Howdy,
Howdy,
I've explored a lot of threads about antennas for Part 15 MW AM, here and elsewhere. It looks like a loading coil which has heavier wire has less resistance. For the time being, I'm trying out a Spitfire TX and a Talking House TX. The coils I've seen made with 24 AWG enameled bell wire seem to be the most prevalent, but they also appear to have significant resistance.
My current deal to just get on the air in town is a CB whip I just removed from my boat. I will mount it atop a 20 ft. mast. I will just bottom-load it for now.
I don't have a problem winding a coil of, say, 16-18 inches of 2 inch PVC pipe using 22 AWG insulated wire if that will work better, but I'm not sure how many turns I'll need of a wire that size on that dia. pipe. IOW, because of its magnetic properties, I don't know what combination of pipe diameter, wire guage, and wire length to build.
Later I will probably build a copper pipe antenna, or possibly purchase an Isotron.
Mucho TIA,
Ken N.
Hi Ken,
The SSTRAN website (click on the panel to the left) has two descriptions of a do it yourself antenna and coil which might give you some idea of where to start.
Neil
Kyule Drake's book here has info on page 28: LPAM handbook
MRAM's site has info here: Antenna story
One of our members built this antenna and provided info here: Manteca Magnum
W5CDT's 1610 antenna and coil: W5CDT 1610 AM
The old PanAxis manual on antennas and coils: Medium Frequency Antennas
Enjoy
Hi Ken and Everybody:
The links above are all really good. Ken, I'm sure you
know this, but I'll just mention it anyway: when you
build something to spec, sometimes it will need to be
changed a little bit, such as the windings on a coil.
With some very good Part 15 antenna systems, just
putting your body next to the antenna might change the
operating characteristics.
Also, I have made coils just by winding a bunch of
unknown wire on an unknown coil form. Just for
experimentation, instead of making coil taps, you can
poke a metal pin into the side of the coil (whatever wire
you chose) and use that for a temporary tap. Just make
sure you actually hit the conductor inside the wire. Then
you can put an alligator clip test lead on and see if you are
getting in the right direction. Be careful with the pin!!!
I almost put one into my hand one day and another day
one went flying and almost went into my eye! So be
very very careful with the "pin tap!" Obviously your
coil design will have to be in the ballpark for this to work.
Best Wishes to everybody!
Bruce MICRO1690/1700 (Off right now to rebuild the
ground system.) And NANO NINETY POINT NINE
(Part 15.239 Or less Yardcast)
P.S. I don't know of any Part 15 experimenter who has
ever used the Isotron Part 15 AM antenna. If anybody
out there ever actually tries it, we all would sure like to
know about that.
Would be interesting to read a back-to-back comparison of the Spitfire and Talking House. Presumably it comes with it's own integral antenna like the Talking House. I suppose a no frills test one against the other exactly as they come would make interesting reading many of us would be interested in. I have thought about buying the Spitfire product, my friend previously had a Gizmo it was 'okay', I guess. I am impressed with the pictures of the circuit of the Spitfire, very clean and professional looking job.
I have an early Gizmo from the same company - good people, good products
And speaking of good products, CWSbytemark has a nice one page air coil info sheet here called Winding Air Coils
I especially enjoyed:
"(The basic) formula is most accurate when the coil length is greater than 0.67 times the radius and the frequency is less than 10 MHz."
And
"Methods of Increasing Q of Inductors
1. Decrease the series resistance of the windings by increasing the wire gage used. Larger wire has a lower resistance per unit length.
2. Spread the windings. Air gaps between the windings decrease the distributed capacitances.
3. Use a powdered iron or ferrite core to wind the coil on. This will increase the permeability of the space around the core."