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mikefox whiskey Profile
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Accomplished DX-er

Registered: 02-2009
Location: Northern Ireland
Posts: 403
Karma: 1 (+1/-0)
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Voltage on antenna/feedline - 'Z' match tuner photos.


I have found recently that my antenna has been attracting a lot of static electricity, especially when there is heavy rain in this QTH, I noticed this when the connection points on my Z match tuner started to spark! anyway after I received a couple of static discharges up my arm I decided to take some readings with a test meter on the ends of the 600 ohm feedline, while the static is there the voltage on the end of the line is between 11 and 18 volts DC!, my equipment is floated from earth, in other words there is no earth connection as the antenna is balanced and does not require one, I have some radials tucked under the skirting board around the apartment where I live though which unfortunately is not on a ground floor.

Anyway I am just wondering if anybody else has had a similar issue or problem and what they have done to solve it.

Here are a few photos of the balanced tuner I use, I'm not sure, but I think these tuners where built around 1972, as you can see though it's in pretty good condition.

Image

Image

Image


Last edited by mikefox whiskey, 10/May/2009, 2:30 pm


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(Forum user name is now SuperNasty)
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Hot Fusion Profile
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Management

Registered: 03-2008
Location: South West England
Posts: 1389
Karma: 7 (+7/-0)
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Re: Voltage on antenna/feedline - 'Z' match tuner photos.


That's a nice dummy load resistor up through the middle there!

OK, as discussed, below is a photo of the coil I was speaking about:

Image

If you wind a couple of these and connect one between each terminal post and the earth of the chassis, and earth the chassis to an electrical earth such as a radiator, that will sort it as any static will be drained straight to earth, but will block any RF and so won't affect the radio signal at all.

I don't know the exact configuration of your antenna - does the feedline feed a balun? If so, there will be continuity between the balanced wires meaning that only one RF choke needs to be made - check this with a continuity checker.

You will notice that the coil is wound in unequal sections - this is usual proceedure for a choke which is to be used on multiple frequencues, and the effect of this is to minimise parasitic resonances within the coil which could cause problems otherwise.

The number of turns is not at all critical as long as there are enough to act as a choke at the lowest frequency you will be using it at - probably 3.4MHz?

Because the impedance of the balanced output for your open wire can be pretty high, you will probably have to wind the coils with rather more turns than shown here - this coil worked perfectly and made no difference to the tuning at 6.6, 50 ohms, but that may not be the case at lower frequencies and higher impedances - the photo is mainly to illustrate the winding technique.

Loads of turns of very fine wire is what will be required, so when you have the equipment together, set aside some time (your finger will ache!) and 'back up' your winding every so often with some insulating tape; There is little in life more frustrating than to have wound on 150 neat turns of hair-thin wire than to accidentally let go and watch the lot spring open.

Have fun! emoticon

EDIT:
Just for scale, the coil pictured here is about 25mm diameter and the former is about 9cm long. The terminal supports were made by cutting off bits of 2mm copper wire and heating them with a soldering iron. They could then be pushed through the plastic under their own heat.

Last edited by Hot Fusion, 10/May/2009, 5:59 pm


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Andy - 26 FB107
10/May/2009, 5:55 pm Link to this post Send Email to Hot Fusion   Send PM to Hot Fusion
 


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