Litz wire for AM ferrite Rod Antenna?

site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html

We look up at this beast from our back window. Something like 22 megawatts of AM, FM, TV, and HDTV...

and we're in a wooden building... no shielding at all. All the scope traces are fuzzy.

John

Ugh!. Thought I had it bad with an interfering 10uV of line scan noise from the PC monitor a few feet away. Even considered seeing if the LCD types were any better. Clearly I'm living on easy street.

How on earth do you cope when designing low level stuff stuff, a screened room any worth?.

We design it to be EMI hard, which you may as well do anyhow. Multilayer boards, solid ground planes, signal bypass caps and ferrite beads, and no low-level opamp type things directly exposed to the outside world. The RF is terrible here, but less intense than a CE suceptability test or a cell phone nearby. And an EMI hard design tends to have better ESD resistance and, actually, just be more reliable.

We do occasionally use an old analog, even tube-type scope, to see low-level stuff. The digital scopes fuzz up seriously and there's not much you can do about it. Interestingly, the 12 and 20 GHz sampling scopes are very clean, probably because they are all 50 ohm coax and SMA connectors.

We do have an old unused bathroom we may convert to a screen room so we can do crude radiated emissions tests. That would be an interesting project.

John

ferrite

site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html

Is that KOGO clear channel (600Khz) in San Diego? Up here in LA area, we have clear channel KFI on 640KHz. They both carry Coast to Coast with Art Bell, George Noory, etc. Some of the stuff is pretty good, but I stay away from the remote viewing, flying saucers, "out of body experiences" and shadow people stuff. Some of the callers ghost stories are very original. I like good story tellers, even if it's BS.

-Bill

Late at night, by candle light, "Bill Bowden" penned this immortal opus:

Nope, it's Radio Gaucha in southern Brazil. When they installed it about 15 years back you could hear it on the telephone! Great for soccer fans but a pain for everybody else. Then they had some crews running around placing filters and what-not all over town and it's pretty much under control now. It still gets in if you're not careful and crystal radios are a waste of time.

- YD.

ferrite

site.http://www.bentongue.com/xtalset/29MxQFL/29MxQFL.html

Doesn't it have a pattern something like this? ("side" view):

IOW, aren't you kind of "in the shadow"?

Cheers! Rich

Sounds pretty reasonable to me. With that Q, I suspect the limit is more the ferrite than the wire type.

How much of the rod's length is covered with the coil? Turns in the middle third produce higher Q than turns at the ends.

Is the wire wrapped right on the rod, or over some sort of insulating tube? Spacing the wire about a wire diameter or so from the rod can improve the Q at the upper end of the band.

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I measured the Qs of a couple ferrite rods, one with litz wire and the other with solid wire of about the same AWG. Both Qs measure around 80 unloaded. I don't see any difference using litz wire. I used a single loose turn of wire to couple a generator to the LC circuit at 533KHz. The 3dB rolloff points occur at around 529KHz and

The rod with the litz wire is loaded by the gate of a jfet, so I believe there is no load, the other rod had no external loads connected.

Not very impressive results, but the bandwidth seems reasonable, and the audio quality is good using a little 2.5 inch speaker.

-Bill

ed

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The rod with litz wire is a original unit from a 1972 Radio Shack AM/ FM modle. The rod is 4.75 inch long by 3/8 diameter with a winding length of about 1 inch (on a paper form) situated about 1/3 the way from one end to allow fine tuning adjustment by sliding the winding slightly up an down the rod.

The other rod with solid wire, I wound myself. It's a little shorter at 4 inches (same diameter) and the winding is similar 1 inch long situated in the middle of the rod on a similar paper form.

I'll run another test at the upper end of the band to see what happens there and report results.

I etched the circuit board with a solid ground plane on one side to avoid possible oscillation problems, but I found I need to space the antenna rod about 1/2 inch away or more to avoid losing signal. This makes the box size bigger than I planned, but I can live with it. Guess it's not a good idea to use a solid ground plane with little AM radios?

-Bill