[Lowfer] Wed 137 kHz test

[Michael Sapp]

Hi All:  Can't pass up an opportunity to test the F/B ratio on my 13'x70'x13' EWE antenna with 11:1 transformers on both ends.

http://i1296.photobucket.com/albums/ag19/wa3tts/WEDTEST_zpsb8c7048c.jpg

Started with the HD-1420>FT-817 on the SW transformer and in-shack termination on NE transformer,

Then switched the HD-1420>FT-817 to the NE transformer and in-shack termination on the SW transformer

at 19:23 EST.  Note how the noise decreased in the NE direction as the background is more blue vs more

violet for the SW direction.  An extra station pops into view and Dex's signal is noticeably weaker, and other

NE stations noticeably stronger.  Nice to see the antenna do what EZ-NEC modeled......


One other note is I had top give-up isolated windings on the antenna transformers to get the termination in the shack to

work (coax primary and antenna secondary windings now common). So that required returning to separate common mode

chokes.  I had taken my 3 bino stack T77 chokes out of service, so I decided to do a equivalent series resistance test

with my Wavetek signal generator and Boonton RV voltmeter.  In a 50 ohm circuit the chokes measured 17 dB at

137 kHz, 20 dB at 185 kHz, and 31 dB at 500kHz.  That is just a figure of relative merit, not what would happen

with the unknown impedance of a coax cable's insulated outer conductor lying on the ground.  With an LCR meter the

chokes measure 2.5mH.

    I had a third choke I previously used in the shack and decided to try something. I had each binocular choke pair stacked transverse---i.e. viewed as six doughnut holes side by side.

I unwound that third 2.5mH choke and stacked the large T77 beads end-to-end (two doughnut hole view for 6 large cable beads) and rewound the choke (75 ohm mini coax).

New choke measured 3.15mH inductance with about 6 feet less cable.  Equivalent series test in 50 ohm circuit showed 20dB of choking attenuation

at 137 kHz, 23 dB of choking attenuation at 185 kHz, and 45 dB of choking attenuation at 500 kHz.  Again, not what one would get in the field on the coax,

but a figure of merit for comparison purposes.  So hopefully over the weekend I get time to re-wind the chokes at the antenna.

I see Amidon has some large Type 75 cable beads for $1.50 each---might have to give them a try at some point......2000u vs 5000u is a big difference in

ferrite permeability.....


73  Mike wa3tts