Panadapter "view" in TX with DUP on - using PS

K9RX
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Panadapter "view" in TX with DUP on - using PS

Postby K9RX » Tue Feb 13, 2018 2:00 pm

I've been using Puresignal for months now ... I've had people stop in and say how narrow the TX'd waveform was ... except on 75 meters. Twice now over the last couple of weeks I've had two different stations break in and say I was spattering - bad. They said i was not TOO strong ... last night the guy said there was significant energy on the USB part of the spectrum. He said it was at best only 20 db down.

Here's the thing - the displayed view, using DUP, showed at least 55 db down on both sides and I had the proper green "correcting" boxes going on.

So ... what gives? I thought what I see on the panadapter while TXing using DUP is indeed my signal - what was going out the coax ... is it possible that it is spattering and yet I'm not seeing it? I asked a local ham to listen ... he was using a Flex3000 ... unfortunately I was only about 25 db above his noise level but he said, although he was a bit confused, that he did see the sloped shoulders starting above the noise floor ...

embarrassing to say the least ...

Gary
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DL2XY
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Re: Panadapter "view" in TX with DUP on - using PS

Postby DL2XY » Tue Feb 13, 2018 4:05 pm

Do you use an external sampler unit behind your Expert2K ?
Is it correctly attached and configured to be the PS sample input ?
Do you have MON and DUP enabled?

Walter
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K9RX
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Re: Panadapter "view" in TX with DUP on - using PS

Postby K9RX » Tue Feb 13, 2018 4:43 pm

Walter, Sorry - left that detail out - indeed I'm using the Expert 2K with a Xtronics XDC-4SO coupler on its output.

I'm seeing what is a clean signal on the panadapter while using DUP ... which I understood was essentially an actual "received" signal display so highly accurate ... and it is at the output of the amp so it is "looking" at the amps output. Its obviously configured "right" because it IS working at least as far as I can see. I can hit the PSA button and it will go to a normal output of about 30 db down to the shoulders ... turn it on and within a couple seconds it recovers to a measured minimum 50 db down with often more like 60 and even 65 db. I HAVE had people tell me they were amazed at how clean the signal was - how they could literally sit right next to my passband, when I'm S9+, and hear absolutely nothing ... note those reports were with a previous 8000DLE (which failed and was replaced) -

but the point of this question is: If I am SEEING it - is that "real"? I don't know if these two reports, both from stations in my call area (i.e. somewhat around me, 200 - 500 km away) were honest or they were just messing with me?

Note unless I'm mistaken MON doesn't need to be on for this ... only DUP and as indicated yes its on.

Gary
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Re: Panadapter "view" in TX with DUP on - using PS

Postby AB2EZ » Tue Feb 13, 2018 6:29 pm

Gary

When transmitting... with DUP active.... the panadapter displays the spectrum of the total signal arriving at the input to RX1.

This consists of the sum of two RF voltages:

a(t): The sample of the amplfier's RF output that is being fed into RX1 from the coupler at the output of the amplifier

b(t): "Crosstalk" arriving at the input of RX1 from sources other than the coupler at the output of the amplifier

Pure Signal acts on a(t) + b(t), not on a(t).

If the amplitude of a(t) is much greater than the amplitude of b(t) than the spectrum displayed on the panadapter with Pure Signal active is approximately the same as the spectrum of the signal at the output of the amplifier.

Quantitatively:

If a(t) is (for example) 20dB larger than b(t) ... then Pure Signal will reduce the IMD at the output of the amplifier (not just the IMD displayed on the panadapter) by approximately 20dB vs. the IMD at the output of the amplifier when Pure Signal is not active. If a(t) is (for example) 30dB larger than b(t) ... then Pure Signal will reduce the IMD at the output of the amplifier (not just the IMD displayed on the panadapter) by approximately 30dB vs. the IMD at the output of the amplifier when Pure Signal is not active.

It appears that you are not actually feeding a large enough sample of the output of the external amplifier into RX1 (when transmitting). In fact, you may not be feeding any of the signal at the output of the external amplifier into RX1 due to a configuaration problem in the Pure Signal feedback path.

Stu
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Re: Panadapter "view" in TX with DUP on - using PS

Postby AB2EZ » Tue Feb 13, 2018 8:24 pm

Adding to my post (above) ... it is my understanding that some ANAN 8000 owners have reported an assembly error... in which the two internal Pure Signal cables that attach to the Pure Signal in and Pure Signal out connectors on the rear of the transceiver are swapped.

Stu
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Re: Panadapter "view" in TX with DUP on - using PS

Postby K9RX » Tue Feb 13, 2018 9:29 pm

Stu,

Ok .... indeed there has been a reported issue with the connections on the back being reversed - but is it even possible that it would work at all?

It DOES appear to be working at least re what I'm seeing displayed. AND when I include the amplifier you can clearly see that the SATT value changes adjusting the attenuation to now accommodate the larger input ... doesn't this all indicate that I AM connected correctly and I have a large enough sample (it iS adjusting for the "proper" value IN the radio after all)?

How could b(t) be of any level relative to the amp output!? The amp output is what 60dbm? Anything that is going to play a significant role, i.e. after the coupler's attenuation, would have to be in the radio - i.e. it would be a radio fault - correct? I again note this is a new radio - when I had those glowing reports previously it was with a different 8000 ... that stated I don't know if I've noticed anything different from one to the other ...

Gary
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Re: Panadapter "view" in TX with DUP on - using PS

Postby AB2EZ » Wed Feb 14, 2018 12:56 am

Gary

It is also possible that the sample of the RF being produced by the Xtronics XDC-4SO coupler is a distorted (non-linear) sample of the RF. There are a number of things that could cause this. For example, the coupler contains ferrite-core transformers. If one of the cores has been damaged by overheating... there could be heavy saturation occurring in that core/transformer when the external amplifier is producing high output power. It is also possible that something like an open ground connection...in one of the cables that connect to the coupler... is causing a transformer core saturation problem.

If the sample of the RF output of the amplifier is not linearly related to the amplifier output signal ... then Pure Signal will be linearizing the distorted sample of the amplifier output that it is being fed...not the actual amplifier RF output signal.

Separately:

If the sample of the amplifier output being fed into RX1 is too large (i.e. step attenuator reading more than 30dB when transmitting)... then the front end of RX1 may be overloading... again, producing a distorted signal for Pure Signal to act on.

Stu
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Re: Panadapter "view" in TX with DUP on - using PS

Postby w-u-2-o » Wed Feb 14, 2018 1:44 am

K9RX wrote:Stu,

Ok .... indeed there has been a reported issue with the connections on the back being reversed - but is it even possible that it would work at all?
Yes, it is possible that it will work under these circumstances, but you can tell because you will see an abnormally low S-ATT value.

It DOES appear to be working at least re what I'm seeing displayed. AND when I include the amplifier you can clearly see that the SATT value changes adjusting the attenuation to now accommodate the larger input ... doesn't this all indicate that I AM connected correctly and I have a large enough sample (it iS adjusting for the "proper" value IN the radio after all)?
Not necessarily. If you are at 1.5KW (62dBm) and are using an Xtronic coupler (-44dB), then your output from the coupler will be approx. +18dBm. Given that the PS auto-attenuate algorithm seeks to obtain +3dBm at the ADC inputs, and your 8000 uses a 14dB pre-amp, then the S-ATT value under those conditions should be approx. 29dB.

What level on the S-ATT are you actually seeing? At what output power level from the amp? And this is on an 8000?

Note also that I do not recommend more than +13dBm on any radio input. There is a danger of damaging things if the S-ATT value is not high enough. The max. no-damage input to the pre-amp is +13dBm. You would be well advised to add a 6 or 10dB attenuator onto the output of the Xtronic coupler.

How could b(t) be of any level relative to the amp output!? The amp output is what 60dbm? Anything that is going to play a significant role, i.e. after the coupler's attenuation, would have to be in the radio - i.e. it would be a radio fault - correct? I again note this is a new radio - when I had those glowing reports previously it was with a different 8000 ... that stated I don't know if I've noticed anything different from one to the other ...
The 8000 doesn't really have significant internal crosstalk. However some of the older radios did. It was not unusual to see feedback signal to crosstalk ratios of only 10dB on older radios (100, 100D, and 200D's with Rev. 15 or 16 PA boards).

See also this thread.

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