Yes, I did an item for the newsletter and the BATC's CQTV magazine many years ago using the video path of a VHS VCR to record NBTV. My aim was mainly to get a frequency response down to DC, but as a bonus I was able to extend the upper frequency limit too.
However, 48 line NBTV at a 12.5Hz frame rate isn't impossible on an audio tape recorder - but it sure needs to be a good one! Basically open-reel, not a cassette.
Say 48 lines with an aspect ratio of 3:2 would need around 72 pixels/line, but could be more or less.
A frame = 48 x 72 = 3,456 pixels (nice number!). At a 12.5Hz frame-rate = 43,200 pixels/sec. Or a bandwidth of 21.6kHz. Add say 10% for syncs etc.= 23.76kHz...I did say it had to be a good recorder! Probably a studio-quality machine running at 15ips/38.1cm/sec. If you apply a Kell factor [1] of (say) 0.8 that reduces the upper bound to 19kHz. Quite possible on a good quality machine, maybe even at 7.5ips/19.05cm/sec...but keep the recording level low-ish to avoid tape saturation.
A machine that runs at these speeds would probably be a good quality device and hopefully well maintained. That's the usual 'direct-to-tape' method.
The VHS machine/system Harry referred to is sampling the NBTV waveform at 31.25kHz, twice the 625 line rate and treating those analogue samples as part of an almost standard 625 video waveform. The biggest headache is the required 50Hz vertical information in this now 'pseudo-625' waveform. No 50Hz, no head-drum or capstan lock. Same applies to 525/60.
There still is/are the standard audio tracks available. Linear or Hi-Fi, mono or stereo if fitted available.
If I were to repeat the exercise today I would encode the NBTV digitally then insert that into the video waveform. That would negate the 50/60Hz vertical sync issue.
But not having a VCR anymore it's most unlikely I'd have a go at it...and these days there are better/easier ways to do the same...have a look at the thread, "Move-E-Stor MkI" for some ideas. This is still a 'work-in-progress' project...though updates maybe slow for a while until I get clear of a large 'real work' project. Plus I need still to buy a new version of Autocad, That's not an insignificant investment!!
Move-E-Stor MkI
viewtopic.php?f=10&t=3116Steve A.
[1] Kell factor.
https://en.wikipedia.org/wiki/Kell_factorThe original item as it appeared in the BATC's 'CQTV' magazine November 2005....almost 17 years ago!! Though again, I would do it differently these days...
However, any further development on this subject should really be posted in the 'Electronic NBTV' section rather than here...