New Aurora converter - help wanted with review
 

I have the new low cost Aurora standards converter on the bench for review at the moment and apart from a couple of minor problems it's working well.

I could do with some help on the RF side of the review. The only 13 channel TV I have working is not a very good set and far from ideal for assessing the multichannel modulator. Is there anyone not too far from me with a good working 13 channel TV (or more than one of them!) who could help. I'm happy to travel to you within a reasonable radius of North Finchley or you could visit my lab.

Your help will receive due credit in the review that I'm writing for the BVWS Bulletin.

Re: New Aurora converter - help wanted with review
 

Hi Jeffery,

I'm sorry but i can't help you with the 13 channel tv, but i would be very interested in your review of the converter.
I have just e-mailed Aurora to find out if these are now generally up for sale as i am seriously considering buying one.
I would much appreciate anything you have to say about this piece of equipment.

Cheers (and good luck finding the tv for the review),
Alan. :thumbsup:

Re: New Aurora converter - help wanted with review
 

If you fancy a trip up to Birmingham I have a Pye 17" 13 channel setthats in good working order. And several 625 sources to select from, Computer, Video, DVD etc...

Andi

Re: New Aurora converter - help wanted with review
 

Thanks Andi but I was hoping for somebody a bit closer. Otherwise I may post it up to David Boynes who has a lot of good sets and experience of evaluating converter performance.

Re: New Aurora converter - help wanted with review
 

Hi,
interestig are the non superhet sets (is this called TRF?) like LV20 TS1105 because they catch
noise near the channel too.
Kind regards
Darius

Re: New Aurora converter - help wanted with review
 

Hi Jeffrey,

What about my sony 9-90?

Maybe a screen shot of a Spectrum analyser showing the RF output?

Cheers
Sean

Cheers
Sean

Re: New Aurora converter - help wanted with review
 

Sean, that's effectively what I'm using except it's the monitor version CVM-90UB. It's hardly a set I'd use for critical assessment. I've already looked on the analyser and seen loads of harmonics which don't matter in a closed circuit environment. Otherwise the RF output looks fine on the analyser. What I need to look for is more subtle things like patterning and sound/vision crosstalk. I've got a suspected patterning problem on channel 10 which could easily be the set and a possible digital breakthrough problem on channel 3.

I'm trying to get hold of John Thompson (not a forum member) who's not too far from me and has a selection of sets. I may also go down to Gerry's museum though he doesn't really have 13 channel sets on display.

The review is going well otherwise. The video output is excellent (no surprises there) and a couple of minor problems I've found will be ironed out before any are delivered to customers. I just need to get a good look at the modulator performance and then I can submit the review to Carl for publication.

Re: New Aurora converter - help wanted with review
 

Hi Jeffrey, the problem is to suppress noise in the channel and a few MHz
up and down. If you have a 50% white screen there should be no moire
visible. The suppression of noise in the channel should be much better than
60dB against peak white.
To put the modulator and converter in one box is not easy!
An unfair trick is to blow the modulator level to more than say 95dB and put an attenuator in front of the set. I am not sure about the motorola IC stand
alone on the low VHF frequencys. The results of the axing there don't make
me optimistic.:-/ But axing is not aurora:)

Kind regards
Darius

Re: New Aurora converter - help wanted with review
 

Hi Jeffrey,

I have just purchased a large Ekco (14"?) set, I hope to collect it this evening, and maybe get it working on Saturday - I wonder if this would help you with the review?

Cheers
Sean

Re: New Aurora converter - help wanted with review
 

Thanks to all of you who have offered help. I went to Gerry's last night and will be visiting a local forum member tomorrow. I hope this will allow me to complete the review.

Re: New Aurora converter - help wanted with review
 

My review will appear in the next BVWS bulletin. Thanks to Gerry Wells, John Thompson and Graham Davis who made TVs available and gave encouragement.

I don't want to pre-empt the printed review but there is no doubt that the new Aurora is a very good design and good value at around £150. At the NVCF we had the chance to compare the Aurora directly with David Robinson's design. Both modulators use the same Freescale chips. On ch9 the performance was almost identical, even when we attenuated the signals which tends to cause more patterning. We did not have time to do comprehensive trials on all channels but we noted that ch10 was still the most susceptible to patterning though the effect was small. To minimise or eliminate patterning there are 2 golden rules.

• Don't attenuate or split the signal (use a distribution amp to feed multiple sets)
• Use good quality cable and connections.

Re: New Aurora converter - review now published
 

My review of the Aurora converter has now been published in the BVWS Bulletin. I am now happy to publish the text here.

Re: New Aurora converter - review now published
 

Yes, I noted that it is in print.

I'm looking forward to reading it at lunchtime tomorrow. It probably means I'm going to get hooked on the vintage TVs as well as wireless - thanks! :-)

Regards,

Re: New Aurora converter - help wanted with review
 

Good morning ,
thanks to Jeffrey for this very interesting review.

It made me thinking and I have some technical questions.

On Page 15 BVWS Journal DC offset you wrote:
„In this design the sync tips are at about 0.2V which will not cause any practical problems.“
Page 33 „...the simple emitter follower output stage.“
So the sync tips are not on the zero rail?! How is this stage made? How much ohms is the pull down resistor of this emitterfollower ?

Another question in the modulator sync tip level page 15.
„The Aurora’s modulator puts them at 10%.“ Means modulation depth is 90% in your case.
In the aurora manual page 20 is written „99% maximum“
But have a look at the data sheet attached:
minimum 87% typical 93% maximum 99% What value should we take?
And with the sound ist is the same, because it goes via the vision input of the other IC.

Kind regards
Darius

Re: New Aurora converter - help wanted with review
 

I think that Darryl should answer these questions but here is my opinion.

The output stage is a simple NPN emitter follower. The emitter resistor is 200R. The base is biased slightly positive.

I measured the minimum vision modulation as 10% at sync tip. I did not look at the manual or the data sheet. It does not matter if the sync tip is anywhere between 0% and 10% provided it is reasonably stable.

I did not measure the audio modulator in detail. If it can only reach 90% modulation I would not regard this as a problem. This is equivalent to 1dB down from the maximum possible. A 1dB difference is just audible by direct comparison

Re: New Aurora converter - help wanted with review
 

Yes, I agree. And maybe you'll get a 99%.;D

The emitter follower with 0.2V sync tip and 200 Ohms pull down causes problems with some for example vintage DIN AV inputs on VCRs. They have a cap in front of the 75 Ohms load and this will cut the sync signal.:( I've seen some modulator schematics using cap loaded emitter inputs too. So this vision output can cause trouble.

Kind regards,
Darius

Re: New Aurora converter - help wanted with review
 

If there is a cap before the 75R termination that is bad design.

Re: New Aurora converter - help wanted with review
 

Yes, definately. But they exist. Was it a common french modulator we discussed here?
It is not a problem to drive them, if you change the biasing of the emitter follower. For example 1 volt at the sync tips. In this case there is enough pull down current.;)

Kind regards
Darius

Re: New Aurora converter - help wanted with review
 

If the modulator is like my design, the sound modulator is set to System I, negative vision mod, and the input is biased by a preset pot which acts as an adjustment for the sound/vision carrier ratio. With this arrangement, 100% sound modulation depth is not a problem, in fact it will go beyond 100% (inverted carrier)! This is because the peak sound power on 405 should be equal to the peak white vision power, but the modulator when working with negative mod, has more than peak white to sync tip range (as peak white is 20% carrier).

Re: New Aurora converter - help wanted with review
 

Hi David,
Sorry,I don't agree. I think there is a confusion with modulation depth and sound/ vision carrier ratio. These are different and independent things.
If you use the vision input for sound and switch the IC to negative vision mode (means PAL vision mode SYSL=0) you'll get something between 76% and 88% typical 82% modulation depth.
If you use your bias pot for the sound/vision ratio adjust it will be lower.
There is a biasing for maximum modulation depth, the sound/vision ratio adjust must be made with the output adding resistors.

Kind regards,
Darius