@uhoh I'm on, let me know when you are there.

@TomSpilker here!

Great! OK, stories about the Stanford Radar Telescope. The transmitter on that telescope couple put out 300 kW as designed, and with some modification could put out 450 kW for short periods. For one experiment, after all the data was recorded (after tracking Venus for nearly two hours, the data reduction revealed the SNR was still too low.

They decided to start earlier in the morning, with Venus lower on the horizon, to give a longer integration. The morning of the first run, the receivers at the control tower at Hayward airport blew out!

That happened every morning for a week, before someone figured out that Hayward was in one of the dish's side lobes! Once they (Stanford) stopped transmitting so close to the horizon, Hayward's problem disappeard.

Holy granola!

Roughly when was this?

1950's? 1960's? 1970's?

Early 1970's, I think. Von Eshleman and Len Tyler told me about it. Both were private pilots.

When first built, the line from the transmitter building to the antenna was an above-ground "balanced line", so two conductors (hefty ones) held a fixed distance apart. But when they started using it at full power, when anything like a bird or a really big bug would fly between the conductors it would trigger arcing between the conductors.

yikes!

Somewhere I have a photo Len gave me, showing such an arc. The lines were about 3' apart, and the arc must have extended 6' above them, a big horseshoe.

This is a private research facility, so not really like a DOE or NSF lab where there are layers of regulation?

When that happened, the arcing made rough spots on the conductors, often with sharp points of melted conductor material (copper). If you tried to start up again without sanding down the lines, the E field concentration around those sharp points made it start arcing again, immediately.

Yes I can imagine that. One big. RF-powered Jacob's Ladder wanna-be.

Air heated from the corona will start to float upwards, so when there's a breakdown it will rise up.

Back then there were fewer regulations. Since the facility was NASA- and NSF-funded they probably had whatever layers there were at the time. I'm sure that now the balanced-line approach would be quickly nixed. After a couple of months of such mess they redesigned the feed, using a coaxial system, all E field contained internally.

Yep, just like the behavior of a Jacob's Ladder.

I'm guessing the FCC got interested at some point as well. ;-)

The coaxial system had an outer conductor diameter of about 30-40 cm, so the internal fields were pretty strong. Because it was enclosed, they needed to circulate water between the inner and outer conductors as a coolant. Because the E fields were so strong, they had to super-distill all the water they used.

Yep, they had to apply for a license from the FCC, and get some waivers.

especially interested after the airport incident.

Was this a solid dielectric coaxial line or air, or high pressure SF6? (like some Tandem accelerators)

You can imagine the electric power that went into this device. A hundreds or so amps on tens of thousands of volts! Every now and then they popped the circuit breakers, which at those power levels sounds like a cannon. The engineering manager in the early days was Lon Raley, a tall and big man. He was once right in front of the breaker cage when they fired, and he spilled hot coffee all down the front of his nice white shirt.

The water served as the dielectric.

Wow! Pure water has a dielectric constant of something like 6 or 8 for RF (only 1.33 for optical) At least at lower frequencies.

Roughy what frequency was this? Maybe a few hundred MHz?

Yep! Hence the need for extreme purity. And yep! Hundreds of MHz. If my memory serves me well, ~300 MHz was their upper limit.

What was receiving the signal? The same dish, or another station?

Right now we're talking about radar observations of Venus, not the Mariner occultations, right?

The main road up there went about 100 m to the SE of the antenna. There was a short spur that went from the main road up to the gate to the antenna, with a cattle guard about 10-15 m from the main road, maybe 4 m wide (distance along the road). When I would run the dish I would run up to that gate, then on the way down jump over the cattle guard!

Ha! Cattle guard is a fence, or one of those flat grates with lots of holes that spook the cattle, but cars can drive over?

Signal received at the same dish. Originally they would transmit until the reflected signal was about to arrive, and they would shut down the transmitter to receive. But they saw that the Doppler shifts were large enough that they could simultaneously transmit and receive, and that allowed longer integrations.

The cattle guard was a flat array of study metal pipes, perpendicular to the road's axis, spaced maybe 9-10" apart and as wide as the road. The spur went uphill to the gate, so I wasn't about to try to jump the guard going uphill!

Oops, the should be "sturdy metal pipes".

The only time I've seen cattle guards is driving between So. California and the East or Midwest. Some of the interstate off-ramps have them.

Yes, these are radar observations, not the Mariner 5 radio occultation.

The first time I saw one I had no idea what it was - completely baffled

Yep, I was too. Although both of my parents grew up on farms, I was always a city kid.

I see 3 or 6 km/sec doppler is 1 or 2E-05 shift. Still, that needs quite a high Q in addition to a very nicely built directional coupler.

This must have been really exciting to be around!

Yes indeed! It was really great that the whole team, both engineers and scientists, were part of the Electrical Engineering department at Stanford. They pulled off some very difficult implementations. Not all of them worked quite as anticipated, such as the balanced line.

Unfortunately I arrived after the primary investigations had already been done. They'd quit using the 300 kW transmitter. Reduced staff made the room for my lab in the transmitter building. Fortunately, with access to a Fully Equipped machine shop!

I need to get some dinner, but this has been fun!

Yes, thanks for taking the time, and "taking me back there", I really enjoyed this!

Good evening

@TomSpilker, @uhoh - this was utterly fascinating to read; seems a real shame that in the way of all things chat it shall disappear in a few months. Certainly doesn't belong in the original Venus question, but can it be captured in a useful way? Maybe a self-answered catspaw question, something like "How did the Stanford Radio Telescope operate at high power levels and what problems arose?". Arguably more of an Astronomy or Engineering SE topic.

@geoffc Thanks @geoffc for that video [Zubrin, 21st Annual International Mars Society Convention] - I just watched and loved it :)

@BlueCoder He is very amusing to watch present