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Technical Topics => The RF Workbench => Topic started by: Charlie_Dont_Surf on September 10, 2020, 0634 UTC

Title: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf 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 (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 (https://app.box.com/v/h5a3lyzgep45pzz49)

EDIT: Fixed the title. It will be great once I learn to spell correctly.
Title: Re: Stretchyman 40 W TX Relaibility Modifications
Post by: ChrisSmolinski on September 10, 2020, 1200 UTC
Thanks for sharing. As an engineer I find design reviews/improvements very interesting to read. You often learn something you can later use yourself.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on September 14, 2020, 0849 UTC
I have developed a drop in PCB and most have already received one, for any that haven't please PM me.

It delays the 24V until the 12V and oscillator is fully up.

Str.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: ChrisSmolinski on December 17, 2020, 1849 UTC
I wonder if there's any mods that can be done to reduce FMing, such as improving (or adding, as I suspect there is none) the stability of the voltage regulation on the oscillator?  (Not sure which wattage version this is)

(https://i.imgur.com/0ymn1N3.png)
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf 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.

Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on December 18, 2020, 0902 UTC
Early versions were Xtal and whilst no FM is audible to the human ear, SDRs are somewhat more critical. There's no way to stop this issue with the first version other than closing your eyes.

All versions beyond V1 use an AD9833 DDS and are not prone to any FM issues.

No one uses Zeners anymore btw and the 5V DDS regulator is an MCP1754S.

Want any info?

Why not ask me?

Regards.

Stretchy.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on December 18, 2020, 2102 UTC
No one uses Zeners anymore btw

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

Quote
- 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.

https://www.marketwatch.com/press-release/zener-diodes-market-rising-trends-with-top-countries-data-technology-and-business-outlook-2020-to-2026-2020-10-13 (https://www.marketwatch.com/press-release/zener-diodes-market-rising-trends-with-top-countries-data-technology-and-business-outlook-2020-to-2026-2020-10-13)


Why not ask me?

He was looking for info and he did. End of story.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on December 19, 2020, 0831 UTC
You're so right..
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: ChrisSmolinski on December 19, 2020, 1325 UTC
Some voltage regulation might have prevented 1 kHz or more of FMing. But hey, it also serves as a transmitter fingerprint  :)   
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on December 19, 2020, 1821 UTC
I'll say again..It's regulated.

It has nothing to do with Voltage regulation at all zenered or not.

There some text around the net explaining another designers issues showing the same problem. Using any Xtal controlled transmitter will show the same Fming issues if viewed on an SDR.

Quote from the text follows....

I tried various means of making an oscillator for 3.615MHz along with a VFO to cover that frequency but I couldn’t get one stable enough. It varied only a few Hertz but that was enough to cause asymmetric sidebands (one sideband output higher than the other). A crystal oscillator would be the ideal solution but as with most components these days, they are not readily available and more than one will be needed for other frequencies. There is a UK company that can make these but they will not be cheap because they are not mass produced. I tried ‘pulling’ a ceramic resonator to frequency and although I could cover the required frequency, it was varying by a few Hertz. This is not detected on air because it’s only a tiny fluctuation but on SDR it can be seen as asymmetric sidebands on the AM transmissions. This shows on average a 6dB difference in levels in the sidebands at low frequencies. It’s not quite so noticeable above 1kHz but it’s there and because it’s there it will be noticed and will commented upon. Fig. 2 shows perfectly symmetrical sidebands at 300Hz. Before SDR no one would know or even care but with many operators using SDR they look for any imperfections! So, a stable oscillator had to be found. I tried a GPS and etc etc...

Ok.

Str.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on December 21, 2020, 0416 UTC

There some text around the net explaining another designers issues showing the same problem. Using any Xtal controlled transmitter will show the same Fming issues if viewed on an SDR.

Quote from the text follows....

I tried various means of making an oscillator for 3.615MHz along with a VFO to cover that frequency but I couldn’t get one stable enough. It varied only a few Hertz but that was enough to cause asymmetric sidebands (one sideband output higher than the other). A crystal oscillator would be the ideal solution but as with most components these days, they are not readily available and more than one will be needed for other frequencies. There is a UK company that can make these but they will not be cheap because they are not mass produced. I tried ‘pulling’ a ceramic resonator to frequency and although I could cover the required frequency, it was varying by a few Hertz. This is not detected on air because it’s only a tiny fluctuation but on SDR it can be seen as asymmetric sidebands on the AM transmissions. This shows on average a 6dB difference in levels in the sidebands at low frequencies. It’s not quite so noticeable above 1kHz but it’s there and because it’s there it will be noticed and will commented upon. Fig. 2 shows perfectly symmetrical sidebands at 300Hz. Before SDR no one would know or even care but with many operators using SDR they look for any imperfections! So, a stable oscillator had to be found. I tried a GPS and etc etc...

I find that explanation a bit problematic:

1) The author of the text you lifted (without attribution or reference, BTW) is talking about a few Hertz of variation. Chris' image shows much more than that.

2) Back in the day, every ham used to use crystals exclusively. Many didn't have VFOs until the early 1960s. I can totally believe that crystal generated signals hop around a little bit. How much? Who knows and if there was only a few Hertz of variation on a CW signal generated from a crystal, it might not have been noticeable in 1950, especially with all the other key clicks and whatever going on. But more than ~20 Hertz variation would have been very obvious on a CW signal. So you are saying that dudes back in the day with their FT-243 WW2 military surplus crystals were FM'ing ~1 KHz all the time? Pffft.

No, I'm sorry, but no one would have been able to make a CW QSO if that were the case and RST 599 reports would have been unheard of.

To be clear - I'm not saying that crystals are perfectly stable; I'm sure that they are not. However, I don't think that the fact that the reference was a crystal in your old transmitters explains all the FMing that Chris shows (and others have reported). So I'm suggesting that there might be something else going on in addition.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: CoolAM Radio on December 21, 2020, 1254 UTC
Why being so negative about comments?

               Keep the Peace!  8)  -  It's almost Xmas!


André
CoolAM Radio - Shortwave
the Netherlands

   
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on February 11, 2021, 0524 UTC
Why being so negative about comments?

               Keep the Peace!  8)  -  It's almost Xmas!


André
CoolAM Radio - Shortwave
the Netherlands

 

Hi André - I am sorry that you feel that way because on the other 364 days of the year people might come to this thread for answers, without the "burden" of being in the "Christmas spirit", and find nothing. It's now nearly 2 months later and we have no answer.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on February 11, 2021, 0546 UTC
Chris - I think that the answer lies in the power dissipation of the crystal.

This makes sense to me because:
a) Where there is power dissipation, there is heat.
b) Where there is heat, there is a temperature change and drifting oscillators.
c) A crystal is pretty simple. What the heck else could it be?
d) I found references that say so. Here is one:

https://worldradiohistory.com/Archive-DX/Ham%20Radio/70s/Ham-Radio-197603.pdf (https://worldradiohistory.com/Archive-DX/Ham%20Radio/70s/Ham-Radio-197603.pdf)

On page eleven, in the third full paragraph in the left column:

Quote
The permissible maximum power dissipation of crystals in the 1 to 20 MHz range, operating in the fundamental mode, is about 200 microwatts and is  similar for overtone operation. ... Operating a crystal above or near this level degrades its stability, and the circuits chosen here avoid this problem by limiting the dissipation.

Further down:

Quote
The main point to remember is  that crystal  oscillators are meant to provide a stable frequency source, not power output. Frequency stability, both short and long term, and crystal life are compromised when an oscillator is operated at an excessive power level.

I have no idea whether Stretchy's circuit goes beyond tolerable limits. I'm just putting this out there for thought.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on February 11, 2021, 0932 UTC
Just to be clear before you slag me off anymore.

The very first ever design I made was an unashamed copy of the venerable LuLu design. Fat better than any other design to date and I must emphasise not my design. All I ever did was make a PCB to make replication a simple matter.

It uses a Xtal which I had to get made at considerable cost (£14 ea.) and managed to get quite a few units made (100 approx).

That was five years ago and all designs since 2016/17 have an AD9833 DDS.

At the time of the first design I was unable to find anyone to write SW to program the DDS but since finding someone and now having the SW it's a no brainer to use and the DDS's are $2 and will prog to any freq upto <12MHz.

There is absolutely no reason why anyone would use a Xtal anymore and even the programmable oscillators for Cardinal are far superior and are perfect for single channel use.

I still suspect most 'simple' Xtal controlled designs to exhibit some form of FM that's visible on an SDR.

So as I must say again it's not my design, however  there are other designs out there that are and Yes you've slagged those off as well....

I'll continue to improve my designs and learn from any mistakes made, I hope they are few and seem to have many happy and repeat customers.

I look forward to seeing any design from particularly yourself or anyone else for that matter that you mass market and build 100+ units.

I doubt (know) that this will ever happen.

I look forward to your reply.

Str.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on February 14, 2021, 0040 UTC

The very first ever design I made was an unashamed copy of the venerable LuLu design. Fat better than any other design to date and I must emphasise not my design. All I ever did was make a PCB to make replication a simple matter.

It uses a Xtal which I had to get made at considerable cost (£14 ea.) and managed to get quite a few units made (100 approx).

That was five years ago and all designs since 2016/17 have an AD9833 DDS.

...So as I must say again it's not my design, however  there are other designs out there that are and Yes you've slagged those off as well....


Your name and email address are on the PCB silkscreen. You probably put your "STRETCHYMAN PIRATE RADIO" stickers (a ripoff of Breaking Bad) on the case too. But now you are claiming because the original design came from someone else that's it's not your fault?

I'm sorry, but you own that problem.

The rate of occurrence of this weird drifty oscillator issue is more than some sort of random, chance occurrence. You shipped "several" of these units but apparently never put them through sufficient validation and or any sort of burn-in to confirm that they stay stable over time.  If you had, then you would have found this issue. Just like you would have found the famous high-voltage snap that takes out either the drain filter cap or the FET or both (and caught on fire in front of me), but you didn't, because you don't know what you are doing and can't be bothered.

Designs get shared and tweaked all the time. There's a fellow named Paul Brokaw, whose Brokaw Bandgap Cell (https://en.wikipedia.org/wiki/Brokaw_bandgap_reference (https://en.wikipedia.org/wiki/Brokaw_bandgap_reference)) is used as a reference in nearly every IC from all manufacturers since the 1970s. There are billions of these things around the world now. By your logic, if someone makes a Brokaw Bandgap and fucks it up, then we should complain to Brokaw and not the person who fucked it up? Riiiiiiighhhhhhht.

You want all the accolades and none of the responsibility.


I still suspect most 'simple' Xtal controlled designs to exhibit some form of FM that's visible on an SDR.

Cool, except that a sudden drift of 1 KHz that Chris showed is not FMing.





I look forward to seeing any design from particularly yourself or anyone else for that matter that you mass market and build 100+ units.

I doubt (know) that this will ever happen.

I look forward to your reply.


So very nice of you to invite me to play the "my balls are bigger than yours" game. Explain to me how many you've shipped has anything to do with your ability to solve problems before they are created? Apparently none. And shipping lots of defective product is the hill you've chosen to die on? And the barrier to entry for whether something is "worthy" or not is not whether it's good, it's just that you've shipped many of them, warts and all?

Also, what good would it be for me to put a schematic out when most of my problem with you is that you are absolute crap at validating and testing? You aren't going to learn those skills from a schematic.

(Shaking my head)

My professional life is in the design, validation and manufacturing and post-sale support of electronics that sells in somewhat higher orders of magnitude than what you are talking about, but please do tell me more about the the 100 you made over the course of a many years. It's amusing to me in a very haughty sort of way.

Since I have been doing this for decades, I've give you a couple of lessons for success:

1) If you don't know something, don't pull some bullshit text off the internet and use it to justify your preconceived notions. Look into yourself. Figure it out. If you don't have the answer, say, "I don't know but I'm looking into it." The smart people I know admit when they don't know something and don't make shit up.

2) Test your shit out extensively. Build 10 and put them through their paces. Leave them on for a long time. Examine design marginalities. Push and pull the design before you ever ship any product.

3) Despite your best efforts (which you have not made, see above), there will be post-sale problems with your products. Don't sweep them under the rug. Fix it or make it up to the customer.

I'll say it again: You want all the accolades and none of the responsibility. You don't know what you are doing, and don't care to know how to do things better.

As for my designs, my employment is somewhat engrossing and I'm not interested in becoming a BIG TIME PIRATE SUPPLIER MOGUL like you apparently are. I get my jollies by shipping good product that doesn't catch on fire right in front of customers.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: redhat on February 14, 2021, 0705 UTC
Boys,

Can we do with a little less hostility?  There is already enough negativity on the web.  If this must continue, please take it elsewhere.

Thanks,

+-RH
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on February 14, 2021, 1153 UTC
Yeh, he's being such a TW*T

Just ignore...
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on March 15, 2021, 2113 UTC
Just ignore...

There you go. Keep your head in the sand and keep thinking that your shit don't stink. At least you are on brand.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Dare4444 on January 22, 2022, 1934 UTC
Use DDS 9850 board with Arduino and 2n7000 for very high quality professional sounding AM signal. I'll paste the code if needed. Its output is 10mW. Feed it to two parallel 2n7000 each with 1ohm source resistor and set the standing current to 15ma each with a variable pot connected to their gates. It's drain can then be connected to the final linear amplifier. No crystals or complex synthesizer needed. A simple Arduino code sets the TX frequency!!

https://ibb.co/3TMm2gb

Arduino Sketch.

#define W_CLK 13       // Pin 13 - connect to AD9850 module word load clock pin (CLK)
 #define FQ_UD 8     // Pin 8 - connect to freq update pin (FQ)
 #define DATA 10       // Pin 10 - connect to serial data load pin (DATA)
 

 #define pulseHigh(pin) {digitalWrite(pin, HIGH); digitalWrite(pin, LOW); }

 // transfers a byte, a bit at a time, LSB first to the 9850 via serial DATA line
void tfr_byte(byte data)
{
  for (int i=0; i<8; i++, data>>=1) {
    digitalWrite(DATA, data & 0x01);
    pulseHigh(W_CLK);   //after each bit sent, CLK is pulsed high
  }
}

 // frequency calc from datasheet page 8 = <sys clock> * <frequency tuning word>/2^32
void sendFrequency(double frequency) {
  int32_t freq = frequency * 4294967295/125000000;  // note 125 MHz clock on 9850
  for (int b=0; b<4; b++, freq>>=8) {
    tfr_byte(freq & 0xFF);
  }
  tfr_byte(0x000);   // Final control byte, all 0 for 9850 chip
  pulseHigh(FQ_UD);  // Done!  Should see output
}

void setup() {
 // configure arduino data pins for output
  pinMode(FQ_UD, OUTPUT);
  pinMode(W_CLK, OUTPUT);
  pinMode(DATA, OUTPUT);
 

 
  pulseHigh(W_CLK);
  pulseHigh(FQ_UD);  //
}

void loop() {
  sendFrequency(1e6);  // Enter freq here, Right now Set to 1000,000 Hz ,1000KHz, 1MHz . Example, for 1540KHz enter 1.54e6 in the sendFrequency bracket above. I hope this is easy to understand
  while(1);
}
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on January 23, 2022, 1115 UTC
https://www.analog.com/media/en/technical-documentation/application-notes/an-423.pdf

Yes, we've known about this for sometime!

25 years!

However generating low power A M. and using a linear isn't very efficient. Plenty of folk still using that method as they don't know any better!

Class E is the way to go, Simple, Efficient, Perfect!

+ DDS's are generally used to generate frequencies these days and are a single chip and as simple to program as an Arduino. Complex synths and PLLs are no longer nessarary.

No point searching the web for any decent designs as all you generally find is a load of old rubbish designs from 30+ years ago.

Modern design are usually confined to datasheets from the manufacturer or others in the know...

Str.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on February 20, 2022, 1813 UTC
No crystals or complex synthesizer needed. A simple Arduino code sets the TX frequency!!

No disrespect to you personally intended but I consider myself to be comfortable enough with microcontrollers and synthesizers to be "dangerous" with them and I don't feel this to be a terribly simple solution. You need a microcontroller, you have had to write software for it, then the output is pretty weak and it will need a decent linear amplifier (which you have not discussed here) to boost the output to be heard farther than 10 meters away. Also, I don't consider the AD9850 to be a particularly simple synthesizer. Perhaps it appears that way if you treat it like a black box and don't know what's going on inside but I don't recommend doing that. (I actually don't feel that any synthesizer is "simple".)

To be clear, there is a need and a place for synthesizers and I don't know how you do a AD9850 (and the like)-based synth without something providing the digital words to them (here, it's a microcontroller) but let's not pretend that this is a simple solution.

So not my cup of tea, but to each his or her own I suppose.

Finally, I'm not quite sure why this ended up here in this thread. It's completely unrelated to the original topic.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on February 21, 2022, 0731 UTC
Indeed, somewhat off topic.

However once you have the code written it's a no brainer.

I have 64ch code for the AD9850 PCBs that are readily available. The opposing squarewave outputs will drive FET drivers directly. Commonly use for class D/E push pull.

Also have single channel software for the AD9833 (<$2) PCBs and use a discrete 3 tran amp to get to 5V p-p to directly drive FET driver for single ended transmitter.

Saves all that xtal nonsense!

Str.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on February 21, 2022, 2147 UTC
I don't know how many versions of your synths you have gone through but the ones that I have used have always ended up a bit lower in frequency than I would like - usually about ~100 Hertz low. We're not expecting WWV accuracy here and the consequences of this are not the end of the world but I think that we can agree that they could be closer to target.

I suspect that a number of the loggings on this website indicated as "xxxx.9 KHz" (more or less) come from your synths, but I can't prove that. Perhaps this is yet another way to identify one of your transmitters on the air.  ;D
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: ChrisSmolinski on February 21, 2022, 2223 UTC
I suspect that a number of the loggings on this website indicated as "xxxx.9 KHz" (more or less) come from your synths, but I can't prove that. Perhaps this is yet another way to identify one of your transmitters on the air.  ;D

There may indeed be a statistical anomaly regarding frequency offsets from integer values in pirate loggings. I will add it to the list of things to investigate  ;D
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on February 22, 2022, 0735 UTC
Well..They aren't GPS locked or anything fancy just plain DDS which rely on the internal clock being exact. Quite easy to reprogram them to a higher (offset) frequency to negate the error.

If anyone would like such, get in touch!

Who cares anyway I wonder?

More window watchers?

Str.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Brian on February 22, 2022, 1811 UTC
I don't know how many versions of your synths you have gone through but the ones that I have used have always ended up a bit lower in frequency than I would like - usually about ~100 Hertz low. We're not expecting WWV accuracy here and the consequences of this are not the end of the world but I think that we can agree that they could be closer to target.

I suspect that a number of the loggings on this website indicated as "xxxx.9 KHz" (more or less) come from your synths, but I can't prove that. Perhaps this is yet another way to identify one of your transmitters on the air.  ;D
I run 2 rigs here. One Xtal and the other a very cheap Chinesium DDS. The DDS is cheaper than an Xtal (about 20 bucks plus a few more for connectors and the rotary encoder), goes up to 50 MHz and is adjustable in 1 Hertz steps. Less drift than the Xtal rig.
Problem is not getting it to be xxxx.ooo but having the way to measure this accurately.
With the DDS, I'm probably more on channel than many legal stations.
Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Charlie_Dont_Surf on February 26, 2022, 2020 UTC
Quite easy to reprogram them to a higher (offset) frequency to negate the error.

Someone asked me privately last year if there was a way to fix the offset. I was very bored over Xmas and finally got around to reverse engineering several of your .hex file codes for 43 meters to figure out corrections and get them a lot closer to the intended target (~ +/-20 Hz off, instead of -100 Hz).

The other thing to note is that there are multiple sources of drift or frequency shifts. Most of them are pretty small and not worth worrying about. The largest one is that the synth takes a big jump of ~ -70 Hertz when the final transistor is turned on. That could be due to many reasons but I'm guessing it's due to supply voltage shift. My corrections take this into account but because of self-heating and temperature drift with time, it can't be better than ~ +/- 20 Hertz over the long term, which I feel is acceptable.

Title: Re: Stretchyman 40 W TX Reliability Modifications
Post by: Stretchyman on February 27, 2022, 0900 UTC
I've made the offer and no one has asked.

I'll ask again.

If you have a programmable TX and the frequency is offset by xxx Hertz please let me know the frequency +/- XXX and I'll send you the revised .Hex file to put you bang on frequency.

Very simple for me to do.

Please get in touch by email.

Str.