Xtronic XDC-4SO RF Coupler

JJ4SDR
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Xtronic XDC-4SO RF Coupler

Postby JJ4SDR » Sat Jan 07, 2023 9:43 pm

Hi,

I will be using an Xtronic XDC-4SO RF coupler with my Alpha 9500 amp, but wondered about the 3000 W PEP rating. That will be plenty enough on SSB. However, I do get on CW quite a bit as well and as Pure Signal doesn't really benefit you on narrow bandwidth modes such as CW I would not be using PS at all.

With the above in mind, will I need to switch out the RF coupler and manually adjustable RF attenuator combo out of the circuit completely when I get on CW? If I put out close to full-legal limit on CW the 3000 W PEP rating won't be enough and might "fry" in case it is in the circuit.

Awaiting your suggestions!
Juha
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K1LSB
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Re: Xtronic XDC-4SO RF Coupler

Postby K1LSB » Sat Jan 07, 2023 11:01 pm

I can't answer the question of what is the max CW power that unit is capable of handling, but just to clarify, PureSignal only benefits signals that are composed of a mix of two or more frequencies in the passband. It has no effect at all on CW.

Mark
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Re: Xtronic XDC-4SO RF Coupler

Postby JJ4SDR » Sun Jan 08, 2023 12:09 am

Mark,

Yes, I know that. I talked to another ANAN user just now and he told me that the RF coupler doesn't really do more than provide a pass-through so the logic is that I wouldn't have an issue on CW even if the RF coupler pass-through is in the circuit. It seems to make sense.

I could also shoot the manufacturer an email.

Just being super careful is all.

Juha
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w-u-2-o
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Re: Xtronic XDC-4SO RF Coupler

Postby w-u-2-o » Sun Jan 08, 2023 12:46 am

There's probably not anything to worry about.

I have one of the original, prototype Xtronic couplers that Dave was making before he went into the real business of making them commercially. At the time he said they were good for 1500W key down all day long.

The 3000W PEP rating supports this assertion.

PEP is a fancy way of saying "peak". Your peak power will not be over 1500W. But, yes, there is nevertheless a thermal limit to consider. Since the common practice is to equate PEP with SSB phone operation, what this means in practice is that a device rated for 3000W PEP should handle an average power of 50% of that. The basis of that assertion is that the generally accepted worst case peak to average power ratio of speech is 3dB, or 50% (and it's normally quite a bit less). Thus a device rated for 3000W PEP should be able to handle 1500W average, continuous power.

That should be enough, but if this is still not sufficiently convincing, consider that the short term duty cycle over a period of less than a few seconds of CW is also approx. 50%. Thus the average power measured over a few seconds during CW operations will be closer to 750W. While the integration period to arrive at that average is perhaps a bit longer than the second or two one might use for phone, it is still pretty short. It's not like it's key down for 5 minutes and then key up for 5 minutes.

Finally, it matters not that the primary coupler path is a "pass-through". That path will have insertion loss. And insertion loss creates heat. So the RF power rating (really a thermal rating) of the coupler is going to be limited by the structure's ability to dissipate that heat.

Run some phone at 1500W. Check the coupler to see how warm it is. Run some FT8 at 750W and do the same. Then run some CW at 1500W for a few minutes and recheck. There probably won't be much of a difference either way.
JJ4SDR
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Re: Xtronic XDC-4SO RF Coupler

Postby JJ4SDR » Sun Jan 08, 2023 2:33 am

Scott,

I really value your very detailed response and explanation. You made your point in a compelling manner.

Not doing FT8 presently, so I will run some tests on CW.

There is something I am not liking too much in terms of what I am seeing on the display when PS is doing its magic (compared to what I saw when using the FR2K-S SSPA), but that belongs in another sub-forum.

Thanks!

Juha
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w-u-2-o
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Re: Xtronic XDC-4SO RF Coupler

Postby w-u-2-o » Sun Jan 08, 2023 12:16 pm

Why did you give up the RF2K for the Alpha?
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w9ac
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Re: Xtronic XDC-4SO RF Coupler

Postby w9ac » Tue Jan 10, 2023 2:23 pm

Three weeks ago, I received an RF-Kit RF2K-S amplifier. 2T IMD performance compares favorably with my Alpha and ACOM tube amps and about 10 dB better than my SPE 1K-FA amp.

The attached images show typical 2T IMD at 1500W from the RF-Kit amp using an Xtronic coupler. I don't normally use it and prefer a capacitive divider, but the result is the same no matter which type of sampler is used. Using an external sampler and not RF-Kit's internal sampler allows me to select one of several desktop amps without having to change sampler cabling.

Paul, W9AC
Attachments
RF2K-S PS-On 40m 1500W.jpg
RF2K-S PS-On 40m 1500W.jpg (324.51 KiB) Viewed 3189 times
RF2K-S PS-Off 40m 1500W.jpg
RF2K-S PS-Off 40m 1500W.jpg (316.25 KiB) Viewed 3189 times

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