Thank you Tim, for your great field test results, and giving us all the gory details.
I still haven't seen any followup from those that were casting doubt on the initial set of tests with the CM-10 and the Whole House 3.
Yes, it's true as Carl said. The CCrane FM 2 does in fact have a sticker on the back, that to me appeared to be actual printing on the case of the transmitter itself. And it looks like there is a hole in the case, under this sticker that lines up with the power output adjustment control.
However, this control IS very small and fragile and I suspect messing with it much through the hole with anything less than great care, with a precision screwdriver, could well destroy it.
I vote easier to take off the back. Remember, upping the power wiill most likely make your transmitter illegal unless you are equipped to measure field strength as you adjust.
TIB
Does anyone know what size the DC jack on the transmitter is?
Standard size 5 mil. X 2.1 center
One test i didn't do, and that has been bugging me since I posted these results is "What happens when you plug in AC power"? As you'll recall from the WH 3.0 and the Decade CM-10 tests, the simple act of plugging in AC power increased the output.
The C. Crane runs on 2 "AA' batteries, roughtly 3 volts. The manual states power can be anywhere from 3 to 6 volts. The supplied AC adapter is 5 volts. Inquiring minds (mine) wondered if plugging in a 5 volt power supply with it's associated cable, would have an effect on output.
So I set it up in the shop in the basement and used the ZTechnology R-506 FIM. Now, I didn't have room to use the calibrated antenna in the shop, and I wasn't seeking actual field strength readings anyway, I just really wanted to see any difference in output between battery and AC power. Using the small "utility antenna" that ZTech provides, and using the dBv scale I did A/B comparisons between battery and AC adapter power. I was surprised by the results. Enough so that I repeated the test multiple times. In each case, switching from battery to the supplied AC power adapter caused a 3.1 dBv LOSS in signal strength! You read that right. 3.1 db LESS output on the supplied 5V power supply! Amazing!
I also noted that the manual says two batteries are expected to run this transmitter for up to 120 hours!
I must say, this is a very nice sounding transmitter, as long as you're within range.
One more test up my sleeve, possibly tomorrow. Stay tuned. 40 degrees and raining with snow in the forcast over the weekend!
TIB
OK what happens if you increase the power but have the antenna down? What field strength do you get? There is a reason I want to know this as well. One could get max range if you keep the antenna down and just increase power and then you'll get the 150-200 Ft range to a regular portable Radio. What size screw driver will I need to fit the hole and or screw the pot carefully? Maybe we don't want to crank it all the way in case we break it. Maybe just a fraction could make all the difference just like a gas peddle on a car. Will I need a jeweler's screwdriver to do this? Really I'd like to know the range you got so we can ask for the correct field strength for the FM initiative. This is something I'm really wanting to know. I'm think however with the antenna down it will make a difference. Plus and this sounds far fetched but on some sites it suggests that the 250 uV/m could be measured from the edge of your property line this to me is a stretch of the imagination but if so well then could explain some things as well as the Frankinmuth, Michigan situation for the TX going ¼ to ½ mile. I have lots to ponder upon here as I look for a TX to replace the SainSonic AX-05B minus the harmonics and spurs.
Less output with a/c adaptor! Who would have thought!
Probably a regulator on board so the varying voltage of 3-6 volts but still....yes you have to be sure you're reading it right!
Mark
So what about the power being turned up? Plug in an AC adaptor and what do you get? Well that sort of really puts a damper on any possibility of any decent range with this thing plugged in. Now we'll have to see what the full power does when plugged in.
The range on these units are fantastic when they're turned up... Remember though they likely aren't legal turned up either.
If I were to move to the Caribbean Islands well technically its in the USA (Sort Of) the rules may be a little more relaxed. Always wanted to live where its always warm. On topic again. What type of range would you get in that hypothetical situation for enquiring minds? Would it be close to the SainSonic's ¼ mile range or 1,000 Ft from a wood house? And since that antenna has a screw I wonder if the antenna could be replaced like the cordless phone I had years ago where I went to Radio Shack and put a 72 inch antenna on the base station of my cordless phone set which increased my range to a mile on a Cobra cordless phone. Look I just want to iknow because of being into Radio and Electronics and like to know the possible range if things change. I believe in the FM initiative so I think it will take place one day.
The other day when I took spectrum analyzer readings of the C.Crane FM2 it showed 52 dBu on the scale. At that time I had never opened the unit and had never changed the internal pot.
When I opened my FM2 for the first time I made a mark where the pot was set and noticed it was ALMOST all the way up but not quite by what I will call a "notch."
Turning the pot all the way up the reading went to 55 dBu, an increase of 3 dBu.
Following the test I turned the pot back down to the mark and closed the case.
Hmmm 3 DB well if that were mW's and you were at 4 you'd have 8mW. It really was not much so I really wonder if the range would have been changed all that much?
Tim in Bovey conducted his professional field strength test on a C.Crane FM2 sent new from the manufacturer, but we cannot assume that every unit they send out is set to the same RF level.
My FM2 also came from the manufacturer, but it was an "orphan," which is their word for "returned for resale" by a previous owner. We do not know if the first owner changed the internal setting, and judging from a slightly upturned edge of the sticker on the rear, they may have. Did C.Crane retest it for compliance? We don't know.
To reach a general conclusion about these transmitters Tim would need to order a few more and test each of them, and he'd need to check mine to see if it matches the "new" (non-orphaned) units.
Because of the lofty and arcane (secret,mysterious) nature of 15.239, we have more unknown unknowns than known knowns.
Rich believes adding an odometer is our responsibility and not that of the FCC.
I don't know why ever waste your hard earned money on a certified TX other than maybe a C. Crane (if you just want to go across the room) because we don't know if we are going to get close to the limit as we seen with the C. Crane. I don't know about you but even $50 is hard to come by when at times I have to figure how I am going to keep my heat going and my electricity paid. With that in mind we know what a Ramsey will do into a rubber duck and we know that the C. Crane is good to the spectrum analyzer. But what we don't know is if there is a way to get closer to max and not go over from a transmitter over the shelf or on line? So the closest thing we have to go by is mW. If 3 mW is a little over on a rubber duck buying a TX with a variable power control may be the answer and since certification does not seem to matter and its the operator's responsibility why not try something like the Signstek CZE-T200 because its low setting is 1 mW and the second is 10 mW (Keep in mind the Ramsey does 25 mW and many part 15ers have used this unit. I'd want to have a TX as close to max legal is I could get and worrying about am I getting ripped off because I'm way under Max Legal is daunting and could even make someone not as into Radio as I am throw their hands up and quit the whole idea. I've seen this in other forums where a member got fed up and quit because they had to worry about the FCC every time they saw someone walking or driving by their house which is really a sad story. To expect a hobbyist to fort out 15K for a meter so they can test a $50 transmitter is extremely INSANE to even conceive of anything close to that notion. And we would have to test every single Transmitter ever placed on the market to say Yes this is legal, No its illegal and oh but wait Carl brought up another fact what about a orphan TX you get as a discount because someone complained about it? Well I'm sure (Can't Prove It) that the company who makes these transmitters and has to deal with irate people saying “I can't even transmit to my desk 6 Ft away I want my money back NOW”. What to do? Crank the power up till you get 1,000 feet to a car Radio for those Light O Rama folks. Again we have a fine line and a decision to make since we don't have a FIM 71. Since Frankinmuth Michigan ran their TX 24/7 and got ½ mile that would be what most folks would do. Heck I'd drive to Frankinmuth, Michigan and take my TX and find another blank frequency in the area and adjust my power and have someone drive and I'd make my TX get the same range as Frankinmuth, Michigan's Christmas town and call it a day. Yes its 12 hrs away from me but more feasible than buying a Potomac FIM 71 to tell. Unless I had a drive in near me that transmitted on FM and got the same range. Then again after the movie or even before it started do the same thing. You may be slightly over, but doubt you'd get a NOUO and if you did you could write back and say that you honestly thought you were following the rules for X drive in had a TX and you adjusted yours to match their range on the same Radio as you didn't have $15K to find out. You even give the address of your comparison. Then agree to turn down the power or ask what to do because you don't know of an easier way bt to drive to locations where there are other part 15 transmitters to make your adjustments to match.
I don't think my idea is so far out of the way. Because like I said there are so many things to effect range and again we just play the guessing game here. We know blatant power like 7-10 watts is over, but when we talk about nanowatts or mW's I don't think its too much for the FCC to allow as something has to be done about the corruption in the government to as where one could be bought in their decision making. I know I'll get a lot of messages on this one!!
timinbovey could make some extra cash measuring field strength for us common Potomac-less folk.
You could send your unit to him, he'd measure it with similar cabling attached, set it, and send it back to you.
Let's see... postage both ways plus Tim's hourly rate....
Okay, it was a stupid idea. 🙂