[hpsdr] New HPSDR card for VHF/UHF ?

[Phil Harman]

Hi Grant,

Thanks for your input. I feel sure that VHF/UHF Atlas boards are in the
HPSDR future so your input is very much appreciated.

If you could find that time the draw a block diagram I think that would
progress the design discussions significantly.

I understand that you are proposing a I/Q up/down converter system using
the same ADC as we used on Janus.

How would such a system compare with a transverter feeding Mercury/Penny?

The reason for my question is the DDC/DDU techniques we have been using
for the past few years overcomes the I/Q phase/amplitude correction issues
required with direct conversion techniques - particularly with the sort of
dynamic ranges you are proposing.

Whilst the art of correcting such errors has advanced in the past few
years, if there was not a significant performance difference then my
preference would be for a transverter approach.

I look forward to your comments.

73 Phil...VK6APH




> ***** High Performance Software Defined Radio Discussion List *****
>
> More numbers, opinions, speculation, dreams...
>
> The FT225RD with Mutek front end has a (measured) Input IP3 of approx.
> 0dBm.
> That's the IIP3 of the whole receiver system, and must not be confused
> with
> figures for just part of the system such as mixers, transverters etc.
>
> The FT225RD is a good benchmark for any new 144MHz designs - for many,
> many
> years it was widely regarded as the best 144MHz transceiver, some still
> consider it so.
>
> I did some system calculations for a design of a 2m direct-conversion
> variant
> of the microwave SDR (uWSDR) project which I presented at the RSGB VHF
> convention in 2009.  This indicates that a system IIP3 of +15dBm is
> achievable
> with a system NF of 2dB.  That's ~100dB spurious-free dynamic range, or
> ~150dB
> blocking dynamic range.
>
> The limiting factor would then be phase noise; -120dBc/Hz at 10kHz offset
> isn't too difficult for a PLL but I'm not sure if that is good enough and
> I'm
> not sure how it compares to the FT225RD, so a better LO may be needed in
> order
> to achieve best-in-class performance.  But PLL technology marches on and
> it
> may be possible to beat this figure now without too much difficulty.
> There's
> also the possibility of a very low spur and phase noise DDS solution using
> the
> AD9912.
>
> The system calculations were based on the LT5517 I/Q Downconverter with an
> SPF5043Z LNA and the same ADC as used in Janus - AKM5394a.  I/Q
> upconverters
> and PA MMICs giving ~100mW are now readily available for 144MHz.
>
> A lot of the initial work has been done for a 144MHz front-end for the
> uWSDR
> project and it wouldn't take a huge amount of effort to produce a VHF or
> even
> UHF version for the Atlas bus with class-leading performance especially
> given
> that Janus is available.  I've done a lot of the ground work for such a
> system
> and would be happy to share it with anyone who could take it further
> whilst I
> try and get the original microwave side of the project kick-started again.
>
> I'll try and get the Powerpoint presentation uploaded to the 'net if there
> is
> any interest, although it's very similar to the one I gave at Microwave
> Update
> in 2007 which is on the website :-
>
> uwsdr.net
>
> regards
>
> Grant G8UBN
>
>
>
>
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