Just perusing the ARRL letter on rec.radio.info and the lead story was
very interesting. It's about the ARRL objecting to the use of some 70cm
frequencies for a commercial event.

This paragraph in particular caught my eye:

"The ARRL called the Miller Motorsports Park choice of
channels 'completely inappropriate. The radio amateurs who
are licensed to use these frequencies are under no obligation
to either tolerate interference or to cease their own operation,
regardless of the interference that might be suffered at any
time' by Miller Motorsports."

Just goes to show how things are different in the US to here in the UK.
Over here we are only secondary users of the 70cm band (the primary user
of just about everything above 2m is the Ministry of Defence) and so we
have to put up with anything and everything, including car alarm keyfobs
on 433.92 MHz as an example. We also only get 430-440 MHz rather than your
420-450.

Even in the 2m band (144-146 not 144-148 MHz..!), of which we are primary
users,we cannot claim protection from interference.

Ah well..!

73 Ivor G6URP

On Sat, 03 May 2008 07:57:45 -0400, Ivor Jones wrote:
Just perusing the ARRL letter on rec.radio.info and the lead story was
very interesting. It's about the ARRL objecting to the use of some 70cm

frequencies for a commercial event.

.....
Just goes to show how things are different in the US to here in the UK.
Over here we are only secondary users of the 70cm band (the primary use
r
of just about everything above 2m is the Ministry of Defence) and so we
have to put up with anything and everything, including car alarm keyfob
s
on 433.92 MHz as an example. We also only get 430-440 MHz rather than
your 420-450.

If I recall properly we're secondary to the military in
that band as well. Indeed, 70cm repeater operators are learning that the
hard way... as many repeaters are having to reduce power or even go QRT
at the request of our military, to protect a radar system.

But the motorsports folks have no regular authority in that band at all.

I'm not sure I understand why they thought they needed amateur spectrum
for that project.

Doug Smith W9WI wrote:
If I recall properly we're secondary to the military in
that [70cm] band as well. Indeed, 70cm repeater operators are learning that the
hard way... as many repeaters are having to reduce power or even go QRT
at the request of our military, to protect a radar system.

But the motorsports folks have no regular authority in that band at all.

I'm not sure I understand why they thought they needed amateur spectrum
for that project.



The Pave/Paws system that is pushing some repeaters off 70cm predates
the complaints by several decades, and I take the military's new
attitude to be another nail in the coffin of ham radio's former
"favorite son" status at the Pentagon.

It used to be that we hams were a corps of operators who could be
pressed into service quickly during a war or other crisis. Now, with
Morse as deeply buried as its creators and military electronics too
secret to be entrusted to soldiers and sailors who haven't been vetted
for security clearances, we're yesterday's news in the E ring.

We'll have to find another reason to justify the allocations we enjoy.
It's going to be hard work, and not nearly as easy as learning Morse
(not that that would help now). We're going to have to get better - in
fact, much better - at public relations: the Red Cross and other
disaster relief agencies have known the importance of image all along,
but now hams have got to get in the game and advertise ourselves as an
anlternative to traditional communications during hurricanes, floods,
earthquakes, etc.

Of course we've had this debate before. Older hams such as I feel that
we followed the program and did what was expected of us, and now I
resend being pushed aside in favor of a Federal Emergency Management
Agency which is, to my jaundiced eye, proficient only at promising what
others will have to deliver and claiming credit for what others have
done. It's a cold, cruel world, and we must get better at telling the
public and the their elected officials how much we do.

Bill

--
Bill Horne, W1AC

(Remove QRM from my address for direct replies.)

Anyone with some level of technical knowledge might wonder why a
billion dollar (boondoggle) "radar system" can't discriminate between
a fixed, known "target" (like a repeater)and one that is moving, comes
from over the horizon which might be something nasty?

Sounds like some real shoddy engineering took place at taxpayer
expense. I can think of 3 or 4 ways to remove false targets w/o
loosing any system level accuracy or sensitivity. In fact, didn't
they perfect that during the cold war?

Gee... Thinking about it some. All Abdulah (or Ivan or whoever)
needs to do is buy a 440 rig, an amp and a yagi and go out as a
"rover"; 3 or 4 kW ERP down the bear's craw for a while then move.

Sigh....


On Sat, 3 May 2008 23:16:09 EDT, Bill Horne wrote:

Doug Smith W9WI wrote:
If I recall properly we're secondary to the military in
that [70cm] band as well. Indeed, 70cm repeater operators are learning that the
hard way... as many repeaters are having to reduce power or even go QRT
at the request of our military, to protect a radar system.

But the motorsports folks have no regular authority in that band at all.

I'm not sure I understand why they thought they needed amateur spectrum
for that project.



The Pave/Paws system that is pushing some repeaters off 70cm predates
the complaints by several decades, and I take the military's new
attitude to be another nail in the coffin of ham radio's former
"favorite son" status at the Pentagon.

It used to be that we hams were a corps of operators who could be
pressed into service quickly during a war or other crisis. Now, with
Morse as deeply buried as its creators and military electronics too
secret to be entrusted to soldiers and sailors who haven't been vetted
for security clearances, we're yesterday's news in the E ring.

We'll have to find another reason to justify the allocations we enjoy.
It's going to be hard work, and not nearly as easy as learning Morse
(not that that would help now). We're going to have to get better - in
fact, much better - at public relations: the Red Cross and other
disaster relief agencies have known the importance of image all along,
but now hams have got to get in the game and advertise ourselves as an
anlternative to traditional communications during hurricanes, floods,
earthquakes, etc.

Of course we've had this debate before. Older hams such as I feel that
we followed the program and did what was expected of us, and now I
resend being pushed aside in favor of a Federal Emergency Management
Agency which is, to my jaundiced eye, proficient only at promising what
others will have to deliver and claiming credit for what others have
done. It's a cold, cruel world, and we must get better at telling the
public and the their elected officials how much we do.

Bill

In article ,
Bill Powell wrote:

Anyone with some level of technical knowledge might wonder why a
billion dollar (boondoggle) "radar system" can't discriminate between
a fixed, known "target" (like a repeater)and one that is moving, comes
from over the horizon which might be something nasty?

Sounds like some real shoddy engineering took place at taxpayer
expense. I can think of 3 or 4 ways to remove false targets w/o
loosing any system level accuracy or sensitivity. In fact, didn't
they perfect that during the cold war?

Take a look at this month's issue of CQ for a possible explanation of
the problem.

To sum it up briefly: PAVE PAWS is a phased-array radar system, with
a large number of individual turnstile antennas on each side. During
reception, the signals picked up by the various individual antennas
are combined electrically/electronically, in ways which cause them to
mix in-pase for signals coming from the desired direction and
out-of-phase for other directions.

Older-generation phased array antenna systems perform the phase
shifting by switching individual phase shifters (delay lines or
similar) in series with the feedlines from the individual antennas.
The delayed signals are then combined and detected. If you want to
point the beam in a different direction, you change all of the
phase-shifter delays.

The newer generation of phased-array radar systems actually digitizes
the incoming signal at each antenna, and then does the linear mixing
(addition/subtraction) entirely in the digital domain.

Why the change? I gather that it allows for both a finer degree of
control of the delays (allowing higher resolution in beam-pointing),
and also allows multiple different delay-and-combine operations to be
performed in parallel (just add banks of DSPs), allowing one to track
multiple targets simultanously.

The disadvantage of this new system (as stated in CQ): it has rather
less ability to reject off-axis signals than the older delay-line
method of phasing. In the delay-line system, off-axis interference
would tend mix out-of-phase *before* it was detected, and would
largely cancel out. In the new system, *every* individual antenna and
digitizer receives the interfering signal at full strength - there's
no phase cancellation in the analog domain.

This would leave the newer systems at a significant disadvantage with
regard to saturation and desensitization by strong off-axis signals.
It's not so much a question of false targets appearing, I think, but a
question of the system losing the ability to detect the real targets.
The digigal method of doing phase-shifting and beamforming is faster
and more precise than the switched-analog method, but apparently
somewhat less robust in this regard.

As Scotty said, "The more complicated they make the plumbing, the
easier it is to plug up the drains."

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Bill Powell wrote:
Anyone with some level of technical knowledge might wonder why a
billion dollar (boondoggle) "radar system" can't discriminate between
a fixed, known "target" (like a repeater)and one that is moving, comes
from over the horizon which might be something nasty?

Even weather radar can do that with drops of water. :-)
--
73, Cecil http://www.w5dxp.com

(Bill Powell) wrote in
:

Sounds like some real shoddy engineering took place at taxpayer
expense. I can think of 3 or 4 ways to remove false targets w/o
loosing any system level accuracy or sensitivity. In fact, didn't
they perfect that during the cold war?

If I was trying to do real-time analysis of such weak signals with the
goal of protecting the nation, I'd take advantage of every technical
and legal option available to me to limit or remove the potential for
interference from very strong local signal sources.

Do you also object to the "National Radio Quiet Zone" in West
Virginia?

--
Bert Hyman | St. Paul, MN |

On Mon, 5 May 2008 11:34:06 EDT, Bert Hyman wrote:

(Bill Powell) wrote in
:

Sounds like some real shoddy engineering took place at taxpayer
expense. I can think of 3 or 4 ways to remove false targets w/o
loosing any system level accuracy or sensitivity. In fact, didn't
they perfect that during the cold war?

If I was trying to do real-time analysis of such weak signals with the
goal of protecting the nation, I'd take advantage of every technical
and legal option available to me to limit or remove the potential for
interference from very strong local signal sources.
Technical for sure but it appears that even technology available to
the general public isn't in (effective) use.
A known and fixed "target" in ANY digital processing system is very
easily noted and then removed from the data stream.
Legal resources? Sounds like the typical "When all else fails, blame
the ham" excuse.

Do you also object to the "National Radio Quiet Zone" in West
Virginia?
Absolutely not! And, all a ham has to do there is to coordinate in
advance. They have MANY issues with RFI from non-ham sources to
contend with there.
Wonder if PAVEPAWS is going to start shutting down microwave ovens and
wireless dog fences next? :-)

Bp
PS - No complaints w/ the government entity but w/ the contractor(s).

On May 4, 11:13 pm, Bill Powell wrote:
Anyone with some level of technical knowledge might wonder why a
billion dollar (boondoggle) "radar system" can't discriminate between
a fixed, known "target" (like a repeater)and one that is moving, comes
from over the horizon which might be something nasty?

I think the radar system can indeed discriminate. One problem, I
think, may be this:

Radar that uses a single antenna for both transmit and receive cannot
"see behind" a
reflecting obstacle, nor an interfering RF source. So the amateur
repeater casts a "shadow"
as it were.

To make it more of a sporting course, the amateur signal is
intermittent, and FM. Which may look
like all kinds of things on the radar display.


Sounds like some real shoddy engineering took place at taxpayer
expense.

Maybe, but probably not. Some things are fundamental limitations of
the physics involved.

I can think of 3 or 4 ways to remove false targets w/o
loosing any system level accuracy or sensitivity. In fact, didn't
they perfect that during the cold war?

Of course the processing system may be able to be programmed to ignore
the amateur repeater - which would make it the perfect place to hide
something.

Remember that the radar system in question is probably being used in
roles it was not originally designed for. That's probably why the
problem didn't show up before. For example, if the radar was meant to
look for high-altitude intruders, things like ground clutter and RF
sources below a few hundred feet could simply be ignored. If the
system is now being adapted to look for low-altitude and water-bourne
intruders, those RF sources become a big headache that the system
wasn't designed to handle.

Gee... Thinking about it some. All Abdulah (or Ivan or whoever)
needs to do is buy a 440 rig, an amp and a yagi and go out as a
"rover"; 3 or 4 kW ERP down the bear's craw for a while then move.

Maybe. But the result would probably be just the opposite: firing up
that setup would announce his exact bearing and altitude. IOW,
announcing "HERE I AM" to the radar system. With no legitimate sources
of RF in the area, and no "shadows" to hide behind, finding the
intruder would be easier and faster.

This sort of thing isn't new. When you don't know the exact threat,
you try to plug every possible hole.

Way back in WW2, the Allies spent a lot of time and expense developing
receivers that had extremely low local-oscillator radiation. Only
approved receivers could be used aboard Allied vessels. The concern
was that enemy U-boats could detect and find Allied convoys by
listening for the local-oscillator radiation. When you have dozens of
ships all monitoring the same frequency using big antennas and
unshielded receivers, the total LO radiation could be heard a long way
off. And while radio silence could be maintained in a convoy most of
the time, the receivers were needed for weather reports, U-boat
warnings, distress calls and such.

It turned out that the U-boats did not listen for the LO radiation
after all. But this was not known until after the war.

73 de Jim, N2EY

On Tue, 6 May 2008 14:03:17 EDT, wrote:

Remember that the radar system in question is probably being used in
roles it was not originally designed for. That's probably why the
problem didn't show up before.

I haven't chimed in because I had a foot on both camps, so to speak.
The problem is not new, and was handled on a case-by-case basis until
it became a "real big" problem when the system was upgraded. Most if
not all of the ham repeaters which fall in the "circle of interest"
for the Beale AFB site were in my District (San Francisco) and I
knew/know several of the repeater owners personally.

A practical example of the problem in the non-military world: One
would have problems using the usual consumer type in-line cable
amplified splitter with a VHF/UHF receiver such as a scanner because
the receiver deals in signals of the order of 0.5 uV or less while the
amplifier is designed to deal with signals in the order of 1 mV or
more and consequently the noise floor is much higher.

Whether the contractor(s) designing the system and/or running the
tests are competent or not is an exercise left for the reader.
--

73 de K2ASP - Phil Kane

From a Clearing in the Silicon Forest
Beaverton (Washington County) Oregon

e-mail: k2asp [at] arrl [dot] net