Tracking down the FCC ID numbers I have obtained the shematic diagrams for the C.Crane FM2 and Scosche FMT4R.
Unfortunately the diagram for Wholehouse 2.0 is not posted due to a "Confidentiality Request" filed by the manufacturer. I wanted to see what the secret switch actually does in the circuit.
The diagram for C.Crane FM2 is much different than the older FM1. One observation is that the diagram for FM1 is so complex it's difficult to study, and the diagram for FM2 is simplified shorthand making it difficult to reconstruct for lack of detail.
The Scosche diagram is not overwhelmingly complex.
I'll eventually get these linked at
Maybe within a week.
Since the Scoche FM 4R is not made anymore it would be cool to make one that runs on electric and battery. The little transmitter could be nice and cheap to build too. Maybe add 75 uS pre emphasis to it and you'd have a nice little transmitter.
The Scosche already has 75 uS Pre Emphasis.
It sounds beautiful.
It does NOT have audio level controls, but they could be added.
Use a nice virtual compressor for your Audio like NextKast has or Breakaway Broadcast. I wonder what the modulation percentage is before it limits it. Hopefully not too high and not too low like 15-25% either.
Today KDX-FM put into service a second C.Crane FM Transmitter, giving us two side-by-side channels, one for the main program stream and the other for editing and auditioning.
The Wholehouse 2.0 has been closed and will undergo deep surgery in an attempt to draw a map of the innards to figure out what that secret switch does.
Once it's put back together the Wholehouse 2.0 will serve as a backup.
Carl was that you that said that the Whole House FM Transmitter 2.0 was a spectoral nightmare with the spurs its generating? It seems to me I read that somewhere.
Carl, it's very simple what the switch does.....it's a high-low power switch switching between two resistors controlling the gain of the final. It's a switch instead of a continuous power out adjust with a potentiometer.
Mark
Too bad it don't have a variable from 0-Legal. As I've said before there are times you don't want to transmit to the neighborhood especially if your just transmitting to your stereo accross the room or your home theater system playing the audio of a movie or meeting or just trying to tune the Audio for when your ready to go Live. That is when things could be interesting if you could adjust from those levels. I suppose he maybe on the same page as I am in trying to construct a variable from 0-Legal.
Yes I'm aware of the difference between A/C signals and + & - with DC......just couldn't find the term to decribe what I was explaining so I just said +. I think Timinbovey knew what I was referring to.
Mark
Yes, TheLegacy, the Wholehouse 2.0 is a spectral mess and that's why I took it out of daily service. It makes a "better than nothing" backup, and eventually I'll sell it.
Mark, you have told me more than I knew before about what the secret switch does, but I still want to see it... maybe a pot could be put in there to do what TheLegacy is talking about.
The C.Crane Transmitters have internal pots to back-down from "legal."
Again just so there is no misunderstanding of what I am trying to say. Nothing illegal simply saying to make the power level from 0-the value of the low power Legal USA setting. Since your not increasing the RF output to the final only decreasing it at times when you don't want or need to transmit to the houses next to you. Just felt the need to clarify this attempt. Thanks
Best Regards.
I agree TheLegacy!
It has been said by persons in the know that some certified transmitters might be set low. If that is true, we have a legal right to "trim" the setting to get on the exact dot.
Or, we have the right to lower power to the level where it does what is needed, which is neat housekeeping.
Let there be no suspicion about it.
If I had a Patomac I'd find out what exactly 250 uV/M @ 3 meters will do. We sort of know what 1,000 uV/M @ 3 meters will do because supposedly Decade sets their transmitters by hand (We'll Not know this till someone has a Patomac and does this). This is an expensive way to find out. Unless one of us wants to start their own transmitter company lol. This too has been my point in all my rants. Its all speculation till we know what it will do. And it seems even if one tests with a Pagomac FIM 71 there will still be questions as the the value of your results. Rather yours is 100% equal to the FCC's measurements. There is so much we'd have to show in data and end the end the FCC can still hand out a NOUO if they feel you are over the limit. Seems FM is going to always be a gray area in any sense.
If it was me, I'd replace any single pole double throw switch with a varible potentiometer.
Yes I am sure we are talking about making the certiication void, but still, working on CB radios all through the years, the output stages always used varible potentiometers to adjust the pre stages and final stages. I believe this can also be done to make sure a unit complies, not to exceed the final output stage legal limit.
Also, some transmitters did not come with any potentiometers for audio input adjustment, I believe adding those should not void the certification either, but I am not the FCC.
Please excuse typos, Windows 10 does not support browser spell check software plugins for IE or Edge.
Bruce.
I operate two C.Crane FM Transmitters, Models FM1 & FM2.
FM 2 sits atop the computer tower so the computer case acts as a ground plane, but FM1 sets atop a wooden shelf right behiond the computer.
An idea popped into my brain... put a CD disc under FM1 to give it something of a ground plane.
Zingo! The field reading on the spectrum analyzer increased +3 dBu.