Hello,
I have just joined this forum and I thought I'd say a few words of introduction. I live in the UK which means I cannot have as much fun as you US guys. FM transmitters are legal here, but the constraints mean that experimentation is practically impossible. I have to settle for feeding RF down coax.
Anyway, I have a fascination for the history of the really simple 'toy' transmitter circuits. Many engineers have tinkered with them at some time in their youth and quite probably many radio amateurs of today were attracted to radio by early fun with these circuits.
I just wish there was more information on the early days of these circuits.
Best,
HMI
Welcome to the forum. There are many here with diverse interests pertaining to radio and perhaps you will some posts on historical radio equipment and circuits.
Feel free to add some of your own.
Neil
Welcome aboard!
If you like to tinker, here is a link to a book I used to build my first home-brew AM transmitter back in '62.
https://dl.dropboxusercontent.com/u/59505579/Using-Electronics.pdf
There are serveral simple radio circuits and others.
The little one transistor AM transmitter, crude at best, was great fun.
By the way, using the FM band in the US is very restricted and most stay away due to the paranoia of regulatory enforcement.
Use of FM in Canada is also restricted, but not as much as in the U.S. - we're allowed 4 times the field strength.
That translates to 600-800 feet (roughly a suburban city block) with an ordinary consumer radio at the receiving end, and up to 1km or so with a very sensitive car radio (1.5 uv or so sensitivity) - a typical car radio probably 1/2 km.
In fact, in Canada, unlicensed broadcasting on FM is probably preferable to AM, given the noise and interference factors, particularly in urban environments, as well as the fact that AM is relatively useless at night with distant stations rolling in and obliterating micro powered signals.
Are AM transmitters also allowed a little more power here too? like fm is?, and do you know the allowable output?
Mark
The simple answer is NO, the rules are the same in Canada as in the U.S. for AM. And the limit is input power to the final RF stage.
Welcome aboard HMI
Recently when reading BETS-1 saw that AM here in Canada is not 100MW into final but field strength. It says 250 uV/M at 30 meters as opposed to FM at 100 uV/M at 30 meters. And interesting enough the rules also say the transmitter for both FM and AM MUST be able to be tuned to all frequencies in each band! So based on that, the transmitters that only have a few selectable frequencies are not complient.
Mark
There are really 2 sets of rules here in Canada. RSS210 is virtually identical to Part 15 in the U.S. for AM. However, RSS210 is intended for experimentation (whatever that is) and it is explicitly stated that BETS-1 is to be used for broadcasting (whatever that is - there are really no formal definitions supplied; I guess if the CRTC or Industry Canada say you are broadcasting, then you are broadcasting).
BETS rules for FM are virtually identical to those contained within RSS210, but you are right, BETS for AM specifies a field strength limit, and not the 100 mw input to the final stage of the transmitter in RSS210.
You will notice that transmitters such as the ProCaster are certified by Industry Canada under RSS210 and not BETS.
I've never heard of anyone getting into trouble for 'broadcasting' using an RSS210 certified transmitter, but technically, I suppose it could happen (particularly if someone complained).
That is one of the reasons why FM is the mode of choice here. A transmitter meeting BETS requirements (from what I've read, you don't need to get the transmitter certified, just be prepared with the specifications in case Industry Canada comes calling) will actually have greater range than an AM transmitter meeting BETS requirements (it's possible to get up to 1km and even a bit more on FM with a sensitive car receiver at the other end - line of sight, of course). And your signal sounds better as well.
The only AM transmitters that I am aware of that are RSS210 certified are ChezRadio's ProCaster and the earlier Talking Sign. Transmitters such as the Talking House, Rangemaster, etc. are not Industry Canada certified and again technically, cannot be used here. We are still allowed to build kits that are RSS210 compliant and use them, such as the AMT5000 - but only for 'experimentation'.
There are several transmitters that are certified here for RSS210 FM - the Decade MS-100 series and the Landmark FM-100 (I have one of these and it works almost as well as the Decade). I am not aware of any others. Both of these transmitters are capable of transmitting to any frequency in the FM band, so they can also be used for broadcasting under BETS.
Also the Wholehouse 3 and the Decade CM-10.
The Wholehouse 3 works great(am using) and has a power boost feature which let's it operate at BETS-1 field strength.
Mark