Help tuning co-phase antenna

[slowmover]

Well, I came across some old moddeling I did and a shot of the field. this is just the antenna with ideal ground, but the 3D shows that field
you may get with a tilt. Just some slight differences mounted on truck mirrors.

The big truck mirror-mount problem is reflect off the cab, sometimes the stacks.

15-20/degrees forward max is “vertical”. After that things start downhill. I didn’t pay for 44” lower shafts for nothing.

The A-pillars on today’s trucks (as with cars/pickups) are huge. And the firewalls are double-plate. The older large cars (389, here) are still 1990s type, generally.

The Peterbilt hoop now in use (versus West Coast arms) still probably needs to be jumped by an RF Bond from within the cab side, upper & lower.

On the Plains it’s an easy assumption that a radio sounding loud & clear is likeliest a Pete 379/389 or a Kenworth W900 as the all-aluminum body provides an excellent ground plane.

Owner-operators hauling cattle, flatbeds, tankers to service AG business. Then there’s OVERSIZE and accompanying vehicles. Plus long-term fleet drivers.

 

[merlin]

It was an older version of SimSmith, but since, I upgraded to SimNEC and won't read my old files.
Quite easy just to start over, as this is moddeling software. Time consuming though, A lot of stuff goes into any form of antenna, feedline and such.

 

[merlin]

The big truck mirror-mount problem is reflect off the cab, sometimes the stacks.

15-20/degrees forward max is “vertical”. After that things start downhill. I didn’t pay for 44” lower shafts for nothing.

The A-pillars on today’s trucks (as with cars/pickups) are huge. And the firewalls are double-plate. The older large cars (389, here) are still 1990s type, generally.

The Peterbilt hoop now in use (versus West Coast arms) still probably needs to be jumped by an RF Bond from within the cab side, upper & lower.

On the Plains it’s an easy assumption that a radio sounding loud & clear is likeliest a Pete 379/389 or a Kenworth W900 as the all-aluminum body provides an excellent ground plane.

Owner-operators hauling cattle, flatbeds, tankers to service AG business. Then there’s OVERSIZE and accompanying vehicles. Plus long-term fleet drivers.

View attachment 163956

I have to disagree a bit, as any part of the truck (vehicle) is real ground where the moddeling is concerned. That slight difference I mentiond is more real world, and you won't find any two the same. A lot more to this than you know.

 

[merlin]

After that things start downhill.

Real world, actually, the oposite it true.
Something like a backhoe on a flatbed, non grounded, could be mapped as parasytic.

 

[slowmover]

Real world, actually, the oposite it true.
Something like a backhoe on a flatbed, non grounded, could be mapped as parasytic.

The difference is noticeable. In favor of upright (in my experience running cophase). Range is affected. The guys running 30-degrees and more fade out.

That’s all I’ll have to say on it.

Would like that we could test it on a big truck with more precision.

.

 

[Joshwyle]

Well that seem to be the problem. I’ve gotten it close but able to adjust. Thank yall

 

[slowmover]

Well that seem to be the problem. I’ve gotten it close but able to adjust. Thank yall

Plastic washer?

 

[prcguy]

Well that seem to be the problem. I’ve gotten it close but able to adjust. Thank yall

What’s the SWR now?

 

[Joshwyle]

Yes washer. After trimming antenna I got my swr down to 1.1 all the way across every channel 1-40. Haven’t been out to try n check distance but anxious to see

 

[slowmover]

“You the stud, now, boy!”
Always use a condom.

 

[Joshwyle]

lol.

 

[slowmover]

Since the topic was raised, some good start points in general:

 

[KC5AKB]

Good advice from experienced hands.

 

[Joshwyle]

So my CB recieved far away but doesn’t transmit but about a hundred feet. My swr last checked was 1.1. I used an 18’ cable as my jumper because I had it. Could that be the problem? Is my CB bad? Could my mic cause short transmission? Cobra classic 29 ltd. It’s what came with the truck. I hv 2 of the same radios and can swap but if it’s likely the mic then I’d hate to swap for no reason. Any thoughts will be appreciated. Thanks

 

[Joshwyle]

Also that’s only with see at max and rf gain at max

 

[slowmover]

Tech-Docs Index

 

[Joshwyle]

Thanks

 

[W4AXW]

I haven't read every post but I haven't seen a mention of what coax harness the OP is using. If it's any form of the OEM coax and connectors/connections then it's time to replace it with a decent RG59 75ohm harness. Truck manufacturers use absolutely garbage coax and make very bad, high impedance connections that will cause a litany of issues.

If I missed a post about coax then please excuse.................

7 3

 

[KC5AKB]

How to Tune Your CB Antenna swr mtr info

 

[jcrmadden]

From the article above...

"If the SWR on channel 40 is higher than that on channel 1, your antenna is too long.
If the SWR on channel 1 is higher than that on channel 40, your antenna is too short."

Thanks for the post @KC5AKB !