This Broadcast Engineering show is also good for audiophiles who are interested in sound reproduction and broadcasting.

The nice thing about being an amateur is that you can do whatever you want, and not have to do what others demand of you! Enjoy! 😊

Where can I contact you?

Agreed. A fascinating video spoilt by waving the camera around and giving me eye strain. I gave up after 5 minutes.

Ours ran as a backup until 2016 when we donated it to a museum. Those were fun when the lamp in the VSWR meter burned out and they'd dump the plate until you figured it out.

Thank you!! Hopefully if you keep watching nerdy stuff, it becomes not so far over your head!

Where can I contact you?

The 4CX250B is the baby of the family. But they work very well in amateur radio amplifiers, typically in push-pull pairs in VHF service. Of course they work well on lower frequencies, too. But if you are interested in doing moon bounce, a pair of those 4CX250s are a good choice. 73 from Bob, WA6WHT ☺️

Aye, when I started in the hobby I bought a set to make my own amplifier, never got it finished though due to.. well... life happened. Still have them somewhere in the storage. 73 de Soren OZ2AEV

Agree

The factory test data calls for 12.7kV. 14 is still high, but I don't think GatesAir would tell a customer to run this tube at over 10kV if they didn't think it could handle that plate voltage.

Check that bias baybeeee

As I recall, their VSWR was 1.08 to 1. That's not bad. But there are some things to be concerned about there, like that Plate Voltage. It seems a bit high to me. And possibly the cavity tuning may be a bit off, too, so that 4CX20,000C was dissipating a bit more than necessary for the rated power output. There are good ways to observe that with a spectrum analyzer, which curiously I don't recall seeing anywhere in the video. Around transmitters like these, a spectrum analyzer is a very useful tool. 73 from Bob, WA6WHT and transmitter engineer for several San Francisco Bay Area TV stations at various times. 😀

Agree I noticed that too I was like WTF is he thinking

The grounding cable on Harris transmitters is covered in a clear cover!

Yes! Those are compressed nitrogen cylinders. We connect them to a dehydrator/compressor unit that maintains pressure inside the coaxial transmission line. Nitrogen is a very popular dielectric gas that prevents the center conductor from arcing over to the outer shield and also keeps moisture out of the line.

This rig is FM which has lots of sidebands, both upper and lower. AM typically has only 2 sidebands, one on either side of the carrier. When you are talking about Single Sideband, you are talking about eliminating both the carrier and the unwanted duplicate sideband. Single Sideband requires linear amplifiers, but FM does not. In fact, to get the efficiency of an FM transmitter to be high, the amplifier chain is very likely running Class C and quite non-linear. But that non-linearity does not distort the transmitter signal at all. A good place to begin learning more about FM and SSB is The Radio Amateurs Handbook by the American Radio Relay League (ARRL) because both FM and SSB are used by amateur radio operators, and the ARRL Handbooks are very well written.

For the 4CX20000C tube used in this rig, nominal filament voltage is 10VDC at approximately 140 amps. GatesAir recommends lowering the filament to around 9 volts after about 150 hours of use to keep the tube from going “soft” too quickly. That was never done to this one and so we’ll probably need to replace it soon.

@@BroadcastBlueprint Consider getting a copy of the classic book on the subject, titled "The Care and Feeding of Power Grid Tubes" by Eimac. They explained a lot about filament management to get the longest life and best performance out of vacuum tubes like that 4CX20,000C. I believe it is available as a PDF as well as in hard copy. As I recall, the PDF was free. I also recommend getting a copy of the data sheet for that 4CX20,000C, so you can see both what the ratings of it are, and also what typical operation as a Class C FM power amplifier looks like About that exhaust air temperature, it seems a bit high to me, but I am more familiar with the 3XC10,000A7 triode running in low band VHF TV visual amplifier service, which means they were running AB1 or AB2 as grounded grid linear amplifiers. But our exhaust air temperature was around 135 degrees F with inlet air of 65 degrees F, so we had a 70 degree delta between inlet and outlet air temperature. And we checked our air filters with a vacuum gauge calibrated in inches of water. Too much drop across the air filters was the reason to replace them because a plugged up air filter can reduce the air flow through the anode of the tube and the cooling of the socket, as well. Higher temperatures lead to grief sooner. Also when you pull the tube, take a very good look at the contact fingers in the socket. One point of failure is weak fingers that lead to higher resistance contacts with that tube. 140 amps at 10 volts can cause some serious finger heating if they are not all making good contact with the tube base. Anyway I liked your video, although a chest mounted camera might have shown some of what you were doing a bit better than the helmet mounted camera did. 73 from WA6WHT, transmitter engineer for KTEH-TV54 and KSTS-TV48, San Jose, and KRON-TV4, and KTSF-TV26, San Francisco. I didn't do all of those rigs at once, however.! ☺️

These days, modern electronic devices introduce a lot of noise and interference. Switched mode power supplies are one of the biggest offenders. So it’s not a matter of transmit power or the type of power amplifier in the transmitter, it’s just that there are a lot of noisy things close to you!

Why have a dummy load and not a tower for it ?

Precisely! Since nitrogen is also a strong dielectric gas, it helps prevent arcing within the transmission line as well.

As an Electrician, I think one of the reasons why that FM broadcast station has so much grounding is because of NEC article 250. Just think about it, the broadcast tower is now a lightning rod 😆 I wouldn’t doubt those transmitters are system/equipment grounded so that if lightning strikes the tower, most of that energy from the lightning would go straight to the ground and bypass electrical and the FM radio broadcast equipment. Back in 2010 I was in a technical college getting my two years associates degree in industrial electrical / systems technology. the instructor took the students and I on a trip to a 911 Calling Center in Apopka Florida, at that time we were learning, basic communication, electronics and NEC article 250 Which talks about grounding(Earthing )and bonding electrical/electronic equipment. As we walked in inside this 911 Calling Center in Apopka Florida, We walked inside the room where the transmitters were, and we knew some of the equipment had discoloration like some equipment had turned black,next we looked at the electrical panel, the whole electrical panel was blown out. The people at the 911 calling Center was spending hundreds of thousands of dollars installing new equipment because of lightning strikes and power outages come to found out some of the cables to the tower. Weren’t grounded, instead of using copper, it was using aluminum cables. It was using hose clamps off of automobiles to cover the coax cables. It was a mess. The antennas weren’t grounded properly. It was crazy, but it was more of a lesson learned while I was in college, and a very interesting one in communication electronics. there’s probably a lot of reasons why this transmitter is malfunctioning. they might want to call an electrician to check the main power source for voltage spikes and THDFs or transformer, harmonics dating factor on Transformers.

All the radiation, with very minor exceptions, is non-izoning. The transmitter manufacturer has responsibility for the inherent safety of the device. As far as a safety officer, the chief is there and is hands-on supervising the process.

The stick is non-conductive and the cable has a plastic insulation.

13kv, i would have thought some hv gloves and facemask would be nice

That's a good question - usually we do run into the dummy load, but we were also getting data on how this transmitter performs when actually connected to the antenna so we know what tuning adjustments we need to make. Typically the dummy load doesn't give you that complete picture.

Agree 👍

The FTD sheet for this transmitter calls for 12.7 kV/2.95 A on the plate for FM+HD hybrid operation at 21.205 kW TPO.

@@BroadcastBlueprint Interesting! Thank you. Just be advised that you're also generating x-rays with that.

Trust me, broadcast engineers, know that broadcast engineers, get cancer, or at least they used to when they had to tweak the exciter by reaching around the tube in the cabinet

@GWDLABS The copper (they are usually silver plated) fingers are to stop RF leakage. That does not stop x-rays. X-rays are much shorter wavelengths and go through those little cracks. Most of the x-rays are contained within the cabinet when everything is closed up properly. However, there are times when troubleshooting that you have to bypass an interlock or color outside the lines. I've been a broadcast engineer for 39 years and seen it all. Once in the late 90's, I was Chief Engineer of 17 stations all by myself, no help. Now I only have 7 stations.

Consider the cost per hour in terms of consumable tubes and electricity use. If the old stuff was better / less expensive to use, stations would be demanding that they be built.

The glass tubes were certainly prettier than MOSFETs.

Yes and yes. The worst part is, you don’t know which one until it’s too late! The gas bottles have nitrogen in them. We run the gas through a dehydrator and fill our transmission lines with it to keep moisture out and prevent the center conductor from arcing over to the outer shield.

Yep Howard I agree with you Read my reply