EEVblog #574 - NEC Analog TV IF Modulator Teardown

Dave looks through the documentation for the vintage 1980 NEC PCN-1205AH 5kW Analog TV Transmitter that used to transmit the CH7 TV frequency in Sydney
He then tears down the HPA-3696 IF Modulator used in the system.

EEVblog Main Web Site:
EEVblog Amazon Store:
Donations:
Projects:
Electronics Info Wiki:

[whitcwa]

Dave, you mention someone using the TV signal as a frequency reference. The TV station I work at once got a call from NASA asking what had happened to our signal. They were measuring the color subcarrier frequency (3.579545Mhz), not the RF carrier frequency. It turned out that they had been using our signal to check calibration on field equipment. We had been using a rubidium standard, but it had recently failed so we went back to a normal ovenized oscillator. It was well within tolerance for broadcast, but not nearly good enough for their purposes. They gave us an HP cesium standard to restore our stability.

[ClosetYeti]

For anyone interested (not that there's anything wrong with the manuals), the physical teardown starts at 0:32:05

[CH_Pechiar]

Analogue TV is an outstanding engineering development. One of the design specifications being that on the transmitter side all the complex (thus expensive) processes should be done to the signals so that the TV sets would be really simple (thus inexpensive), in order to achieve the widest audience possible. The gamma pre-equalization to match the nonlinearity of the CRTs, the number of frames and timings to use the line frequency as the reference, the use of POV and the concept of interlaced lines in order to reduce required bandwidth, etc. Moreover, when colour was introduced it had to be done in such a way that B&W sets will still work (backwards compatibility). Colour was added to a signal that was not design for that and this by itself is a great achievement. 

[scotshabalam]

The thing i love about this piece of equipment is that it's clearly intended for the owner to be their own service technician.

[taylorschuller]

"If you have to ask for the price, you can't afford it." That is the most true statement i have heard all day.

[sumatoborukiSaru]

37:15 "Some weird-ass, old style lamp" IS a lamp. It's a tattle-tale neon that glows when the fuse is blown.
1:02:40 to 1:04:25 Looks like they recapped the entire PSU.
 The main filters are very modern, non NEC brand & the control PCB is filled with Hitano EXR caps from WES.
1:09:12 The 'sha' in Kinsekisha is dervived from kaisha, meaning 'company' in Japanese.
 So, to a Japanese person, it would read as Kinseki Co. Lab.
 Somebody within NEC obviously thought it was a gross error to exclude the honorific 'sha' from
 the name & 'pencilled it in' just before printing. :))

[hankus]

I've been looking for the gizmo the cranks the audio up several DBs when a commercial is being aired, but haven't seen it yet.

[oriole]

I always make time for Dave's vids even when I'm busy. ;) An important thing to realize is that even though construction techniques may change with time, the laws of physics do not. This type of gear gives a comparatively clear idea of how different system requirements were painstakingly addressed. Modern gear is all simulated with $250k RF & EM software, but this gear is basically manufactured from the combined engineering experience of that time. Whatever needed to be calculated, was done manually.. and RF & EM math is no walk in the park. NEC probably lost a lot of their "vertical integration" (when a company manufactures many of their own components for their products) when China and Taiwan became prominent in their industry. Same deal happened with Sony and others. Sony used to be all made in Japan. Then a mix of Japan & Taiwan. And today, basically whatever country is cheapest.. which isn't even China anymore. :)

[terrywilson]

The SAW filter at 1:01 in your video is the vestigual side band filter (VSBF). It would be used to filter out the upper(higher frequencies)of the lower sideband from the video modulator output to create the final "vestigual sideband signal", which is quite a critical requirement to keep things within the correct bandwidth before it's fed to the IF mixer and then RF amplifiers hence it has to be in a temperature regulated oven. in otherwords only the full upper sideband is transmitted and the low frequency portion of the lower sideband so everything thats needed fits within the 7Mhz TV channel bandwidth.

[themainproblem]

At a former employer, they had a communications hub for communications to all stores.  It was built with NEC gear and it was just amazingly nice in construction quality.  Even the electrical service panels were just gorgeous!  Beautifully designed and executed.  First rate all the way around.  NEC rocks! 

[Maxxarcade]

That thing has some beautiful construction.  I had to LOL at the replacement Jamicon cap that someone put in there.  Looks like that may have been done in the 90's.

This makes me want to dig out my 1950's military signal generator and do a video about it.  It's all tube based with big oil caps, and has the same immaculate construction.

[usoppbarbosa]

when i see the amount of work put into getting a clean TV signal out.. it makes me think.. if TV channels did put the same effort for content creativity, i'd still own a TV today :)

[paulstubbs]

Dave, the TV derived frequency standard idea you referred to was NOT done from the RF carrier frequency, but from the video sync frequency of 15.625KHz, which was usually derived from a Caesium etc atomic reference back at the TV station, not at the transmitter site.
As the transmitter bandwidth is about 5.5MHz, a TCXO is fine.

[dawson]

I love it when 'future dave' sends a message about component names.

[RadioChief]

I maintained a higher powered version of a very similar model NEC transmitter on channel 6 over here in the states. Two 30 kW transmitters paralleled for 60 kW into a circular polarized antenna. It was a very well behaved transmitter. Well thought out design. Sadly at the end of the analog era it was unceremoniously removed and sold for scrap.

[ersonthemesa]

I can almost smell that vintage. Great video and I loved the TV Xmitter tour too. Cheers !

[CookingWithCows]

So now Dave is going to run his own pirate TV channel to bring EEVblog over all of Baulkham Hills :D

[MrCapacitator]

The oscillator was not invented at the same time, Gouriet actually invented it 10 year before Clapp. Gouriet in 1938 and Clapp in 1948.
 Due to wartime security Gouriet's oscillator design was kept secret until after WWII, the same circuit was then independently discovered by Clapp and published by him.

[WarpRadio]

seeing this, even now, today, still makes me drool- in awe and give me that "warm fuzzy feeling" that makes me want to break out some old RF equipment and start playing with it again :)

[johncrunk]

These TV videos stirred memories from the past. Although the stuff I worked with in the military in the 60's packed a bit more power, the quality and heft of the equipment was about the same. Good job!