Amateur Rigger's Diary (very long)

"Terry" wrote in message
ups.com...
On 28 Feb, 16:28, "Bill Wright" wrote:


That could well not be a Gp A but a channel 33 aerial!


No Bill! As far as I know there is no such thing! All aerials
commercially available at (and before) BBC2 launch (Crystal Palace
[ONLY!] April 1964) were sold/marketed as "Group A" aerials.
Yes they should have been, but no they weren't!

The one I
remember at the time (Antiferance? Aerialite?) had a folded dipole of
sheet metal which was wider on the 'outside' than the split side.
Could this be the Belling Lee UHF aerial which become the inspiration for
the the Antiference Trumatch after Antiference took over Belling Lee's
aerial dept.? The junction box was detachable and held by two plastic headed
light blue screws. Before that Antiference used a dipole made from a strip
of matal with a balun hanging below. This was a liability because it was
expensive to make and water got into the gap between the balun and dipole
insulator. Anti embraced the BL dipole with gusto, and patented their
derivation of it. See my website for examples.

Mine
worked fine when BBC1 & ITV appeared (Ch26 & 23 respectively) in late
1969.

Anything available before that (1964) would have been either a Ch34 or
Ch44 aerial (or both) - original test tx from CX which ceased 30th
November 1963.

I have pictures of those prototypes on my website, incidentally.

When BBC2 started from Emley Moor there was a period when we were using
Aerialite aerials that were optimised for ch51. My memory is that the box
was labelled 'Emley Moor'. When the other channels started up on UHF we had
a few problems. BBC1 in particular could be very poor, and in quite a few
instances we had to replace the aerials. I have seen several of these old
aerials recently enough to be sure that they really were narrowband. These
aerials were distinctive because all the directors were the same length.
This situation also applied to Belmont. We were using ch28 aerials for about
six months, as I recall.
I also remember that J Beam were selling their PBM aerials (the early ones
with the straight 1" dia support arm) in versions suitable for specific
channels, although I can't remember details.
Of course none of this should have happened, because the channel group
system was in existence. But I suppose the manufacturers were keen to
produce aerials with the best possible gain on the BBC2 channel. Every
little bit of gain was important, given the terrible valve tuners then in
use. And at the time many people couldn't really envisage the other channels
moving to UHF. We have a similar situation today, in which it is irritating
that DAB yagis have such poor gain, this being due to their large bandwidth,
which is not at present necessary.

Bill

I also remember that J Beam were selling their PBM aerials (the early ones
with the straight 1" dia support arm) in versions suitable for specific
channels, although I can't remember details.
Of course none of this should have happened, because the channel group
system was in existence. But I suppose the manufacturers were keen to
produce aerials with the best possible gain on the BBC2 channel. Every
little bit of gain was important, given the terrible valve tuners then in
use. And at the time many people couldn't really envisage the other channels
moving to UHF. We have a similar situation today, in which it is irritating
that DAB yagis have such poor gain, this being due to their large bandwidth,
which is not at present necessary.

Bill



Over on alt.radio.digital Richard L would have U believe that DAB receptions
is "just so" wherever U are in the country and you don't need aerials either

Yes those valve tuners were awful but then again it was the state of play at
the time. The Germanium transistor ones were better, but the Silicon ones
eclipsed them and made for a vast improvement in reception
--
Tony Sayer

"Bill Wright" wrote in message
...

The problem is that if you amplify one diplexer input the gain of the amp
will have to be notionally subtracted from the diplexer's discrimination
of that input.

That should read " . . . the diplexer's rejection on that input of channels
outside that input's nominal range."

Still not clear is it?

Bill

"Phil Cook" wrote in message
...
Doctor D wrote:

My in laws in Chessington have an Aerialite 10A which has been on their
roof
more or less since Crystal Palace began group A UHF transmissions in the
60's. It's still completely intact, unlike neighbouring aerials of far
more
modern vintage.

1,2 and 3 have always been perfect, 4 & Five suffer slight ghosting, and
Five obviously struggles a little with 37 being out of the old group A
band.

Last year they purchased a Panasonic DVD recorder with built in Freeview.
I
was ready to upgrade the aerial, but to my surprise this old chap provides
rock solid DTTV at signal levels in the 90's!

Hardly surprising since all the DTT Muxes off CP are in band.


It surprised me, since the aerial and co-ax are 40 years old and the house
backs on to the A3!
I was expecting reasonable signal levels, but was also expecting impulse
interference problems.

"Doctor D" wrote in message
...
I was expecting reasonable signal levels, but was also expecting .

I got impulse interference problems this afternoon. I was in Comet and I
nearly got a new plasma on impulse, but the wife interfered.

Bill

(B-boom)

On 2007-02-28 02:53:16 +0000, "Bill Wright"
said:


It's 2.45 and I'm ****ed, so E & O E.

However, assuming 16QAM,

Level (in a normal environment, straight off the aerial):
-27dBmV too dodgy to work
-20 most likely will work but not reliable
-15 will work
-10 safe.

In a quiet environment knock mebbe 3dB off. Of course the lower levels
will need an amp to get as far as the receiver, unless it's on the roof.

s/n:
35dB: lovely
25dB: OKish
20dB not OKsh
15dB dodgy, very dodgy. Get Freesat.

Bill

I confess my confusion. Marky quoted 45dB microvolts/metre. Bill is
using negative dB millivolts. Somebody please enlighten an amateur (or
an "armature" as some of the great unwashed like to spell it).

Col

"Colin Blick" wrote in message
news:2007030122093916807%[email protected]
On 2007-02-28 02:53:16 +0000, "Bill Wright"
said:
I confess my confusion. Marky quoted 45dB microvolts/metre. Bill is using
negative dB millivolts. Somebody please enlighten an amateur (or an
"armature" as some of the great unwashed like to spell it).

Marky was quoting dBuV (dB related to one microvolt). I tend to think in
dBmV (dB related to one millivolt) because the numbers are smaller when
working on distribution systems. The difference between the two is 1:1000,
or 60dB. There is a regretable trend for amplifier manufacturers to quote
maximum output figures in dBuV because they sound more impressive. They also
sometimes quote a figure that's accurate only when the amp is carrying two
analogue channels (a very very outmoded convention) when they should be
quoting figures appropriate for five analogue channels and six muxes, and
for amps that have a single path for VHF and UHF they should allow for six
FM carrier at -15dB relative to the analogue TV video carriers and ditto
three DAB muxes.

Bill

In article 2007030122093916807%[email protected], Colin Blick
writes
On 2007-02-28 02:53:16 +0000, "Bill Wright"
said:


It's 2.45 and I'm ****ed, so E & O E.

However, assuming 16QAM,

Level (in a normal environment, straight off the aerial):
-27dBmV too dodgy to work
-20 most likely will work but not reliable
-15 will work
-10 safe.

In a quiet environment knock mebbe 3dB off. Of course the lower levels
will need an amp to get as far as the receiver, unless it's on the roof.

s/n:
35dB: lovely
25dB: OKish
20dB not OKsh
15dB dodgy, very dodgy. Get Freesat.

Bill

I confess my confusion. Marky quoted 45dB microvolts/metre. Bill is
using negative dB millivolts. Somebody please enlighten an amateur (or
an "armature" as some of the great unwashed like to spell it).

Col


FWIW..

Microvolts per metre is a field strength measurement, like in say FM
planning where 54 dB above 1 microvolt metre is the desired level for
rural stereo reception etc...
--
Tony Sayer