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'[EE]: Definition of "pulse" - amateur radar again'
2001\09\06@013453 by Sean H. Breheny

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Hi all,

This is a question which is an extension of the amateur radar discussion
which I started a while back. I have been looking around at what is
available out there and it seems as though X band (10GHz) would be the best
place to start. I noticed, though, that the FCC doesn't allow amateur
operations in the 10GHz band which use the "pulse" emission type. Roughly
speaking, I would think this would rule out most types of range-reporting
radar. However, I'd like to know exactly what is defined as pulse? For
example, if I were to maintain a constant output power, but FM modulate the
output so that there was a quick ramp in frequency (say a microsecond long)
followed by a drop in frequency where it sat for a millisecond, and then
the whole thing repeated over and over, would this be considered a pulse
emission?

Thanks,

Sean

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2001\09\06@025554 by Vasile Surducan

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On Thu, 6 Sep 2001, Sean H. Breheny wrote:

> Hi all,
>
> This is a question which is an extension of the amateur radar discussion
> which I started a while back. I have been looking around at what is
> available out there and it seems as though X band (10GHz) would be the best
> place to start. I noticed, though, that the FCC doesn't allow amateur
> operations in the 10GHz band which use the "pulse" emission type. Roughly
> speaking, I would think this would rule out most types of range-reporting
> radar. However, I'd like to know exactly what is defined as pulse? For
> example, if I were to maintain a constant output power, but FM modulate the
> output so that there was a quick ramp in frequency (say a microsecond long)
> followed by a drop in frequency where it sat for a millisecond, and then
> the whole thing repeated over and over, would this be considered a pulse
> emission?
>
 Yes. Could you tell us what output power range are you thinking at ?

Cheers, vasile

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2001\09\06@105303 by Sean H. Breheny

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Hi Vasile,

Probably around 100mW, not very high but high enough that amateur
privileges would have to be used. Where does one go to find out the
definition of pulse? How did you know that this would be considered pulse?
In the FCC regs, there is a definition of "pulse" as an emission type, but
it, somewhat recursively, uses the word pulse in the definition. To my
mind, the normal definition of a pulse usually involves sudden steps in
amplitude, so I think they should mention exactly what they mean if an FM
waveform could be considered to be pulsed even though it has constant
amplitude. What if I fed audio consisting of a set of pulses into a regular
FM transmitter?

Thanks,

Sean

At 08:29 AM 9/6/01 +0300, you wrote:
>   Yes. Could you tell us what output power range are you thinking at ?
>
>Cheers, vasile
>
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2001\09\06@112312 by J.Feldhaar

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Hi Sean,

I think I will wager an opinion on this issue.

The border between a modulated signal and a pulse is not clearly defined, like
the wideband vs. spread spectrum systems. I would always characterize a
modulation as having a certain center frequency/-ies and then describe the
modulation, thus deriving the information about occupied bandwidth.
One could (and you're a HAM too) take a chain of telegraphy signals as a pulse
train, describing the frequency of occurrence, the rise and fall times and the
peak amplitude, as well as the center frequency of this signal. The other way
of looking at it is to treat it as an AM signal with a commuted modulating
signal.
Especially on the issue of the clicks heard in telegraphy even a HAM tends to
look at this like a pulse spectrum to explain the clicks and their correlation
to rise- and falltimes of the carrier. I like this example when teaching for
the HAM licence in Germany, because it's simple to comprehend and you can
immediately to a practical test on the band.
For a pulse, and especially a radar pulse I would put the following parameters
forth (Chirp is another matter, hehehe):
Peak Power
Duration
Repetition rate
Risetime
Fall Time
Skew in Amplitude
Skew in Frequency

I am writing a book on spectrum analysis presently, so I have lots more of
information - if required.

Anyway, the idea of amateur radar is very interesting indeed!

Greets
Jochen Feldhaar DH6FAZ

"Sean H. Breheny" schrieb:

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2001\09\06@112645 by David VanHorn

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At 10:25 AM 9/6/01 -0400, Sean H. Breheny wrote:
>Hi Vasile,
>
>Probably around 100mW, not very high but high enough that amateur
>privileges would have to be used. Where does one go to find out the
>definition of pulse? How did you know that this would be considered pulse?
>In the FCC regs, there is a definition of "pulse" as an emission type, but
>it, somewhat recursively, uses the word pulse in the definition. To my
>mind, the normal definition of a pulse usually involves sudden steps in
>amplitude, so I think they should mention exactly what they mean if an FM
>waveform could be considered to be pulsed even though it has constant
>amplitude. What if I fed audio consisting of a set of pulses into a regular
>FM transmitter?

If interpreted strictly, it would seem to prohibit CW, which is supposed to
be legal everywhere.

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2001\09\06@121803 by Harold M Hallikainen

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       I have a feeling that a "pulse" emmission is JUST a pulse (not a pulse
modulating a carrier). A pulse by itself would be very wide band. A
"pulsed carrier" (such as typically used by radar) would have its
bandwidth determined by the rise and fall time of the pulse. Actually,
it's just DSB AM with a square (or rectangular) modulation waveform. If
the modulating pulse is run through a low pass filter, the resulting
bandwidth on the RF channel is twice the cutoff frequency of the filter
(assuming it's a brick wall filter).  This is similar to a "key click
filter" on a CW transmitter.
       The FCC is looking at pulse modulation, also known as ultra wide band
modulation. See, for example,
www.fcc.gov/Bureaus/Engineering_Technology/Notices/2000/fcc00163.t
xt .

Harold


On Thu, 6 Sep 2001 10:25:48 -0400 "Sean H. Breheny" <spam_OUTshb7TakeThisOuTspamCORNELL.EDU>
writes:
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2001\09\06@131328 by Douglas Butler

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How about a "digital" signal consisting of a FM square wave?  You
transmit a carrier for a time coresponding to your max range.  The you
suddenly shift the transmit frequency by your IF frequency for the other
half of the 50% duty cycle square wave.  Echos from the first half would
be recieved by your IF during the second half and vice versa.  This
simple constant power binary FM signal would be hard to forbid as a
"pulse" emission,

Sherpa Doug

> {Original Message removed}

2001\09\07@021002 by Vasile Surducan

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If you think at pulse definition being in one of the triangulation car
detector system, a pulse is any electromagnetical radiation ( AM or FM
modulated or not) which has a rise and a fall time.
So, if you are thinking to various approval papers probably will be
difficult. 100mW/10GHz is enough power. If you'll experiment a long time
in open space with this transmitter be aware about the cummulative effect
of the radiation for the soft tissues ( brain, livery etc )
The rules said you can stay only in max 20mW/cm2 of microwave radiation.
And believe me, after 4 hours you'll be nervous.
This is valable for GSM talking also. A GSM phone trying to link in a bad
network is emitting about 2W to 6W at 800/900 MHz near the brain !

Vasile

On Thu, 6 Sep 2001, Sean H. Breheny wrote:

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2001\09\07@042412 by Graeme Zimmer

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Doug,

> How about a "digital" signal consisting of a FM square wave?  You
> transmit a carrier for a time coresponding to your max range.  The you
> suddenly shift the transmit frequency by your IF frequency for the other
> half of the 50% duty cycle square wave.  Echos from the first half would
> be recieved by your IF during the second half and vice versa.  This
> simple constant power binary FM signal would be hard to forbid as a
> "pulse" emission,

But if you slew the frequency fast enough to be useful, you will be creating
virtually the same sidebands as if you simply switched it on and off.

........................... Zim

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2001\09\07@061207 by Michael Maiorana

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CW is a legal emission in this band, right? Is there anything stopping you
from transmitting CW "pulses" that are formated as a beacon, including your
call sign, and using those pulses as your desired signal? Seems to me that
you could have the best of both worlds.
Regards,
Mike M.

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2001\09\07@063059 by Graeme Zimmer

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> CW is a legal emission in this band, right? Is there anything stopping you
> from transmitting CW "pulses" that are formated as a beacon, including
your
> call sign, and using those pulses as your desired signal? Seems to me that
> you could have the best of both worlds.

It depends on the rise and fall times......... Most any pulse which is fast
enough for radar will generate an excessively wide signal, eg, will cause
interference to other services.

Additionally, a ham license is quite specific about what forms of
transmission is authorised.
Radar isn't one of them (depends on the country of course).

I would think that genuine Radar experimentation would be routinely covered
by applying for a special class license.
After all, engineers often develop new radar systems, and they do have to
test them !!!

............... Zim

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2001\09\07@065410 by Vasile Surducan

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On Fri, 7 Sep 2001, Graeme Zimmer wrote:

> > CW is a legal emission in this band, right? Is there anything stopping you

CW is legal in X band only in some countries. But my question to Sean is
how will measure the time between the rise time of the output pulse and
the reflected pulse if he will have a continuous wave emission at the same
output power which will produce major interferences and multiple reflected
waves from the target to his receiver. There is a classic tehnique for
this job ?
If he will change the modulation frequency with a 1:10 ratio which maybe
it's ok the result will be almost a microwave pulse...
Or I'm thinking wrong ?

Vasile

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2001\09\07@101816 by Sean H. Breheny

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Hi Zim,

I'm interested in your statement that radar is not allowed under a ham
license. Perhaps you are right, but I don't understand why, in the U.S. at
least. FCC regulations for ham licenses in the U.S. do not specifically
state for what purpose you may transmit, they only state for what purpose
you may not transmit (for example, it does say that you cannot broadcast,
under most circumstances) As for emission types, there are many types, and
in addition, you are allowed to transmit the "test" emission type which can
be almost anything (except that it does say it cannot be a pulse type
transmission unless it is in a band where that is specifically allowed, and
there are several where it is allowed, but 10GHz is not one of them).

I read somewhere that the reason why there is the pulse restriction is
primarily to prevent interference with real radars.

So, as far as I can see, radar should be legal provided the emission type
is allowed and that it doesn't conflict with the broadcast restriction (and
since beacons are allowed, I don't think it would conflict).

I have no specific attachment to 10Ghz, its just that I found a source for
some nice high-power (100mW) gunnplexors at good prices and they are only
at 10Ghz. Getting that power level by other means above  2 or 3 GHz
frequency seems to me as if it will be difficult.

My idea behind the FM emission type is to send chirps followed by running
the gunn source at a CW frequency about 50 or 70 MHz lower, creating a 50
to 70MHz IF output of the received signal.

Sean


At 08:34 PM 9/7/01 +1000, you wrote:
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2001\09\07@145433 by Douglas Butler

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So practically "Pulse" emision should be defined by its bandwidth.
Could one (leagally) make a spread spectrum amateur radar?

Sherpa Doug

> {Original Message removed}

2001\09\07@161214 by gtyler

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Another way to do it is to frequency modulate the carrier with a triangle
wave. If you then mix a portion of the tansmitted signal with the recieved
one you get a difference freqency that is proportional to range out the
mixer. I once worked on a Design for a collision prevention system for
overhead cranes that used this principle.
George Tyler
{Original Message removed}

2001\09\07@212044 by Graeme Zimmer

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Sean,

> So, as far as I can see, radar should be legal provided the emission type
> is allowed and that it doesn't conflict with the broadcast restriction
(and
> since beacons are allowed, I don't think it would conflict).

I'll leave aside the issue of whether the FCC would consider it legal or
not...

The main problem will be not causing interference to others. Any useful
radar signal is going to be rather wide and a terrible source of
interference,
but perhaps you can get away with it on 10Ghz..

> My idea behind the FM emission type is to send chirps followed by running
> the gunn source at a CW frequency about 50 or 70 MHz lower, creating a 50
> to 70MHz IF output of the received signal.

The two most likely candiates have already been mentioned here.
You should research the triangle wave FM method and the various Spread
Spectrum radars....

The Triangle (Doppler) FM method is about the easiest to implement and
originates many years ago with the simple radio altimeter...

Lots of references on the net.

www-path.eecs.berkeley.edu/PATH/Publications/PATH/PRR-97-19.pdf
www.st-and.ac.uk/~www_pa/Scots_Guide/RadCom/part15/page2.html
http://vyger.freesoft.org/radar/Guardian/
http://www.docjava.com/scanners/rangefin.htm

etc ......

..................... Zim ............... VK3GJZ

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2001\09\08@085438 by Peter L. Peres

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Imho the FCC wants to preclude the construction of anything that
resembles radar by amateurs, and worded its spec like that.

You can still obtain a signal that allows a range to be calculated from
reflexions if you use a digital (or sufficiently large modulation index -
like TV H sync pulses) FM (or AM) bit stream modulation such that the
transmitter is not on or not on the frequency of an expected echo at the
time when the echo is expected.

In other words you send noise modulation and receive in the 'holes'
between sending (i.e. on the complementary deviation frequency for FM or
on the carrier, during TX pauses for AM). If the modulation pattern is
random with a period longer than your range and speed high enough to allow
for your resolution then you should be able to aquire the target reflexion
from one of the holes. Then you can 'adjust' the bit stream so it just
happens to allow good reception around the expected echo from the aquired
target (by putting two or three holes good for reception around the datum
where the next echo is expected to arrive in time, in the bitstream to be
sent next).

The only real problem with this is the transmitter power. Because of the
radar equation you will need to own shares in the electricity company to
operate such a thing, even leaving out legality and the practicalities of
running 10kW or so continuous into a directional antenna in the presence
of humans.

You can try to use existing emissions to do that however. Like TV
transmissions and such which are in the correct power range and isotropic
radiators with well-known origins, like beacons, local FM radio
transmitters and such.

I think that you could arrange for a az/el movable antenna that could lock
onto aircraft that simply reflect local TV and FM broadcasts. Using
several static or mobile receivers in a grid and some math you could
probably obtain a map of the air above you, using just UHF TV stations as
fixed transmitters.

I think that the thing that the USAF (?) said could reveal stealth bombers
to the enemy relies on similar technology.

Peter

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2001\09\10@020937 by Vasile Surducan

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On Fri, 7 Sep 2001, Sean H. Breheny wrote:

>
> I have no specific attachment to 10Ghz, its just that I found a source for
> some nice high-power (100mW) gunnplexors at good prices and they are only
> at 10Ghz. Getting that power level by other means above  2 or 3 GHz
> frequency seems to me as if it will be difficult.
>
> My idea behind the FM emission type is to send chirps followed by running
> the gunn source at a CW frequency about 50 or 70 MHz lower, creating a 50
> to 70MHz IF output of the received signal.
>

 Sean, could you tell me more about that "gunnplexors " They are gunn
oscillators only ? On waveguide or microstrip ? There are some
restrictive condition when you try to modulate a gunn just from supply.
And almost sure you'll have a parasitic AM also.

Cheers, Vasile

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2001\09\10@075501 by Sean H. Breheny

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Hi Vasile,

These are actually the units from M/ACom. They are careful to call them
"varactor controlled gunn oscillators" rather than traditional gunnplexors,
I was just using a shorter term. They are a gunn diode, varactor diode, and
a schottky (spelling?) mixer diode all together in a little package with a
waveguide flange as output. You can FM modulate the varactor rather than
the supply on the gunn. They have been used in a popular 2 megabit/sec
amateur radio wireless data link on the web, so it seems as though they are
capable of fast FM modulation and detection.

They are US $70 a piece, with a 10mW gunn diode, and for US $45 you can
replace that with a 100mW gunn.

Sean

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2001\09\11@060835 by Vasile Surducan

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Thanks, Sean
Nice module, we had design and produce for own purpose 10GHz 100mW impatt
oscillators and some 50mW gunn oscillators. Whith a varactor FM
it's ok. Only the price looks a litle bit expensive...
It seems you need a horn antenna for this device.
However 2Mb/sec looks to be a slow rate for a 10Ghz carrier.

Cheers, Vasile




On Mon, 10 Sep 2001, Sean H. Breheny wrote:

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