[TenTec] OT: coax versus parallel wire, insulated wire for aerial

[Dr. Gerald N. Johnson]

On Sat, 2008-06-07 at 08:30 +0800, Marinus Loewensteijn wrote:
> Have not followed the Bazooka discussion in its entirety since I feel it goes a bit far OT. However one of the last postings raised a question in my mind due to the reference to the Late Cbik with whom I had some interesting and pleasurable email exchanges.
>  
> One item he mentioned that by using insulated wire alone one can get a 
> large reduction - up to 6dB - reduction in static. Perhaps this is one 
> aspect that plays a role.

That's true when the static is precipitation static, e.g. charged snow
or rain collecting on the bare wire. Or not contacting the wire because
of the insulation. There won't be any effect on static from lightning,
whether near or far.
>  
> I am using PA0FRI's S-match and like it very much. It gives me extra input filtering and galvanic separation of the antenna and in my location / environment it has really cut down in static and interference. Recently I have decided to replace all my PL259 - SO239 connectors with N connections. In this process I was also looking at coax and in this process I came across the (far) more expensive professional types of coax like LMR 400, LMR 195, RG 142, RG 223 etc.
>  
> Some of the marketing blurb was that these types of coax have less
>  problems with locally generated interference. Somewhere else one 
> ham stated that he preferred to have a remote ATU and have the 
> antenna at least 20 meters away from the home because of all the 
> interference he got from all the modern day electronic equipment 
> in the home with its switched mode power supplies.

Those premium coaxes have far better shields than the cheap stuff sold
for TV and through Radio Shack that barely have braids at all, and then
sometimes made of aluminum. So its harder for local interference to be
picked up and then if the house has those bad noise makers, is when the
current balun at the antenna has a good chance of helping keep that
noise picked up on the outside of the braid from getting to the radio.
Noise the reaches the antenna will still be heard.
>  
> What I like to find out is have any of you experimented with the 
> same antenna and feed it with parallel wire and having the ATU 
> in the shack versus having a remote ATU and feeding the ATU with
> high quality (double shielded) coax and how the perception was 
> of which solution has the lesser amount of interference?

I know from building duplexors for a 2m repeater that single shielded
coax has maybe 40 dB attenuation through the shield and that doubled
shielded has better than 90 dB attenuation. This shows when using single
shielded cables to connect the duplexor to the test equipment. Its
possible to tune for the 95 dB transmission null, but with single
shielded cable, that null is gone if any cable is moved. With double
shielded coax the null is not affected by coax position in the test
setup.

A balanced line,  if perfectly balanced and closely spaced should have
little pickup,  but the well shielded coax line with the current balun
at the antenna should pick up less on the feed line.
>  
> Many thanks in advance, Marinus, ZL2ML.

73, Jerry, K0CQ