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Messages - Charlie_Dont_Surf

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The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications
« on: December 18, 2020, 2102 UTC »
No one uses Zeners anymore btw

I'll just leave this here for you to contemplate:

- Zener Diodes Market" is valued at 878.1 million USD in 2020 is expected to reach 1067.6 million USD by the end of 2026, growing at a CAGR of 2.8% during 2021-2026, According to New Research Study.


Why not ask me?

He was looking for info and he did. End of story.

The RF Workbench / Re: Stretchyman 40 W TX Reliability Modifications
« on: December 18, 2020, 0717 UTC »
I don't have the schematic for his frequency synthesizer so I can't help you.

The only thing I can say is that he now has what may be a zener diode on the switched 12 V input to the synthesizer/FET driver. (Or maybe it is a TVS device.) A zener might help.

I will note that later versions appear to to be more stable; I noted no FM'ing on the units I tested.

I'm surprised that this hasn't made this forum yet. It's been out for 5 days. You people are slipping.


General Radio Discussion / Re: Antenna wire, get your cheap antenna wire
« on: September 26, 2020, 1924 UTC »
"This listing was ended by the seller because there was an error in the listing."

Here's his virtual store so look around for what you want: https://www.ebay.com/sch/iwc2carl/m.html?_nkw=&_armrs=1&_ipg=&_from=

I bought a 50-foot roll of 2-conductor, 14-AWG, stranded wire at (insert name of US big box DIY hardware chain whose name begins with "L") and I have come to like this stuff for ground radials because it's heavy, lays flat for the most part, and doesn't get tangled up like smaller-diameter, solid conductor wire does. It was very easy to split apart so a roll of 50-foot, 2-conductor because becomes a roll of 100-foot, 1-conductor in a matter of minutes.

The RF Workbench / Re: NOT A Replacement For Your Stretchy Audio Amp
« on: September 13, 2020, 2053 UTC »
For those reading this and trying to understand what is going on, the TPA3116 modules that I have seen seem to generally have their own boost power converter and can work off 12 to 24 V DC, internally converting whatever it receives to 24 V DC to power itself. This means that they produce 24 V maximum on the audio output. Unrelated, but they also usually have reverse polarity protection.

*edit* I forgot that this is a 40W TX requiring 48V peak mod, and have not yet found an COTS audio amp IC that will run at that supply voltage. 

That same particular vendor that I linked to has some Sure amps that can do as much as 60 V into low impedances:

The drive capability is overkill for the Stretchy boxes but hey, it's not too expensive, not physically large and of course, includes protection mechanisms along with the audio LPF, of course.

I considered ditching the transformer and going straight PWM for my "cannibalization" of the Stretchy box but decided to keep the transformer. The cannibalization is already enough disruption for right now (IMO) and I felt like minimizing the amount of messing around. The messing around will come later.  :D

Sure appears to make some that can do up to 120 V. (Scroll down on the linked datasheet.)

Might be time to build a simple PWM modulator?

** WARNING: Thread drift.  :D **

Oh, I agree that this can be done too. I have some things in the works.

With the number of little Class-D audio chips on the market for the portable consumer electronics applications, there are a number of options. In the portable application arena, they do not use big LPF inductors on the speaker output of the Class-D amp; instead they rely on the speaker and speaker wire inductance to do the filtering, and it's usually good enough that most consumers don't notice or live with the artifacts.

My thought was that since these chips put out a PWM signal but at a voltage and drive current level that isn't going to modulate a transmitter well, simply add a follower/level-shifter after the PWM chip which will do the heavy switching and let that modulate the transmitter thought appropriate LPF filtering. As a simple feasibility check, I obtained an Adafruit PAM8302 module and put that output into the gate of a IRL510 which I had in my supply and chosen because of the low threshold voltage. It worked well enough that I am going to put together a test board with the PAM8302 driving a real FET driver and then a good FET and some filtering to drive a TX B+ input.

I can't be the first person to propose doing this.

Equipment / Re: 250 foot V Beam Antenna Aimed To Europe
« on: September 13, 2020, 2002 UTC »
No doubt the long coax run is heavily influencing what impedance values I see here in the shack, as well.

Yeah, that's where I was going with that question. I don't have much experience (i.e., none) with terminated wire antennas so I was surprised by the relatively tame impedance variation across the wide bandwidth, so at first I was thinking that the long coax feed was reducing the return loss. However, thinking about this some more (and thinking out loud), that's the whole point of a terminated wire antenna: relatively tame impedance variation across frequency.

I really only had one viable location for the feedpoint that would allow me to run two 250 ft wires in the correct directions, mostly dictated by the locations of trees (both to use for support, as well as staying away from other trees that would make installation difficult or impossible) as well as staying away from other antennas. That meant it's some distance from the house, as well as (unfortunately) aimed at the house.

These are the trade-offs and compromises that have to be made. That's life.

Good signal on the Left Coast, S9 on peaks at 0159 UTC.
SSTV image at 0200.
0225 - "Ch-ch-ch-Cherrybomb"

Equipment / Re: 250 foot V Beam Antenna Aimed To Europe
« on: September 13, 2020, 0124 UTC »
How long is the coax feeding this antenna?

Fair signal and listenable on the Left Coast. S4 on peaks. ID at 0102 UTC.

Good signal on the Left Coast. S7 on peaks at 0037 UTC, about 60-90 minutes before sunset here.

Dialogue between a woman and a man.

0114 - signal to noise ratio is improving as we approach sundown. S7 on peaks.
0120-0124: SSTV
0125: Reggae/Ska version of "(Take Me Home) Country Road".
0139 - No signal.

Just barely perceptible on the Left Coast. I can see the carrier feedthough on my waterfall and hear some music through the noise. We have daylight for another hour or so here.

The RF Workbench / NOT A Replacement For Your Stretchy Audio Amp
« on: September 12, 2020, 2244 UTC »
In the process of debugging the myriad of power-on transient issues with my Stretchyman 40 W TX, I managed to kill the Class-D audio amplifier that serves as the modulator (through a transformer). It appeared to develop some instability issues trying to drive the modulation transformer while it was fed through a few feet of test clip wire. I could see it developing a "motor boat engine" sort of oscillation and before I could completely understand the issue and decide exactly how I wanted to remedy it, the output died and it started drawing a lot of DC current. I don't understand exactly why this happened. It is made to drive speakers through several feet/meters of wire but perhaps the impedance of the modulation transformer with the extra L from the test clips and the added parasitic C put it into instability.

I wanted to replace it but since the original supplier to Stretchy does not appear to be selling these any more, I started looking around for replacements.

I don't know if there is one but I am here to tell you one that is NOT a replacement: https://www.parts-express.com/tpa3116d2-2x50w-class-d-stereo-amplifier-board-with-volume-control--320-699

I found it online. It looks very similar to the original amplifier. I didn't even bother telephoning to see if the dimensions were close because I assumed that the customer rep would not have that information. For $7 US, I just bought it instead. Once it arrived, three problems came up.

  • The placement of the volume knob and the audio input jacks are not in the right place to fit the holes in his enclosure. This is pretty much the show-stopper.
  • There is no 12 V regulator that you would need to power the DDS and FET driver. Though it does have a switched volume knob and I did find the PCB trace with the switched DC input voltage, so one could connect that to the input of a 12 V regulator.
  • Despite my best effort, I was unable to put the module in PBTL (mono) mode. The TPA3116D2 datasheet is clear that the two L inputs need to be DC-grounded when powering on to enable PBTL mode, and then one can take the mono output off the L and R outputs, with the L+ shorted to L- and R+ shorted to R-. In any case, despite finding what I am 99% sure were the two L inputs to the TPA3116D2 and grounding those, I was unable to get the module to work in a mono mode, as described by the datasheet.
Since it didn't fit the enclosure holes anyway, I didn't bother messing with it any further. Since I went to the trouble of making Stretchyman's TX not self-destruct (so far, anyway), I will probably pair it with a different mono amp and put it in another enclosure, since nothing available with sufficient drive seems to fit the existing enclosure.

Just wanted to give people a heads up that this product is not a drop-in replacement.

Following up:https://www.hfunderground.com/board/index.php/topic,71438.msg240668.html#msg240668

The RF Workbench / Stretchyman 40 W TX Reliability Modifications
« on: September 10, 2020, 0634 UTC »
It's been a few months since I visited this forum or posted here. I've had other things going on (e.g., keeping my employment). You might remember I wrote up the issues on Stretchy's 40 Watt TX here:https://www.hfunderground.com/board/index.php/topic,67747.msg230885.html#msg230885

Some of you wrote me to tell me that you had exactly same problem. Some of you asked for more detail. I finally got back to looking at what needed to be done to modify for reliability in August and this is the result. For the two of you that wanted to see this, here it is.  :D

Link: https://app.box.com/v/h5a3lyzgep45pzz49

EDIT: Fixed the title. It will be great once I learn to spell correctly.

Much of Cuba was simply too far over the horizon to get a strong-enough TV signal from aircraft flying in U.S. airspace. Still, the effort moved ahead.

What people saw, Armstrong said, was “a moving shadow of an image of . . . something. At something like 4 a.m.”

I'm thinking that a TV transmitter on an airplane is likely moving too fast for clear reception on anything but receivers fairly close to the transmitter, hence the ghosting. The blimp might have been a better choice from that perspective.

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