vlf antenna question
 

Hi all,

I have a wireless fence, which operates at 17 kilohertz. It is used to
create a wireless fence to keep our dog confined to area close to the
transmitter and works in conjunction with a shock collar (the receiver
is carried by the dog).

We haven't used it yet, but the literature suggests the range is
around 90 feet.

I found the transmitter schematic on the FCC website. The transmitter
is nothing more than generic audio amplifier chips fed with 17
kilohertz signals from what appears to be a PIC or ASIC device. The
antennas are large (8-9 inch) air wound coils that have MANY turns on
them.

I'd like to increase the range without spending much money-so I want
something quick and dirty::

If I disconnect one of the built in antennas, can I hook up the
transmitter to an external antenna consisting of many turns of wire
mounted in the basement (say a 5 or 10 foot diameter loop)?? Would
this give the transmitter more range, or would the range be the same
as the smaller loops that are built in?

Thanks,

A

On Mon, 28 Mar 2005 13:27:45 -0500, Albert wrote:

I'd like to increase the range without spending much money-so I want
something quick and dirty::

Hi Albert,

Hmm, more range? You should be able to fry that puppy within a
country mile if you do that.

Perhaps you should describe your goal instead of your intended method.

73's
Richard Clark, KB7QHC

Hi Richard,

We live in the country, and have all kinds of room for the dog to run.
Despite the fact that we are 700 feet from the road, the dog insists
on going to the road and chasing cars. We are worried for the dogs
safety, hence we purchased the 'wireless fence'.

The design has quite a few safeguards in it and it is very well
thought out.

BUT, it has a 90 foot maximum range. I'd like to extend the range out
to 300 or 400 feet without spending alot of time and money. The
solution offered by the manufacturer is to purchase an additional
transmitter and run them both at the same time. This is a very
expensive remedy and it only gives a modest increase in the range.

My 'goal' is to have an increased range so the beagle can have a
little more area to run in while keeping her away from the road.

Can you offer any suggestions that don't cost alot or require alot of
time to implement?

A



On Mon, 28 Mar 2005 10:48:22 -0800, Richard Clark
wrote:

On Mon, 28 Mar 2005 13:27:45 -0500, Albert wrote:

I'd like to increase the range without spending much money-so I want
something quick and dirty::

Hi Albert,

Hmm, more range? You should be able to fry that puppy within a
country mile if you do that.

Perhaps you should describe your goal instead of your intended method.

73's
Richard Clark, KB7QHC

On Mon, 28 Mar 2005 14:04:03 -0500, Albert wrote:

Can you offer any suggestions that don't cost alot or require alot of
time to implement?

Hi Albert,

I presume by this "range" that the beagle moves unhindered WITHIN the
range of the antenna, and outside of this range she gets a shock (or
some form of behavior modification).

If that is accurate, then boosting range would accomplish your goal.
The problem I had was presuming that the antenna was at the perimeter,
and if your dog penetrated towards it, entering its field, that this
would "modify" her behavior. I am more familiar with antenna
perimeter fences were a collared pooch approaching such a fence would
be -um- stimulated.

Anyway, as you have already noted the design of the transmitter and
the antenna both, then you have options with both. Using the same
antenna, you could feed your transmitter into an unused stereo (or
monaural) amplifier and use that to drive the antenna with more power
(say 1 to 5 Watts). Then you could adjust the range with the volume
control. If this worked, you could then go out an buy a dedicated
audio amp kit ($10-$20) that fits this power range.

Another method is to replace the antenna with conductive stakes driven
into the ground. At this frequency, ground conduction has a fair
range. It was one method of communication that was used with trench
warfare during WWI. The further apart the stakes are, the better. I
would add that this comes with some shock hazard and is certainly not
within the warrantee of the product (but nothing suggested here will
be). As this a strictly an experimental long shot, try the simpler
suggestions above.

73's
Richard Clark, KB7QHC

On 2005-03-28, Albert wrote:
Hi Richard,

We live in the country, and have all kinds of room for the dog to run.
Despite the fact that we are 700 feet from the road, the dog insists
on going to the road and chasing cars. We are worried for the dogs
safety, hence we purchased the 'wireless fence'.

The design has quite a few safeguards in it and it is very well
thought out.

BUT, it has a 90 foot maximum range. I'd like to extend the range out
to 300 or 400 feet without spending alot of time and money. The
solution offered by the manufacturer is to purchase an additional
transmitter and run them both at the same time. This is a very
expensive remedy and it only gives a modest increase in the range.

My 'goal' is to have an increased range so the beagle can have a
little more area to run in while keeping her away from the road.


I might be missing something here, but wouldnt increasing the range of the
transmitter/antenna combination reduce the amount of room that the dog has
to run in? Increasing the range, would trigger the collar when the pup was
farther away from the perimeter - confining the pooch to a smaller area.

What is the design of the reciever on the dogs collar? You don't have to
increase the range of the transmitter, you could just increase the
sensitivity of the receiver. If the xmitter is really running at about
17khz, then a 1/4 wave whip (about 2.75 miles) attached to the dogs collar
might work. If that does not work, you could at least reel the dog in when
she gets a bit too close to the road.



--
Alex / AB2RC
Linux is user friendly, however it is not idiot friendly

On Mon, 28 Mar 2005 11:44:33 -0800, Richard Clark
wrote:
l.

Hi Richard and Alex,

Both of you thought the wireless fence involved a buried loop, which
is NOT the case.

The transmitter is NOT connected to a buried loop, the antenna is in
fact contained within the plastic case of the housing. The antennas
are 8 or 9 inch air would coils with MANY MANY turns of small gauge
wire.

My question is.....

If I disconnect the internal coils, can I replace them with much
larger coils of similar inductance that would probably be in the
basement (out of the way)??

Thanks,

A


The problem I had was presuming that the antenna was at the perimeter,
and if your dog penetrated towards it, entering its field, that this
would "modify" her behavior. I

Putting a ferrite core in the windings of the antenna would extend its
range, wouldn't it ?
- or are you working on a way to shock the neighbor's puppy ?
:-)

I auume these thing work in reverse of conventional thinking. I assume
that as long as the receiver is receiving a signal, the dog does not get
shocked. If it strays too far and the receiver loses the signal...ZAP!
However, modifying the transmitter would violate its Part 15
certification and the owner might be the one to get the ZAP (from the
FCC)...

Scott


AB2RC wrote:

On 2005-03-28, Albert wrote:

Hi Richard,

We live in the country, and have all kinds of room for the dog to run.
Despite the fact that we are 700 feet from the road, the dog insists
on going to the road and chasing cars. We are worried for the dogs
safety, hence we purchased the 'wireless fence'.

The design has quite a few safeguards in it and it is very well
thought out.

BUT, it has a 90 foot maximum range. I'd like to extend the range out
to 300 or 400 feet without spending alot of time and money. The
solution offered by the manufacturer is to purchase an additional
transmitter and run them both at the same time. This is a very
expensive remedy and it only gives a modest increase in the range.

My 'goal' is to have an increased range so the beagle can have a
little more area to run in while keeping her away from the road.



I might be missing something here, but wouldnt increasing the range of the
transmitter/antenna combination reduce the amount of room that the dog has
to run in? Increasing the range, would trigger the collar when the pup was
farther away from the perimeter - confining the pooch to a smaller area.

What is the design of the reciever on the dogs collar? You don't have to
increase the range of the transmitter, you could just increase the
sensitivity of the receiver. If the xmitter is really running at about
17khz, then a 1/4 wave whip (about 2.75 miles) attached to the dogs collar
might work. If that does not work, you could at least reel the dog in when
she gets a bit too close to the road.

On 2005-03-28, Albert wrote:
On Mon, 28 Mar 2005 11:44:33 -0800, Richard Clark
wrote:
l.

Hi Richard and Alex,

Both of you thought the wireless fence involved a buried loop, which
is NOT the case.

The transmitter is NOT connected to a buried loop, the antenna is in
fact contained within the plastic case of the housing. The antennas
are 8 or 9 inch air would coils with MANY MANY turns of small gauge
wire.

OK, then this is very different from other "invisible" fences that I have
seen. It would appear that this device is designed to keep the dog close to
the transmitter, and then shock her when she strayed too far - when the
receiver on the collar lost the input signal.

I think that device would not give you all that much control as to what kind
of coverage area you can have. Also what would happen if the collar lost
the xmitter signal due to other reasons (dog goes behind a trash can/metal
shed/other large metal object)? Personally, I would return it, and get the
type that used a buried wire -- or just train the dog not to stray too close
to the road by other means.

That being said, it might still be easier to increase the sensitivity of the
receiver. What type of antenna is on the dogs collar? Also - what is the
brand and model of this unit? It might make tracking down the soultion a bit
easier.

--
Alex / AB2RC
Linux is user friendly, however it is not idiot friendly

Scott,

Your question brings much complication to a matter that should be easy
to answer. I'll do my best to avoid getting bogged down in the
explanation.

The transmitter has a very long range, much longer than 90 feet. I
believe the dogs collar hears the signal for a very long distance.
But, that the collar does not issue a correction if the dog wanders
past the range of the transmitter. If the collar acted in this manner,
it would preclude the dog from RE-ENTERING the protected area from the
outside of the 90 foot range.

In order for the collar to initialize, it must hear the transmitter
(initially). If the transmitter is turned off, and the collar is
turned on, no corrections are issued.

Also, if the collar is properly initialized and operating, abruptly
turning off the transmitter DOES NOT result in a correction being
issued. Corrections are only issued IF the dog is in the intermediate
zone, which appears to be a 3 foot wide area.

This type of operation is necessary to safeguard the dog, even though
it complicates the hardware some.

At 16 kilohertz with horrendously inefficient transmitting antennas, I
doubt there would be an FCC problem, especially with a modest boost in
ERP. The Earth and the solar system generates much noise on those
frequencies as well, we could probably increase the transmit power
quite a bit without creating problems.

Hope this helps.

A



On Tue, 29 Mar 2005 12:09:27 +0000, Scott
wrote:

I auume these thing work in reverse of conventional thinking. I assume
that as long as the receiver is receiving a signal, the dog does not get
shocked. If it strays too far and the receiver loses the signal...ZAP!
However, modifying the transmitter would violate its Part 15
certification and the owner might be the one to get the ZAP (from the
FCC)...

Scott

Modification of the receiver is not an option for several
reasons.........

-

The Earth and solar system make alot of noise on these frequencies. I
suspect the receiver is designed to be somewhat insensitive in order
to avoid problems with noises generated by Mother Nature.

-

The schamatic of the dog collar is not available, the manufacturer
chose to make type acceptance documents 'private'. There is a record
of the receiver, but all details are unavailable to the public.

-

The receiver assembly is in an enclosure that can't be opened,
probably to insure operation if the collar gets dunked in water (some
dogs enjoy swimming). It also appears to be potted, the black epoxy is
visible in the port provided for adjusting the correction level).


-

A



That being said, it might still be easier to increase the sensitivity of the
receiver. What type of antenna is on the dogs collar? Also - what is the
brand and model of this unit? It might make tracking down the soultion a bit
easier.

On Tue, 29 Mar 2005 13:02:28 GMT, AB2RC
wrote:

Also what would happen if the collar lost
the xmitter signal due to other reasons (dog goes behind a trash can/metal
shed/other large metal object)?

Hi Alex,

At 17KHz this is virtually impossible. It would be like trying to
hide behind a house in Aceh when the wave came in.

73's
Richard Clark, KB7QHC

On 2005-03-29, Richard Clark wrote:
On Tue, 29 Mar 2005 13:02:28 GMT, AB2RC
wrote:

Also what would happen if the collar lost
the xmitter signal due to other reasons (dog goes behind a trash can/metal
shed/other large metal object)?

Hi Alex,

At 17KHz this is virtually impossible. It would be like trying to
hide behind a house in Aceh when the wave came in.

Forgot about the frequency there for a minute ... 17khz is a very long wave

Either way, the whole concept of this specific device seems sort of
backwards for it's intended purpose.

--
Alex / AB2RC
Linux is user friendly, however it is not idiot friendly

Is there a webpage of the manufacturer which contains any details of the
device in question? A picture can be worth a 1000 words....

Regards

--
Hay, if'n ya'll cun't konstructivly partecipete in this har disscusion, haw
aboot speel-checkin it fer me?


"Richard Clark" wrote in message
...
On Mon, 28 Mar 2005 13:27:45 -0500, Albert wrote:

I'd like to increase the range without spending much money-so I want
something quick and dirty::

Hi Albert,

Hmm, more range? You should be able to fry that puppy within a
country mile if you do that.

Perhaps you should describe your goal instead of your intended method.

73's
Richard Clark, KB7QHC

I Hope I misunderstood or you have thought about it:

If the collar shocks the dogs when it stops receiving the transmitter's
signal... What is going to happen to the dog when the transmitter
eventually stops working (exhausted batteries, mains cut or simple
malfunction)?

Toni

John,

If you have broadband, I can send the files to you. There is nothing
on the manufacturers website. It's all on the FCC website, although
the schematic is marginally readable as it was scanned at low
resolution.

Let me know if your email address in your usenet post is correct and
whether you can receive the large files.

A

Is there a webpage of the manufacturer which contains any details of the
device in question? A picture can be worth a 1000 words....

Regards

Ahhh! Then there must also be a transmitter in the collar to "answer
back" to the stationary transmitter? If so, maybe the thing works on
the amount of time calculated for the signal to travel round trip. A
radar mile (2 miles round trip) is about 12 microseconds, if I recall.
Rountrip at 90 feet would be something like 183 nanoseconds. If THIS is
how the unit works, running a kilowatt wouldn't make a difference. It
would require changing the interval time that the transmitter waits for
check-back. Maybe I'm making this too complicated ;) It must be
simpler and then I would think they would use something other than 17
KHz....interesteing!!

Scott


Albert wrote:

Scott,

Your question brings much complication to a matter that should be easy
to answer. I'll do my best to avoid getting bogged down in the
explanation.

The transmitter has a very long range, much longer than 90 feet. I
believe the dogs collar hears the signal for a very long distance.
But, that the collar does not issue a correction if the dog wanders
past the range of the transmitter. If the collar acted in this manner,
it would preclude the dog from RE-ENTERING the protected area from the
outside of the 90 foot range.

In order for the collar to initialize, it must hear the transmitter
(initially). If the transmitter is turned off, and the collar is
turned on, no corrections are issued.

Also, if the collar is properly initialized and operating, abruptly
turning off the transmitter DOES NOT result in a correction being
issued. Corrections are only issued IF the dog is in the intermediate
zone, which appears to be a 3 foot wide area.

This type of operation is necessary to safeguard the dog, even though
it complicates the hardware some.

At 16 kilohertz with horrendously inefficient transmitting antennas, I
doubt there would be an FCC problem, especially with a modest boost in
ERP. The Earth and the solar system generates much noise on those
frequencies as well, we could probably increase the transmit power
quite a bit without creating problems.

Hope this helps.

A



On Tue, 29 Mar 2005 12:09:27 +0000, Scott
wrote:


I auume these thing work in reverse of conventional thinking. I assume
that as long as the receiver is receiving a signal, the dog does not get
shocked. If it strays too far and the receiver loses the signal...ZAP!
However, modifying the transmitter would violate its Part 15
certification and the owner might be the one to get the ZAP (from the
FCC)...

Scott

Nothing but a little receiver and a buzzer in the belt. The wire
radiates and the lil bitty receiver detects it and the little dog
regrets his closeness to his boundaries.

Butch

Scott wrote:

Ahhh! Then there must also be a transmitter in the collar to "answer
back" to the stationary transmitter? If so, maybe the thing works on
the amount of time calculated for the signal to travel round trip. A
radar mile (2 miles round trip) is about 12 microseconds, if I recall.
Rountrip at 90 feet would be something like 183 nanoseconds. If THIS is
how the unit works, running a kilowatt wouldn't make a difference. It
would require changing the interval time that the transmitter waits for
check-back. Maybe I'm making this too complicated ;) It must be
simpler and then I would think they would use something other than 17
KHz....interesteing!!

Scott


Albert wrote:

Scott,

Your question brings much complication to a matter that should be easy
to answer. I'll do my best to avoid getting bogged down in the
explanation.

The transmitter has a very long range, much longer than 90 feet. I
believe the dogs collar hears the signal for a very long distance.
But, that the collar does not issue a correction if the dog wanders
past the range of the transmitter. If the collar acted in this manner,
it would preclude the dog from RE-ENTERING the protected area from the
outside of the 90 foot range.

In order for the collar to initialize, it must hear the transmitter
(initially). If the transmitter is turned off, and the collar is
turned on, no corrections are issued.
Also, if the collar is properly initialized and operating, abruptly
turning off the transmitter DOES NOT result in a correction being
issued. Corrections are only issued IF the dog is in the intermediate
zone, which appears to be a 3 foot wide area.

This type of operation is necessary to safeguard the dog, even though
it complicates the hardware some.

At 16 kilohertz with horrendously inefficient transmitting antennas, I
doubt there would be an FCC problem, especially with a modest boost in
ERP. The Earth and the solar system generates much noise on those
frequencies as well, we could probably increase the transmit power
quite a bit without creating problems.

Hope this helps.

A



On Tue, 29 Mar 2005 12:09:27 +0000, Scott
wrote:


I auume these thing work in reverse of conventional thinking. I
assume that as long as the receiver is receiving a signal, the dog
does not get shocked. If it strays too far and the receiver loses
the signal...ZAP! However, modifying the transmitter would violate
its Part 15 certification and the owner might be the one to get the
ZAP (from the FCC)...

Scott

Hi Scott,

I suspect you are making it more complicated than it is. I have the
schematic for the transmitter, which is the part that stays indoors
and needs AC line power.

The only receiver is the receiver in the collar.

There has to be some logic in the collar though because it has to
initialize (won't issue corrections unless it hears the transmitter
when the receiver is first turned on).

After the collar is initialized, it will not issue corrections if the
dog (somehow) gets outside the 90 foot area and tries to re-enter.
This means that once the collar loses the signal completely, it won't
issue a correction when the collar acquires the signal again.

If the transmitter is powered down completely (after proper
initialization) the collar will not issue a correction either.

So, it's a smart receiver and is well thought out. But, all these
functions can occur as the result of logic contained within the collar
mounted receiver.

Last night, I looked at the signal using spectrum lab's vlf receiver
program. When I zoomed in on the transmitters signal, I noticed that
there were sidebands occurring every 15 hz. I will post another
message with more details.

A


PS..................

The vlf transmitter frequency is around 17 Khz. At first, this seemed
like an odd choice for a wireless fence.

But, I've done much research into vlf, and hte frequency selection
makes much more sense now!

VLF is used because the signal penetrates the ground better, meaning
that the received signal strength doesn't vary much if the dog goes
swimming or during a rain storm. Also, the signal strength changes
very little if the dog tries to crawl 'under' the fence. The signal
strength stays about the same if the dog turns towards or away from
the transmitter as well.

It also doesn't matter whether the dog walks behind a tree or
obstacles such as small buildings, dog houses or trash cans.

Because the wavelength is so long, these obstacles don't impact the
field strength much. A vhf/uhf transmitter would have very serious
drop outs with these types of obstacles.








It must be
simpler and then I would think they would use something other than 17
KHz....interesteing!!

On Wed, 30 Mar 2005 08:31:08 -0500, Albert wrote:
Last night, I looked at the signal using spectrum lab's vlf receiver
program. When I zoomed in on the transmitters signal, I noticed that
there were sidebands occurring every 15 hz. I will post another
message with more details.

Hi Albert,

This could be an ID modulation to serve the receiver's logic. In
other words, correction is based upon both signal strength AND
modulation.

Thus the received signal strength has to fall to a certain level that
is still above noise level (not complete drop-off) to insure that
corrections are not applied due to power failure at the transmitter
(and to allow registration at power-up).

VLF is used because the signal penetrates the ground better,

This was what I described as the subterranean communications channel
used in the trenches of WWI. I would still suggest a power boost over
building a ground dipole. The design of the amp is trivial, and kits
are available to do the job for less than $20.

73's
Richard Clark, KB7QHC

This could be an ID modulation to serve the receiver's logic. In
other words, correction is based upon both signal strength AND
modulation.


I think it's even simpler than that... It could be based on the signal
strength alone.

As long as the received signal is treated in an analog manner, it
would be easy to tell the difference between a strong and a moderately
strong signal. I'd bet they don't do anything as sophisticated as a
digital decode to identify the transmitter.

Be on the lookout for 'vlf transmitter, part II.......coming to this
newsgroup soon. Basically, I ran the transmitter into a spectrum
analyzer and saved the output spectrum of the transmitter. It's very
interesting and leads to another whole set of questions.

Regards.

A

On Wed, 30 Mar 2005 18:09:13 -0500, Albert wrote:
This could be an ID modulation to serve the receiver's logic. In
other words, correction is based upon both signal strength AND
modulation.

I think it's even simpler than that... It could be based on the signal
strength alone.

Hi Albert,

Given the features you've imputed to the design, transmitter drop out
(loss of AC power) would be indistinguishable from puppy border
crossings.

Or, yes, it could be signal strength alone (still argues for a simple
Amp any 'splanation considered).

Part Deux of the mysteries of the VLF is looked forward to.

73's
Richard Clark, KB7QHC