SWR is never consistant

[Unit562]

After around 3 hours of trying to tune the PRO520XL I picked up and getting random SWR, I've almost given up on the transmitter. I've been googling and browsing forums as well, and can't seem to find anything about a similar issue anymore.

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[mmckenna]

Tell us about your antenna system. SWR is a measurement of how well your antenna is radiating the energy, and not much you can do on the CB to impact that.

 

[Unit562]

Tell us about your antenna system. SWR is a measurement of how well your antenna is radiating the energy, and not much you can do on the CB to impact that.

I might have already replied, it was a premature click on "send" and its hard to tell as I'm still in the "posts must be approved" stage. I'm using a Midland window mount, on a side glass as my Buicks front and rear windows have WAY too much going on and render the antenna useless.

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[jassing]

Are you measuring SWR consistently? (ie: don't measure in the garage, then take another measurement in an open field)

"thru glass" mounts have a lot of loss, some glass has some reflective material in it which can interfere...

The key is to measure swr at the same place/conditions -- ANYTHING can change swr: weather, a tree, another car, a person, wind, etc.

What SWR meter are you using?

 

[mmckenna]

Window mount antennas are going to give you issues.

If the glass is tinted or has defroster wires, it's going to be an issue.
The car needs to be out in an open area away from buildings, lamp posts, anything metallic that will reflect energy. All the doors need to be closed with you inside testing.

Unless you are moving around, the SWR would likely be consistent. If you can watch the SWR meter move without anything else happening, you might have cable issues.
Make sure the cable isn't pinched in a door, window, trunk lid, etc.
Make sure the radio is properly powered, ideally both positive and negative directly to the battery. Be wary of cigarette lighter plugs.
Make sure the radio is well grounded. This might mean running a short wire jumper from the radio chassis to the vehicle body.
Make sure you are using the right cable and the connectors are properly installed.

 

[BloodandRoses]

Yep your going to need a real antenna..Maybe a mag mount...

 

[prcguy]

Its been a long time since I installed a glass mount CB antenna, but I do have a lot of experience installing a few dozen of very first ones designed and sold in the 1970s. The are basically an end fed antenna with the coax wanting to be the other half of the antenna and the coax will radiate some just like the antenna whip.

If all the coax is routed in its final run close to the vehicle body then it should give a stable reading but if your in the middle of testing it with coax flopping around inside the vehicle it will give inconsistent readings. Is that the situation you have right now?

 

[Unit562]

Its been a long time since I installed a glass mount CB antenna, but I do have a lot of experience installing a few dozen of very first ones designed and sold in the 1970s. The are basically an end fed antenna with the coax wanting to be the other half of the antenna and the coax will radiate some just like the antenna whip.

If all the coax is routed in its final run close to the vehicle body then it should give a stable reading but if your in the middle of testing it with coax flopping around inside the vehicle it will give inconsistent readings. Is that the situation you have right now?

No, its routed behind interior panels and under the seat.

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[Unit562]

Are you measuring SWR consistently? (ie: don't measure in the garage, then take another measurement in an open field)

"thru glass" mounts have a lot of loss, some glass has some reflective material in it which can interfere...

The key is to measure swr at the same place/conditions -- ANYTHING can change swr: weather, a tree, another car, a person, wind, etc.

What SWR meter are you using?

Same spot, same conditions, ill get 1 and 40 to read the same, wait on Chan 19 for a few minutes, go back to 1 and 40 to check it aagain and SWR is wildly different. I'm using a workman SWR-2T

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[Unit562]

Window mount antennas are going to give you issues.

If the glass is tinted or has defroster wires, it's going to be an issue.
The car needs to be out in an open area away from buildings, lamp posts, anything metallic that will reflect energy. All the doors need to be closed with you inside testing.

Unless you are moving around, the SWR would likely be consistent. If you can watch the SWR meter move without anything else happening, you might have cable issues.
Make sure the cable isn't pinched in a door, window, trunk lid, etc.
Make sure the radio is properly powered, ideally both positive and negative directly to the battery. Be wary of cigarette lighter plugs.
Make sure the radio is well grounded. This might mean running a short wire jumper from the radio chassis to the vehicle body.
Make sure you are using the right cable and the connectors are properly installed.

None of the above.

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[prcguy]

Since the coax is probably hot with some RF I would expect to see some changes in SWR as you handle the SWR meter or touch the radio, etc. Can you make a measurement where you do not touch any metal parts of the meter or radio and key down for a time to see if its stable under those conditions?

If its stable when you are not handling the coax or SWR meter then you might be able to tune it and button it all down and you can use some big snap on ferrite chokes to reduce RF on the coax. If its not stable under the above conditions I would test the coax run separate if there is a connector at the antenna end and/or test the antenna with another chunk of coax.

No, its routed behind interior panels and under the seat.

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[Unit562]

Since the coax is probably hot with some RF I would expect to see some changes in SWR as you handle the SWR meter or touch the radio, etc. Can you make a measurement where you do not touch any metal parts of the meter or radio and key down for a time to see if its stable under those conditions?

If its stable when you are not handling the coax or SWR meter then you might be able to tune it and button it all down and you can use some big snap on ferrite chokes to reduce RF on the coax. If its not stable under the above conditions I would test the coax run separate if there is a connector at the antenna end and/or test the antenna with another chunk of coax.

ill see if I can dig up some of those chokes at work. Another thought I'm having now while waiting for my good old iron block to warm up is, I might try shortning the coax. I imagine it sitting in a pile under the seat will cause issues?


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[k7ng]

Yes, you might find things work more predictably with as direct a run, within reason, of coax as possible between the radio and the antenna. Sometimes it doesn't seem to matter, other times it does, but in general, you don't want it rolled (or piled) up.

 

[Unit562]

Yes, you might find things work more predictably with as direct a run, within reason, of coax as possible between the radio and the antenna. Sometimes it doesn't seem to matter, other times it does, but in general, you don't want it rolled (or piled) up.

I may at this point fabricobble a mount together for the trunk and run a firestick. Seems easier at this point than trying to bandaid the window mount.

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[radioman2001]

Bad ground causing coax shield to become part of the antenna, water in coax or antenna, antenna moving while doing SWR, person standing too close to antenna, vehicles moving by while doing SWR. There are many reasons why you can get this kind of results.

 

[Unit562]

Bad ground causing coax shield to become part of the antenna, water in coax or antenna, antenna moving while doing SWR, person standing too close to antenna, vehicles moving by while doing SWR. There are many reasons why you can get this kind of results.

None of those are issues, coax ohms perfect and has no shorts, I tune my antenna on joint Base Lewis McChord in one of the clearings they use for artillery.

I tried tuning again yesterday, same spot, got 1 and 40 to read equal and waited. Read SWR on both channels again and it was out of tune again. I'm starting to wonder if something in the base of the antenna where you tune it is broken.

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[FiveFilter]

Quote: "I may at this point fabricobble a mount together for the trunk and run a firestick. Seems easier at this point than trying to bandaid the window mount."

This is the better part of valor. A through-the-glass mount works pretty good at VHF/UHF-class frequencies, but falls on its face in the big 11-meter class. I'm not saying this is the source of your SWR problem, but if you want to talk more than a mile, I'd get a proper antenna out there on top of metal. I'm partial to mag mounts because I remove them when not on the highway, but the edge-of-lid mounts are known to give good results with neater wire ingress that is less prone to entrance damage from opening-and-closing the lids.

 

[Delivers1234]

HI. I also went to check my bearcat 880 settings. the swr is off. I have no idea why. and the swr jumps around. i cannot pin it to anything though.

the center pin cable is open (no flow). the antenna is also (open) no flow from the center pin...

please keep posting. it helps me follow along.