My old J-38 straight key

The second thing was change the demodulator envelope adjustment from 100 Hz/step to 50 Hz/step. This allows you to create a properly centered demodulator envelope of an odd width, such as 300 Hz, or to cut the bandwidth all the way down to 50 Hz — a little extreme perhaps, but amazingly usable if the received station is stable.

Lastly, I experimented a bit with the audio notches to see how to best tailor the audio, and I found that with the Q of a notch set to about the third hashmark from the right of the Q scale, the notch was narrow enough to sit right on the upper edge of the demodulator envelope. I’ll give a detailed example:

I prefer to listen to CW at 1000 Hz. So to create a 100 Hz wide CW demodulator, I first select CWL (this is better than CWU because the receive frequency is “right side up”, or goes up when you tune up.)

Then I set the audio scope with SPE, FIX, and 2kc. This lets me see the CW range I’m interested in for precise tuning purposes, and puts a vertical line right at 1000 Hz, dead center where you want the signal.

Next, I adjust the lower demod envelope edge to -1050 Hz, and the upper demod envelope edge to -950 Hz. This produces a 100 Hz wide window precisely around 1000 Hz.

Next, I press SDR and set the SDR Bandwidth / Sample Rate to 50 kHz so CW tuning is as precise as possible.

Optional, but I may adjust S+ and S- even narrower, and set the DSP FFT to a higher value like 8192 so the signals are finely resolved on the display. Follow this by using GS to adjust the gridding to taste.

Next, I turn on a notch and set it for 1050 Hz, with the Q slider set to the third index marker from the right. This reduces a bit of the ringing that such a sharp filter produces; you need to keep the notch pretty narrow if your demodulator is narrow, though, or it’ll impact the actual signal, which you don’t want.

CWO is left at zero; adjust AGC to taste. I like it longer, around 5000 ms if the signals are stable and similar in strength to one another in a conversation. Single source signals like W1AW broadcasts, I always set to as long as I can get away with. Keeps the S/N as high as possible.

Finally, I press DSP and set the Mouse Click Resolution to 10 Hz. This affects not only point and click, but also, critically, the resolution at which the mouse roller steps the tuning.

Now we’re ready to go. Find the CW signal using the RF spectrum display and the waterfall, drag the demodulator envelope over to it, and use the mouse roller (while positioned over the spectrum or waterfall) to fine tune the CW signal until it is dead center on the audio scope. Time to copy!

I think you’ll be most pleasantly surprised by what you can do with this if you’re a CW aficionado.

One question for you CW fans: Given that CWU tunes backwards – that is, when you move the frequency up, the CW tone goes down – does anyone think that CWU needs to be kept? I’m considering removing it, as space is at a premium, and I can’t think of a use for it that isn’t better served by CWL. Please answer in the comments for this post. Barring any contrary feedback, I’ll remove it.

Waiting…

Sigh.

On other fronts, they’ve finally fixed the multi-monitor shortcomings in OSX; menus, full screen apps, etc. Kudos. Even iOS got a little love with folders that can hold many files, instead of just a few.

The new OSX makes me willing to go for a new Mac Pro, or at least, it seems that way with the limited information I have now. I can put the old fella up in the ham shack where it will do a fine job with the SDR up there; and the new hotness will (of course) drive my desktop, save me time on compiles and just about anything else… and I admit, I run my SDR from my desk even more often than I do in my ham shack. Not just testing, I like the sound of a radio in the background.

The question is, newest model that can only run three displays and has only a small internal SSD? Or the current generation that can do more displays and has room for standard internal HDs?

Apple really does test my patience. It’s been several years since they really gave the Mac Pro much attention, and frankly, I was getting close to building a Hackintosh or buying the current generation. Will they get the Mac Pro out in time? Should I go for newness, the current generation, hacking, or something used off EBay? I feel information-deprived.

Tune in this fall for the next installment of “As the Apple Worms.”

  Screen shot: http://www.flickr.com/photos/fyngyrz/8675326983/in/photostream/lightbox/
    Downloads: http://fyngyrz.com/?p=915
Documentation: http://fyngyrz.com/sdrdxdoc/sitemap.html
      Changes: http://fyngyrz.com/sdrdxdoc/changes212.html

  Screen shot: http://www.flickr.com/photos/fyngyrz/8675326983/in/photostream/lightbox/
    Downloads: http://fyngyrz.com/?p=915
Documentation: http://fyngyrz.com/sdrdxdoc/sitemap.html
      Changes: http://fyngyrz.com/sdrdxdoc/changes212.html

So this one time, my mother and I were out in the car waiting for our order, across the street a little bit diagonal to the pizza place, right next to the Texas Hot Dog emporium. A roller grill, the usual range of hot dog goodness, but after all… hot dogs. We were not there for hot dogs. It was summer, and our windows were down.

So we’ve been there just a couple minutes, and out of the pizza place comes the pizza guy himself, all preoccupied. Into the Texas Hot Dogs place he strode, and just moments later, he’s out with a short armload of seriously gussied-up hot dogs. My mother — a legitimate gourmet with a long list of excellent reasons for choosing this particular pizza place — is watching this with, no kidding, her mouth hanging open.

He sees us and waves, then realizes the situation, shrugs with his free arm, and lets fly: “Me, I like hot dogs.” My mother chuckled, her incredulity defanged by his obvious good humor, and off he went, presumably to finish making our pizza, which I am sure was lovely, if for no other reason than I remember no exceptions whatsoever.

I still don’t know exactly what to think of that guy. But me? I like pizza.

But it’s done now. I think. Perhaps.

However, should you encounter weirdness, by all means let me know and I’ll see if I can work out what I did wrong, or whatever. Sorry for being down, wasn’t my intention.

Cheers!

–Ben

I have opened one of the “poppers” up on the bench, and with the buffer amplifier signal cable to the power amplifier disconnected, the popping noise remains, so it’s definitely not in the audio path on the buffer amplifier board. The buffer amp is connected to the power amp via an electrolytic, so there’s no problem unplugging the buffer from the power amp.

There’s another problem with this unit, too: I see somewhat random engagement of the high power rail mode for the amp, but this is not co-incident with the clicking coming from the speaker.

When the high/low power state switches randomly, the associated relay clicks, which is audible at very low volumes, and this is obviously not the design intent. Erratic high/low power switching problems are going to be nearby QU05, very likely the electrolytic CU08, the diodes DU01 and DU02, or QU05 itself. I’d suspect CU08 first.

The main amp PCB shows evidence of excessive heating towards the front of the chassis, where the driver section is located. Unfortunately, it looks to me that the mechanical assembly is complex with regards to the main amp and attached heat sink; taking it apart looks to be quite a big deal, my vision has become very poor, and I don’t actually need the amp, so I’m just going to close up. However, at least this exonerates the buffer amp and provides a pointer as to how to troubleshoot high/low rail power issues.

If anyone locates a specific component that is responsible for the clicking and popping, I would very much appreciate hearing about it; I’m willing to hack in a replacement electrolytic from the component or solder side of the board if that’ll solve the problem. Likewise, if circumstances lead me there — if one of my working MA700′s fails and I really need to fix one of these “poppers” — I’ll post what I’ve learned.

I’ve put the service manual for the MA700 online here.

–Ben, AA7AS

Well, it was nice while it lasted. Sigh.