Electromagnetic Videos

More "Mirrors"! Visited the Dominion Radio Astrophysical Observatory in the British Columbia interior on Saturday when they had an open house. It is quite a renowned radio observatory and pioneered very long baseline interferometry.

More recently it has become known for detecting "fast radio bursts" with CHIME, the cylindrical shaped reflector telescopes you can see on the right of the 2nd photo which can scan large sections of the sky at once.

On the left of the 2nd photo you can see beginnings of an array of 512 (!) dish telescopes currently being assembled. The rusty poles in ground are the mounting posts for the new dishes as they are brought in from the on-site manufacturing building shown in the last photo. This amazing array of telescope will continue the work of CHIME.

I have an indirect connection to this observatory: my PhD supervisor and dear friend, Dr George Aitken (sadly no longer with us), was part of the expedition in the late 1950s that found this ideal site for the observatory. He was a undergrad student at the time and told me the story of how they loaded up a bunch of old military trucks with radio gear and had a wonderful time exploring the interior of BC one summer, looking for a radio quiet valley that was also within reasonable range of a nearby town or city. And what a perfect site they found - surrounded by uninhabited hills with a nice fairly flat area in the middle. George went to do signal processing first for radio telescopes and later for optical. Perhaps his greatest legacy is the use of AI to adaptively pre-deform optical telescope mirrors to undo the effects of atmospheric turbulence that makes the stars twinkle and smear images. Demonstrating that it was possible to do this over 25 years ago (before he retired), only recently has AI processing become fast enough (with GPUs) go actually deform the mirrors in real time and much further developed versions of those original ideas are being implemented today in new and existing telescopes.

Here is the link for the observatory’s Wikipedia page: en.wikipedia.org/wiki/Dominion_Radio_Astrophysical…. Well worth a visit if your visiting the (beautiful) BC interior, particularly if they are having an open house.

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5 days ago | [YT] | 32

Electromagnetic Videos

Took this photo yesterday - if you visit Vancouver don’t miss this bit of electromagnetic history. on the corner of corner of Kingsway and Boundary Road (www.google.com/maps/place/49%C2%B013'56.1%22N+123%…) .

These classic telephone microwave link horn-reflectors are on top of the old phone company building, disconnected long ago but still intact. Apparently they linked to Salt Spring Island / and Vancouver Island, to Washington State to connect with the AT&T Long Lines network, and toward Chilliwack and the Trans-Canada Microwave link.

The sloping top of the horns are the parabolic microwave reflectors to create a nice uniform beam to the next tower. These reflectors are mirrors - and work exactly like the mirror in this recent videohttps://youtu.be/ntV3lXuv3Y0 . Like satellite dishes, the parabolic shape focuses the beam.

At the bottom of the horn on the right you can see what looks like a cut-off piece of pipe - an it is - a microwave waveguide - which would have gone to the amplifiers down below. Its like a metallic piece of optical fibre. Or a coax with the center wire removed. Waveguides are still very much in use. The coax with the shield removed is the opposite of this - a Goubau line as in this video https://youtu.be/it5UMt0lL8I

1 week ago | [YT] | 1

Electromagnetic Videos

Goubau Line use today!

If you saw the Goubau Line video ( https://youtu.be/it5UMt0lL8I ) you might find this interesting:

Below is a photo of a Goubau Line sent to me by Paul Volz at BESSY II, a synchrotron light source in Berlin. He uses it as part of his work optimising devices used in the synchrotron light source. Neat to see how perfectly built it is compared to my crude one. Note that he only has one cone because he uses refections (Time Domain Reflectometry )from the far end for his measurements.

1 week ago | [YT] | 0

Electromagnetic Videos

@rfengr00 posted in the Goubau Line video's comments about doing a simulation of a bent Goubau a few years ago. Here is a link to a short video of the simulation https://www.youtube.com/watch?v=oFHKd...

1 month ago | [YT] | 78

Electromagnetic Videos

There was so much interest in the Goubau Line video I thought some of you might be interested in a good textbook on electromagnetics - how electric and magnetic fields intertwine to make things like EM waves - light, radio waves etc, and how they travel in and around wires and cables like Goubau lines or coax, or inside structures like fiber optics/waveguides.

Probably the most iconic textbook on the subject (and one I would highly recommend) is John D. Kraus "Electromagnetics". Kraus was a real engineer and his book combines theory with practical applications. However, be warned - you need to know vector calculus (not just just basic first year calculus) to understand this or any other book on electromagnetics.

The scan below is from my well worn copy (3rd edition) that I have had since I was a student. Newer editions are available that include more recent things like fiber optics and microstrip antennas that we find in cell phones. The core theory is all the same - I would suggest a used older edition (like the one have) for $25 or so - newly printed current edition books are generally in the $100+ range.

And I should add - in the 3rd edition in the photo - see page 588 and 589 for Goubau lines.

1 month ago (edited) | [YT] | 130

Electromagnetic Videos

GIT DOWNLOADING issues for

“Electricity Doesn't Actually Need a Return Wire” (the Goubau Line video)

Some of you are having trouble downloading the documents I posted on git. Here is what works for me.

1) After clicking on the link to the git repository I provided, click on the name of the file you want to download.

2) Then click on the download icon. Once your browser has downloaded the file use whatever pdf viewer you normally use or a browser to view the document.

Let me know if this works! If you have a suggestion of a better place to dump files like this let me know!

Below are a few images showing the steps:

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1 month ago | [YT] | 32

Electromagnetic Videos

VIDEO TAPE DUPLICATION in the VHS and Beta days

Viewer Dan Tibi who has beein in the TV business for years was kind enough to answer my question, one that a number of you have asked me.

MY QUESTION TO DAN: I have heard there was a method of
duplicating tapes by making a master tape with higher than normal
coercivity material and then running it though a machine bringing it in
close contact with the normal coercivity blank tape and the magnetic
pattern would transfer in a fairly simple process. It certainly makes
sense from a magnetic theory standpoint, but I can see a lot of things
that might make it hard to do in practice like just getting enough
magnetization transferred to the blank tape. Have you ever come across
that method of duplicating tapes?

DAN'S RESPONSE Duplication using actual VCRs:

Yes they did have the machines hooked up by remote. It was unbelievable what they did. So the machines were in blocks of 720 machines. I have no idea why they picked that number and I always thought it was a bizarre number. So there was 1 person for those 720 machines. All of the machines had auto loaders so that person would make sure all of the machines were loaded and they would collect all of the completed tapes. When anything was ready they would flip a light switch to a light that was above their section. Kind of like the light above a cash register at a supermarket to let people know that register is open. Then there was a tape operator on the head end side that played the master back. They would look out and make sure all of the sections that needed to record were ready. They may had only one bank of machines to all of them. Once they knew all the machines were loaded and ready to record they would start the playback of the master 1" tape and then put the VHS machines into record. They told me when they put all 10,000 machines into record at the same time that they could actually feel the building move. It was rare they would use all the machines for just one title. Like when I was there they were running 3 different movies at the same time. I don't know how they determined what the brake down of how they would run each job. After the dub was completed all 720 tapes from that section were taken to QC and 719 of them were spot checked and one random one from that section was 100% QC'd to ensure that pass was good before distribution.

DAN'S RESPONSE Duplication using DOUBLE SPEED VCRs and DIRECT MAGNETIC Transfer:


So they had 3 different types of duplication at that facility. The above was a huge portion of there operation but they also had a 1" B format machine that was modified to playback at double speed. That feed machines that would record at double speed but they would play back normal at home in a normal VHS VCR. They were looking for ways that they could be more efficient and make more money in the same period of time. And the best version of that was what you were asking about. Sony made that device and it was called a sprinter. The master was on a loop of tape that was pulled through and rubbed up against the raw stock and the dub was made. In that version they used a huge pancake of stock and let it fly. When the pancake ran out of tape it was moved to a different location in the facility and they would load the VHS cassettes. Since the pancake was a very long piece of tape with many, many recordings of the movie on it they recorded a tone after the movie so the machine would know where to stop the pancake so they could cut the tape and add the leader to the cassette. It was a pretty amazing thing that they could do. So if you ever watch a VHS tape all the way to the end after the end of program and you hear a 1k tone that meant it was copied on a sprinter.

The few hours that I was there were pretty incredible. I got to see the side that so few people even know about. It was so cool when I first got there and saw one of my tapes on one of their machines playing and I said to a tape operator there that I made that tape. We put stickers on the reels that had the playback machine number the record machine number the horizontal blanking and the vertical blanking and our initials. His response was we always wondered who DT was. Then when they showed me their vault it was mind blowing how many tapes were made by me.

Another thing that was crazy about the normal speed duplication was that every tape they made had a barcode on it and it had a lot of information including what VHS machine it was recorded in. So when the people putting the blank tapes into the auto loaders they had to make sure they put the correct tape into the correct machine. Also the blank stock was loaded to the length needed for that movie. It wasn't just a 120 loaded for every movie. They loaded each cassette with the proper amount of stock. That way they could squeak out a little more profit. It's a trip that a couple of cents really adds up when they are making millions of tapes.

Something I always that was interesting was that they didn't bill the studios per copy but instead they billed them for time like satellite time.

TWO LINKS about DIRECT MAGNETIC Transfer I found after readind Dan's email:

homevideo.wikitide.org/wiki/Sony_Sprinter
www.otari.com/support/vintage/t710/index.html

4 months ago | [YT] | 11

Electromagnetic Videos

Drop Frame Timecodes in NTSC

Viewer @Andrew-ep4kw was kind enough to post areally nice explanation of Drop Frame Timecodes often used with NTSC in th ediscussion for this video "29.97 frames per second for video - why not 30?" https://youtu.be/VOl0Bi2G9U0 . Thanks Andrew! Here it is:

A consequence of the 29.97 frame rate is that standard SMPTE time code needed to be modified. SMPTE time code is a system than numbers each frame with an 8 digit number formatted as HH:MM:SS:FF. For example a frame has a number of 01:10:20:00, which meant that it was 10 minutes and 20 seconds into program, assuming it started at 01:00:00:00. You could time out a TV show by using SMPTE time code. The problem was, 29.97 footage did not have an even number of frames per second, and timecode needs that to be accurate.


The solution was the same that was used to make the calendar accurate. Just like we have an extra day added every 4 years to keep the calendar in line with the seasons, engineers skipped 2 frames at the top of every minute to make up for the lower frame rate. They called it drop frame timecode. So, going past a minute on regular timecode would be 1:00:59:29 to 1:01:00:00. The same sequence in drop frame would be 1;00;59;29 to 1;:01;00;02. Skipping two frames in the numbering sequence means the duration indicated by timecode matches the actual playback time, despite the slower frame rate.


Standard timecode is still used for short content where the frame rate mismatch doesn't compound into a timing error. So, things like commercials and promos were typically standard timecode while longer things like TV shows were always drop frame. The way to tell the difference is standard TC always uses colons, such as 1:00:00:00 while drop frame uses semi-colons like 1;00;00;00.

5 months ago | [YT] | 6

Electromagnetic Videos

NTSC - some fascinating insight from Patrick Bryant in response to "How we slowed down electricity to create Color TV"

Patrick's comment:

Retired video engineer here (ABC and CNN): This is an excellent description! We engineers, back then, nicknamed NTSC "Never Twice the Same Color."

The biggest problem with transmitting NTSC was differential gain and phase (changes in amplitude and phase between black and white scenes). Differences in gain caused an inaccurate saturation of colors, and differences in phase caused hues to be inaccurate. People perceived changes in hues to be much more objectionable. For example, a deeply red dress appearing slightly pastel red (reduced saturation) due to differential gain was much less objectionable than a red dress appearing purple due to differential phase. Faces often turned green when moving between dark to light scenes.

The Europeans developed color TV later and had the luxury of improving on the US system, and used Phase Alternating Line (PAL) that averaged out the differential phase errors. The French decided to use SECAM (Séquentiel couleur à mémoire / Sequential Colour with Memory) which we American engineers nicknamed the "System Essentially Contrary to the American Method," and transmitted the color information in FM instead of AM to also compensate for differential gain. Once an American viewer got over the apparent flicker of 50 hertz video fields, as opposed to American 60 (59.94) hertz field rates, PAL and SECAM looked much better than NTSC. The hazard of being first.

Peter's response:

Thanks so much times two - once for the kind words and and once for answering a question I always wondered about - namely what was the dominant cause of phase errors in NTSC.

So if I understood correctly (let me know if didnt) the amplitude of the black and white signal had the effect of slightly shifting the chroma phase as it passed though amps in the signal path. If thats the case I'm even more intrigued as to what might have caused that effect. All that I can think of at the moment is the slight changes in semiconductor junction capacitance as the voltage across a junction rises and falls a exploited in varactor diode. That wouldnt explain the issue happening in tube amps. So what am I missing? NTSC/PAL/SECAM - as a kid I experienced all three - NTSC in Canada, PAL in (West) Germany, and SECAM in Iraq in the 70s.

I dont remember being bothered by 50Hz flicker as a kid, but sometime in 2005 or 2006 I was visiting Germany and stayed in a hotel that still had CRT TVs in the rooms. I sure noticed the 50Hz flicker. Funny thing is I dont remember noticing the NTSC hue change based on the person being in a dark or bright area. I do remember having to occasionally tweak the hue on the odd progam, presumably because somewhere along the broadcast chain someone hadnt adjusted the phase perfectly. And after the 70s I dont remember needing to that very often if at all. I do sort of remember some older tube color TVs that seemed to have the hue drift slightly as the set heated up - in fairness to them that would have been 1960s TV in the late 70s/early 80s when I was fixing them while I was in high school. So all sorts of components may have become less stable with age.

Patrick's response:

I was a transmitter engineer in the 70s for a time. The biggest cause of differential phase and gain was the transmitter. Many transmitters in the 60s, and a few in the 70s, were what we called "forced color" because they were implemented before color TV was available. A 50 KW transmitter was a major investment that stations were reluctant to replace. One station in Los Angles, KCOP, pushed their old forced color transmitter into the mid 70s. Differential phase was irrelevant to monochrome video, and differential gain only caused unrealistic contrast changes that weren't very noticeable. Getting a 50 KW vacuum tube to operate perfectly within its linear transconductance transfer curve, especially when it was operating at its limits, was impossible. It ran at the knees in the curve between black (100% output) and white (12.5% output). Put a chroma subcarrier on top of that, and both gain and phase were distorted by the nonlinearity. The problem got worse as the tubes aged.

The FCC set a limit of 5 degrees differential phase and 5% differential gain, but there was no real enforcement. Stations self-certified each year with "proof of performance tests," and more than one station I knew of had a set of new tubes that they would swap in only for the yearly tests. A pair of new Eimac 4CX25000 power tetrode vacuum tubes needed for a 50 KW transmitter cost approximately $200,000 each in today's dollars. Stations milked those tubes for every last useable minute of service life.

The hue shifting with temperature was also a real issue for tube-based vidicon cameras. At ABC studios in Hollywood, each stage had a "Senior Video" operator whose sole job was to continually adjust all the cameras on an operating stage for color matching. The drift was mostly thermal. Move a camera under a stage light and it would rapidly drift away from the others. It was an intense job. If you saw changes in hue or saturation on a CRT, it was mostly due to thermal differences between the red, blue and green "guns" (cathodes) in the CRT tube itself. Sony trintron CRTs had only one gun and didn't suffer from this effect. The reason stations had such large technical staffs was -- in analog -- everything is constantly drifting.

They also needed strong men in the maintenance department because lifting a CRT studio monitor or a camera was a two-man job. The switch to digital made everything so much simpler and less physics-based. The technical challenges in broadcast television are miniscule today to what they once were. That's why I switched to cyber security 30 years ago -- where everything is still complex and continually broken.

Peter's response:

That is fascinating! I had never heard of "forced color" but its sure makes sense that at thos costs, stations would have been reluctant to upgrade to a new transmitter designed for color. Swapping tubes for the annual tests - thats a bit of history you dont read about. Didnt know about camea heating messing up vidicon color or how trinitrons were more stabe color wise. And continuously adjusting color on the cameras - wow!




Thanks so much Patrick! Really appreciate the time you took to tell us about the first few decades of NTSC!

The original video is here https://youtu.be/EPQq7xd3WdA

9 months ago (edited) | [YT] | 14

Electromagnetic Videos

Costa Rica Space Radar

If your lucky enough to be in the north west area of Costa Rica and want a bumpy drive through the sugar cane fields, take a look at Space Radar installation that monitors low earth orbit satellites and space debris.

Its located here www.google.com/maps/place/Costa+Rica+Space+Radar/@…

Unfortunately there isn't anything like an information booth and you can only see it though a wire mesh fence, but you can get a really good look at the reflectors and use a cell phone right at the fence to take photos though the wire mesh like I did.

They have a great video here https://www.youtube.com/watch?v=faLZd...
and more information here leolabs-space.medium.com/introducing-costa-rica-sp…

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9 months ago | [YT] | 14