Well I rebuilt my old W3DZZ antenna and its creating a lot of RF noise in the shack unfortunately... Not sure why?

I have a 1:1Balun right at the feedpoint and a common mode choke about 3m away in the roof. Then the coax runs into the shack, approx 4m away.

What I have noticed is the coax is crap... RG58 but the kind with no makers branding and the shield is weak! Probably only 60-70% shielding, if that.

The diamensions are 6.5m->10.5m-<-10.5m<-6.5m. The wire is 1.2mm silver plated stranded copper wire. Outter is PVC total wire diameter 2.5mm.

Do you think it the coax thats causing me all the trouble?

Regards


Neil

I would say that the coax is not RG58 if it is only 2.5mm in diameter and probably the cause of all your problems.

Edit: just re read the post.

Very confusing, which measurements are what?
6.5m coax then 10.5m wire ?

I think that's the measurement of the antenna wire.

What are you experiencing in the shack "RF noise" wise, is it that your rigs meter is registering a higher noise floor and the signal to noise level has deteriorated?

That's the antenna wire. Sorry I didn't make that clearer. The coax is 5mm but the shield is very poor.

https://www.truckerswereld.nl/rg58-coax ... gJOW_D_BwE

This is the right image of the cable / shield.

This RG58CU look far better already.

https://www.hamshop.nl/coax-connectoren ... 58-cu.html

In my defence I thought I was buying RG58 coax cable and didn't realise the vast variety and different quality of this cable!!!

Regards


Neil

Ah!!! Trap dipole!

The choke could be in the wrong place or just crap for the frequency involved.
The coax could be crap.
The balun could be crap.

Try a dummy load on the end of the coax and see what happens.

If problem goes away, suspect choke or balun.

I actually see speckles dots (pink) appearing on my LED computer monitor. Especially in the darker area's it becomes vary noticable. Then the computer control will drop completely once the power gets too high and the noise peeks.

Without a common mode choke I couldn't get past 20~30 Watts. With the bifilar wound common mode choke in my roof I can get to 60~80 Watts before the noise (speckles) start coming back on the computer monitor. Full discolosure, I spliced the common mode choke inplace with barrel connectors since there is no way for me to get hold of PL259 connectors right now due to COVID.

So the antenna is usable on FT8 but not SSB.

Thanks, thats a good point. It will have to wait now until the weather turns better, once this cold front clears out. If its the choke, that's on me since I wound it today on a 240 T63 core. The Balun was bought "Hamking" BU200, 2000W (PEP). I wanted to benefit from an encapsulated product. Has to be better than what I can cobble up, right?

Shouldn't the w3dzz also have a length of 75ohm coax for matching?

I wouldn't say that bought is always better.
But building the correct choke for the frequency in use does matter.

What is the construction of the choke? Eg: two wires wound or coax wound? How many turns?
It also should be as near to the antenna as possible.
A choke at the rig end is also a good idea.

Other diagnosis ideas include powering the radio from a battery so it does not have a physical connection to the mains supply that the monitor is connected to. This will tell you if the rf is being passed through the radio to the mains supply.

Also if the monitor is the only thing affected then fit a choke to the monitors supply and video lead.

Check that the antenna wire does not run close to mains with g.

I am currently making a GM3SEK mains filter which I hope will sort a few rf problems in my shack. Not cheap , but apparently extremely effective. And cuts down received noise as well.

Also...,T63!
T43 probably a better choice so I'm told.

I should have taken a picture of the choke. I believe its Schaffner wound.

1, two wires x 14 turns on the left side
2, two wire x 14 turns on the right side
3, then crossed wired at the ends so the centre and shield run on both sides of the toriod.
4, 1mm magnet wire.
5, 4x barral connectors to splice it into the coax. I know its not good practice but the best I could do at the moment.

I did a quick VNA sweep for of the choke for 20, 40 & 80m which are the bands of interest for this antenna. And yes some designs use the 75 ohm coax but again I don't have any and everything here in Holland is closed due to COVID. The choke did work, just not well enough!

The noise is visible on the monitor but its on the USB cables too. Not sure about the mains, that's another good point to check when the family is out of the way.

Unfortunately, one leg of the W3DZZ does run very close to the roof for about 7~8m before projecting out over the front drive in clear space. The other side running to the back garden doesn't have that issue.

t63 is that not a powdered iron toroid? if so its probably useless as a choke you need ferrite.

Then its a 43 because its a powered iron toriod. My mistake, for some reason I had 63 in my head...

Oh dear.....


Neil.... if it is a powdered iron as you say, then a) it isn't a t43 and b) it is useless.

I'd post a picture for verification but I can't so I won't. Its definitely not USELESS, but it might not be optimal?

How do you post a picture here from flickr anyway???

They do look like these toriods but its a long time ago when I bought them. https://gm3sek.files.wordpress.com/2019/01/G3TXQ-RC.pdf