[Lowfer] MP XES & XKO on Sun afternoon & some bench tinkering

[Michael Sapp]

Hi All:  Here's a screen shot from last Sunday of MP, XES on DFCW, and XKO.

http://s1296.beta.photobucket.com/user/wa3tts/media/mpxesxko_zps289946fc.jpg.html?sort=3&o=0#/user/wa3tts/media/mpxesxko_zps289946fc.jpg.html?sort=3&o=0&_suid=134987981023007600816596432965


  I figured out that my Heath HD-1420 VLF converter I recently picked up on ebay has an input that is not Lo-Z---after taking a closer look at the schematic and installation notes suggesting a single wire feed to the SO-239 center pin.  So I tried a 10.5:1 isolated winding transformer that I have been using on a BC-453 and I seem to have enough voltage to drive the JFET, although the impedance match is likely not that that great.  That change and adding the VE7BPO 533 kHZ bandpass filter to get the 50KW BC stations attenuated seems to allow the JFET in the front end to operate in a linear manner.

    The unun is 2 turns input and 6.5 output on three in-line BN-73-0302 binocular ferrite cores, which is what the BC-453 gave the best performance with and what I had available (I built two for back to back testing purposes).  Insertion loss test with my Wavetek generator and Booton CA91 boat anchor RF voltmeter shows 1/2 dB per transformer at 137 kHz.  I may try a 16:1 transformer next.

    MP and XKO have been audible the last two days, MP stronger in daylight and XKO stronger at night. I'm surprised my two EWE antennas still have some front to back at 137 kHz. I will try to get some screen captures of MP and XKO showing the reception on the NE and SW antennas the next few days....

  Here are a few youtubes hearing MP and testing the transformers and 533kHz filter....

MP audible

http://www.youtube.com/watch?v=VEclbEcQhH8&feature=channel&list=UL


Unun test
http://www.youtube.com/watch?v=eelVaFgaVl0&feature=channel&list=UL


Filter test
http://www.youtube.com/watch?v=N4dHFdreAlc&feature=channel&list=UL


If anyone has a thought on re-biasing the MPF-105 in the Heath VLF converter to a lower impedance (600 ohm range) I would be most grateful.  Phasor math is not one of my skill sets....

73  Mike wa3tts