vlf transmiter, need more range

[Albert]

Greetings all,


We need a wireless dog fence, such as the PIF-300 shown at:


http://www.petsafestore.com/inwirfen.html


It forms a 90 foot diameter zone and runs at 17 khz. The transmitter
weighs 5 pounds (not including the wall wart power supply).


I have no idea what's inside the think, but it's an expensive item,
over $200 dollars for the transmitter and collar. I am hesitant to buy
one without any idea whether I can improve the range!


We would like to buy one, but want 500-700 feet range. Since the
collar assembly (the rx) is sealed, I was hoping to hop up the
transmitter.


Does anyone have any experience with these beasts. I have no idea what
type of antenna it uses, most likely a loop with a ferrite core and
the coil makes a resonant circuit at 13 khz, probably has a single
transistor....

My first thought is to add an external wire antenna, which should
increase the range alot even though it still wouldn't be very
efficient.


Does anyone have any practical knowledge of antenna technology at 17
khz? Best to add an amplifier or try to add an outbord antenna?

Thanks.


Al

 

[Travis Jordan]

Does anyone have any practical knowledge of antenna technology at 17
khz? Best to add an amplifier or try to add an outbord antenna?

External antenna. It's on their web page:


If you have a larger than average yard, consider purchasing an extra
boundary kit. The boundary kit includes additional wire and flags.

 

[Albert]

consider purchasing an extra

boundary kit. The boundary kit includes additional wire and flags

There is no wire in this kit, it's wireless.

The manufacturer sells an additional transmitter, which is very
expensive.

My question was regarding methods for hopping up the transmitter or
adding a better (external) antenna.

Can you help?

Thanks

Al.

 

[Travis Jordan]

My question was regarding methods for hopping up the transmitter or
adding a better (external) antenna.

Increasing the transmitter power significantly or adding an external
antenna would violate Part 15 rules and also invalidate the FCC type
acceptance. Having said that, here's the transmitter schematic.

https://gullfoss2.fcc.gov/prod/oet/forms/blobs/retrieve.cgi?attachment_id=60365&native_or_pdf=pdf

 

[Albert]

OK, thanks very much Travis.

It appears easy to modify or to bulid another unit, reproducing the
coil is probably the toughest part.

I'm not familiar with the ic's, but should be able to locate data for
them.

I'm really quite surprised to find that there is not a single
transistor oscillator, but that sure looks like the beast!

I don't think there is a part 15 regulation for 17 khz. because it's
almost audio frequency. If there was a part 15 for frequencies that
low, they would have to type accept every audio amp that has a
transormer or coil associated with the output, wouldn't they?

I can't imagine 17 khz going very far, especailly since the 'antenna'
is so short relative to the carier frequency.

I do thank you very much for the help and wish you the best.

Al

 

[Travis Jordan]

I don't think there is a part 15 regulation for 17 khz. because it's
almost audio frequency. If there was a part 15 for frequencies that
low, they would have to type accept every audio amp that has a
transormer or coil associated with the output, wouldn't they?

The U.S. RF spectrum allocation starts at 9.0khz and unlicensed devices
must conform to Part 15.

9.0 to 14.0khz is allocated for radio navigation use (in the U.S. the
now mostly obsolete Omega system was the largest user of this spectrum).

 

[Bob Shuman]

Are you sure the transmitter actually uses such low "carrier" frequency? I
have not looked a the schematic that was posted, but I don't see how this
could actually work at that frequency since as you yourself admit, this is
in the high audible freq. range.

I would think that the collar based receiver might emit the 17Khz tone when
the animal wearing it strays beyond the RF transmitter's range. I would
think though that the transmitter itself would use an approved FCC RF
frequency in the Mhz or low Ghz range.

Bob

 

[Travis Jordan]

Are you sure the transmitter actually uses such low "carrier"
frequency? I have not looked a the schematic that was posted, but I
don't see how this could actually work at that frequency since as you
yourself admit, this is in the high audible freq. range.

It is magic.

 

[Albert]

I would think that the collar based receiver might emit the 17Khz tone when
the animal wearing it strays beyond the RF transmitter's range.

Hi Bob,

The 17 khz frequency sounds a little odd to me also. But, there is
some literature on the website that indicates that's the frequency of
the transmitter.

I have a few ideas regarding WHY they use such a low
frequency...........

First, they probably have experience at vlf. There are other models
that use buried wire to define the dogs limits in travel. You can bury
an antenna at these lower frequencies, which is why they are used for
navigation and communication with submerged submarines.

But, obviously, the range has to be very limited because the thing
doesn't have an external antenna. Even if it did, the antenna would be
a poor radiator because the antenna is so short relative to the
wavelength.

Also, direct conversion receivers at these low frequencies are very
easy to build, a single transistor and a diode detector is easy to
build and cheap.

If I was designing the thing, I'd use 433 Mhz, where simple and low
cost data receiver and transmitter chips are available and do not use
much power from the battery.

Check out the schematic, there are 3 chips that feed different
windings on a transformer and the time constants in the schematic
don't make sense for transmitters in the MHZ and higher range.

Regards,

Al

 

[Albert]

The U.S. RF spectrum allocation starts at 9.0khz and unlicensed devices
must conform to Part 15.

9.0 to 14.0khz is allocated for radio navigation use (in the U.S. the
now mostly obsolete Omega system was the largest user of this spectrum).

OK, thanks Travis, I learned something new!

Regards,

Al

 

[Travis Jordan]

The 17 khz frequency sounds a little odd to me also. But, there is
some literature on the website that indicates that's the frequency of
the transmitter.

Actually, the fundamental emission frequency is 18.7khz.

https://gullfoss2.fcc.gov/prod/oet/...t=500&calledFromFrame=N&application_id=91640&
fcc_id='KE3IF100'

 

[Albert]

Actually, the fundamental emission frequency is 18.7khz.

It has a 32.76 Khz crystal, wouldn't the transmit frequency be around
16.3 khz?

Does anyone know the identity of the single chip that has 32 pins and
appears to drive each of the LM1875T transmiter chips? I can't make it
out on the pdf I downloaded.

Thanks,

A

 

[Travis Jordan]

It has a 32.76 Khz crystal, wouldn't the transmit frequency be around
16.3 khz?

The ASIC is likely a PLL synthesizer, so the output frequency isn't
necessarily an even multiple of the MO frequency.

 

[Albert]

The ASIC is a 'black box' and we can't really determine the rf output
frequency by looking at the chip itself.

However, the 3 driver chips are 20 watt AF amplifiers. That tells us
that hte output has to be less than 20 Khz.

The wall wart looks physically small, so it's a reasonable to assume
the output power does not come anywhere near 60 watts...

I looked the pictures on the fcc website and I see that the coils are
not in a transformer configuration....they appear to be one coil for
E-W vertical polarization, one coil for N/S vertical polarization and
the third chip drives the coil for omnidirectional horizontal
polarization.

Since the chips aren't on a very large heatsink, it is probably
possible to easily increase the output by properly heat sinking the
drivers and by increasing the drive to each amp stage (after checking
part 15 rules and regulations).

My guess is that the coils will easily withstand the additional output
power.

Once again, I say thanmks to all who commented and helped me figure
out what was inside that unit.

Regards,

A

 

[Albert]

Hi Travis,

I hope you will see this, not sure how often you monitor this NG.

I have searched the FCC part 15 document looking for antenna and power
limits at 17 KHz. But, I can't find anything.

Do you have any more information?

Also, are you able to find any information on the Radio Systems
PIF-275, which is a receiver for the IF-100 transmitter you helped me
out with previously.

Thanks,

A

 

[Travis Jordan]

I have searched the FCC part 15 document looking for antenna and power
limits at 17 KHz. But, I can't find anything.

The emission limits are included in the test documents. As I recall the
fundamental emission as tested was about 25 uV/meter below the limit at
300 meters.

I didn't look for information on the receiver, but if you can determine
the type acceptance number you can look it up on the FCC web site --

https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm

 

[Albert]

Thjanks Travis.

I'm into the search url now, they have 22 products registered (KE3)
prefix. I'll search them all as the summary doesn't describe the
product very well.

GL.

A