Aurora converter possible design change

[tubesrule]

I'm evaluating a change to the SCRF converter design that would allow for more features at the same cost, like 405 NTSC color in the standard unit. This change would eliminate the passive audio trap filter in favor of a digital one. This means better characteristics and no adjustment to drift, but it also means that when operating in the converter bypass mode, no audio filter would be provided in the video path. This filter is used to make sure that no frequencies in the video signal that are close to the audio carrier frequency will cause noise in the audio. Normally this isn't a concern as there are usually no frequencies this high in the video, or at least none of substantial power.

So my question is has anyone ever used the converter bypass mode, and would anyone care if this were to change?

Thanks,
Darryl

[Panrock]

Hi Darryl,

I have used the modulator only (converter bypass) feature on occasion since I have a fair few old 405-line VHS tapes. I doubt if anything off them would get up to 3.5 MHz though. In any case nowadays I use my Domino for this task so no worries.

In the past (for the hell of it) I used to put 625 colour through my David Looser Ch1 modulator and watch on a multi-standard JVC. Then vision buzz on the sound did become an issue but it was still easy to remove with a little rejector trap in the vision input.

Thanks for the great product.

Steve

[Boom]

I'm a bit lost here Darryl. I asked before about adjusting the filter to try and cure slight VOS and was told to leave it well alone!

In the event I think the VOS buzz was probably just a bit of rf overloading. An attenuator seems to stop it. Maybe if it was an adjustable feature users might try to adjust a fault out by twiddling it and run into trouble?

Maybe I have misunderstood what you mean?

Dave

[murphyv310]

Hi Darryl.
Like steve I do occasionally use the modulator only feature.
I think though if I do buy another the mod would be fine as I would only use one of my Auroras for bypass mode.
Cheers
Trevor

[tubesrule]

Thanks Steve. I was also thinking that a simple external filter could be used if required, but probably wouldn't be needed in most cases.

David, there is a variable cap on the current unit that is set during assembly and should never require readjustment. You can adjust this cap by using a spectrum analyzer or oscilloscope, but it would be difficult to just use the audio. Overload can cause audio buzz as you mentioned, and an antenna pad will help that situation.

Darryl

[ppppenguin]

405 line video source material is going to become less important over time. Hence the video bypass "modulator only" facility is becoming less and less useful.

Can we assume that all the folks who will need video bypass already own an Aurora? I'd be pretty sure of that. Unless you know otherwise.

[Dave Moll]

My long-term plans include using a modulator (such as an Aurora in modulator-only mode) to send the 405-line output of my RT Russell test-card generator to my 405-line sets, so I would be sad to see this avenue closed unless it were necessary for the future development of the Aurora.

[tubesrule]

This change is certainly not required, and I'm thinking it may be better to leave well enough alone at this point. It was just something that came up with the addition of a new fpga in the same family. It would seem to make sense that having the filter would be a benefit to more people than say 405 NTSC would be, but I welcome more feedback.

Darryl

[peter_scott]

Could we have 405 / 240 (Baird) instead?

Peter

[tubesrule]

Hi Peter,
Probably not. The problem here is you really need to save one field of the 625 input so that you can blend it with the second field to create the progressive image required by 240. That requires about 200KB of memory. Alternatively you can just throw one field away, but you still need about 100KB of memory since you need to stretch the one 20ms input field out to 40ms. This converter design relies on the internal memory of the fpga, and there just isn't that much available.

Darryl

[BGmidsUK]

Interesting idea. Though I haven't gotten round to making any 405-line recordings yet, I do intend to experiment with this. Assuming it would still work OK for video sources such as those from 405-line video recordings, I can't foresee a problem. Though it's unlikely I'll be experimenting with 405 colour in the near future I wouldn't rule it out entirely! Especially having seen the impressive results on David's set (Fernseh)


BG

[tubesrule]

Update and a couple more questions:

After a lot of number crunching, I'm going to basically leave the design alone. The sound trap will stay, so using the modulator by itself will not change.

I am still looking for cost saving ideas to keep the price in check, or possibly lower it. With this in mind I have a couple more questions.

1) Does anyone use the equalization pulse mode in 405? My guess is this really doesn't provide much benefit, and generating the original 405 signal to spec is all that is required. True?

2) This is a more radical idea; removing the internal option switch and replacing with a digital scheme. This means there would never be a reason to open the unit up as all user control would be from the outside. I envision something like the following:

Say there are 4 options for the unit. When you press the user button, it will flash yellow X number of times (X being 1 through 4 for this example) showing the particular option, and then red or green to show if the option is on or off. Pressing the user button again takes you to the next option and so on. Holding the button down on any option toggles between red (off) and green (on). The scheme would always return to the option you left off with, for example if the converter bypass is at option 3 and that was the last one you changed, then the next time you go into this mode it would start at position 3. This way you don't need to scroll through the possibilities to get to the same option.

The plus side to this scheme is cost and no need to open the unit. The down side is you can't just look at a switch like you can now and see what state each option is in. Thoughts?

Please be honest as I won't be offended if I've gone too far on the second proposal

Darryl

[Boom]

Originally Posted by tubesrule

Please be honest

Mine works absolutely fine so IMHO leave well alone.

[Patrick Dixon]

If you go for the soft options option, I'd suggest a program mode that can only be entered by pressing and holding a button within a few seconds of (or on) power on. You would then have the option to review current settings and change things in a similar way to your suggestion.

I have some stuff that can be programmed by pressing a button in normal use, and it's a pita if you accidentally press the button and it resets itself ...

[cobblerscottage]

Hi Darryl, I have been trying to contact you but your Email address keeps bouncing back! Perhaps you can Email me then I can ask your advise about my 4 Aurora's.

Leslie Hine

[brianc]

Originally Posted by tubesrule

1) Does anyone use the equalization pulse mode in 405? My guess is this really doesn't provide much benefit, and generating the original 405 signal to spec is all that is required. True?

Equalising pulses were never used in 405 line transmission so why would we need them now? Interlace was not good on some sets because of design but that's how they were. Don't let's cure their problems, they're part of the charm of vintage TV receivers.
Cheers
Brian

[BGmidsUK]

I do have the equalizing pulses set to "on" on mine but I can't say there is any noticeable difference, and to be honest I'd be more than happy with an authentic signal. I only switched them on to see if it would have any effect on the poor synchronization on my Sony TV9-90 sets.

The option button is a great idea. Much better than opening the unit and possibly risking static damage etc..


One thing I'd love to see (either included as an option in the unit or available as an add-on) is a proper filter so the Auroras can be ganged up and/or combined with the antenna/cable distribution. This is something I'm happy to pay extra for.


Brian

[tubesrule]

David,
We engineers just can't seem to leave well enough alone Since I will need to build more units very soon (down to 2 left) I thought I would take the opportunity to reduce the cost if I could do so without impacting the functionality. I have made some internal changes that in no way affect the operation but make it easier to setup during production.

Patrick,
The user button is recessed and requires a paper clip or the like to operate. This really isn't that different from what's required now with the dip switch that requires a paper clip and removal of the top. Since there are so few options, and I doubt people ever change them from factory or after they make initial adjustments, so it just seemed like a good area to reduce cost if possible.

Leslie,
PM sent.

BrianC,
Those were my thoughts exactly. I don't think the eq pulses are a good option since it looses something of the original signal which is what this converter is all about, and their effectiveness on a set that wasn't designed for them is questionable.

BrianG,
Ah, your response came in just as I was typing this. Thanks for verifying that the eq pulses really do have limited value. I think this one is decided.
You are spot on with the main reason I thought of the push button for the option switch; no reason to ever open the unit and risk possible damage. Everything will be accessible from the outside. It's also nice that you don't need to keep putting those philips screws in an out.
I've thought about an output filter to reduce the harmonics, but the problem is compounded by the agilent modulator. The output filter would need to track the channel switch which would complicate the design. Alternatively a filter could be set above the highest channel, but this would then have little effect on the worst harmonics of the lower channels. I'll revisit this one before sending the build out, but I'm not hopeful.

Thanks for all the feedback guys,
Darryl

[ALANS ANITAS]

Hi Daryll

As a prospective owner of an Aurora, I would not like the setup controlled by a number of presses of a button. Trying to set such devices as infra red remote controls and car radios etc. I find it annoying if you accidently key in the wrong code, you then have to start again. A dip switch is much easier, and you can see at a glance the settings.

I'm afraid my purchase will have to be delayed a while as our one year old cat had to be rushed to the Vets with a leg injury. We do'nt know how she became injured, but we have been told it could cost quite a lot of money to fix.

Regards

ALAN

[ppppenguin]

I'm not a great fan of "push button A for 5 seconds, then button B while standing on one leg" type of user interfaces. I know that in the real world you may want more functionality than you have space for real knobs but it doesn't mean I like it.

I approve of the EQ pulse option (even if rarely used) because it allows users to investigate the old debate on the subject and the adequacy or otherwise of sync separator designs.

Please drop the sleep option.