- March 16, 2005 at 8:43 pm #6328dmfalkParticipant
Total posts : 1
OK, I need some help here from any of the electronicly-creative types, here…
I need an inexpensive, reasonably simple and Part-15-compliant experimental FM TX solution with both SCA channels, primarily for fleapower testing. Seems my hangup is that I’ve been unable to find a simple, but sufficiently-usable narrowband FM modulator that I could inject into an existing FM (stereo?) modulator circuit or chip.
I occasionally write reviews of radios I encounter, particularly the more unusual types, like AM stereo and SCA-capable radios, but as I live in an SCA-less town, yet own an SCA radio (which I’ve used on trips), I’d like to try fleascasting SCA- Especially if I do get my hands on other SCA radios for reviewing.
d.m.falkMarch 17, 2005 at 4:45 am #12121PhilBGuest
Total posts : 45366
This sounds like a job for an fm stereo/sca test generator…very expensive I’m sure, but watch ebay for a while and maybe a reasonably priced unit will come up.
Part 15 FM is terminally crippled by the FCC power limits. It is unlikely that anyone dabbling in this would also know of a way to inject SCA into their signal. Just my oppinion.
Phil BMarch 17, 2005 at 10:02 am #12122dmfalkGuest
Total posts : 45366
[quote:87a40eba8a=”PhilB”]Part 15 FM is terminally crippled by the FCC power limits. It is unlikely that anyone dabbling in this would also know of a way to inject SCA into their signal. Just my oppinion.[/quote:87a40eba8a]
A simple understanding how FM stereo is made should give a clue, I would think- Namely, that the pilot and stereo information are subcarriers which ride in audio frequencies above the mono baseband audio.
Those who know how to add RDS (which seems to be quite a few) would know how to add SCA, similarly. All SCA subcarriers are are narrowband FM carriers centered at +67kHz and +92kHz, with deviation of about +/-8kHz.
Some FM designs do allow access to the final FM modulator, after the pilot and stereo portions are matrixed, modulated and inserted.
Here’s what the baseband frequency spectrum looks like, courtesy of one such SCA radio manufacturer:
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