Aurora vs Dinosaur

[Jac Janssen]

A quick comparison (please excuse the bad photos):

Video output of the Hedghog:
   

Video output of the Aurora SCRF405:
   

Pineapple:
   

Domino:
   

old Aurora MSC:
   

Dinosaur:
   

All viewed on this "precision" monitor:
   

I do not have (m)any sets that can reproduce the 3 MHz bars, so just the video outputs of the standards converters for now.
Only the Aurora SCRF, Hedghog and Domino have an RF output.
The Dinosaur obviously has a problem getting the definition bars of 2.5 and 3 MHz in the right place.

Jac

[Richard_FM]

All viewed on this "precision" monitor:


I do not have (m)any sets that can reproduce the 3 MHz bars, so just the video outputs of the standards converters for now.
Only the Aurora SCRF, Hedghog and Domino have an RF output.
The Dinosaur obviously has a problem getting the definition bars of 2.5 and 3 MHz in the right place.

Jac

Slightly OT but has that set been modified to display 405 lines?

[Jac Janssen]

Yes it has.

It can now display 625, 525, 405, 441 and 567 line pictures.
(Although 405 and 441 with bad linearity.)

   

Jac

[ppppenguin]

Jac, thanks for the practical demonstration.

From memory I recall that the BBC CO6/509 digital converter used a subcarrier notch ahead of the ADC. This was to prevent the colour dot patterns being converted to something potentially horrible looking on 405. Inevitably this limits the resolution, just as it does on older colour TVs. Good comb filter decoding in PAL was always much harder than in NTSC. The TVP5150 as used in Aurora SCRF and Hedghog does a pretty good job, with minimal artefacts. I've also used the SAA7118 which isn't quite as good.

If you know your 625 source is monochrome then you don't need any filtering but the decoder can't work this out for itself unless the burst isn't present.

[Mike Watterson]

OT

As for SDR, only the most expensive ones will be doing direct synthesis for TX (or ADC for RX) at much over a few MHz. Where "a few" is not well defined but might be as low as 10MHz or as high as 50MHz. Typically they will work at IF and use up (TX) or down (RX) conversion. not really my field but they may well use quadrature conversion. Mike, as you found, many will be working at very much lower IF.

Frank Cuffe and I both did some work on DDS for Band 1. He got a decent result for 45MHz vision using a sample rate around 200MHz. DACs for this sort of speed are readily available. I think his was 14 bit. I did a rough trial at about 16MHz with about 80MHz clock. My setup (borrowed from another project) wasn't really suitable . for anything higher. It's all written up somewhere here on GVR.

TX and /or Generation is MUCH easier than RX (or video capture):
* DACs are easier to do MUCH cheaper and faster than ADCs. Even resistors and FPGA or PIC output pins can do to generate video up to at least SVGA.
* While oversampling makes output filters simpler, it's less critical than input filters for ADC. The 48 KHz of MP3 doesn't mean 24 KHz or even 22kHz audio. It's to make the antialiasing filtering simpler. A sharp filter just above the required band creates ringing / poor transient performance and pass band ripple. Even FM radio needed filters to limit deviation and also later to prevent interference to the 19kHz pilot for the DSBSC 38KHz L-R channel. The CD Audio 44.1kHz was a compromise for achievable anti-aliasing filters, below the 22.050 KHz, and to suit the digital tape archive based on a Sony helical scan system. Later A/D was done at twice or four times rate to have "better" cheaper analogue filters and then DSP decimation to 44.1 KHz. Probably there shouldn't be much difference in frequency response for FM radio, CD, MP3 or DAB. The differences are in distortion, especially at lower bitrates of DAB and MP3. Low bit rate (digitally created distortion) is worse for people with poorer hearing.
* DDS can be done in SW + DAC, discrete HW, or ADI single chips. You can use DDS with say a 20MHz IF and then upconvert to 50MHz to 1GHz etc. Higher frequencies, 5GHz to 400 GHz may use a second IF in the 450MHz band and a monolithic filter for the unwanted sideband. DDS has been done for DVB-S, DVB-T, DVB-C and DAB. Usually the DAC o/p is in the 50MHz band. Most DVB-S, DVB-T, DVB-C and DAB test gear and feeds for transmitters uses IF, with a filtered conversion to desired band. For my 10.240GHz DVB-C transmission experiments I replaced the modem uplink input (5 to 65MHz band and the uplink for data is normally 0.8, 1.6, 3.2 or 6.4MHz) with the IF out of DVB-T/DVB-C/DVB-S PCI card in the PC, at about 50MHz. The MPEG2 multiplex stream was encoded in advance with MPEG4 / H.264 SD and HD channels, which took all day for a 2 hour loop on a PC. You need seriously expensive gear to encode multiple TV channels in real time.

[Richard_FM]

Yes it has.

It can now display 625, 525, 405, 441 and 567 line pictures.
(Although 405 and 441 with bad linearity.)



Jac

That's very interesting, almost worth a thread on it's own.

[ppppenguin]

From Jac's description, I think he's using the set as a video monitor. So there are no RF system issues with different standards. The problem will be the line timebase. 625, 525 and 567 are all close enough in H frequency that there should be no problem. But 405 and 441 are rather lower frequency which means it can be hard to optimise the line output stage. Getting both line scan and EHT right at the same time could be a challenge.

[peter scott]

A quick comparison (please excuse the bad photos):

Video output of the Aurora SCRF405:


Jac

Well it looks like I need to revisit my Aurora 405 line performance and apologise for suggesting less than 3 MHz performance. Will check again when I get home.

Peter  

[ppppenguin]

When viewing test card C from an Aurora on a professional 405 line monitor (Prowest PM14/1) either at Dulwich or at home the image is so sharp you could cut yourself on it. Assuming the "£$%^& Prowest is working. Both need attention AGAIN Though recently when I've been doing 405 to 625 experiments the 405 images have been from an Aurora SCRF and the resolution has looked a bit down. I didn't do a full investigation (and must do it soon) but strobing out the test card F frequency bars on the 405 output suggested something wasn't quite right.

When I next get this back on the bench I'll have another look. I know that the later Auroras have a digital notch filter at the output to reduce vision on sound. This also affects the video output unless it set to channel "0". IE modulator turned off. I think the earlier Auroras had an LC notch in the feed to the modulator only. But a sound notch shouldn't significantly impact video BW.

[Jac Janssen]

Well it looks like I need to revisit my Aurora 405 line performance and apologise for suggesting less than 3 MHz performance. Will check again when I get home.

Peter  

Hi Peter,

As before, I am very impressed with the bandwidth / focus of the CRT in your 901!
   

This seems to be an ideal set to test the Aurora under similar conditions.
I'm looking forward to the results.

Jac