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[Sticky] Television Receiver Intermediate Frequencies

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Pieter H
(@pieter-h)
New V-Ratter Registered
Posts: 16

@synchrodyne 

Hi Steve,

interesting point you bring up there! I've done two quick checks on the "38,9 MHz emergence".

In the 1952 Philips Electronic Application Bulletin that introduced the intercarrier concept, the reference design is still based on the then standard 23,5MHz VIF as used by Philips. Which indicates that intercarrier introduction and 38,9MHz standardization were not linked. Although it effectively was within Philips: the 1953 TX1720 chassis introduced both these innovations.

Nevertheless, in my early Philips TV history I have made the link by stating:

In an inter-carrier receiver the video and sound remain combined throughout the entire IF chain up to and including the video detector. The output of that detector will now be the video baseband signal as usual but with the modulated sound on a sub-carrier at 5,5MHz, the picture-sound distance in the Gerber-norm. (In other standards the video-sound distance differs of course). The advantage is then that the remaining audio chain is much more low frequency up to the FM detector, avoiding more complex IF circuitry. The down side is that the combined video plus audio IF chain needs to be more wideband to pass both signals. Probably as a consequence of this the IF frequencies further moved upwards to a picture carrier of 38,9MHz and a sound carrier of 34,4MHz.

I then did a quick check on Radiomuseum.org on the VIF of German and Dutch (Philips) TV sets from 1951 to 1955. I will make a more detailed table one day for my site, but the summary is as follows:

1951: Philips 23,5, Metz 23,75, Schaub 25,7, Telefunken 25,75, Saba 26,2, Grundig 26,75, Greatz 27,75, Loewe 37,5

1952: Philips 23,5, Blaupunkt 25,5, Telefunken 25,75, Nordmende 26,0, Nora 26,5

1953: Blaupunkt Saba 25,5, Lorenz Schaub 25,7, Braun Telefunken 25,75, Grundig 27, Loewe 28,75, Graetz 29
         Siemens 35,35, Metz 38,5, Philips 38,9

1954: same as 1953

1955: Kreft, Metz, Loewe, Neckermann, Nora, Saba, Schaub, Tekade all switched to 38,9

This seems to mean, to my total surprise, since I have not seen any reference to this fact, that Philips introduced the 38,9MHz. At least when looking at Germany and the Netherlands, which were jointly the biggest CCIR-B market. Whether this was purely a "follow the leader" mechanism (Philips was establishing itself as a leading brand in Europe), or that Philips proposed this value to some (CCIR?) standardization body and the others followed, or that such a body had proposed the 38,9 and Philips was the first to adopt, is not clear yet and deserves some further research.

Other observations:

  • the Loewe 37,5MHz in 1951 seems to have been a one-off case, since on the next chassis they were back at 28.75MHz.
  • as in the UK chassis, Philips was originally on the lowest IF of all, but then in one go made the jump to the standard high value
  • it seems there was some industry consensus that higher IFs were better but not (yet) prescribed, see the values of Siemens and Metz in 1953. I would expect there is a conference or journal paper from around 1951/2 analysing this need, and driving this consensus. I haven't found that yet.

Interesting topic! I'll try to find more data on this.

Cheers, Pieter

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Posted : 30/12/2021 5:41 pm
Synchrodyne
(@synchrodyne)
Reputable V-Ratter Registered
Posts: 421

To recap on previously posted items:

The EBU TV IF survey of 1952-54, of which a précis was provided in Wireless World 1954 July, showed 38.9 MHz as the expected future VIF for Germany and the Netherlands.

The Fewings & Fife BIRE paper of 1955 included this in its bibliography:

W. Holm and W. Werner, "Choice of an intermediate frequency for television receivers to suit the C.C.I.R. standard," Funk und Ton, 8, pp. 129-138, 1954.

As far as I know, both authors were Philips employees, but Funk und Ton was a German publication. I imagine that the article included the calculations that pointed to the choice of 38.9 MHz as the VIF for the CCIR system (later system B). That may explain why it was labelled as being the “CCIR IF”. But whether it included any information about which organizations, if any, adopted it as a standard is hard to say. Whereas in the RTMA and BREMA cases, each trade organization commissioned the development work, in the 38.9 MHz case, it might have been a Philips initiative that then became a de facto standard, and possibly a de jure standard.

The CCIR started reporting TV IFs in 1959 Los Angeles meeting report. Whilst it noted the trend towards national standardization, in general it did not record who the standards issuing authority was in most cases, EIA (nee RTMA) being an exception. A reasonable inference is that the CCIR itself was simply reporting, and not promulgating standards or apparent standards.

Cheers,

Steve

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Topic starter Posted : 30/12/2021 11:11 pm
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