Thank you for your chart.
I know that a vna with two ports is better than an antenna analyzer to make s21 measurements.
I've got to buy a vna soon.
Alfredo Mendiola Loyola
I looked back at my notes from early to mid 90's. I couldn't find the acutal data but I will (hand written). I tested the W2DU bead balun (50 pcs slipped over the coax) and another commercial balun on a large toroidal core, coax cable wound (~10turns). Both had 77 (much higher perm than the -61 or 43 or -52). Both had a maximum choking Z of 1500 to 2000 ohms. There was a peak but it was broad and gradual indicative of low Q. I am using the W2DU ( I never discard anything)inside a transmatch which is now part of some tinkering in regard to currents on balanced transmission lines. In this transmatch, the common mode Z looking in is about 1500 ohms at 3.5 MHz which agrees with the sketchy notes at the low end.
In regard to instrumentation, even the HP 8753, that is pretty old now, that uses directional couplers is not that great at impedances in the extremes. For this reason, there are other Z measuring instruments that use bridges and 4 terminal methods to measure the extremes. See Agilent's Impedance Measuring Handbook that is available on-line for more info in this area. Very interesting material for the measurements being considered here. It will point out the strengths and weaknesses of the various techniques.
I will look for that handbook Pete,
Originally Posted by WB2UAQ
PS - found it on Agilent's site: http://cp.literature.agilent.com/lit.../5950-3000.pdf
Charlie , thanks for the handbook .
Steve, I see where K9YC recommends Mix 31 for 160-10M. What do your measurements compute for 7 turns of RG-142B on one and two FT240-31 type cores. The actual Fair-Rite number is 2631803802
Last edited by KM1H; 08-10-2012 at 01:33 AM.
Thanks. Thats not bad at all for under $7 each. YC uses 5,6, and 7 cores and varies the turns and the results get pretty peaky. Instead of stacking more cores what happens if a duplicate is placed X distance away; say a 1/4 wave on 10M?
I mentioned RG-142 since it readily available in surplus at low cost; I use it for lots of things around the station
If you place the duplicate 1/4 wave from the feedpoint, it will make hardly any improvement to the peak CM impedance seen at the feedpoint. Placing them both close to the feedpoint achieves the CM1+CM2 impedance you would expect.
Originally Posted by KM1H
I've seen two chokes of different design placed in tandem to achieve wider bandwidth. That works well provided the CM impedances are predominantly resistive; otherwise you have to be careful you don't have +jX on one choke and -jX on the other, at some frequency!
Good info and thats what I'll do with the ones for the 160/80/75 parallel inverted V's.
As far back as the mid 80's I was using 43 and 77 mixes on coax and the only way to test was with a calibrated FS meter looking for radiation further down the coax. It seemed to work especially well on the 160 verticals and the 40M yagi where I had been getting into neighbors electronics but not TVI with just a long string of the large 43 mix.
Can you send us the choke impedance derived from S21 measurements with 17 turns of RG58 on one FT-240-43 toroid (chart)?
Last edited by OA4AJP; 08-13-2012 at 01:07 AM.
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