Much less expensive to build then to buy. Save $200.
I always wanted to try a Part 15 transmitter
with an Isotron. About 30 years ago a guy I
know put TOO MUCH transmitter power through
an Isotron and it caught fire and melted.
That was a dumb thing to do. I know they work
great it you stay within the rated power figure,
whatever that is. And it was a long time ago.
I read that link. The guy tested the Isotron on
the AM BCB, and it worked - but I wish he had
been using Part 15 power levels. That would
have been helpful.
And it seems as if the Isotron can be a good
receiving antenna too. It seems to cut down
on noise in some situations. Considering its
design, I wonder if it acts like a balanced "magnetic"
Very Best Wishes,
Brooce, Still Experimenting,
West Hartford, CT
NOISE AND STATIC RADIO
Can someone tell me how antenna bandwidth affects audio response? I see vague references to how the Q of the coil affects sound, but no explanation of it. I have a Harris C-Quam exciter and was looking at the Isotron to use with it at part 15 power settings, but have seen comments about it being a narrowband antenna. Does this mean it can't be "eq'ed out" for response up to 10 khz? Thanks.
A carrier which is amplitude modulated carries the audio information in the sidebands, one above and one below the carrier frequency. The total bandwidth of the signal is twice the highest audio frequency in the modulating signal. For proper operation the antenna must radiate the signal including the sidebands.
A coil loaded antenna acts as a band pass filter which radiates energy within the band pass frequency range. A hi Q antenna has a narrower bandwidth than a low Q antenna. If the Q is high enough to reduce the signal at the edges of the sidebands then the effect is that the higher audio frequency information is lost and the audio will lack high frequencies at the receiver.
I don't know about the Isotron so can't predict if this effect is present but now you have some theory.
i see that guy's 522khz version of the antenna only has a wire going up the length of the pipe. i would wrap that part in aluminum sheet flashing to get better bandwidth
That's a good explanation of how antenna bandwidth affects the sound quality, Radio8z. Who could imagine a coil designed for RF frequencies could have a narrow enough bandwidth that it can effect the audio response itself.
That's probably one of the compromises made in those transmitters with loading coils wrapped on a toroid core. They peak up the signal well enough, but the Q isn't quite as high, so it doesn't affect the audio, and the tuning wouldn't be as critical.