vlf transmitter, part II

Yup, it's there. Any idea what the X-Y-Z coils do?

John

This morning, I put my 17 Khz vlf transmitter (petsafe wireless fence) on spectrum lab running on my laptop. What I saw has put me in a tailspin.

I have the schematic and the screen captures showing the output spectrum for anyone who wants to email me, aballen at colby dot edu.

Using spectrum labs built in vlf receiver and a short antenna wire, I was able to display the output spectrum of the transmitter without any problems. BUT, I'm at a loss to explain the output spectrum.

Around 18 Khz, there is a peak. Exactly 15 Hz below and above the peak is a smaller set of peaks, presumably these are the sidebands that the receiver recovers. BUT, there is a peak every 60 Hz that slowly gets weaker as the spectrum moves away from the (center) largest peak. Each one of these smaller peaks has upper and lower sidebands as well. There are many of these peaks, not just a few.

I wish I could attach the gif's and the schematic diagram of the transmitter, but I think binary attachments are forbidden here.

For those who didn't read the original post, here's a summary. I purchased a petsafe PIF-300 wireless fence to make an invisible fence to contain our dog. The unit has a 17 Khz transmitter that runs in the house from ac power. The small battery powered receiver is mounted on the dogs collar and gives an audible warning and a correction IF the dog tries to go past the transmitters range.

The url for the product is at:

Here's my question...

Why would they use a transmitter with such a wideband output and containing so many spurs? Is there any kind of simple receiver that can properly recover the transmitter?

As I said before, send me an email and I'll be happy to forward the schematic and the screen captures showing the output spectra.

A

Hey John, good to hear from you.

It's already posted there, look under the same titlle as this message, you should see the text articla and a second message to download the attachments.

A

Your concerns are valid.

The logic in the receiver is 'smart'.

It has over-run logic that detects the speed of the dog by looking at the slop of the signal decline. If the dog tries to over-run the boundary, the beeper sounds faster and there are more aggressive corrections administered.

If the dog does manage to leave the confinement area, the receiver does not issue a correction. Again, the receiver is smart.

Even if the transmitter fails completely and abruptly, the receiver does not issue a correction.

If the transmitter is off and the receiver is energized without hearing the transmitter..there is no correction issued.

Can you add anything to my relevant to my original question?

A

Hi John,

Those are the antennas. Each consists of 8 or 9 inch diameter coils, air dielectric. I can't even begin to count the turns on them, but they all appear identical.

There are 3 of them, one for E-W, one for N-S and one pointed straight up and down. The manufacturer claims a spherical radiation pattern, the 3 coils are meant to approximate a 3 dimensional omnidirectional radiation pattern.

I believe the chip that drives all 3 transmitter sections is an ASIC, which means it could be almost anything inside that lil' buggar.

Regards,

A

PS: I believe the dc blocking cap(s) between the output and the coils are designed to be series resonant at 17 Khz, thus presenting a rather low impedance to the audio amp chips.

Hello Albert,

Even though I don't know how this one works just one word of caution: Many RF fencing schemes have the effect that when the dog leaves the permitted area he or she gets a shock. But if in hot pursuit of the evil one (cat) they might blast past that point, not even being able to stop in time from 30mph or so even if they wanted to.

Now that the cat is on a roof or tree the dog decides to sneak back. Tail tucked under and all. Maybe nobody had seen it... Hopefully...

Upon re-entry the shock applies again, "punishing" the dog for the good intention of returning. This is important to check when buying a system. We decided to do the classical training. Repeated stops at the gate, rewards when the dogs obeyed and sat etc.

Regards, Joerg

Hello Albert,

Yes, that would be a pretty nifty method.

I still can't see the schematics in a.b.s.e., just the text. Maybe my news server though.

Anyways, 60Hz sound like ripple from a non-regulated power supply. The

15Hz sidebands could be modulated onto the carrier to avoid that the system locks onto noise, for example noise coming from the flyback transformer of a large TV set. The TV line frequency is really close.

Regards, Joerg

sounds like power supply ripple getting into the Tx. also, you could be getting some grounding effects in your soil that is getting carried with it from your Electrical service of your home.

these are just a guess.

our friend just had one installed, he has it set for 8 feet radius and i am told the receiver has a 2 step level option in it. when it starts to receive the signal from around 15 feet it starts to beep, when it hits with in 8 feet it zaps the dog. i would think 15 feet should be enough between the warning and zap.

Hello Jamie,

For our Rottie mix it would be, for our Shepherd mix it certainly would not be enough.

Regards, Joerg

Perhaps the subcarriers are used to doppler-detect (the dog's) velocity?

How much of the 60Hz do you see without the transmitter turned on? I would not be surprised if it has something to do with direct pickup of your mains frequency by the antenna.

Paul

Still I would not go for 60 Hz for obvious reasons.

Paul