Dueling Selecta- A Tennas (NOT Banjos)

[NQC]

Hey All,

Last night I decided to try out something that I had seen that originally used two  stand alone large/outboard  home brew ferrite bar/ tank "antennas" for Co Channel "pest control" application .

The idea was to  fully null the pest with the receiver's ferrite first.Then place one outboard  bar to boost the desired station  coupling it  along SIDE of the  rig's internal  ferrite and the other outboard bar off the END of the rig's ferrite to deepen the pest's null.

Since I don't have any  big  ferrite, I decided to try two basic/no jack  model Select- A -Tennas instead. The results  were intriguing.

I tuned into "My favorite Co Channel " (starring Ray Walston and Bill Bixby ) 740 for  CFZM  vs very  local  WJIB which was still huge at 5 watts night power.

The expected orientation did not pan out at all, at least on the Super Radio I and these air core loops.. Trying to deepen JIB's attenuation by aligning one of the loops null to the rig ferrite null did nada, at least for me in this case. Changing the distance , etc, didn't work at all. All  action was  attained  by coupling both loops peaks "broadside" to the ferrite.

Odd, since  loop peaks are  much more "vague" than the "black hole "  of the  null  (after fifty years of playing around I am STILL amazed by radio !).

The best configuration seemed to be having one loop at one end of the ferrite and the other at the opposite end and on the opposite side of the radio cabinet. That way both loops "boosted" the SR-1 for Zoomer but had as much physical separation as possible.The only null action was in the  radio's  ferrite.

Even MORE wacky was that loop closer to JIB loop "liked"  a more  "conventional" 90 degree coupling angle, yet the other one ""needed" to be at 45 degrees in order for the entire set up to work. And of course like  previous single loop  experiments, all placements (rig, loop 1 and loop 2) HAD to be exact to within 1/8 to 1/4 ". If any parameter was off, even a tiny bit, you heard zilch (except a slight or moderate JIB artifact depending on what they were playing).

Zoomer rolled up and down (as usual), but never really came up to much  beyond weak or a bit better , even after a while of being parked on frequency. Zoomer's transmitter  antenna  null is in my direction (not   "optimal"), and also  propagation  seemed kind of  crumby as well.

I  repeatedly tried it "barefoot" , going over to  only the JIB closer loop  during these marginal conditions. No dice.Every time I tried.But when the second loop was brought back in, Zoomer came back in (WHEN the  QSB "cooperated").

So the takeaway ,at least to me under these conditions and set up , is that the second loop  WAS useful, even in this situation of two stations nearly 180 off from each other (which is a "challenge").

The next target is 650 with regional WSRO vs THE LEGEND (WSM). Both are  ALMOST in the SAME direction from me. If I can tame SRO even a tiny bit and  bring SM up a TAD , I'll call it a big victory. "We'll see".

BTW, I  really miss my MFJ 1026 .

Your mileage may vary on all of this  and no warranty is implied .

K

[syfr]

Interesting set of experiments!

I suspect that the two loops couple to each other, providing strange results.   SuperRadio I is a legendary AM DX machine :-) 

I really enjoyed reading about WJIB . FIVE WATT nighttime limit. That has to be a record minimum!

[NQC]

Hey Syrf,

Yes, it was fun to mess around with.

I am really liking the SR-1. I bought it recently as a package deal along with a Select-A Tenna for fifty clams , which was a very good deal. I had one many many years ago , can’t recall whether it broke or if I sold it.

I know some people who have been on air at JIB. A few “ interesting “ things have happened over there.The owner, Bob , is an absolute sweetheart. He ran several stations commercial free out of his own pocket ($$$$! !!!) for many years but now does a fund raiser to cover his cost.He has also saved a number of small AM stations from going off the air, one recently on Cape Cod. In total he has maybe 8 AM and some FM translators around our region, mostly in more Northern New England.

The master control for the network is at WJTO 730 in Bath , Maine. The 223 ft JTO / FM translator tower is located behind his home.

K

[syfr]

That is very cool.  I'm totally amazed that the FCC would allow a 5 watter on the air...I'd love to know more of the nitty gritty of his fight to keep his footprint among the big guns/syndicated stations in the Boston area. What a treat to have in the community. Thanks for bringing this up.

[NQC]

Hey Syfr,

The tower / building that now transmits JIB has been on the air under various call signs ( that went broke) for many years before Bob bought it.

I think having the personal resources to keep her on air is the main reason why it has lasted.

Now that he has a following it seems that his annual fund raising is enough to keep WJIB, net control WJTO ( Maine) and the smaller outlets on air.

FWIW, the original JIB call sign here in Boston was a “beautiful music “ big signal FM operation that eventually tanked and got sold off to a new owner and a new format.It had no connection to Bob at all.

K

[syfr]

This should be the subject of an article somewhere, thank you for the info.

I wonder if there are any other AMers who are operating QRP like this. I had a Collins AM BCB transmitter that was a 250 watter and I thought *it* was qrp (a pair of 4-250s modulated by another pair) . 5 watts is amazing.

[Area51]

I don't know if folks aware of the free IRCA reprints that are online now. There is a treasure trove of mediumwave articles in there. Some are relevant to the multiple loop discussion on this thread.

A few that come to mind are:

A-058 The 3-Parallel Loop Adcock System
A-061 Four Wall Loops for Better Nulls

The last one can be combined with the first one, and seems to be something worth experimenting if you want to try multiple nulls on a frequency. I expect that you could use a ferrite bar radio on a rotating turntable with these too. Testing that would be fun.

I haven't tried any of these but I will someday.

The address of the index to the articles is (they are all pdf files):

https://www.ircaonline.org/editor_upload/File/reprints/irca-reprint-index.pdf

And the International Radio Club of America main site address is:

https://www.ircaonline.org/default.php

There is a lot of reading in there that'll keep someone busy for a while.

[NQC]

Hey 51,

Awesome list of articles !

LOTS of reading to do over there.

Thanks, K