Amplifier two-tone test

K9RX
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Re: Amplifier two-tone test

Postby K9RX » Sun Oct 20, 2019 1:04 pm

Anan 8000DLE

Using 2 tone test with Expert 2K-FA I see -65db or better. I see typically -60 on SSB.

Using 2 tone test with Elecraft KPA1500 (2XLDMOS) I see -50db. I see typically -45 to -50 on SSB.

Both at ~1200W out.

Disappointing as for other reasons I'm switching to the KPA1500, but from what I understand its the nature of the beast with LDMOS devices. Nothing the amp maker can do about it.

Gary
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w-u-2-o
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Re: Amplifier two-tone test

Postby w-u-2-o » Sun Oct 20, 2019 1:35 pm

Gary,

Those are very good numbers, which suggests you did might not have performed same test as Rob Sherwood, NC0B.

Unless I am interpreting Rob's results improperly, what they show is that Rob used PureSignal to linearize the 7000DLE only, then used the 7000 as a linearized exciter to drive the amp with the cleanest signal possible. This makes sense, as he would be hard pressed to find a lab-grade signal generator capable of 30 to 50W of output.

The amp, on the other hand, is left to operate in its natural state, i.e. without PureSignal linearization. The intent being to show how poorly, or well, the amp performed from an IMD standpoint when provided with the best input signal possible, certainly better than it would normally have from a more typical amateur radio transceiver.

The results are completely predictable. No amateur radio, or amateur radio amplifier, has good IMD performance at its specified maximum RF output power level. Obviously this makes a strong case for additional linearization methods, hardware and/or software-based, for ham radio equipment.

Indeed, Rob's results are a best case scenario, as the two tone signal will allow the power meter to read very accurately. Imagine how bad this gets when people raise their drive in order to see consistent maximum power readings when running phone on their average reading power meters.

It would have been interesting to see what the performance was for each amp running at half specified maximum RF output power, just to see if there was any improvement.

Also, it's a bit confusing that there is only a single table of 7000DLE measurements. One would think the drive conditions for each amp would be a little different.

73,

Scott
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Re: Amplifier two-tone test

Postby w-u-2-o » Sun Oct 20, 2019 3:39 pm

Helmut wrote:Comparing the IMD at the output of the amplifier with an Analyzer or other SDR-Radio with sufficient attenuation to the RX in DUP mode on the Anan - should give the same results when RX Bypass on TX is checked ? The Anan gets the feedback via RXBypass input (7000dle) and the internal coupler is bypassed - so it displays the real output IMD after the amplifier on the Anan RX.

Therefore it is no need the check the output after the amplifier with an Analyzer or SDR ?
That is actually incorrect. As soon as you check Bypass on TX then RX1 looks at the Bypass input for PureSignal corrections. If you are using a coupler on the output of an external amp to look at this signal via the Bypass port then PureSignal will be linearizing the external amp.

The only way you can use ANAN series hardware to do this experiment properly is to a) use a model with a second ADC (200D, 7000, 8000), attach the external coupler output to RX2 (the second ADC input) and watch on RX2. Meanwhile you must leave Bypass on TX OFF.

73,

Scott
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Re: Amplifier two-tone test

Postby w-u-2-o » Sun Oct 20, 2019 6:53 pm

Helmut,

We may each be writing about two different things. To clarify:

If you select Bypass on TX and have the Bypass port connected to an appropriate coupler, then you are indeed seeing what is coming out of the coupler when DUP is ON.

The problem is that you cannot do that and perform Rob's experiment. Bypass on TX must be OFF on the 7000 in order for the 7000 to switch to the internal coupler during TX so that only the 7000 is linearized, as the experiment requires that only the 7000 (or whatever hardware you are using) is linearized, not the amplifier.

If you wish to perform Rob's experiment, then Bypass on TX must be OFF, only the radio is linearized, but you can monitor the output of the amplifier coupler on RX2 if you wish.

73,

Scott
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Re: Amplifier two-tone test

Postby w-u-2-o » Sun Oct 20, 2019 9:26 pm

Helmut wrote:So there is no need to check after the Amplifier with another coupler on the Power-Meter to an Analyzer or second SDR-Radio - as the results are the same - as I measured today and posted in this thread before.
Unless you are doing Rob's experiment. Then you have to use another path other than Bypass to monitor the output of the amplifier. I hope you understand that.
K9RX
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Re: Amplifier two-tone test

Postby K9RX » Sun Oct 27, 2019 7:31 pm

Helmut,

I can't say. I don't know if the issue is something associated with the structure of the LDMOS devices or not. That was my thought, that it was associated with the LDMOS construction - its a hell of a lot of power in one very small package vs. with the Expert 2K at least there are 8 MRF151's.

Assuming the PIN diodes are biased off when transmitting I'd not think they'd have an impact - or if so only at higher powers ... if they are conducting at all they'd be damaged in an instant so one has to believe they're doing their job and are off when they need to be. Are there other suggestions/tests done that suggest PIN diode switching increases IMD?

Gary
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