Antenna Choke

Can anyone tell what a choke is and do you use at the top or bottom of the a mast. I found the size. of a choke. 10 1/2 inch round by 5 1/2 times round. Thank you.

A choke helps prevent stay rf entering shack in simple terms , later I will post a article on chokes for you . Ferite chokes are better than airwound

Matt CTX Admin

I use a air choke on my Vector 4k and on my previous Solarcon a99 as i was getting RF in my workshop/shack.

7 turns of tightly wound rg8 around the scaffold pole just below the antenna connection,works a treat and stopped all rf..

I use a bug ferite clamp behind my rig and one at antenna feed point . Yes it's for hf but same principles apply . Even on my qrp portable antenna I use a choke .

73 , Matt. CTX Admin

A bit of reading: http://karinya.net/g3txq/chokes/

And the important chart for rolling your own. If making an air wound one 110mm PVC waste pipe you can get from MKM etc is perfect:

Matt86 wrote:

I use a bug ferite clamp behind my rig and one at antenna feed point . Yes it's for hf but same principles apply . Even on my qrp portable antenna I use a choke .

73 , Matt. CTX Admin

Not seen or  Heard of one, have you a Pic or Link to one?

Thanks

Clip on ferrites gravedigger. Only downside is that you need to use several of them to get the same choking capacity as looping the cable through one several times.

If you look at the spec for a ferrite you'll find it lists the impedance for a set number of turns at a given frequency. You'll find that just running the wire through it might give you 250 Ohms of choking but 3 loops through it gives you 1k Ohm. So without looping the wire through them you'd need to use four clip on ferrites all next to each other to give the same choking capacity as just one ferrite with the cable wrapped around it in three loops.

When you're buying ferrites you need to get the right mix as different mixes perform differently at different frequencies so you can get one that works well at VHF but does nothing at HF. Unfortunately a lot sold, definitely at radio rallies but even by CB or amateur radio shops, are not marked or not stated what mix they are so they could be doing nothing at all for 11m. What you need for CB is either Mix 31 or Mix 43.

Northern Crusader wrote:

A bit of reading: http://karinya.net/g3txq/chokes/

And the important chart for rolling your own. If making an air wound one 110mm PVC waste pipe you can get from MKM etc is perfect:

Awesome site, but I believe he posted some more recent updates to his testing before he sadly went silent key.

I use either 31 or 43 mixes with RG58 to cover the HF bands I need, but you can see for 11m, mix 61 gives the best choking.

Torroids can be got cheaply from mouser.com, BTW.