Hedghog 625-405 standards converter

[Murphyv310]

Hi.
Thanks for the info Steve.
Some of the changes appear to be very small and I wonder if the customer or even the engineer would have seen any notable changes on screen or the way the receiver operated after these alterations?
Today i believe we are blessed with very good standards converters for our hobby through the work of dedicated people like Darryl & Frank

So far I would like to add this.
Hedghog........
Good points:
Excellent conversion
Accessible front switches
Cool running
No motion artefacts
Covers all Band one & three channels.
Switchable Aperture (2, 3 & 6 line interpolation)
Switchable audio test tone, off, 400Hz, 1Khz.
Conversion video output

Not so good points.
PM5544 internal test pattern, not a big issues though.
Unable to program a user test image.
No audio level control.
Not useable as standalone modulator

The advantages out weigh the disadvantages though and overall the converter is a very competent.

..................................................................................................................................................................................
Aurora SCRF converters.
Good points.........
Small size.
Tried and tested over many years
Test card C stored image
Can be programmed with user test image
Audio level control.
Good conversion with only very occasional motion artefacts.
Availability of NTSC 405 line colour..... to order!
Can be used as a standalone modulator
Conversion video output

Not so good points.
Fiddly dip switches on early models and even more fiddly setting up on later types
Slight HF rolloff that gives the picture a very slight flat appearance.
Runs warm in the smaller case.

So not a lot to choose being fair, both do a very good job.
My own summing up and of course is my own opinion is the Aurora is well known and has had a tiny amount of failures often caused by the operator, it is compact and easy to use, to my mind the small disadvantages are not a big problem, but I am making observations.
The Hedghog being the new kid on the block as yet has not been around long enough to test the reliability, I suspect though it should be as reliable as the Aurora. I particularly like the front switches, which are much easier than the DIP switches in the Aurora that means opening up the case, switching the test pattern on or off on the Hedghog is also an advantage rather than removing the video or audio leads or the signal on the Aurora, so the Hedghog can be more or less left in place whereas the Aurora may have to be moved more often. This is pretty minor being fair but the Hedghog is a little more user friendly.
Like I've said, subjectively the Aurora does look a little bit more flat than Frank's Hedghog, certainly I never complained before and I'm still not complaining, where you do see the difference is on a bigger screen with a set that has good alignment and the difference is notable.

Finally I'd say the Hedghog has the edge, weighing up the user switches, the aperture switch and a slightly less flat picture that is my reason, yes there is a few small niggles in the Hedgehog but being fair nothing to really cause concern.

I will be running both converters on a regular basis and any reliability issues or problems and I will post up.
Again many thanks to Frank for his generosity with giving me the converter.

[`FRANK.C]

Hi Steve
Thanks for the documents, they are very good quality scans.
I note that the front porch in the days of 5:4 were quite short 0.5 uS aprox. also the introduction of pedestal in 1956.

Hi Trevor
Some good points there you cant beat another set of eyes looking at something.
The MC44BS373 are great modulators and not having direct access to them is certainly a disadvantage, an extra phono connector or switch either electronic or mechanical would have sorted that out. Not having an external audio gain control was an oversight. To have one would just have meant a slight PCB change and fitting a vertical rather than a horizontal preset.

One great thing about building your own is you can build whatever way that suits yourself the best.
I think it very unlikely that any commercial design would use toggle switches as the cost is too high. A 10 pole DIP switch would cost less than half of one toggle switch. There is also the extra costs of larger PCB and case needed to accommodate them, probably would cost more to assemble and possibly larger delivery costs. Which all adds up to make it not viable.
I was thinking afterwards that I could have fitted a LCD display and push switches for less. I still prefer the toggle switches.

Frank

[ppppenguin]

Trevor, I don't see how an Aurora SCRF can give any motion artefacts. It doesn't have a field or frame store so inherently has no temporal or interfield processing. It may be possible for the decoder chip to give some motion related effects but the same chip is used in both Aurora and Hedghog.

Frank has written of the realities of design for manufacture. The Aurora has been tightly costed, the Hedghog much less so. If, like Frank, you're making a few prototypes then a few pounds on the bill of materials matters little. If you're doing a fair size run then costs matter a lot more.

[Murphyv310]

Hi Jeffrey.
I do occasionally get "stuttering" on fast moving scenes on all my auroras that are not apparent on the 625 line source material, so far I've not seen this on Frank's converter. Like I said earlier I'm going to be running both over the next few weeks and even months, perhaps the Hedghog will display the same issue....... Only time will tell as it is not a consistent issue.

I totally agree regarding the costing. David Boynes did tell me that his TTL converter ran into four figures so impractical for hard pressed collectors.

[Murphyv310]

Hi.
Just an update on the converter.
Since my last comment in March I decided to put the Hedghog on constant test, it has now been running 24/7 since the 16th March, fed from a freeview box tuned to RTE1 I thought this would give the converter a run for its money as RTE can be iffy from the ninimux, as it can occasionally drop out on wet days. During this time there were no problems and the converter is running faultlessly.

[`FRANK.C]

Hi Trevor
That's great news, thanks for doing that. Sorry for the very late reply, I had to pull the plug on vintage stuff for a while. Just starting to slowly wind it up again on the variac .

If anyone is interested I have started to upload the files for this project to a site here.

Frank.

[djrm]

Greetings everybody, I'm a new member here.
I found this site whilst looking for a signal source for my Ekco TMB272 which I have just aquired.

I've always wanted one of these portable TVs since first seeing one back in the '70s and one came my way last week, my first TV restortion project.
I have a raster and the receivers are working using a RaspberryPi to generate RF signals and making sounnd and patterns.
I do not have any information about test and re-alignment, just a schematic available as yet.

Frank's Hedghog design looks just what I want, especially as I alredy have some of the parts and a little experiance with the Altera FPGA in microprocessor emulations.

Frank, do you have any spare bare circuit boards available please?
Kind regards, David.

[ppppenguin]

David, welcome to GVR. Frank's Hedghog is an impressive design, showing that it's possible to achieve professional standard results with fairly limited resources and a lot of perseverance.

How have you used the R-Pi to generate 405 signals?

I'm susrprised I can't find a Trader sheet for the TMB272 but it's in the 1956/57 volume of R&TVS. At least that's what the cumulative index says. My copies are packed away at the moment so I can't check.

The TMB272 is unique for that era as a mains/battery portable. It also has an earthed chassis which makes it relatively safe to work on. Due to the earthed chassis, compact design and 12V capability the BBC modified them to use as low cost video monitors. Especially for OB use. The power input connector is rare. If you have one with your set you are lucky.

[djrm]

How have you used the R-Pi to generate 405 signals?

I have only got sound and modulation 'squiggles' using the raspberry pi as a am/fm modulated signal generator, I used the software from here: RF GENERATOR WITH THE RASPBERRY PI. The pi fm radio software has been used to test the Ekco VHF radio
I'll describe my set in another thread. David.

[`FRANK.C]

Frank, do you have any spare bare circuit boards available please?

Hi David
I have a couple left over if you would like one send me a PM with your address etc.

Frank