Antenna Feedpoint Coax Choke

[prcguy]

Finally got 12T of 75-ohm RG59 on FT240-61 done; pair. Oriented port & starboard. Was unable to assemble with split-loom cover in place.

Took pretty much the whole of 6’ jumper to accommodate bend-radius restriction (60mm). It also took time to figure out how to thread cable without inducing torsional twist.

Still need a thumb-size piece of wood dowel or pvc pipe to go in center: no cable overlap, and also against ring interior.

View attachment 158531

View attachment 158532

Its predecessor was a tad bulky to fit and to be secured under antenna mount in use without constant revision. But proved concept over broad range of conditions.

— A “better” coax choice for 75-ohm (didn’t uncover that) which could be wrapped almost tight around ferrite toroid might use but 3.5’ of cable as reports of those using RG400 in 50-ohm apps suggest.

The addition of these jumpers causes the coax run to radio (each side) to now be 24’. Depending on which truck I’m in — if new coax run needed — I’m definitely going to cut down the harness leg lengths to what’s needed versus bundling up some of it.

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If all this is for a co-phased pair of antennas like on mirror mounts, you don't want to mess with the coax length of a factory co-phasing harness made of 75 ohm coax. The co-phasing harness is a 50 ohm power splitter and the coax lengths are critical for matching. If you need to extend a factory harness its best to add 50 ohm coax to the center common point or to extend the two antenna sides with equal lengths of 50 ohm coax since the harness is designed to provide a 50 ohm match where each antenna usually connects.

Once the co-phasing harness has done its job splitting the signal equally at the two antenna connections you can do anything you want on the antenna side as long as you treat it as a 50 ohm system from that point on. The reason you want equal lengths of coax on both sides if you extend them is different lengths will cause a phase imbalance between the two antennas possibly making them directional to one side or the other.

 

[merlin]

WOW. This thread boggles my mind. I started driving interstate semi back in 1972. The good old days of CB and big wheels rollin.
By that time, I was a decade amateur and ASEE. I specialized in antenna systems. This thread is so overkill people don't want to read through all of slowmovers specifics, much less understand. "High performance mobile CB" WUT? It doesn't work like that. 'DIPOLE' on a semi ? WHY,
you can get equal performance from 'ONE GOOD ANTENNA'. Co-phasing a pair of them will help radiation pattern where you want it, 'IF IT IS INSTALLED properly'. You don't have common mode problems if everything is grounded properly and that means no external chokes on coax.
Back on post #5, you don't radiate outside the coax or receive noise, with good coax.
You cant buy a truck stop radio and make it perform better than it does, not on 11 meters.
That is why I opted for a $1500 radio. Alternator whine, can't hide from that, but you can near eliminate it with an alternator noise supressor and maybe your stiff ferrite choke on the radio power leads. And keep leads as short as practical.
My Freighliner had a 100 amp service bus under the dash, even has a filter capacitor to ground. No problem there.
Running the I 5 corridor, Most drivers I could hear were out to 10 miles or more and If I could hear them, they could hear me.

 

[prcguy]

WOW. This thread boggles my mind. I started driving interstate semi back in 1972. The good old days of CB and big wheels rollin.
By that time, I was a decade amateur and ASEE. I specialized in antenna systems. This thread is so overkill people don't want to read through all of slowmovers specifics, much less understand. "High performance mobile CB" WUT? It doesn't work like that. 'DIPOLE' on a semi ? WHY,
you can get equal performance from 'ONE GOOD ANTENNA'. Co-phasing a pair of them will help radiation pattern where you want it, 'IF IT IS INSTALLED properly'. You don't have common mode problems if everything is grounded properly and that means no external chokes on coax.
Back on post #5, you don't radiate outside the coax or receive noise, with good coax.
You cant buy a truck stop radio and make it perform better than it does, not on 11 meters.
That is why I opted for a $1500 radio. Alternator whine, can't hide from that, but you can near eliminate it with an alternator noise supressor and maybe your stiff ferrite choke on the radio power leads. And keep leads as short as practical.
My Freighliner had a 100 amp service bus under the dash, even has a filter capacitor to ground. No problem there.
Running the I 5 corridor, Most drivers I could hear were out to 10 miles or more and If I could hear them, they could hear me.

The problem with some semi trucks is a large mirror on each door and nearly everything else is fiberglass. The mirror assembly is nowhere near large enough to provide a ground plane for the usually co-phased antennas on the mirrors so the coax becomes part of the counterpoise and its hot with RF. Adding a second tuned whip to the mirror pointed downward and grounded makes each mirror mount antenna into a dipole which is now mostly self contained and relies much less on the tiny useless ground plane its been given.

Adding CMCs to the feedpoint of each antenna minimizes RF on the coax and also helps keep RFI that might be picked up on the coax shield from reaching the antenna and being received to some extent. I first used the dipole concept on big rigs in the mid 70s working as a professional installer and it cured a lot of problems back then and still can today and 2ft or 3ft Firesticks were my antenna of choice back then for the grounded dipole side since we were a major Firestick dealer.

I had most of the big semi trucks mapped out in the 70s like which ones had more alternator whine, which ones had fiberglass doors vs metal and could make up a list of needed items for a potential customer before they even shut their rig down and walked into our store. There were a few steel roofed big rigs back then and my first choice for those was a good base loaded antenna in the center of the roof, even though it gets slightly blocked to the rear from a tall trailer.

 

[merlin]

To a level, I agree. Newer mirrors even lack upper and lower brackets, make mounting an antenna impossible.
But still, mirrors are not mounted to fiberglass, there is door frame underneath, and then a good ground strap frame to door frame.
IF there is no other option but mirror mounting, then the dipole should work fine, but I would mount to the cab before that option.
Simpler is better. My truck, the left mirror supported a Hustler RM-11S on a 15 inch rigid mast. The right, the same thing except a
RM-40S . That one just would clear 13'6".
I did have option to mount a Wilson 1000M center of the cab. That part aluminum and long sleeper would have worked, but the 1000M
I used on my pickup with mag mount.

 

[slowmover]

ARIES A-18 PPP CoPhase harness is what’s scheduled for next install, this time on a new version Kenworth t680. Unlike some other offerings, it is solely two (2) RG59 legs which come together at a PL-259.



So if I have this right:

1). Wrap ft240-61 as feedpoint chokes, both antenna ends.

2). Needs two identical jumpers as extensions to accomplish required turns.

3). Jumpers need be 50-ohm, not 75-ohm (not RG59).

— Question is what coax is a good choice given the need to wrap the toroid in a snug manner?

Bend radius chart for RG8 or RG58 isn’t encouraging. Especially as my earlier experiments show it requires almost the whole of a 6’ jumper (creating 24’ harness legs).

These are going to be out in gale force winds. (70-MPH; 10-12,000 miles/month). Bug and dirt collectors. Each antenna isn’t going to be subject to more than 100W as the needed crutch for mirror arm antenna mounts (SIRIO 3/8) and that for seconds to 2-3/minutes.

Cover as per this ideal?

Post in thread 'electrical tape for outside connections'
electrical tape for outside connections

Commscope 221213

The jumper/ferrite would be self-contained under cover, so-to-speak.

Thx.

.

 

[slowmover]

Example of OEM, as-delivered:



53’ Dry Van. No more reefer for awhile.

PRO COMM aftermarket mounts.

Mine’s modified for a HD stud.
Factory gets bypassed.
That stud gets taped over.




This mount allows some forward tilt. Factory isn’t strong, and can’t run tall.

From earlier t680 with 7’ Skipshooters. PALOMAR ENGINEER MC-1-500-50 Mini-Choker on leading edge of arm secured with zip-ties.



Beehives gone, now it’s an SS stud. There’s no good stud since Kale quit making his, and I only have one. Used bronze thrust washers to fill gap from PL-259 shell to mount base as connection isn’t “tight” re center conductor.

Didn’t hurt as MFJ tuner plus a PDC SWR meter both showed under 1.5:1 with or without power added (KL-7505v).


Of the three main fleet trucks (other two are 579 Pete, and FTL Cascadia) the t680 is hands down easiest and best antenna setup/performance.

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[slowmover]

Antenna Stud a weak link for running tall (see earlier discussion on problems of same).

JBC930SS - ProComm Heavy Duty Stainless Steel CB Antenna Stud​

JBC930SS - ProComm Heavy Duty Stainless Steel CB Antenna Stud

JBC930SS - ProComm Heavy Duty Stainless Steel CB Antenna Stud

www.wearecb.com

Is the closest thing to what’s wanted for handling a heavy antenna in high winds (non-custom; custom, such as BREEDLOVE is far more desirable).

As the mount plate is aluminum, I run thinnest film of BURNDY Penetrox between them. Winter weather road treatment fluids or salt in Midwest & Plains is hell on big truck antenna systems.

Cover the lower as per above post.

RF Bonds are from mirror-mount bolts (and door hinge jumpers) then jump-by-jump down firewall to frame rails.

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[niceguy71]

Received the other end yesterday:

View attachment 151751

SlowMover you've given me so many great ideas and solutions and I'll always be so very appreciative. thank you
I bought the same choke hoping to get my noise level a little lower... even half a line on my signal meter would make me happy...
my radio seems to be S2 to S3 most of the time... and I'm told that's pretty good. if I listen to the ham channels it goes to S1... I wish the CB channels were that quiet.... you seemed pretty excited by this choke and that was good enough for me.

I had a friend ( VERY smart guy) tell me it would do nothing for me... unless I had a problem.... but I said heck I'll try it.......
I took the coax off the back of my base station and put a 6 foot jumper and the choke in place ....... NO WAY to ever get to the top of my mast again... unless I get 3 guys and a 100 feet of rope over the house and spend a couple hours of time ( it's staying put until it dies) so I could only put it on the radio end..... I have removed and reinstalled it 25 times ... each time I sit and listen as best as I can and see where the noise level is on the Signal meter... I study the noise level and put the chake back in line.....
.. it has done absolutely nothing for me.
I have no complaints about trying an experiment. but for me I couldn't recommend it.
I plan to test it on the mobile and hopefully it will help a little bit.. but my mobile doesn't have as much noise as my base station.... I think it's just the old signal meter on the old President Grant doesn't show as much noise as the 5555 N II does.
so happily, I'm pretty much done with my base station and mobile... not many people in the hobby say that... but once I have some thing working... I generally don't make a change.

 

[slowmover]

SlowMover you've given me so many great ideas and solutions and I'll always be so very appreciative. thank you
I bought the same choke hoping to get my noise level a little lower... even half a line on my signal meter would make me happy...
my radio seems to be S2 to S3 most of the time... and I'm told that's pretty good. if I listen to the ham channels it goes to S1... I wish the CB channels were that quiet.... you seemed pretty excited by this choke and that was good enough for me.

I had a friend ( VERY smart guy) tell me it would do nothing for me... unless I had a problem.... but I said heck I'll try it.......
I took the coax off the back of my base station and put a 6 foot jumper and the choke in place ....... NO WAY to ever get to the top of my mast again... unless I get 3 guys and a 100 feet of rope over the house and spend a couple hours of time ( it's staying put until it dies) so I could only put it on the radio end..... I have removed and reinstalled it 25 times ... each time I sit and listen as best as I can and see where the noise level is on the Signal meter... I study the noise level and put the chake back in line.....
.. it has done absolutely nothing for me.
I have no complaints about trying an experiment. but for me I couldn't recommend it.
I plan to test it on the mobile and hopefully it will help a little bit.. but my mobile doesn't have as much noise as my base station.... I think it's just the old signal meter on the old President Grant doesn't show as much noise as the 5555 N II does.
so happily, I'm pretty much done with my base station and mobile... not many people in the hobby say that... but once I have some thing working... I generally don't make a change.

As it’s my health & wealth (and in Mobile) I’ve had an open wallet and willingness to try as conditions are always changing. CMC may be more easily fixed with a base (speculation).

What was fine for days and weeks all of a sudden isn’t in heavy traffic and — now — heavy rain. And the guy next to me has something in his vehicle that’s having a serious effect on my rig.

I’m willing to pay for that moment of help in a high risk situation.

I’ve written, too, about the use of Bandpass Filter for 27-MHz. I’ve tried to be clear about my experience with anything I’ve used.

— Treat both ends of coax with RF/CMC filters pays. (BPF probably won’t.) I’ve made a point thats it’s in mobile, as that’s my experience.

“Can I clearly understand everything I can hear?”

Antenna + Coax + (2) filters = price of AT5555-N2

That’s the same rule as the rifle optic having doubled the price of the rifle. (Right choice).

I can “hear” both radio & system in that DRX-901.

I also believe that when I need the help, I may not realize I am receiving such.

FWIW, your range test vid of looking for an empty channel was not only done with right equipment (I linked it again a few days back elsewhere), but also showed you have a good system in the first place. Great audio (vid) and great sound from radio rig showing a VG antenna system as well.

.

 

[prcguy]

Antenna Stud a weak link for running tall (see earlier discussion on problems of same).

JBC930SS - ProComm Heavy Duty Stainless Steel CB Antenna Stud​

JBC930SS - ProComm Heavy Duty Stainless Steel CB Antenna Stud

JBC930SS - ProComm Heavy Duty Stainless Steel CB Antenna Stud

www.wearecb.com

View attachment 167229

Is the closest thing to what’s wanted for handling a heavy antenna in high winds (non-custom; custom, such as BREEDLOVE is far more desirable).

As the mount plate is aluminum, I run thinnest film of BURNDY Penetrox between them. Winter weather road treatment fluids or salt in Midwest & Plains is hell on big truck antenna systems.

Cover the lower as per above post.

RF Bonds are from mirror-mount bolts (and door hinge jumpers) then jump-by-jump down firewall to frame rails.

.

I hate those ProComm mounts, there is no female part of the SO-239, the center pin of the PL-259 just crams up unto the Allen socket head of the cap screw and is held by the connector thread tension. If the connector unscrews just 1/20th of a turn there is no longer any pressure to keep the center pin connected and its intermittent as f#*k.

 

[slowmover]

I hate those ProComm mounts, there is no female part of the SO-239, the center pin of the PL-259 just crams up unto the Allen socket head of the cap screw and is held by the connector thread tension. If the connector unscrews just 1/20th of a turn there is no longer any pressure to keep the center pin connected and its intermittent as f#*k.

Right. And we tried alternate suggestions. None of which were satisfactory. I made the linked one work.

.

 

[slowmover]

ARIES A-18 PPP CoPhase harness is what’s scheduled for next install, this time on a new version Kenworth t680. Unlike some other offerings, it is solely two (2) RG59 legs which come together at a PL-259.

View attachment 167222

So if I have this right:

1). Wrap ft240-61 as feedpoint chokes, both antenna ends.

2). Needs two identical jumpers as extensions to accomplish required turns.

3). Jumpers need be 50-ohm, not 75-ohm (not RG59).

— Question is what coax is a good choice given the need to wrap the toroid in a snug manner?

Bend radius chart for RG8 or RG58 isn’t encouraging. Especially as my earlier experiments show it requires almost the whole of a 6’ jumper (creating 24’ harness legs).

These are going to be out in gale force winds. (70-MPH; 10-12,000 miles/month). Bug and dirt collectors. Each antenna isn’t going to be subject to more than 100W as the needed crutch for mirror arm antenna mounts (SIRIO 3/8) and that for seconds to 2-3/minutes.

Cover as per this ideal?

Post in thread 'electrical tape for outside connections'
electrical tape for outside connections

Commscope 221213

The jumper/ferrite would be self-contained under cover, so-to-speak.

Thx.

.

Recommendation on this problem?

.

 

[G7RUX]

I hate those ProComm mounts, there is no female part of the SO-239, the center pin of the PL-259 just crams up unto the Allen socket head of the cap screw and is held by the connector thread tension. If the connector unscrews just 1/20th of a turn there is no longer any pressure to keep the center pin connected and its intermittent as f#*k.

I have come across aproblematic installation with one of these mounts. It needed a ball of solder on the tip of the pin so it would crush into the socket on the bolt, then it was pretty stable once the backnut was locked in place with a bit of shellac.

Whilst I didn't like this part of the mount, the rest was very solid.

 

[slowmover]

I have come across aproblematic installation with one of these mounts. It needed a ball of solder on the tip of the pin so it would crush into the socket on the bolt, then it was pretty stable once the backnut was locked in place with a bit of shellac.

Whilst I didn't like this part of the mount, the rest was very solid.

Looks good. Thanks for that.

 

[slowmover]

RG303 getting the nod most often for winding baluns in my reading.

Found this quote from W8JI:

“ . . The RG400 or RG142 is the same internal cable as the RG303, except the RG303 has one shield.

The power rating and loss is exactly the same.

The RG303 is a little easier to wind, works the same, and cost a little less. If I was winding a choke or balun, I would prefer RG303.”


I haven’t found rg303 assemblies, but this assembly in rg400 X2 @ 4’ length (haven’t determined ideal length) looks reasonably priced at $14/ea with free shipping (UHF right angle male to UHF female ends; American Coaxial brand; eBay store).

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