Category: radio

A tale of amplifiers.

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Here’s a story I’ve been meaning to tell for a while.

Once upon a time, there was a wonderful isle of dreams, and a television station built upon it. To carry the sounds to accompany its magically delivered pictures, there was a set of audio distribution amplifiers.

And oh baby what amplifiers they are….

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The guys on the right. Ignore the dark power lights, they're soldered in incandescent...

And their, uh, not the best side

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The company stuck around until 1985

And now the heart:

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Those of you who are like me will also notice, this is six individually transformer isolated outputs and one transformer isolated input.

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Fairly simple amp stages.

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The dual power supply. One regulator on each end. This is the older design; the newer one has two separate regulator cards.

These lived happily until one day, one regulator card let out a biiiiiig fart.

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For comparison, this is what the other end looked like:

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Oh how it stank that morning on the wonderful isle of dreams!

The finest nose on the isle located the stench and an engineer set to restoring the precious music of the angels to flow beyond it. Fortunately he found only two channels still in use, each feeding one output… Thus:

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Emergency passive near unity gain audio distribution system.

This engineer was haunted from that day by the knowledge that some very mission critical audio still runs through that stack and the amps aren’t getting any younger.

However, they are, at least, better than the modern equivalent.

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I'll just take my chances with the old Ramko Research shit boxes, thanks

Well look at that… A Daven.

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Penny & Giles, eat your conductive plastic hearts out.

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The tab at top is the cover lock; push it and turn to remove it for cleaning and service

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…

Big silver contact studs lead to the resistors inside.

In normal service these would be lubricated with Daven oil. This is a total mystery to me — it’s been out of production for decades, and I have no idea what a proper substitute would be.

The only other place I’ve seen rotary switches this hardcore are in avionics.

The Daven step attenuator was used in older broadcast consoles — I’m not sure on the details but I’ve heard that WVUM had one.

HF antenna fail.

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Before using any conductive objects, LOOK UP. If there are power lines nearby OR within range such that the object could fall and hit them on the way down, STOP!!!

Otherwise the whole world will laugh at you after you EXPLODE your radio and knock out power to a fairly large area…

Image by WU2F, link to Reddit thread.

Fail
Oh sure the antenna’s DC grounded, it’ll be fine

 

The ham responsible all but vaporized a nice Flex Radio HF transceiver, power supply, and the electrical wiring in his camper. LUCKILY, nobody was injured, but it could VERY VERY EASILY have been much worse. You don’t get a second chance with contacting power lines.

For extra lulz, let’s see if he tries to sell this radio for what it’s ‘wurf’ on eBay in the future. 😉

RF safety? What’s that? WMBM-AM’s tower.

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No no of course not, you can’t burn things with RF unless they’re inside the microwave.

Presenting WMBM-AM, Miami Beach, Florida.

The tower stands in a courtyard behind Radio Bar. The courtyard is fully enclosed. Except…….. The bar uses it as an entrance and exit and storage area and leaves it open to the public.

Sorry for blur in these images, I was unable to stop laughing.

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Pretty hallway.

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To the right just inside.

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To the left just inside.

Note that this tower is not on insulators. It is [barely – see below] grounded. The transmitter output goes to a three wire skirt that starts well up out of reach and is fed by, uh, let’s visit that later

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Kinda sorta ground. One small wire, about 6 gauge.

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See that red square? That’s the transmitter output. Right there. It’s like seven feet up in that corner. You can see the two pipes in the photo above. Only a chain and defaced warning sign (not even a standard RF exposure warning sign) separate bar guests and that.

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Possibly remains of an older feed to the tower…. even more exposed.

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No, the tower lights don’t work.

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Dafuq?!

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This has apparently been how it’s stood for years.

On a side note, here’s an at&t installation. The old vault is on a berm above ground to protect it from storm surge. The VRAD, used to supply PooVerse I mean UVerse television, internet, and kind of sort of phone, not so much.

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You’re, uh, welcome.

The Harris Quest FM

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I could write volumes on how awful and ridiculous this box is, but… Here, I summarized it in one image: if you add thick eyebrows, a moustache, and a goatee to it, it looks every bit as malevolently untrustworthy as it truly is. They’ve been out of production for a long time (cheers were probably heard all over Quincy when the order to discontinue them was made) and certain key parts are looooong gone.

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Cool ferroresonant power supply though.

The fix for easily moved radio knobs

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First off, our radio knobs were too easy to turn, causing them to get unexpectedly muted or knocked off channel.

Second, I fail so hard at shitposting. I always want to just fire up WordPress and drop a useless shitpost on here then I think of something actually useful and informative. What follows is a failure to shitpost.

I’m still not exactly calling this a great post because I’m too lazy to edit the images.

Step one: pull the knobs off. Pull straight up. The knob may be tight on the shaft, just don’t apply excessive force in any direction if it is. Be patient. On this Hytera it was pretty easy to pop off.

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The recess here is what we’ll be modifying. Cut two little circles out of craft foam, mouse pad, inner tube… Whatever rubbery thing you have handy… Or use rubber o rings. It don’t matter.

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If there’s no hole in them yet, fold in half and cut a slit.

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Press it down the shaft and all the way into the recess.

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Reinstall the knob. Test to see that it moves and has more resistance. If there’s no effect, add another layer. If it doesn’t fit back on there, remove it and try a thinner material.

This took me about two minutes per radio I did it on and eliminates annoyance like nobody’s business.

The first time I did this mod was on a Baofeng, so I’m gonna add the shitpost tag. You’re welcome.

Harris Z power supply rectifier notes.

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For future reference to myself and everyone else, so I don’t have to keep searching my email every freaking time:

On the Harris Z series transmitters, the SCRs used on the rectifier board may be either one of two kinds. They may be a current part made by Littelfuse or a discontinued one made by (this has escaped my memory banks, sorry!)

If you have the newer board, you have Littelfuse S6055R SCRs on it. If you have the older board, your SCRs can be replaced with the S6055R. If you’re me, you replace them with the S8055R, which is the same part in every way EXCEPT that it can handle 800V reverse voltage instead of 600. (Probably comes in handy in avoiding blowout during power surges?)

Here’s yer SCR.

Troubleshooting: You will receive fault code PSx_TAPy where x is the power supply number and y is the tap number. Try clearing this fault as it may be set by a voltage transient. If it recurs in the same place, disconnect ALL power to the transmitter and pull out the power supply drawer from the bottom. You will need a second person’s assistance. I found it easiest after removing the blower from the back as well. Test each fuse on the rectifier board identified by the fault. If you find blown fuses, change them and try again. If you find fuseholders that look like they’ve been hot, change them.

However, if the fault persists and the fuses and holders are all good, change the SCRs. Using a vacuum desoldering iron will help a lot. I used my Hakko 808.

Voila….. no more jet turbine mode. 😉

Maybe it wasn’t a typo?

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A while back I spotted this.

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Imagine my surprise seeing the package has been redesigned and still says the same thing about the vswr!

I’m now officially recommending this antenna for all deployments of Harris Stingray units, Bluetooth spammers, over modulated pirate FM’s advertising strip clubs, and iHeartMedia stations.

The oddball embedded spectrum analyzer

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It’s no secret, the Technicolor home cable gateway sucks. However…. if you have one, try http://10.0.0.10:8080 in Chrome or Safari…. (Link will just error if there’s nothing there).

Voila— you have your very own 21st century Graph Channel.

There’s a RF spectrum analyzer in there. Now, it’s not a GREAT one, the minimum frequency resolution is a big wide 6 megacycle wide sweep…. but it’s there.

cable-specOverall view, you can see the bands used for upstream and downstream, divided by a blank band around 100.

That band has some spiky bits in it. What are they? Well… I live within walking distance for the transmitters for a couple of 100KW ERP FM’s…

ENHANCE! There’s 93.5 “The Bull” W228BV-FX; 106.7 WDXJ-FM + HD, 105.9 WBGG-FM, and a few others, all leaking into the cable system at fairly harmless looking levels. I suspect Comcast simply leaves this band of spectrum empty on their cable system to make life easier in the face of RF leakage. (??)

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I’ll code a GUI interface in Visual Basic…
The view goes in just enough to make the analog carrier and HD sidebands of WXDJ-FM visible and distinct. It looks like the lower one MIGHT be suppressed a bit – this is an interference mitigation feature present in modern HD exciter firmware from Harris/GatesAir, Broadcast Electronics, and Nautel. You can back it down a bit to be all cool and avoid adjacent channel interference.

cable-iboc
I dunno — you can’t expect a spectrum analyzer built into cost engineered nasty home internet CPE to be the best thing ever, but it’s still fun to play with.