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By a stroke of luck, today we were blessed with a sunny 58 degree day, just what I needed to schlep out into the test field once again with the C. Crane FM 2 transmitter that arrived over the weekend while we were in Kansas visiting my Son and his family. The rest of the week is forcast for 30’s and rain. So I had to jump at the chance.
Same idendical test setup as the previous tests. Same field, same location, same calibrated (by Potomac) Potomac FIM-71 field intensity meter. Same setup, 3 meters between receive and transmit antennas, both antennas exactly 7 feet above ground as outlined in the Potomac manual, etc.. etc.. Tests were run operating the transmitter on brand new “AA” alkaline batteries. Here are the results.
The C.Crane website, other sellers websites, and the included manual state that the coverage for this transmitter is “between 30 and 75 feet, line of sight with no obstructions”. Well, this is exactly right. As delivered, in ” out of the box” stock condition, the field strength at three meters was 110 uV/m. This is of course EXTREMELY LEGAL. In fact this is less than half the legal limit of 250 uV/m. This was with both antennas horizontal. If I changed the transmitter antenna to vertical it dropped to 43 uV/m, but that is to be expected. I brought the Tecsun PL-310et radio with me to see what sort of actual distance I got, and the receivers dBu scale dropped to zero at a measured 35 feet but I was still able to hear the signal by carefully orienting the radio antenna for best reception, although with noticeable hiss. By 40 feet away I couldn’t hear the signal at all. So, quite literally, the transmitter as shipped covered to about 35 feet. This is in wide open space, line of sight.
You may know (or not) that inside this transmitter there is a power output control potentiometer. You can find all sorts of websites and even YouTube videos showing how you can turn up the power for “better results”. Of course none of these posters have any clue if their transmitters remain legal once they turn this control. So, there I was, standing in a field wondering….. I didn’t bring any tools with me at all. But I did have the small Swiss Army knife that I always carry, and darned if the screwdriver blade didn’t fit just right to remove the screws to access the inside of the transmitter! There are two screws under the little rubber “feet” on the transmmitter bottom, and one inside the battery compartment. Remove the back carefully making sure to clear the input level control and the power adapter jack. Now, I didn’t want to get into a complicated testing routine here, I just wanted to turn it up to full power and see what she’d do. I watched the FIM as I turned the control and verified that COUNTERCLOCKWISE increases the power. I gently turned it all the way CCW, put the back on, and returned it to test position and manned the meter. With the output turned to full, the field strength at three meters was now at 5850 uV/m! That’s a heck of a jump and over 23 TIMES the legal USA limit.
Naturally I thought…. wonder if this would be legal in Canada! So I hoofed the FIM out to 30 meters (98.4 feet) hoping it would come in under 100 uV/m. Nope. Full power at 30 meters gave me a solid 270 uV/m, nearly three times the legal limit in Canada.
Just for the heck of it I did a quick reception test with the Tecsun with the transmitter on full power — I was out well past 250 feet with clear signal and about 4 dBu on the meter. I got tired of walking. I’m sure I could have gone quite a bit further.
So, the result is… The C.Crane FM 2 is clearly legal as shipped, and by a wide margin. Access to the “secret” power output control is pretty easy and if you had access to an accurate FIM you could indeed readily adjust it to full legal US output level limits.
The audio input cable is built into this transmitter. So any testing or use would have to include the audio cable. You’ve seen how plugging the cable into other transmitters greatly increased their output. This one is clearly built with setup done with the built in cable at the factory. It also tunes down to .5 steps, e.g. 92.75 mHz. Which seems silly to me unless you’re receiving it on an old school “dial” type radio.
I didn’t do any serious testing for audio quality — what I heard on the FIM and the Tecsun sounded just fine. I also didn’t set up the Spectrum Analyzer to test either. Perhaps when I have more time and I’m sutck indoors over our 6 month winter 🙂 I rather like this transmitter. It’s solid, sits well on a table, comes with an AC adapter and is easy to operate. I just might hang on to this one to use to distribute station audio around the studio.
TIB
Total posts : 45366Oh wow I was wanting to buy one already turned up since I can’t see well. I thought the out of box was way too low. I also heard there was a way to simply peel off the sticker to get to the screw I need to turn up. Interesting. I’d like to know just how far this thing would go and would have been interesting for test sake to see what exactly 250 uV/M would have done to the range. We’ve never seen that however at high power seems to beat the Whole House FM Transmitter 3.0. So my question is do I buy this to replace my SanSonic and rev up the power? I’d like to know just how easy this is to get to. Hope the sticker would come off and I can get to the knob or someone find one already modified.
Before I buy this I want to know what it does to a spectrum analyzer. I’ll see if I can find a modified one on Ebay.
Total posts : 45366I seem to recall the C Crane FM1 being clean on the analyzer. IIRC, only the FM1 has the easy access power mod Where you can just peel the sticker.
The stereo separation on these are amazing.
Don’t bother buying one off eBay, just grab an FM1 off C Crane.
Total posts : 45366No, there is NO access to the power adjustment with a sticker removal. In fact, I don’t even SEE any stickers on this at all!
You’ll have to pop out the two little rubber “feet” on the bottom and remove the small Phillips type screws under them, then also remove a small Phillips screw in the battery compartment. Once this is done the back cover comes off quite easily and the adjustment control is right there, very obviously mounted, that you turn with a screwdriver. Turning it counterclockwise increases the power. I’ve read on various sites that this control is somewhat delicate and some users have reported breaking them. But people with some electronic experience probably realize that a tiny PC mount style potentiometer is a rather delicate device!
It may have been the previous model that had the adjustment under a sticker, but definitly not this one.
Clearly if you adjust the power it’s pretty easy to wind up WAY over the legal limit.
When we discuss range, they will ALL be the same at the same field strength power. 250 uV/m is just that and it will only go so far. It’s like saying a Ferarri goes faster at 60 miles an hour than a Chevy does at 60 miles an hour. Even if you went with some sort of improved antenna it works BECAUSE it’s a gain antenna that is increasing the radiated signal. You could line up every Part 15 FM transmitter on Earth and if they are all adjusted for 250 uV/m at 3 meters, they’re all going to have the same range given the same geographic conditions. I only tested range with this one because it was lower powered than the others I tested and I wondered how far it would actually go.
I did note that this transmitter has a shorter antenna than the Whole House 3.0 or the Decade CM-10 that I tested. But again, changing the antenna voids the certification.
There’s a (rather crappy) video on YouTube of someone showing how to make the adjustment, but it’s blurry and poorly lit, but it’s at:
TIB
Total posts : 45366Tim is correct on all points.
Only the original version of the C Crane FMT had the easy access.
Another part to watch out for is the volume knob, which CAN break when removing the case. For a safety precaution, turn the volume up all the way before opening.
Total posts : 45366Very good info you have given us.
The Ccrane seems the best of them all. Continuously power adjustable to meet rules.
But not Industry Canada certified so technically we can’t use here.
To Thelegacy….this is the best for you! If you know how to adjust it to the FCC max. you can get someone to do it for you.
Mark
Total posts : 45366I’ve been watching for Tim’s C.Crane FM2 Test every five minutes seven days a week and ZING, hear it is!
It’s really a head spinner fitting Tim’s report into my smaller and more limited experience with my C. Crane transmitters, including a 1 and a 2.
Tim, you were fooled by the sticker, which IS on the rear of both models, made to look like part of the black plastic surface and neatly fit into a rectangular depression in the case.
It looks like the sticker on mine had been peeled back by a previous owner, it is an “orphan” unit, which means it was returned for a refund and saved me $10.00.
Now the details of my situation, starting with the C.Crane FM2.
I have never opened it, it is exactly the way C.Crane sent it. Question is, did the previous owner peel off the seal and turn it up?
Start your full attention span now… on my spectrum analyzer the C.Crane FM2 has exactly the same signal strength as the FM1, which I DID OPEN AND BOOST THE POT. But, however, important to mention, I failed to note where the pot was set on the FM1 before I turned it up, and it was hard finding the slot with the mini-screwdriver through the hole in the back of the case under the sticker, so maybe it was already turned up.
Both transmitters have exactly the same signal strength on the spectrum analyzer as both my Wholehouse 2.0 in its U.S. configuration as well as the Scosche FMT4R, with it’s 6-inch shield-in-the-audio-cable antenna.
Who’s on first?
EDIT POINT: Even though the FM2 does have a label on the back I DO NOT KNOW if the adjustment is accessible through a small hole the same way as it is on the FM1.
Total posts : 45366Is there a real difference between the FM1 and FM2? If not it may be better for me to get the FM1 and mod it. Yes I’ve seen the video. Being legally Blind just scared I’d break the wire. Maybe I could get a sighted person to help me to do it. At least it would be cleaner than the SainSonic. Still trying to decide if I want to have a modified C. Crane or try hard for teh Whole House 3.0. Didn’t the FM1 have hum? Trying to figure how to get rid of that however.
Total posts : 45366One important thing we do not know is whether the FM1 can be turned up as high as the FM2, as Tim found it adjusts to a very high signal level.
A feature of the FM2 that could help you, TheLegacy, is the green LED that flashes when you are modulating at a good level, and a red LED that flashes for over-modulation. By comparison the FM1 only flashes for (red) over-modulation.
The audio quality of both is professional and excellent.
The so-called “hum” in the FM1 has been exagerated because of the difficulty of describing signal noise with English language. It is not an AC type hum. It is a very low level whine or warbling-whistle that can be heard on silent carrier or super low level audio. But guess what? With processed audio it cannot be noticed at all.
I send my main programming all day on an FM1 using Stereo Tool processing and I never hear the background sound.
The FM2 is used by me for audio editing, where more quiet times are part of the process and a very silent carrier is preferred.
Since I do have the means to re-set the RF output of the FM2 back to where it is now, I will adjust it to maximum and see how it compares to the FM1. That will answer the problem I expressed in my first sentence.
I’ll have the report done by early tonight.
Total posts : 45366The C.Crane FM2 when set to maximum by way of the internal potentiometer (pot) has 7 dBu more RF field strength than the C.Crane FM1, according to measurements taken by my spectrum analyzer with sending and receiving antennas horizontal across a distance of 10’10”, audio cable plugged into the computer with silent carrier.
Of course when set for 15.239 both transmitters would be equal.
Tim found the pot in the FM2 worked CCW, and I have observed that the pot in the FM1 works CW (clockwise).
Both pots can be accessed from the outside by removing the sticker on the back, the FM1 has several holes so it takes care to pick the right one, and the FM2 has only one hole.
The case of the FM2 is a lot easier to open than the FM1.
Another day older and too poor to be in debt.
Total posts : 45366Wow I’d really like a pe mod FM2 is sounds but I’d settle for the FM1 if nothing else. The 2 would really help me with the modulation. What type of range did you get? Wonder of I put a long wire on it if I’d get the 1/4 mile I got with my SainSonic minus the harmonics and spurs. I did have some listeners and I want to get back on air. Only bad thing is that I can’t do 87.9 on the C. Crane. I could just go back to making sure that the 96.3 frequency is blank or something like that. What about the Scoche with a super long audio cable? would that get me closer to the range I got with the SainSonic minus the harmonics? Something has got to give here as I’m looking for a great TX. 900 Ft isn’t too bad however as some reported with the modified TX.
Total posts : 45366I have stopped bothering with range tests for these little FM transmitters. It has always been about the same. I drive down the driveway (100-feet) it gets slightly noisy, down the street about 3 houses it starts to drop like a helicoptor out of gas.
This small differences between a few dB doesn’t make these things jump to life.
Keep in mind, I am using the manufacturers antennas.
The only way to boost these C. Cranes above what they do “out of the box” is get them up in the air with high-gain antennas.
The big jump in power observed by Tim suggests to me that even such rule breaking field strengths aren’t enough to cover the kind of range some are talking about.
Total posts : 45366Yea cuz my SainSonic AX-05B got 1/4 mile on a rubber duck on the first floor. I was pleased till I found about the harmonics and spurs. Then I pulled it off the air. I thought by cranking the C. Crane all the way up I’d get that range too and without the harmonics. Well looks like I’ll need the Whole House FM Transmitter 3.0 and use the secret mode to get the same range. That will get me 310 mW a little shy of 500 mW. Should get the same results. I guess I could only hope that by cranking up the C. Crane I’d get 900 Ft as reported by those who did the mod. Unless they turned down the TX later again and the mods didn’t get the same range as before. Its weird.
Total posts : 45366A 1/4 mile range is not legal On FM.
Total posts : 45366Neither is operating on 87.9 or 87.7, at least right now.
When Rich did his field strength chart for a legal U.S. field strength using the NEC 4.2 software (which is recognized by the FCC in place of real world measurements), you would get a field strength at 100 meters of 6.5uv/m with an antenna mounted at an elevation of 10 meters. You can hear a signal with that field strength with a good car radio (some have sensitivities of under 1uv with 20db SNR. In fact, you would likely be able to hear a signal with field strength of half that, taking your range out to a maximum of 200 meters (but probably less, given the other factors that we’ve seen affect FM range – it would be nice to see a chart for the field strength at 200 meters). But that’s about it. Of course, there’s the logistics of getting your transmitter with attached antenna up that high, feeding it power and audio, and protecting it from the weather. But it is possible.
1/4 mile, which is about 1300 feet (or about 400 meters) – highly unlikely. And that’s for someone sitting in their car. Sitting in their house, much less than 200 meters, even with an elevated antenna.
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