RF choke question

[n7lrg]

Hey all, got the Y-Quad erected, guyed nicely and has survived 2 pretty good wind storms here on Camano Island WA. The SWR is great and did not change from what I had measured when it was on the ground.

I built 2 RF chokes to defeat common mode RF by winding them around some PVC pipe. I had read it was not a good idea to install them on the boom near the feed point as it would be "in the field" so they are mounted on the tower. You can see they are right next to my knee.

The antenna has great rejection when pointed away from stations and has great gain (5 S-units) for stations in Canada as well South of Seattle. My received signal reports about 3-4 S-units gain over my 1/2 wave ground plane. I thought that number should be a little higher,

My question is - can these RF chokes be de-tuning my 12w ssb output power as I do/will not use an outboard amp. See pics, 73.

 

[RFI-EMI-GUY]

The chokes are common mode so should not affect the signal passing through the coax. The insertion loss in the chokes should be negligible. You might want to snap some ferrite chokes on the coax just above the rotor loop, to augment them.

 

[prcguy]

The chokes you made are probably not defeating common mode RF, you would have to measure any benefit and tune the number of turns and that type of choke is usually of little or no value. You need a choke with ferrite to actually absorb the common mode currents on the feedline and not bounce them back to the antenna to be bounced back again. This is if your chokes are tuned perfectly and if not the common mode currents just pass them by.

You can make a very effective choke by wrapping 12 turns of RG-58 size coax trough an FT-240-61 mix core which costs about $10. That will provide maybe 30dB of isolation at 26-30MHz where I estimate you would be lucky to have 5 or 6dB now. If you can find some RG-142 or RG-400 coax its the same size as RG-58 but will handle several kW of power.

I like to make the chokes with cable mount SO-239s so they can plug in the feedline anywhere. Here is a very sloppy version I made that has a male and female connector and these are best used right at the feedpoint of the antenna. You would screw the male connector right on the antenna and your existing feedline into the female. I included another picture of how the windings cross over the core half way through the total number of turns. I covered this one in electrical tape because the sun can wreak they ty-raps over time and the tape will make it last a little longer. The only bad effects you will get from your existing choke or this type is the insertion loss of the cable used in the choke which is just a little above zero loss at 27MHz.

 

[RFI-EMI-GUY]

I am puzzled why the manufacturer (MACO?) tells you not to put the chokes on the boom. If you are cancelling out common mode, having them on the boom close to the feedpoint, should be a great place to minimize pattern distortion.

 

[prcguy]

Yes, if the length of coax between the feedpoint and choke are just the right length and you have common mode currents that coax will become a radiating element skewing the antenna pattern, affecting VSWR and causing other problems. Choke it at the feedpoint.

I am puzzled why the manufacturer (MACO?) tells you not to put the chokes on the boom. If you are cancelling out common mode, having them on the boom close to the feedpoint, should be a great place to minimize pattern distortion.

 

[n7lrg]

I'll try the ferrite chokes. Maco did not say not to place the chokes where I did. It was from another reading I found. I'm thinking I may remove them to see if by having them there I didn't accidentally create an "antenna" inside the beam. I'll report back as to what I did and the results, thanks all.

 

[prcguy]

I would bet a little $$ that you have much more technical knowledge than anyone that works at Maco.

I'll try the ferrite chokes. Maco did not say not to place the chokes where I did. It was from another reading I found. I'm thinking I may remove them to see if by having them there I didn't accidentally create an "antenna" inside the beam. I'll report back as to what I did and the results, thanks all.

 

[slowmover]

The chokes you made are probably not defeating common mode RF, you would have to measure any benefit and tune the number of turns and that type of choke is usually of little or no value. You need a choke with ferrite to actually absorb the common mode currents on the feedline and not bounce them back to the antenna to be bounced back again. This is if your chokes are tuned perfectly and if not the common mode currents just pass them by.

You can make a very effective choke by wrapping 12 turns of RG-58 size coax trough an FT-240-61 mix core which costs about $10. That will provide maybe 30dB of isolation at 26-30MHz where I estimate you would be lucky to have 5 or 6dB now. If you can find some RG-142 or RG-400 coax its the same size as RG-58 but will handle several kW of power.

I like to make the chokes with cable mount SO-239s so they can plug in the feedline anywhere. Here is a very sloppy version I made that has a male and female connector and these are best used right at the feedpoint of the antenna. You would screw the male connector right on the antenna and your existing feedline into the female. I included another picture of how the windings cross over the core half way through the total number of turns. I covered this one in electrical tape because the sun can wreak they ty-raps over time and the tape will make it last a little longer. The only bad effects you will get from your existing choke or this type is the insertion loss of the cable used in the choke which is just a little above zero loss at 27MHz.

View attachment 110498View attachment 110499

FWIW, there is available UV-Resistant zip ties. A telecom item. Search online. (Same for Flame Resistant, but it’s of a different composition).

I’d still wrap with 88 or something, but there’ll be other places also benefitting.

 

[mmckenna]

FWIW, there is available UV-Resistant zip ties. A telecom item. Search online. (Same for Flame Resistant, but it’s of a different composition).

I’d still wrap with 88 or something, but there’ll be other places also benefitting.

Standard black zip ties are almost always UV resistant. Good zip ties will say it on the package, but I think every one I've ever used was UV resistant, even the crappy Harbor Freight ones.

It's always a relaible way to tell if the installer is any good.

 

[slowmover]

Standard black zip ties are almost always UV resistant. Good zip ties will say it on the package, but I think every one I've ever used was UV resistant, even the crappy Harbor Freight ones.

It's always a relaible way to tell if the installer is any good.

Some may say it , but don’t bet on it for mobile use.

The premium for tested or certified or whatever may be worth it to some folks with some installations.

.

 

[prcguy]

When I was working I always specified UV resistant Ty-Raps going back 30yrs or more for our stock room supplies and also for any vendors working on site. If its real important to stay in place you move up to Panduit stainless steel cable ties and the proper tension tool.

FWIW, there is available UV-Resistant zip ties. A telecom item. Search online. (Same for Flame Resistant, but it’s of a different composition).

I’d still wrap with 88 or something, but there’ll be other places also benefitting.

 

[mmckenna]

Some may say it , but don’t bet on it for mobile use.

The premium for tested or certified or whatever may be worth it to some folks with some installations.

I guess I just don't buy crappy ones, because I've never had an issue with any of the black ones I've purchased.

And +1 on the stainless steel ties. I usually use those outdoors where it's critical.

 

[slowmover]

I’ve walked up to big truck mirror arms and pretty much just pulled the “secured” coax right off.

I mentioned it for other readers maybe not aware of such.

 

[Duckford]

Amazon.com: Yarachel 50PCS RFI EMI Noise Suppressor Cable Clip for 3.5mm/ 5mm/ 7mm/ 9mm/ 13mm Diameter Cable : Electronics

Buy Yarachel 50PCS RFI EMI Noise Suppressor Cable Clip for 3.5mm/ 5mm/ 7mm/ 9mm/ 13mm Diameter Cable: Noise Filters - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

I use these cheapo snap on beads, and they are fantastic on 10/11 meter. In fact, the cheapo beads are made out of not just a good ferrite mix, but actually the IDEAL ferrite mix for high HF. They are very cheap and work very well for CB.

Snap five at each end of the coax and virtually all problems disappear, you get better transmit and receive. They've dropped some of my sound floors by a few S units. Protect them with some electrical tape from UV and your done.

Those coax chokes never made much sense, you increase attenuation by lengthening the feedline, wasting money on feedline, and technically they don't work very well at all.

These chokes aren't the best for low band HF. Those get to be very pricey, and I've bought high end chokes from Palomar for ham radio use. Very pricey for those ferrite mixes, and I've also bought some of their big pipe bomb looking 1;1 chokes which work very well. But, they kill RFI.

For CB radio, the cheap off the rack ones will work wonders. I encourage everyone and anyone on CB to try them. Big difference.