Antenna Feedpoint Coax Choke

[slowmover]

Someone needs to make a coax cable with the jacket impregnated with ferrite. LOL 😆

Joke or not for the relative short run involved in mobile help will pay for itself.

Onion-layers, as once one has dead-quiet DC power, further sources of noise become “audible targets”.

There are “neighborhoods” (relative term) I can drive thru which feature unreal amounts of noise.

The problem is that this could be when one may most need best ears.

I was trying to listen to AM-19 yesterday going eastbound into Fort Worth on IH-30 . . and was having a hard time trying to understand why/where/what a backup on IH-35 was occurring. Hell, IH35E or IH35W?

My pickup truck isn’t yet optimal, but even if it was this sort of problem co-exists going into any major metro, Skip or not.

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[AB5ID]

Common mode noise and RFI can be a killer, the more ferrite the better.

 

[slowmover]

Common mode noise and RFI can be a killer, the more ferrite the better.

That’s my roadgoing professional experience by which I hope others take heed.

$80 at one end and $90 at the other end of transceiver-to-antenna RF Chokes for the big truck seems expensive, but this ain’t a Basement Barney rig.

The notable increase in RX clarity is instant (same as the experience of NRC), and reports of TX clarity bolster the perceived increase in ease of obtaining responses.

We several of us the other day were using MyRadarPro to track a severe 60-MPH storm front across a 30-mile gap while heading away from each other (not nearly that far apart; looking at what we saw as control to the feed provided).

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[slowmover]

Common mode noise and RFI can be a killer, the more ferrite the better.

It’s good as a joke.
Don’t forget powdered shungite.

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[AB5ID]

I put on my shungite underwear when I play with the big ol' Johnson 😉.

 

[slowmover]

Common Mode Current Meter

https://www.qsl.net/on7dy/Documentation/Common%20mode%20chokes/A%20simple%20common%20mode%20currents%20meter.pdf

At QRZ

Common Mode Current: Testing/Detection​

https://forums.qrz.com/index.php?threads/common-mode-current-testing-detection.938767/

Thx, @crawdad on WWDX

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[slowmover]

If not linked earlier:

Common mode choke question.

May be a dumb question but does one have to wind coax tightly around a toroid ring to effectively build a choke..I have excess coax in my installation Enough to make 7 or so 20 inch loops through a toroid ring.. Would this tidy up the excess and create a choke at the same time..or does it need...

forums.radioreference.com

Project Status

Ordered some rg316 jumpers last night after using some heavy string to simulate windings for good ballpark length requirement. Whether it’s 8, 10, 11, or 12 wraps it will have adequate coax.

Expense was low so hope that quality is good. A NANO-VNA still needed, but will have to wait.


Took me awhile to decide what exact gear to use in this installation (now, and possible future). Had resisted breaking up the big truck radio rig as it was years in the making, but if I go back to work I don’t think it’ll be OTR. Meaning, less sophisticated will be fine. Next was to free up some funds.


Installation in General:

Getting headliner reinstalled will be a nice thing. The Hellbilly look has gotten old.

— LIDO seat headrest speaker mount is very next purchase in order to hold W-M DSP CLEARSPEAKER. The two cables are already run down Port B-pillar.

— Main power will enter cab on 6-AWG and then run to overhead on 10-AWG. Two distribution centers; at footwell and again overhead (POWERWERX PD-75 and 4005 RigRunner; respectively).

— Antenna dialed-in that last bit (Texas 1800 thread). Several others also tuned.

— Found several geographical high points in “my” region to conduct tests from being parked. One truly local (IH-20 only) and the other I should be able to hit nearly all of Ft Worth (not really running adequate power to get east of IH-35W).

I’ve heard at least one VHP rig getting out quite far from driving past that high ridge (broadcast towers). I’m hoping clarity plus a KL203 does the job. (45W radio-only to 125W peak is idea; with or without little amp).

I’ll swap jumpers to ask impressions of ferrite-filtered versus a “no toroid” jumper. Will be on the 107” whip. (Change antennas around once that’s done).

In the meantime just sitting and burning diesel — with the radio rigs that can & can’t hear me — I should be able to get a good idea of High Plains substitute RX distances via AM-19 from IH-20, US-287 and IH-35W North.

S/NR improvement is so big, IMO, that the pickup truck radio install has been hanging until this thread topic portion fully addressed.

I may have more work to do via pickup truck noise sources, but that can be done while at home.

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[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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Why the 75ohm chokes?

 

[slowmover]

The two legs of coax are 75-ohm on a co-phase big truck harness before they’re combined into the 50-ohm single which attaches to radio.

— Adding length to 18’ legs not advisable (you earlier mentioned).

I’ve beaten the previously-used PALOMAR units to death. (300k miles). So just left them until a re-fresh (which didn’t occur). Got out of that truck.



“Whips-around” Skipshooter 7’ with too much tilt for SWR due to A-pillar interference.


8’ SIRIO 5000 3/8 (Ideal SWR).


Several antenna changes. But never a bombproof way of both aligning & securing the 500. Which is why I wanted to use ft240-61 and cover with tape (etc).

Running 70-MPH across Great Plains is hard service at 5-600/miles per day.

Pickup truck now the sole focus.
Low profile to fit under headliner.

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[prcguy]

The two legs of coax are 75-ohm on a co-phase big truck harness before they’re combined into the 50-ohm single which attaches to radio.

— Adding length to 18’ legs not advisable (you earlier mentioned).

I’ve beaten the previously-used PALOMAR units to death. (300k miles). So just left them until a re-fresh (which didn’t occur). Got out of that truck.

View attachment 187569

“Whips-around” Skipshooter 7’ with too much tilt for SWR due to A-pillar interference.
View attachment 187570

8’ SIRIO 5000 3/8 (Ideal SWR).
View attachment 187571

Several antenna changes. But never a bombproof way of both aligning & securing the 500. Which is why I wanted to use ft240-61 and cover with tape (etc).

Running 70-MPH across Great Plains is hard service at 5-600/miles per day.

Pickup truck now the sole focus.
Low profile to fit under headliner.

.

If the chokes each have the 18ft recommended lengths of 75 ohm coax and make up the power divider with 50 ohm coax from the chokes to the antennas then ok. Otherwise you don’t want to add more 75 ohm coax to the 18ft power divider. I would think the chokes go right at the antenna feedpoints fed from the 75 ohm phasing harness and if so the chokes should have 50 ohm coax. Once you do the power divider split with the 18ft harness it should go right to each antenna feed point and if you have to extend that you would use equal lengths of 50 ohm coax or when adding chokes they should have equal lengths of 50 ohm coax.

 

[slowmover]

If the chokes each have the 18ft recommended lengths of 75 ohm coax and make up the power divider with 50 ohm coax from the chokes to the antennas then ok. Otherwise you don’t want to add more 75 ohm coax to the 18ft power divider. I would think the chokes go right at the antenna feedpoints fed from the 75 ohm phasing harness and if so the chokes should have 50 ohm coax. Once you do the power divider split with the 18ft harness it should go right to each antenna feed point and if you have to extend that you would use equal lengths of 50 ohm coax or when adding chokes they should have equal lengths of 50 ohm coax.

Thanks for clarification.

— I didn’t have enough slack in harness legs to wrap a toroid, unfortunately. The big truck radio rig is set aside for now.

— Determining which 50-ohm coax type for the pickup coax system based on bend radius was next. RG316 got the nod (short total length used; looks like 3’ or less per toroid).

— I don’t run “big power”. 50-150W Peak (intermittent) depending on vehicle and gear. Usually just the radio with amp bypassed. If I someday add a KL503 or something I’ll revisit this.

In all — (2) device jumpers plus single long jumper — it’s about about 9’ of RG316

Radio — 411CB — KL203 — 8’ TTL length end-to-end / Toroid-to-Toroid — Antenna.


To state the pickup truck system (delayed in completion after a health crisis):

PRESIDENT Texas 1800 7’ on BREEDLOVE #601.

PRESIDENT 45W Lincoln II+ V.3

(w/ PRESIDENT DigiMic; and
PRESIDENT Liberty Wireless Mic)

WEST MOUNTAIN RADIO ClearSpeaker DSP Speaker

MORGAN SYSTEMS 411CB 11M Bandpass Filter

RM ITALY KL-203


The mock-up that’s now waited an age:



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[slowmover]

Pickup Truck
Single Antenna

(1) ea; (96”) RG316 jumper (8’) with (2) FT240-61 toroids each wrapped (11) times came to:

2.5’ per toroid

3’ center section.

Can’t hear much but Skip during daylight unless a big truck with 40-50W is going past on IH-20 ten miles away . . . but the Super Bowl comes in a little more cleanly.

Point-to-Point distance once radio is mounted is 1.5’. Two in-line devices will add 16” total extra of coax. 9.3’ coax run once done.

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[slowmover]

View attachment 187685

Pickup Truck
Single Antenna

(1) ea; (96”) RG316 jumper (8’) with (2) FT240-61 toroids each wrapped (11) times came to:

2.5’ per toroid

3’ center section.

Can’t hear much but Skip during daylight unless a big truck with 40-50W is going past on IH-20 ten miles away . . . but the Super Bowl comes in a little more cleanly.

Point-to-Point distance once radio is mounted is 1.5’. Two in-line devices will add 16” total extra of coax. 9.3’ coax run once done.

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This first impression for the record:

Forgot to note that I had an immediate reduction in S-Meter reading on AM-19 after installation. Engine-off, relation to structures, etc, a parked constant. (Had one P-E unit in-line previously).

— This is experience consistent with having the CMNF-series filters/chokes installed into big truck coax harness; the MyAntennas choke also.

BPF not yet installed.

I was able to increase RF-G a slight amount such that first position SQ was unaffected.

Assuming this works out long-term the investment thus far is $34 for (2) FT240-61 ferrite toroids and $17 for (1) 8’ RG316 jumper.

$50 before tax/shipping for, “upgraded coax”, into a pickup truck.

There are better components for this task, but — as noted above — it’s in fitting to available space that drove the pickup purchase, and for the big truck it’s the external mount which wouldn’t align.

— It’s hoped that having treated each end of the short coax run pays off for performance and install space requirements. Low price was lagniappe.

Also, after install is complete every component will have an improved case ground. Radio and Antenna are quite close.

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