Tvi filters

Hi all, do tvi filters work both ways, I know they only let CB frequencys though but do the block inbound rf interference back to the rig as I get a lot of noise and just wanted to know before I buy

Thanks

Hiya Bert,

(Or is it Dave? You seem to have two names in your profile now but I've been calling you Bert before.)

A TVI filter isn't going to get rid of any common mode noise issues it being a low pass filter with the ground connection not isolated. I do believe that what you've described before as S9 of hash before along with your long length of coax is common mode noise problems more than anything.

I think someone suggested that you try to coil up some of your coax to provide choking and you mentioned 1:1 chokes before? Have you tried any of this sort of stuff out yet?

Here's a link to some great work done by the now unfortunately silent key Steve Hunt (G3TXQ) :-

http://www.karinya.net/g3txq/chokes/

If you take a look at the graph he did some extensive measurements with typical common mode chokes and the frequencies they're effective at. The air choke section shows that 5 turns of either RG58 or RG213 provides effective choking at CB frequencies and should help a lot.

You really need to wind the coax tightly next to each other though around a suitable former with 4.25 inches diameter being approx 100-110mm which is about the size of a soil waste pipe or maybe even a large plastic Coke bottle size. Otherwise the choking frequency could be well off and not do a proper job.

Maybe there's enough of a length in your coax to make such a winding near the rig end or even better at the antenna end without pulling everything all apart?

Worth trying out first rather than taking stabs in the dark with other options and maybe wasting time or money.

Do remember that we had rather a large solar storm recently (loads all summer long really this year!) so sometimes the CB frequencies have been 'dead' and sometimes nothing but loads of noise. I experienced about S7-S9 before it eventually dropped back to my usual low S1 or less with this recent storm.

Anyway, I hope that helps and that you get to the bottom of your noise woes as it can all get rather frustrating.


All the best,
Victor

Hi thanks for the info it's Bert but I hate it so I use my middle name on here and when I'm on
 I have tried an air coil but not any good, maybe I didn't make it correct I will try again

No worries there and I shall call you Dave from now on.  

I'm surprised the air choke didn't work if wound as the data suggests but hopefully the CMC choke being delivered will help out.

73

Yes please 🤪