COAX CHOKE

[pkmak12]

I will be setting up my new Imax 2000 with the GPK in the next few weeks. I just got LMR400 delivered yesterday and made a choke using 4" PVC pipe with 10 turns around. I am wondering if thats too many turns or not. I also give TVI to my neighbors old tube TV but not her new one. Right now I have a A99 up and the bottom of the antenna is not clearing the roof. The Imax will be raised higher clearing the roof with the GPK. Your feed back is much welcomed.

 

[HomerBB]

Use 5 wraps only.

 

[W5LZ]

Ten turns is probably a little too much, but since you've already got it wound, leave it alone. That TVI isn't just from feed line radiation, if any, it's from the antenna and it's being as close to the affected TV as it is. There's more RF coming off of that antenna than there -ever- would be from the feed line, and that's the typical source of most TVI. That poor old feed line gets blamed for things it usually has nothing to do with.
- 'Doc

 

[Robb]

Need to use a 8" pvc for RG-8 type coax (LMR-400 is RG-8 type coax - meaning it is .40" in diameter); RG-58 type coax (RG-59 coax is .250" in diameter) and uses a 4" pvc.
But you are doing the right thing by asking.
Homer is right about the 5 turns too.
(Keep the choke away from the metal mast to keep the choke form being made ineffective too)

Congrats on putting up a new antenna!

 

[pkmak12]

I went to Home Depot and Lowes and they only carry the 4" pipe.
I did the Choke over and did 5 turns on the 4' pipe. Just trying to help fix TVI.
I already offered to buy them a new TV, but they declined. Maybe a Beam antenna pointed at their TV with 5,000 watts...lol (just kidding)

 

[Se7en]

I went to Home Depot and Lowes and they only carry the 4" pipe.
I did the Choke over and did 5 turns on the 4' pipe. Just trying to help fix TVI.
I already offered to buy them a new TV, but they declined. Maybe a Beam antenna pointed at their TV with 5,000 watts...lol (just kidding)

LoL

Sent from Outerspace, on the DarkSide of X.

 

[mackmobile43]

buy them a high pass filter

 

[Robb]

Just a FYI . . .

There is a fair reason why RG-8 coax is supposed to use a 8" pvc coil form instead of a 4" pvc coil form. When RG-8 coax is coiled too tightly; the center conductor in the center of the coax will deviate from its center position. It will no longer act as with 50 ohms of impedance when that happens. Maybe not today or tomorrow, but after time and exposure to the elements it will deviate. RG-58 coax won't have this problem on a 4" coil form. If the RG-8 coax has a gentle radius turn around a 8" coil form; then this problem won't happen.

Just thought I would give you a heads up and the reasons why.
Hope that makes it clear now . . .

 

[pkmak12]

Thanks for the info.I will try a few plumbing supply stores.

 

[HomerBB]

Get yourself a Clorox jug from any retailer. Use or toss out the bleach and use the jug as an 8" form.
Also, there are the 8" diameter waxed cardboard column forms. Another potential source is to take some of the composite flower bed edging and roll it into an 8" form.
Or is all else fails, just wrap the coils without a form and tape or zip tie them to themselves.

 

[GnG8d]

Overmodulation.

 

[pkmak12]

Just made a 8" using ties and electrical tape, 5 turns around. Thats it guys when the new antenna comes its going up like that. Thanks everyone for your knowledge and input.

 

[Cozy]

If you go with PVC, remember NOT to pick the black ones... they contain carbon wich is nearly cancel the choke you just made. Go with the white ones.

 

[binrat]

Get yourself a Clorox jug from any retailer. Use or toss out the bleach and use the jug as an 8" form.
Also, there are the 8" diameter waxed cardboard column forms. Another potential source is to take some of the composite flower bed edging and roll it into an 8" form.
Or is all else fails, just wrap the coils without a form and tape or zip tie them to themselves.

I've used a plastic coffee can, I forget which brand but it works as well.

 

[Captain Kilowatt]

Just a FYI . . .

There is a fair reason why RG-8 coax is supposed to use a 8" pvc coil form instead of a 4" pvc coil form. When RG-8 coax is coiled too tightly; the center conductor in the center of the coax will deviate from its center position. It will no longer act as with 50 ohms of impedance when that happens. Maybe not today or tomorrow, but after time and exposure to the elements it will deviate. RG-58 coax won't have this problem on a 4" coil form. If the RG-8 coax has a gentle radius turn around a 8" coil form; then this problem won't happen.

Just thought I would give you a heads up and the reasons why.
Hope that makes it clear now . . .

That really only hold true for the foam type cores. The RG-8 with the solid polyethylene core is not affected and the centre will not migrate.