Except that whip antennas are 1/4 wave long or thereabouts, so it resonates about 58 MHz.
There is such at thing as a plate modulator, where a big audio amp modulates the plate voltage of the transmitter's final stage. Way back in the day, that was attractive because the TX final could operate Class C, without causing unacceptable audio distortion.
(Amateur transmitters were regulated by the DC power input to the final stage, so you could get a lot more RF that way while still staying legal.) AM is inefficient, however, because only half the TX power is in the audio sidebands. SSB is a much better use of both power and (especially) spectrum.
A plate modulator often used the same type of tube as the TX final, because it takes a _lot_ of audio power to do that.
The output tube of the circuit you posted runs at way less than a milliamp, so you aren't going to do much modulating with it. Also a plate modulator doesn't connect right to the antenna, because there's a tank circuit and output filter in the way, so the antenna isn't sitting at the plate potential of the TX final stage, and jiggling it up and down won't do anything.
(Takes me back, sure and it does...I learned a lot of electronics from my trusty 1966 ARRL Handbook. Just about killed myself building a TX power supply when I was about 14.)
I was never interested in being a ham - all they seemed to do was talk to other hams about being hams - but I did read the Radio Amateurs Handbook when I was a kid, and learned a lot. I have the 1946 edition here. No, I didn't buy it new.
I did manage to almost kill myself in other ways. I got across a tube TV power transformer once, the ends of the B+ secondary, and that left me shaking for days. Kids nowadays are afraid of touching a board powered by +5 volts.
And we did find a shopping bag full of shotgun shells in an empty house one summer...
--
John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers
An end-fed half-wave whip would be 115MHz and fairly high impedance (high voltage drive), although I agree that the 270k anode resistor is still way too high.
It's still possible it could be an RF transmitter, but not from what is shown here. Example: using parasitic grid or cathode wiring lengths as tuned resonators. Then you could have a tuned-plate, tuned-grid oscillator at the ~58MHz others have mentioned. Piss-all power output, would be lucky if it's even DX-able (also, AM or CW if that).
It would do just fine as a high gain audio preamp, if the output were connected to another jack. Why it says antenna, who knows. Maybe he wanted a source of electric field for other reasons. Maybe he didn't have a clue whatsoever!
That may well be true, but if so, this circuit isn't one of his best, or wa s meant humourously. Do you have others you could post?
It's to improve the spectral purity of the transmitter, match its output to the antenna for maximum efficiency, and isolate the antenna from the very dangerous plate supply of the transmitter final stage.
Well, most any given transmitter at any given moment will be operating in s ome narrow band, e.g. 980 +- 3 kHz for an AM talk radio station. You design the tank and filter/matching network for the desired frequency range.
There are exceptions, e.g. ultrawideband radar, but they're rare.
This is just a basic broadband amplifier. Can be used for any frequency. Th e antenna length specified is ad hoc I would say. The amp itself would work for any frequency the tubes and the coupling caps can do.
Uses ? Hard to say but it reminds me of something. Old days of TV shops, se lling TVs, new or used. One shop took an amp, stuck an antenna on the roof up high and ran the signal through an amp into an antenna in the showroom. All you neeed was a little piece of wire on one of the antenna terminals an d you got a perfect picture on all channels. the signal transmitted from th e antenna swamped anythong coming in off the air along with any multipath. Worked pretty good.
the only clue in that circuit is the antenna legth, and it doe snot say muc h. At one frequency it is a 5/8 wave, at another 1/4 wave and so forth. The re are no other frequency determining components in it. Eother he was a kid not knoing, or it was meant to be broardband. The 51" antenna can transmit at any frequency, but efficiently at only certain ones.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.