to adjust the antenna at all. I spent about 10 min straight testing the SWR in all of these conditions.

The back of the radio near the antenna connection seemed hot, as well as the section of patch cable attached to it. Is this normal and if not could it have been a result of this extensive testing? Can this cause damage to the radio? I already blew up a functioning 1983 Cobra 19, I don't feel like messing up another radio...

Thanks,

Mike
Link Posted: 7/31/2009 5:06:07 PM EST
Like posted above, the antenna bandwidth isn't too wide. Not much you can do about that except change antennas.
2 to 1 isn't going to hurt it. The warmth is from the final transistor operating and this is normal unless it burns your finger.
Link Posted: 8/1/2009 4:04:09 AM EST

Originally Posted By KB7DX:
Like posted above, the antenna bandwidth isn't too wide. Not much you can do about that except change antennas.
2 to 1 isn't going to hurt it. The warmth is from the final transistor operating and this is normal unless it burns your finger.

Thanks, yeah it didn't burn my finger, but when I reached down to remove the patch cable my finger touched it and I was like, "dang, thats hot". It didn't burn me but it was uncomfortable. I tried talking on it last night and I wasn't getting any responses. I will try today on the way to and from work.
Link Posted: 8/1/2009 6:11:02 PM EST
Originally Posted By claybreaker12gauge:

Originally Posted By KB7DX:
Like posted above, the antenna bandwidth isn't too wide. Not much you can do about that except change antennas.
2 to 1 isn't going to hurt it. The warmth is from the final transistor operating and this is normal unless it burns your finger.

Thanks, yeah it didn't burn my finger, but when I reached down to remove the patch cable my finger touched it and I was like, "dang, thats hot". It didn't burn me but it was uncomfortable. I tried talking on it last night and I wasn't getting any responses. I will try today on the way to and from work.


You might try moving your antenna mount and see if that helps I once had a 4 foot firestick mounted on the bed rail of my truck behind the cab and could not get the SWR below a 3. I moved the antenna away from the cab and SWR came down to 1.5 also the type of coax you use can affect SWR as well I use either RG8 or the mini 8 coax. I have also seen the length of the coax make a difference in SWR.
Link Posted: 8/9/2009 5:49:13 PM EST
Thanks for all the responses guys! I talked to the folks at Firestik Antenna and they told me that with my setup this is what I should be expecting. They suggested a taller antenna but unfortunatley I can't get any taller antenna or it will hit the parking garages at school. I am transmitting an average of 2 miles, with clear signals both ways it seems.

What I am wondering though is whether or not I can damage the radio by transmiting under or near powerlines. There are some times when I am parked directly under powerlines or driving along side them -> and transmitting at the same time. I figured it wasn't good for it, and last thing I want to do is blow up another radio.

Thanks

Mike

Link Posted: 8/10/2009 8:35:25 AM EST
Originally Posted By claybreaker12gauge:
What I am wondering though is whether or not I can damage the radio by transmiting under or near powerlines.

No. If the antenna gets close enough to touch or arc from the powerlines you'll have a lot more to worry about than your radio.
Link Posted: 8/10/2009 9:37:35 AM EST
do you have a good ground on the antenna mount and did the antenna and mount come with a plastic washer? i have seen problems with both, ground not being good enough and the washer being installed wrong.
Link Posted: 8/10/2009 5:00:26 PM EST
I don't think transmitting near power lines will affect the radio, however, transmitting in a tunnel or parking garage may.
Link Posted: 8/11/2009 6:13:52 AM EST
You will not damage the radio transmitting under or near powerlines, nor will you do any damage under a bridge or in a tunnel.

You will have decreased ability to tx and rx under a bridge or in a tunnel.

In either case don't worry about it.
Link Posted: 9/18/2009 5:48:55 PM EST
For some reason, my SWR reads roughly 1:1 from 1-28, and then the SWR skyrockets past that. Past 34 it's almost 3:1.

I think it may be my ground, but it's drilled right through the rear wall of my 02 wrangler. I could just have a shitty antenna too, though.
Link Posted: 9/18/2009 6:00:04 PM EST
Antenna too long probably. Antenna analyzers are SOOOO much more useful than SWR meters in looking at antennas.
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