I recently purchased a Decade CM-10 (now discontinued) from a Canadian reseller on e-bay - it was supposedly a demo model.
I had issues right from the get go on the audio and range. Audio was very low, warbly and range was bad (barely a few feet). After some trouble shooting, it turns out that the ground isolator, which works on every other transmitter I have, was causing problems. Once removed from the audio chain, things started working properly.
Even though theoretically this transmitter should be tuned to Canadian BETS limits, range is still poor compared to other transmitters I own, such as the MS-100. I suspect that this is a Part 15 tuned unit, as its range is on par with the Maxell P-13 I recently purchased and did a quick review on (to be fair, range is a bit better, but the Maxell is intended as an ipod type transmitter, not a serious broadcasting device).
You generally get what you pay for, and this transmitter's cheap Chinese origins are apparent in the audio quality. Although admittedly subjective, it's not nearly as 'full' and nice sounding as the Decade MS-100 or my Landmark FM-350 (about on a par with the Maxell). Bass is lacking, and it sounds somewhat tinny at high frequencies.
I can't drive the modulation nearly as high as I can on the MS-100 or Landmark either - here, it's also comparable to the Maxell.
I've contacted Decade to see if there's a way to determine the country of tuning. I've also asked if there's a way to transmit in mono only. I'll post the results when I receive them.
Interestingly enough, even with its relatively short antenna (not tuned, at least in terms of length), I find that the transmitter's range is substantially more at lower frequencies - I obtained the maximum (several hundred feet before fence boarding on my car radio began) at 88.3, and it went steadily down as the frequency went up (just over 100 feet before fenceboarding at the high end of the band on 103.9).
Other than frequency agility and the potential ability to tune to Canadian standards, there really was little to recommend this device over the Maxell P-13. And the Maxell cost me US$1 (plus shipping).
Unless you can find one of these really cheap on the used market, I wouldn't recommend shelling out the money. There are much better alternatives available at the same or greater cost (US$100+), and much cheaper ones that give you equivalent quality.
And I wouldn't touch the untweaked Chinese transmitters readily available, based on this experience.
I think that's why Decade discontinued this model as it was inferior to the others they make.
Some others with stereo transmitters I've read on these forums changed it to mono by removing the crystal but with the CM-10 which other than a transistor removed and a resistor change here and there it's a CZH-05B and the rest is the same. The stereo generator chip is enclosed in metal housing under the board for the display and jumper links soldered from the other circuit board make it almost impossible to take apart to get to the crystal near the main IC stereo generator.
I had one and yes it worked OK but as you found when compared to the MS-100 the audio was inferior. And understandably so.
I'll bet the audio is set to 50 uS not 75 uS on the premphasis.
I had the CZH-05B what a piece of junk. If that thing had more power you'd be splattering the FM band in several places.
If the Decade uses the same power supply as the 05B expect all sorts of noise and crap in the audio too.
Legal part 15 FM is not worth it unless your yardcasting or high rise multi family casting to residence in the same building. AM is king for legal Hobby Broadcasting in the USA.
The CM-10 was powered down to Part15 limits with a resistor network at the output statge. So essentally it was a dummy load with an antenna attached.
Remember talking to Decade about this and asked what changed between the ones sent to Canada locations and US locations and for US locations those 2 resistors were added at the antenna and for canada it was a transistor removed and bypassed in the output. The other changes were to the tuning to make it go from 88.1 to 107.5 for BETS-1 compliance and the antenna which had to be permantly attached.
But the rest is still a CZH 05B branded Decade.
They had the Chinese company modify it for the legal US and Canada operation I guess to offer a less expensive model.
With the audio I found that there was a high pitched wine heard when just the carrier enough to be annoying when close to it.
Not HI-FI by any means.
I would think that the preemphasis is for North America, since Decade did make changes to the transmitter for this market.
All those things about audio quality said, it still sounds OK. Comparable with much cheaper ipod-type transmitters, which sound OK. Just not up to the standards set by the better FM transmitters made by Decade themselves, Broadcastvision, etc.
I guess I might have to take the cover off the unit to check for what market the transmitter is intended. I was hoping that there might be some sort of indication on the label, such as serial number ranges.
It sounds like it might not be a simple fix if this is indeed a U.S. transmitter to move it to Canadian limits.
Just realized that Canadian units tune differently, as Mark stated. Unfortunately, it turns out that this is indeed a Canadian-tuned unit. I don't understand why the range is so poor compared to other RSS210 and BETS devices I have - it is comparable (just a bit better) to my Maxell P-13 Part 15 certified transmitter.
I wonder if Decade hand tunes these things, or just makes the mods that Mark talks about and then lets them out the door, knowing that they'll be below (but not just at) Canadian limits. Unlike the MS-100 (but then, that's a lot more money).
Having looked inside these things I am not sure there is anything to tweak. Changing the resistor values at the feed point would void the certification at least from a FCC perspective.
It would void Canadian certification as well.
You won't find anything by looking at the citcuit boards to know what country it was for. You will see one of the output transistors removed and a jumper. The ones for the USA may have... as another member, quite a while back, posted a picture of two resistors at the antenna which mine didn't have. The tuning had to be modified to stop at 107.5 for the BETS-1 compliance but maybe someone in the USA who has one will know if that was done on all of them.
If you just have the carrier with no audio you will hear and annoying high frequency whine when close to the radio no matter what 12 volt supply you use. Turning the mic control around 2 oclock sort of lessened this a bit.
I use the line input for the transmitter, and hear no whine. It's just not as full a sound as I get with my MS-100 or Landmark FM-350.
I attempted to take off the cover, and didn't succeed, as the antenna seems to be fastened rather securely within, and didn't want to mess anything up. I note that the serial number of the device starts with a "C", so my ever-sharp mind suspects that this is indeed supposed to be a Canadian tuned unit (the "C" is printed on the label, with the rest of the serial number stamped in). I also suspect, using Sherlock Holmes-like deduction, that U.S. models might be a "U" or "A" or something similar printed on the label.
I still haven't heard back from Decade (through their web contact form) so I e-mailed them directly with my questions.
it's easy to tell if you have a USA or Canadian transmitter. If you can hear it two blocks away it's Canadian. If so, and it's marked USA, it's not legal.
TIB
The 4 screws on the front and back come out and then you lift the top cover up and off. May need a little wiggling.
The front panel is held on by the two controls( pulling off the knobs will show the nuts). The back just pulls off as the antenna is attached to the inside board and the antenna just extends through the back hole. But nothing there indicated US or Canada...in fact it's a CZH 05B circuit board.
Decade is closed on the weekend but Michael Carrier is very good at answering inquirys.
Not so easy to tell, really. It should be a Canadian model, and yet I can't hear it 2 blocks (I start getting dropouts after 100 feet on my car radio). Anyway, hopefully there is some sort of indication, such as on the serial number, that lets you know the official designation. I may just have a dud.
Answers directly from Decade.
There is no way to tell between U.S. and Canadian models (at least from the outside).
The transmitters are tuned at the factory - presumably for each market.
Range should be better above 100 Mhz. This is definitely not true with my transmitter - its range is doubled at 88.3 compared to 103.9.