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Author Topic: Stretchyman 40 W TX Reliability Modifications  (Read 8598 times)

Offline Charlie_Dont_Surf

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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.
« Last Edit: September 25, 2020, 0602 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline ChrisSmolinski

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Re: Stretchyman 40 W TX Relaibility Modifications
« Reply #1 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.
Chris Smolinski
Westminster, MD
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Offline Stretchyman

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #2 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.
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline ChrisSmolinski

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #3 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)

Chris Smolinski
Westminster, MD
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Offline Charlie_Dont_Surf

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #4 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 don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Stretchyman

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #5 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.
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline Charlie_Dont_Surf

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #6 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


Why not ask me?

He was looking for info and he did. End of story.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Stretchyman

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #7 on: December 19, 2020, 0831 UTC »
You're so right..
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline ChrisSmolinski

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #8 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  :)   
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
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Offline Stretchyman

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #9 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.
« Last Edit: December 19, 2020, 1828 UTC by Stretchyman »
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

Offline Charlie_Dont_Surf

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #10 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.
« Last Edit: December 21, 2020, 0530 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline CoolAM Radio

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #11 on: December 21, 2020, 1254 UTC »
Why being so negative about comments?

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


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Offline Charlie_Dont_Surf

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #12 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.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Charlie_Dont_Surf

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #13 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

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.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Stretchyman

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Re: Stretchyman 40 W TX Reliability Modifications
« Reply #14 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.
« Last Edit: February 12, 2021, 1645 UTC by Stretchyman »
'It's better to give than receive' so why Rx when you can Tx!

                                              ;)

 

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