BBC Low-VHF (Band I) TV
(41.50 MHz - Oct 20, 1978 - 1630 Z)
Made with an SX-62 receiver and random longwire outdoor antenna. Note the audio of
another BBC transmitter ("... today ...") fading in and out at round the 12-sec point in this mostly-musical 32-sec clip.
For some FIVE Solar Cycles (17-21) the low-band VHF BBC TV signals were
widely-used propagation indicators. The service had been started in 1937
(suspended during WW2) and persisted until very late 1984 when their UHF
color-service of 625-lines had finally achieved "total" coverage. There
are several URL's that do go into great historical detail on BBC TV.
The Proceedings of the IRE had two excellent articles by Goddard on the
subject of trans-Atlantic BBC, French, and German TV reception in 1936-39.
January 1939 (pp. 12-15) and November 1939 (pp. 692-695). They go into
much detail on the equipment used and some results comparing ionosonde
data and field strengths. I became aware of these c. 1979-81 via K5KS,
who supplied me with Xerox copies - which, unfortunately, don't show how
well those photos of the kinescope BBC images in them must have looked!
However, a recently-found site appears to have a superb display.
These channels had provided 405-line resolution at 25 frames/sec with
the video being positive modulation and the AM audio situated at 3.5-MHz
LOWER than the video carrier. Several complex off-set schemes were used
which sometimes enabled the precise identification of the individual
transmitter being received - since, for the most part, BBC-1 programming
was done in simulcast (with the occasional breaks for regional news).
Ch B1 Ch B2
audio 41.50 48.25
video 45.00 51.75
The Ch B2 audio coincided with the still-existant continental European
Ch E2 video - which often made for a squealing mass of AM heterodynes on
that 48.25 spot along with the intense 50-Hz video vertical-sync buzz!
Cycle 17 had notable instances of both Ch B1 audio and video being
received in North America - with the next two Cycles providing even much
higher trans-Atlantic MUF paths. Any Cycle 20 effects like this went
largely unreported (though my 1970 VHF Utility DX Column in the WTFDA
VUD publication did get a few). The stronger Cycle 21 rapidly rekindled
very widespread interest!
Any simple low-VHF AM receiver could get the BBC audio, but extracting
a watchable video signal was a challenge. The simplest way was to obtain
a UK TV set that would tune in their channels (and hope that local two-way
or paging signals in that range wouldn't obliterate things!) Even though
many sets were being tossed away by 1979 I wasn't lucky enough to get one.
Well, one could still listen to the raucous "buzz" from it. (I had at
least one instance of some strong 51.75-MHz video being detected here.)
(Oct 31, 1978)
(With the same equipment as had been used for the audio.)
WB2CPA on Staten Island likely had the most-dedicated effort in Cycle
21 at getting European TV video signals (not just the BBC). Details of
his methods appeared in a recent past issue of "405 Alive" magazine.
Note that the 45-MHz video was a nice match for the i.f. used in US TV
sets. With a tuned preamp one could inject the signal into that. It'd
still require that the local horizontal and vertical oscillators be then
readjusted to obtain the sync. In the horiz case that meant down to near
10-kHz - which would then cause some loss in the TV set's flyback-derived
high-voltage, and thus its screen's raster would also dim/shrink.
Also, since the modulation polarity was inverted vs the US system
any image obtained this way would be a negative. The severe multi-path
ghosting that F2 introduces adds complications as does the dispersion
effect rarely giving good audio results (from 41 or 48) when the 45-MHz
video was at its best. (It always helped to have the sound to give a
clue as to what that blurry six-armed figure on the screen was doing!)
Using a Hamtronics preamp into the i.f. of a 9" JC Penney 1971 tube set
I was able to make such attempts during 1979-82. Though several 35-mm
SLR photos were taken the vertical blanking bar is about the only thing
that is easily recognizable on any of them! Of course one had to be very
careful not to become too involved in this aspect and thus risk missing
some rare DX that might appear on 50-MHz proper (though far more likely
if dealing with the 48.25 vs 45 signals). In that era there were very
few Europeans authorized to transmit on 6-m, with most of the contacts
being of the 28-50 MHz crossband variety.
Some on the US east coast had it a little easier with one less
ghost-generating hop required - or things like the Massachusetts
state police transmissions on 45-MHz blowing the video away as here.
Also, this area's US Army medical helicopter dispatch used 41.5 (and
soon learned when those big BBC carriers wouldn't let them!)
The elimination of this "relic" service was one of many steps that
has enabled a wider expansion of access to the 50-MHz band in Europe.
G3COJ has made a recent comprehensive history of the G-land efforts
towards that over the decades.
Page created before November 24, 1997
Page last modified: March 17, 2002