Older model CC Crane FM Xmtr quick mod works out nice!

Be prepared for some comments about the legality of doing this modification. This site does not promote activities which go beyond the Part 15 rules which includes equipment modifications intended to do so, however the results of this modification are in a gray area since the field strength is not known but the reported range is what might be expected from a transmitter compliant with 15.239.

One thing is certain, by modifying the device the certification is no longer in effect. What is not certain is whether it is still operating within the limits.

Neil

Good points. I don't know if this would be much of a defense, but from time to time, I've seen kits that include statements within their documents expressing that the assembler / user has all responsibility to ensure the kit functions within the legal limits. So basically, could I say that I've homebrewed a device from the carcass of a used CC Crane, and assume all responsibility for keeping it within those limits?

The certification is to allow the manufacturer or seller to market the transmitter. Presumably, a certified transmitter will meet the legal requirements of Part 15 but there are no guarantees that this is the case.

The proper use of a device, certified or not, is the responsibility of the owner/operator.

Neil

Bought the entry level RTL-SDR dongle, and, running it with the SDR# software. Used it to compare the waveform of several commercial FM stations to that of my C.C. Crane. MY C.C. Crane suprisingly "dirty"! Spikes out at +/- 200 KHz, even without audio input, 2nd harmonic only 35 to 40 DB down! I'm going to be looking at home brewing a replacement transmitter soon!

Using the dongle/SDR to achieve a spectrum analyzer on your computer is probably a very smart part 15 solution which I want to try also.

You mean "specs" out I gues (not "spikes" out) and 200 kHz is the allowed bandwidth for FM so you're good there and 15.209 only requires being 20 dB down so you're in very good shape at 30 - 40 dB down... in other words YOU DON'T HAVE A PROBLEM with the C.Crane.

But if you do go to something better consider a Ramsey FM30B.. stunning masterpiece.

Thanks, Carl, let me explain better: 200khz down from center carrier, and 200khz up, there are narrow sharp peaks of energy (spikes) showing. There are also larger ones at 100 kHz up, and 100 kHz down. So I guess I'm 400KHz wide? They are there even when I feed no audio to the transmitter! This is my first day with the SDR so I have more experimenting to do. What scares me most is that the transmitter waveform looks so different from any of the commercial stations, although I did find some that had neat square "shoulders" on their waveform that made them as wide as me, I'm thinking that's HD radio, etc. As I get a chance, I'll start taking photos of the waves I see. Does this forum have photo sharing capabilities? If not, I can always put them somewhere else for folk to see. Thanks again!

Wow, I get what you're saying... 400 kHz wide is like having two stations next to each other.

Both my C.Cranes (V1 & V2) have ordinary looking waveforms on a spectrum analyzer... a lot of the stations like a lot "dancier" and "wilder" I guess because they have sophisticated audio processing that pushes modulation to the max.

There is a way to post pictures here, but it's got to be linked from another location such as a website. Maybe there's another way.

One possible explanation for the spikes you are seeing is that sometimes the phase locked loop circuitry output can contain such artifacts due to the way the loop maintains lock. The 100 kHz off carrier looks suspiciously like it could be the operating frequency of the PLL reference since the channel spacing is twice this (or multiples thereof). I have seen contributions from the reference on the output of other PLLs used for different applications.

Neil

It is funny how these toy transmitters are certified and do worse in specs than say a Ramsey or even a Mobile Black Box. In order to get a clean certified transmitter it seems as though you have to spend $125 for a Whole House 3.0 or at least a Decade MS-100 is good (if you can get one anymore). I'd probably even trust a part 73 Decade and keep the power turned way down to 1-5 mW into a rubber duck to stay legal. If you check your range and get 300-800 Ft to a car digital Stereo your probably OK. But I still say operating in a large city may draw more attention that could be unwanted. Good luck staying out of trouble.

Don't forget, even without program audio applied, the stereo pilot tone of 19 KHz is still present.

Usually 10% or less, some of these transmitters have excessivily higher pilot tone levels.

If that's the case you may be seeing some of that on the spectrum analyzer.

The C Crane is an Excellent little transmitter. The early models did have some noticable variance in range. If you want to further boost your signal to maximize what you're allowed under 15.239, follow C Crane's recommendation and clip a 32 inch wire to the little antenna. I wouldn't quite call the C Crane a "Toy Transmitter", those mp3 junkers are the real "toy" transmitters.

FWIW, what the heck happened to the original (and proveable) opinion that most Ramsey kits were junk? Especially the entry level garbage they had.

At anyrate, the most coverage I ever got out of a C Crane was 900 feet on a clear day which is about all you can expect anyway. Expect a more stable coverage area of around 200 feet.

Thank you all. Great info I did take a couple of shots, I will look for the best way to post. I do have facebook, I suppose it's possible for some of you to friend me and see them there, but, some folk avoid Facebook & some use it so we'll see. For now, let me say that the worst of these spikes are about 35 dB down, the ones that are farther out are about 50 dB down. The antenna, roughly one meter of wire, is clipped to the drapes inside a bay window on the 1st floor of an old farm house that was built out and converted to apartments. Walking around the neighborhood with a Grundig traveller G8 II, I am seeing about an 80 foot radius / 160 foot diameter coverage area. In this area, that''s about 20 households who would potentially hear it. My goal is to take it up to a 200 foot radius, I see in the regs some mention that the FCC understands these things to be used out to 200' so that''s my target. After that, I'll look at the AM side of things & maybe go AM / FM. I am brodcasting royalty free music as legally downloaded from www.musopen.org. Classical Orchestra format. More later, and thanks again!

Pll loop filter noise is very poor on the mk1 C Crane tx, if it is noisy at audiable frequencies, then it is highly likely to be poor at ultrasonic frequencies.

I did have a look at one some time ago, but ruled out a simple cure for them, the layout of the pcb is a problem too.

Still for the money you don't expect perfection, you get what you pay for.

MRAM1500 suggested that the pilot tone could cause this and this is reasonable but wasn't the pilot tone crystal removed? Maybe if the crystal is removed the pilot oscillator is free running but I still believe it is PLL artifact that is causing the spurs.

Regarding posting pictures here, this can be done by posting them on a host site (I use PostImage.org and some use Photobucket for examples) and then copying the URL link into your text. If you do this, please use the PREVIEW button to make sure it works before using the SAVE button.

Neil