The Collapse of Puerto Rico’s Iconic Telescope [April 5th, 2021 New Yorker]
Hi Jim,
On 2021-03-31 01:33, Lux, Jim wrote:
On 3/30/21 2:56 PM, Wes wrote:
You would know better than I, but I was thinking of physical size;
100m v. 70m.
Obviously a BIG difference in TX power.
Wes
It's all about EIRP, baby.
I know they're talking about half a megawatt for GB, but I don't see
it happening. They've spent so much time making it "radio quiet",
putting a big honkin transmitter there seems odd. Just think, a
return loss from the feed of -30dB (which is pretty good) is good
fraction of a kilowatt.
Multiple directional couplers to get rid of the energy might help, but
when you are at that level you are pretty well matched anyway.
I think a phased array of some sort is more likely (both for Tx and
Rx) - the cost of RF parts has come down a lot, and, as we on this
list know, phasing them all up to a fraction of a gnats eyelash is
doable. Fiber optics are cheap. And you can form multiple beams
simultaneously (the LEDA correlator at OVRO-LWA forms hundreds of beams).
Yeah, well, there is another thing that bites you, phase stability and
phase control. I've seen the specs of such a baby, and you need to play
a few tricks and have multiple feed back points. It is doable. You gain
some and you loose some. Phased array is for sure the modern approach on
things. Technology have advanced so it's not too hard, but you want to
have a fair amount of self alignment capabilities.
What is a challenge (and hasn't really been solved) is how to do
cryogenic feeds in mass production. DSN looked at building an array
of 100 receivers, and nobody would sign up to delivering 100
cryocoolers that would have sufficient MTBF. But transmitting -
that's easy.
In that case the request was not aligned with what industry could
deliver. Sounds like there is room for an advancement program to push
the capability of the industry, so requests like that can be made. Then
that faces challenges to have large enough volume to have multiple
vendor being able to bid on it, and make sure multiple vendors do get bids.
Cheers,
Magnus
Jim, how large is the Goldstone antenna to which you referred?
Dana
On Tue, Mar 30, 2021 at 4:01 PM Lux, Jim jim@luxfamily.com wrote:
On 3/30/21 6:40 AM, Wes wrote:
Was a pity. China's FAST is receive only. I believe that leaves
Green Bank as the biggest transmitting telescope.
More likely the Goldstone Solar System Radar function of DSN on the 70m
(DSS-14) - 500kW in X band at 8560 MHz
There is a new transmitter for GB - but it's a demo - 700 W and
temporarily installed up at the feed for a test. I don't know what
frequency. People are pitching a 500kW system, but we shall see.
I remember 417s. I had them in a copy of a design by W2AZL. I also
had a two-meter preamp I designed using 416Bs. Of course uW cooled
preamps are not unusual now, but back then a blower on a receive
amplifier was unusual :-)
Wes Stewart N7WS
On 3/30/2021 4:06 AM, ew via time-nuts wrote:
GOOD Morning Tom Thank you for the super information Read it over
and over. To me no joy, sadness for Astronomy, Science, Puerto Rico
and the US. China is now the leader with a 500 meter unit! Did follow
it since the seventies because of the low noise receivers. Remember
the 417 Triodes? I had some for Ham use.
Any body knows what happened to its Maser?
Bert Kehren
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On 3/30/21 5:42 PM, Magnus Danielson wrote:
What is a challenge (and hasn't really been solved) is how to do
cryogenic feeds in mass production. DSN looked at building an array
of 100 receivers, and nobody would sign up to delivering 100
cryocoolers that would have sufficient MTBF. But transmitting -
that's easy.
In that case the request was not aligned with what industry could
deliver. Sounds like there is room for an advancement program to push
the capability of the industry, so requests like that can be made. Then
that faces challenges to have large enough volume to have multiple
vendor being able to bid on it, and make sure multiple vendors do get bids.
They did all that. Got some prototypes. Cryocoolers of that size are
sort of a specialized thing, apparently. It's probably in some
technical reports from about 15 years ago. JPL did a bunch of
experiments - we temporarily had a couple of 6m and a 12m dish installed
on lab, and I think there was one down on Caltech campus.
Here's a presentation from Sandy Weinreb
https://descanso.jpl.nasa.gov/seminars/abstracts/viewgraphs/DSN_array_dev_program.pdf
and one from Joe Statman
https://descanso.jpl.nasa.gov/seminars/abstracts/viewgraphs/DSAN_040729.pdf
If you read them, note the dates for the missions - JWST, Lunar Hab, etc.
On 3/30/21 5:58 PM, Dana Whitlow wrote:
Jim, how large is the Goldstone antenna to which you referred?
70 meters.
They do bistatic radar with Tx at Goldstone and Rx at Green Bank (and
Arecibo, when it was live).
What Arecibo had was a monster UHF transmitter (420 MHz) - DSN has big
S-band and X-band transmitters.
The Solar System Radar is a lesser known aspect of the Deep Space
Network. But that's how we knew about Venus's rotation period, etc.
Dana
On Tue, Mar 30, 2021 at 4:01 PM Lux, Jim jim@luxfamily.com wrote:
On 3/30/21 6:40 AM, Wes wrote:
Was a pity. China's FAST is receive only. I believe that leaves
Green Bank as the biggest transmitting telescope.
More likely the Goldstone Solar System Radar function of DSN on the 70m
(DSS-14) - 500kW in X band at 8560 MHz
There is a new transmitter for GB - but it's a demo - 700 W and
temporarily installed up at the feed for a test. I don't know what
frequency. People are pitching a 500kW system, but we shall see.
I remember 417s. I had them in a copy of a design by W2AZL. I also
had a two-meter preamp I designed using 416Bs. Of course uW cooled
preamps are not unusual now, but back then a blower on a receive
amplifier was unusual :-)
Wes Stewart N7WS
On 3/30/2021 4:06 AM, ew via time-nuts wrote:
GOOD Morning Tom Thank you for the super information Read it over
and over. To me no joy, sadness for Astronomy, Science, Puerto Rico
and the US. China is now the leader with a 500 meter unit! Did follow
it since the seventies because of the low noise receivers. Remember
the 417 Triodes? I had some for Ham use.
Any body knows what happened to its Maser?
Bert Kehren
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe
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On 3/30/2021 4:33 PM, Lux, Jim wrote:
On 3/30/21 2:56 PM, Wes wrote:
You would know better than I, but I was thinking of physical size; 100m v. 70m.
Obviously a BIG difference in TX power.
Wes
It's all about EIRP, baby.
I know they're talking about half a megawatt for GB, but I don't see it
happening. They've spent so much time making it "radio quiet", putting a big
honkin transmitter there seems odd. Just think, a return loss from the feed
of -30dB (which is pretty good) is good fraction of a kilowatt.
But AFAIK the system is bistatic (pseudo-monostatic) so there's no local
receiver to be subjected to transmitter leakage. We worried about leakage in
the pulse doppler radars I'm familiar with; AMRAAM and Phoenix missiles, but
even they were bistatic for most of their flights, tracking off the aircraft
fire control radar which had significantly higher ERP. Only when close to the
targets did they go active.
Wes
RX up here at Green Bank
Lester B Veenstra K1YCM MØYCM W8YCM 6Y6Y
lester@veenstras.com
452 Stable Ln (HC84 RFD USPS Mail)
Keyser WV 26726
-----Original Message-----
From: Wes [mailto:wes@triconet.org]
Sent: Wednesday, March 31, 2021 2:34 PM
To: time-nuts@lists.febo.com
Subject: [time-nuts] Re: The Collapse of Puerto Rico’s Iconic Telescope [April 5th, 2021 New Yorker]
On 3/30/2021 4:33 PM, Lux, Jim wrote:
On 3/30/21 2:56 PM, Wes wrote:
You would know better than I, but I was thinking of physical size; 100m v. 70m.
Obviously a BIG difference in TX power.
Wes
It's all about EIRP, baby.
I know they're talking about half a megawatt for GB, but I don't see it
happening. They've spent so much time making it "radio quiet", putting a big
honkin transmitter there seems odd. Just think, a return loss from the feed
of -30dB (which is pretty good) is good fraction of a kilowatt.
But AFAIK the system is bistatic (pseudo-monostatic) so there's no local
receiver to be subjected to transmitter leakage. We worried about leakage in
the pulse doppler radars I'm familiar with; AMRAAM and Phoenix missiles, but
even they were bistatic for most of their flights, tracking off the aircraft
fire control radar which had significantly higher ERP. Only when close to the
targets did they go active.
Wes
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To unsubscribe, go to and follow the instructions there.
On 3/31/21 11:33 AM, Wes wrote:
On 3/30/2021 4:33 PM, Lux, Jim wrote:
On 3/30/21 2:56 PM, Wes wrote:
You would know better than I, but I was thinking of physical size;
100m v. 70m.
Obviously a BIG difference in TX power.
Wes
It's all about EIRP, baby.
I know they're talking about half a megawatt for GB, but I don't see
it happening. They've spent so much time making it "radio quiet",
putting a big honkin transmitter there seems odd. Just think, a
return loss from the feed of -30dB (which is pretty good) is good
fraction of a kilowatt.
But AFAIK the system is bistatic (pseudo-monostatic) so there's no
local receiver to be subjected to transmitter leakage. We worried
about leakage in the pulse doppler radars I'm familiar with; AMRAAM
and Phoenix missiles, but even they were bistatic for most of their
flights, tracking off the aircraft fire control radar which had
significantly higher ERP. Only when close to the targets did they go
active.
In the airborne radar environment, typically the other receivers already
are designed to take a fairly high signal without damage (after all, you
get painted by someone else's radar). They may have a limiter on the
input (there are low capacitance back to back schottky diodes for this),
and you accept the loss in signal or raised noise floor from the
protection circuit
But for radio astronomy, they don't want to give up anything - these
receivers have noise temperatures in single digit K and they are
optimized for "small signal" performance.
All those wideband cryogenic receivers for other frequencies are what
people would be nervous about. There are other receivers at GB, not on
the 100m GBT, too. You'd worry about a stray reflection from some
structural member shooting a few hundred watts toward your sensitive
radiometer which burns out at femtowatts or something like that. The
feed would be designed with some illumination taper, so there's still
going to be spillover and scattering. If the taper is -17dB, the power
density at the edge of the aperture is down 17 dB from the center.
100m is about 7800 square meters, so the average power density with a
500 kW transmitter is about 63 W/square meter. That's a pretty big power
density.
http://www.naic.edu/~astro/sdss5/talks/ReceiverSystem.pdf
In some ways it's like high power laser labs. It's not the direct beam
you worry about - nobody is going to put their hand in the beam path.
It's the stray reflection when something gets bumped and falls across
the optical bench and reflects a stray beam at 0.01% power into your eyes.
On 3/31/2021 11:57 AM, Lux, Jim wrote:
In some ways it's like high power laser labs. It's not the direct beam
you worry about - nobody is going to put their hand in the beam path.
It's the stray reflection when something gets bumped and falls across
the optical bench and reflects a stray beam at 0.01% power into your eyes.
I did consulting at Coherent Laser Group working on CO2 lasers.
In that lab, actually, many people had the misfortune of accidentally
putting their hand or arm in the invisible beam. You could see the
scars on their arms. There were also accidents where the laser
burned the ceiling, etc. Very scary place to work; fortunately,
I never got injured. They made lasers up to 1kW optical power out.
Rick N6RK
During my days at UTC I was among other things responsible for our Industrial Laser Group. We sold some 50 KW CW CO2 lasers! We had the only aero dynamic window that allowed a vacuum on one side. When not in use you put a pencil through it. Patented. Bert Kehren In a message dated 3/31/2021 3:17:21 PM Eastern Standard Time, richard@karlquist.com writes:
On 3/31/2021 11:57 AM, Lux, Jim wrote:
In some ways it's like high power laser labs. It's not the direct beam
you worry about - nobody is going to put their hand in the beam path.
It's the stray reflection when something gets bumped and falls across
the optical bench and reflects a stray beam at 0.01% power into your eyes.
I did consulting at Coherent Laser Group working on CO2 lasers.
In that lab, actually, many people had the misfortune of accidentally
putting their hand or arm in the invisible beam. You could see the
scars on their arms. There were also accidents where the laser
burned the ceiling, etc. Very scary place to work; fortunately,
I never got injured. They made lasers up to 1kW optical power out.
Rick N6RK
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
I have not yet heard what GB wants to do, but if it's long range work
(return time of
10's of sec or longer), the problems related to T/R switching, Tn
degradation of the
receiver, etc, get a lot more tractable than one might suppose.
At Arecibo, the S-band radar was intended solely for long range work. A
big part ot
T/R switching was to use separate (optimized) feeds for transmitting and
receiving,
and swap feeds during turnaround. The receive feed was covered by a
carefully-
fitted sliding cover during transmit times, which provided excellent
isolation. There
was a microswitch to sense cover position and which would block
transmission if
it was not satisfied.
Feed horn turnaround time was about 7 seconds as I recall.
The transmitter was basically operated CW, and the "imaging" technique was
"range-
Doppler". So, the transmitter was run for slightly under the round-trip
travel time, then
feed turnaround was initiated, timed to finish shortly before the leading
edge of the
return was expected. The receiver would do its thing for the duration of
the return.
Note that it was also necessary to completely shut down the beam current of
the
transmit Klystrons during receive so that shot noise on the beam did not
spoil the
receiver's noise temperature. After the receive interval was finished, the
feeds were
again swapped and a new cycle was started. During each transmit period the
crew of scientists would have time for a preliminary look at the
just-recorded data
to see if anything was going wrong.
OTOH, Arecibo's 430 MHz ISR for ionospheric studies clearly had to have
almost
instantaneous turnaround time, and arrangements were rather more complicated
(more so than I can take time to describe at the moment). But they worked
well,
and loss in the receive state of some big PIN switches in the path was
tolerably low.
The first 35-40 dB of TX-RX isolation came from use of a "turnstile
junction", with
the remainder coming from the PIN switches.
For both radars, the non-participating receivers would also be covered, but
with
a simpler flap arrangement, some powered by small DC motors and some by
small pneumatic cylinders.
Dana
(retired from Arecibo Dec 2016)
On Wed, Mar 31, 2021 at 2:30 PM ew via time-nuts time-nuts@lists.febo.com
wrote:
During my days at UTC I was among other things responsible for our
Industrial Laser Group. We sold some 50 KW CW CO2 lasers! We had the only
aero dynamic window that allowed a vacuum on one side. When not in use you
put a pencil through it. Patented.
Bert Kehren In a message dated 3/31/2021 3:17:21 PM
Eastern Standard Time, richard@karlquist.com writes:
On 3/31/2021 11:57 AM, Lux, Jim wrote:
In some ways it's like high power laser labs. It's not the direct beam
you worry about - nobody is going to put their hand in the beam path.
It's the stray reflection when something gets bumped and falls across
the optical bench and reflects a stray beam at 0.01% power into your
eyes.
I did consulting at Coherent Laser Group working on CO2 lasers.
In that lab, actually, many people had the misfortune of accidentally
putting their hand or arm in the invisible beam. You could see the
scars on their arms. There were also accidents where the laser
burned the ceiling, etc. Very scary place to work; fortunately,
I never got injured. They made lasers up to 1kW optical power out.
Rick N6RK
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.
time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send
an email to time-nuts-leave@lists.febo.com
To unsubscribe, go to and follow the instructions there.