Total posts : 45366
That’s pretty much what I was thinking, Greg.
With a crystal radio for AM BCB, if you make it open air you can use an old-fashioned round oatmeal box for a form (which is pretty close to the size for the open air coils in the sstran type antenna’s loading coil). But using a ferrite rod, it’s considerably smaller physically.
At first, I assumed that the ferrite rod option might be too high-q (not allowing enough bandwidth for reasonable voice/music) or too lossy for some reason for it to be effective for transmitting. But then hearing that the talking house transmitters use it, I got to thinking it obviously must be at least reasonably practical.
I note that “hot” 160 M antenna coils like the “Texas Bugcatcher” are open air, but as scwis mentioned in another thread, they’re also different from the sstran style coils in regards to dimensions, wire guage, spacing and etc.
I figure there must be reasons why the air-core is chosen for the sstran style antenna, and reasons why the talking house uses sliding ferrite, which is what I am mostly wondering about. I was thinking that if the TH (talking house) can use ferrite effectively and even goes so far as to incorporate an auto-tuner, then logically it might be possible to use a smaller ferrite core coil and use a small motor like the TH does to tune it, maybe not automatically, but remotely would be useful enough.
I haven’t taken the plunge to AM yet, so I’m still pondering over the assorted options. The TH sounds good to me at this point if I can find one at a good price off ebay, since it’s frequency agile, and it’s FCC type approved or certified (I don’t recall which offhand, but in either case it has a sticker on it where the manufacturer claims it’s legal which could demonstrate that so far as I knew it was legal provided I haven’t messed with it). A Hamilton would be way beyond my budget at this time, I’d rather avoid kits since they seem to fall in a nebulous area so far as I could tell reading part15, and I’m not sure as I want to start with homebrewing without running some sort of a rig first so I have some idea if my homebrew is putting out as well as a commercial part15 rig. The sstran is also tempting even though it’s a kit, but though I’ve built some kits I haven’t tackled one that compact and complex in a long time. My concern there is that I could spend more time debugging it and hunting for solder bridges and overcooked parts than I spend running it.
Also I have an attic, and having read an instruction book for the TH, it indicated that trying higher floors was a good idea. I figure the added elevation of 3rd floor above the aluminum siding would get the transmitter above many of the trees in the area while staying inside the manufacturer’s instructions and recommendations.
But if I do end up going with homebrew, then ground level mounting with a loaded vertical within the 3M rule would be the obvious choice and I’m thinking ahead to tuning. Even if I go the TH route, if there’s some obvious (to people who know more of such things) reason why the ferrite core should be avoided, it’d be good to know it before buying one.
Basically trying to figure out enough of the how and why to make a somewhat educated choice. This forum has been excellent for ideas and information. The amount of technical and innovative expertise here is very impressive. Kudos to all, by the way.