[hpsdr] Hermes Pure Signal

[Helmut]

Hi Warren,

Many thanks for response. 
I believe Alfred is presently on vacations and not available for more
detailed information.  The previous tests did also not include special
intractable amps with significant memory effects. But it’s a nice challenge
to succeed with minimal complexity at least for most cases. We are also
squinting to this low-cost RED PITAYA board, which has basically all onboard
we hams need: Two 14 bit ADCs, coherent 125 MHz sampling source, Xilinx Zynq
7010 SoC CPU/FPGA, 1 Gbit-Ethernet and two RF output ports (14 Bit DAC).
This small board is already working fine with mRX PS v.3.3.6.!!! Tests have
to continue.

Enjoy upcoming Holiday Saison.

73, Helmut, DC6NY

-----Ursprüngliche Nachricht-----
Von: Hpsdr [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Warren
C. Pratt
Gesendet: Donnerstag, 17. Dezember 2015 17:13
An: hpsdr at lists.openhpsdr.org
Betreff: Re: [hpsdr] Hermes Pure Signal

***** High Performance Software Defined Radio Discussion List *****

Hi Helmut,

I believe you are correct in all your statements.

We had a team member who worked on applying the feedback technique that 
Alfred is using.  The bottom line is that I believe that team member 
then became very busy with work activities and so we abandoned the 
approach.  There are two issues with that approach ... one should be 
very solvable.  The solvable issue is getting the delay matched between 
the two paths ... this is really just a matter of determining the exact 
differential delay since I have already implemented software to provide 
arbitrary sub-sample delays.  The second issue which will have some 
effect on the quality of the result is that, in the dual-down-conversion 
approach, the CIC and FIR filters are matched in characteristics like 
overshoot and passband ripple.  I believe this matching allows us to 
achieve a better result.  I don't know how much better since we don't 
have a working example of the other approach.

73,
Warren  NR0V

On 12/17/2015 7:05 AM, Helmut wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi,
>
> I do understand the desire of Atlas-based-HPSDR owners for digital
adaptive
> pre-distortion and their question why nearly the same hardware doesn't
work
> with PS.
> As far I know - hopefully Warren will correct me, when I'm wrong - two
> separate RX-DDC-paths are employed in the current PS version: One path
> converts the analogue 'distorted' feedback-signal from the amp into a
'fast'
> data-stream, followed by the digital I-Q mixer and CIC filters for down
> conversion into the baseband. The second equal RX-path is fed directly
with
> the 'fast undistorted' TX- data stream, collected at the DAC input and
> up-converted from baseband to the operation frequency. As the
nominal-actual
> comparison has to be made in the baseband (or better in the PC) this
> solution was chosen to provide the necessary correlation of the samples.
> It's meanwhile an approved way to provide the essential information for
> error correction of amplitude and phase, but  it's also evident that this
> design requires a lot of FPGA resources and that the necessary 'high
speed'
> data transport between Mercury and Penny via the given Atlas structure is
> not possible.
> As mentioned in a previous post, Alfred, HB9EPU made another approach for
> his Atlas-based HPSDR: He used the 'standard' RX-path in Mercury for the
> feed-back signal in Dupe mode to feed one port of the baseband 'sample
> comparator'. The other port is supplied with the corresponding 'clean' TX
> samples. His kind of sample correlation makes things easy to apply on
> Atlas-based-HPSDRs with good results. Two different solid state amps (300W
> and 700W) show under his adaptive pre-distortion application acceptable
> IM-performance of around 50 dBc.
>
> Sorry, when using too much bandwidth.
>
> 73, Helmut, DC6NY
>
>
>
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