TheRadioBoard

[Dan McGillis]

After reading Gil Stacy’s article on ferrite antennas for the Ultra-Light radio, http://www.dxer.ca/content/view/57/77/ , I decided to try one myself. We take a little Grundig Mini 300PE pocket radio along when we go camping, and it would be nice to boost it’s reception capability without having to throw a lot of wire into the trees. And, since I’m a radio novice,building a simple outboard tuner would be a good learning experience.

The tuner/ signal-booster is an inductively coupled loop antenna - but to sound modern I call mine an “Electromagnetic Energy Harvester”.

It uses a surplus dual gang 270 pf capacitor (with phenolic insulators) from Leeds Radio and a ferrite-assisted coil. The coil is 60 turns of 165/46 litz, close-wound directly onto an Amidon 0.5”X4” ferrite 61 rod. A layer of carpet tape on the rod holds the wire in place. The coil’s inductance is about 260 uH - which doesn’t seem critical; 240 uH worked about the same. I assume that the litz and a fairly low loss ferrite rod result in a moderately high coil Q.

My “harvester” is wired as a “Tuggle Tuner” because I’ve been impressed by this configuration for crystal set antenna tuners, and, for crystal sets.

The little tuner is housed in a plastic box and the pocket radio lays on top so that their ferrite-assisted coils are magnetically coupled. The AM radio’s internal ferrite rod needs to be about 2-3” from the tuners’ ferrite rod - parallel and centered, or end-to-end. Maximum signal is broadside to the ferrite rod(s).

The only problem with the Tuggle tuner arrangement was that it wouldn’t tune below about 610 khz unless an antenna/ground was connected to it. Tuning to 1700 hz was no problem. Putting a 150 pf ceramic disk capacitor across the A - G terminals brought the low end tuning down to about 530 khz WITHOUT having to connect an antenna. I’m guessing that the capacitor acts like the capacitance of a long (high capacitance) antenna.

The results are amazing. (Us novices are easily amazed.)

a.) WITHOUT an antenna, the tuner is selective and directive, tunes to about 530 khz and gives a BIG volume boost. It can bring-up stations that are otherwise inaudible!

b.) WITH an 11 foot piece of wire for an antenna (but no ground), the volume increases beyond (a). The tuner still tunes to about 530 khz, but it’s tuning seems less sharp and there is little-to-no directivity. This is a good configuration when searching for stations. On some frequencies I got more volume if the antenna wire was hooked to terminal G rather than A.

c.) With the 11’ antenna wire on terminal A, AND a 6 inch long “ground rod” hooked to terminal G, the signal volume increases even more and the tuning seems to broaden a bit more also.

This is probably elementary “old hat” stuff to a lot of the folks here. But I enjoyed building and experimenting with this little add-on. The tuner is easy to tote, fun to use, and really boosts the output from our pocket AM radio - without using an antenna wire. And it makes a decent little antenna tuner for a crystal set to.

73, Dan

[Ham-er]

Nice work Dan,

Now do the same except use a bigger ferrite rod.

Uhm That thing is great for AM BCB but what about the SW bands?

73's

[Dan McGillis]

Thanks for the comments Ham-er.

I thought about using a 7.5” rod - I have a couple. But about a year ago, Jim Shaffer (the ‘Electronic Technician’ over on Rap’nTap) evaluated some of my ferrite rods for me. He found that my 4” rods had much lower loss than the 7.5” rods. Better annealing I guess. So, based on that, I decided to use a 4” rod (which keeps the capacitor and rod a little farther apart too). I was afraid that the additional ferrite losses of the 7.5” rod would more than offset the gain from its higher relative permeability. If I read the rod permeability charts right, for type 61 material, my 7.5” rod has a urod about twice that of the 4” rod. So it should have about twice the loop output - all else being equal. But I was afraid it might have more than twice the loss of a 4” rod. Anyway, that’s my story FWIW.

The little tuner doesn’t do diddley for short wave reception. This Grundig only tunes the SW bands from about 6 - 18 Mhz. It’s 20” whip brings in lots of SW. I did wrap a coil around the whip base - and that seems to boost the SW volume quite a bit when I attach a short antenna wire to it.

Fun stuff.

73, Dan

[tkilboy]

Hey Dan,

Thanks for posting that. I think I may whip one up for my Kaito 1103. I've always been disappointed with the Kaito's performance with the wire antenna which they furnish, seems to work best with whip only. Maybe this will give it the boost it needs.

Tim

[peeblesoriginals]

Dan,

I've made similar set-ups like this in the past and they do work well.

In my neighborhood and addition would have to be made. Another circuit, using as a trap. My 860kHz and 1550kHz situation would be highly enhanced, with this "supercharger", and would need to be calmed down to hear stuff around them.

I built a similar setup for a guy that lives a long way up the Columbia Gorge. AM stations are rather sparse there, but he was able to hear the local Portland, OR stations very well. Seems he wanted to hear some particular talk show

Nice job! Glad this works well for you. . .

Mike
_________________
Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com

[Dan McGillis]

Thanks for the comments fellas.

Tim, let us know how you make out.

Mike, I wonder what that particular talk show was
We do some camping up along the shores of Lake Superior, and I'm curious to see what this loop does in the boonies.

73, Dan

[tkilboy]

Hey all,

I'll email George Noory & Art Bell and ask them what that show might be. I'm a closet listener myself, great when sleep doesn't come.

BTW, If there are any Phil Hendrie fans out there, remember his Art Bell spoofs?

Oops, I guess I'm out of the closet now.

Tim

[peeblesoriginals]

Members,

"Mike, I wonder what that particular talk show was "

Beats the heck out of me. . .I don't know one from another,
when it comes to those guys.

I compare talk shows to congress. . ."Much ado about nothing"

Only time I ever hear bits and pieces there, are when I'm seeing
how a new set will perform. Seems like most of the callers sound
to be about 1/2 to 3/4 in the bag. . .I'm sorry, the only AM radio
I ever listen to is one of my torches at 1550, which plays "Nostalgia"
music. . ."The best music of our time".

Fact is, I'm thinking of building a crystal set that tunes that station,
only and in everyway enhanced to get the best and most audio
out of it. . .

Hope that slot always plays that same format. . .If it ever goes back to
talk, then

1550 has an interesting history. . .It was originally 1550-KVAN,
which was originally 910-KVAN, which was relicensed to 910-KISN,
later. KISN was our original rock station, and all the younger set
including myself, listened to it, as FM wasn't away from
classical formatting, yet.

When KVAN-910 was still active in the middle '50s, it was mostly CW,
and a local Vancouver, WA station. . .Willie Nelson was a DJ there and
this is where he REALLY got his start. . .Playing Gigs in Vancouver,
and across the river in Portland, OR.

Your history lesson for the day. . .

Mike
_________________
Radio experimenting is serious fun, so have fun and don't get too serious!
http://www.peeblesoriginals.com

[Dan McGillis]

The frequency response of my Tuggle tuned coupler was interesting. By itself, without an antenna, it would not tune down to 530 khz. I needed to add a 150 pf capacitor across the A-G terminals - either in the form of a capacitor, or, an antenna.

There’s a nice analysis of the Tuggle tuner by Ramon Vargas Patron (3/14/04) at:

http://www.schmarder.com/radios/tech/Analysis-of-theTuggle-front-end.htm

Ramon shows that the equivalent capacitance (Ceq) of the Tuggle tuner that resonates with the coil inductance (L) is given by:

Ceq = C*[ (2*Ca+C)/(Ca+C) ],

where C is the capacitance of each of the 2 equal capacitors in the tuner, and Ca is the antenna’s capacitance. I know there are calculators on the web that use this equation.

I used Ramon’s analysis to plot-out the coil inductance (L) required to resonate the Tuggle dual gang capacitor down to 530 khz. The inductance needed depends on the antennas’ capacitance (Ca) which is small for short antennas, and large, maybe 200-400 pf, for long antennas. The plot is shown below. It’s “busy” but useful.



The capacitance (C) of the Tuggle capacitors is on the horizontal x-axis. I’ve seen dual gang capacitors with C = 110, 270, 365, 450 pf, etc. The coil inductance (L) needed to resonate the Tuggle tuner at 530 khz is on the vertical y-axis. There are a series of curves, each corresponding to a different antenna capacitance (Ca).

For example, if the Tuggle tuner uses a dual gang 270 pf capacitor like mine (270 on the x-axis) - AND - the antenna’s capacitance is 150 pf, the inductance required to tune down to 530 khz is about 240 µH. My coil is about 240 µH.

[ ie -- go to 270 on the x-axis, go up to the yellow curve for Ca = 150 pf, then go over to the y-axis to find (L). ]

Without an antenna (Ca = 0), I would need L ~ 330 µH to resonate at 530 khz.

If the Tuggle tuner had a dual gang 450 pf capacitor instead of my 270pf, (and Ca was still = 150 pf), from the plot, I would only have needed L ~ 160 µH to get down to 530 khz.

The other stuff on the plot just shows what happens to the upper tuning limit as the minimum capacitance (the capacitor’s + stray capacitance) varies.

Ramon's analysis and the derived plot seems to nicely explain what I observed with my Tuggle tuned coupler. And, it takes some of the mystery out of choosing an inductance for a Tuggle tuner.

Maybe it’s old news, but it’s still fun stuff.

73, Dan