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Author Topic: Stretchyman 40 W TX Reliability Modifications  (Read 798 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 »
"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!

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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
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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.

"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!

         15W and100W models available.

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                                              ;)

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.
"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!

         15W and100W models available.

                   Buy one from me, NOW!


                                              ;)

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
netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 900 ft Horz skyloop / 500 ft NE beverage / 250 ft V Beam / 58 ft T2FD / 120 ft T2FD / 300 ft south beverage / 43m, 20m, 10m  dipoles / Crossed Parallel Loop / Discone in a tree

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 couldnít 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 Ďpullingí 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 itís 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. Itís not quite so noticeable above 1kHz but itís there and because itís 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!

         15W and100W models available.

                   Buy one from me, NOW!


                                              ;)

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 couldnít 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 Ďpullingí 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 itís 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. Itís not quite so noticeable above 1kHz but itís there and because itís 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 »
"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?

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