Hanninton Multiplex; Reception of Digital Radio Channels (DAB)`

"Mark Carver" wrote in message
oups.com...
I don't disagree with any of that, but my practical experience is that
a vertically polarised FM (Band II) dipole responds very well to Band
III DAB signals. This group's rigging guru Bill Wright has ISTR
discovered much the same ?

Yes. Of course if the DAB signals are weak you need a proper DAB aerial. But
normally a vertical dipole cut for FM will do both bands.

Bill

charles wrote:
In article ,
Bill Wright wrote:

"Mark Carver" wrote in message
oups.com...
I don't disagree with any of that, but my practical experience is that
a vertically polarised FM (Band II) dipole responds very well to Band
III DAB signals. This group's rigging guru Bill Wright has ISTR
discovered much the same ?

Yes. Of course if the DAB signals are weak you need a proper DAB aerial.
But normally a vertical dipole cut for FM will do both bands.

ah, an 1/8th wave dipole ;-)

You mean a full wave dipole ? :-) (Band II used at Band III)

In article .com,
Mark Carver wrote:

charles wrote:
In article ,
Bill Wright wrote:

"Mark Carver" wrote in message
oups.com...
I don't disagree with any of that, but my practical experience is
that a vertically polarised FM (Band II) dipole responds very well
to Band III DAB signals. This group's rigging guru Bill Wright has
ISTR discovered much the same ?

Yes. Of course if the DAB signals are weak you need a proper DAB
aerial. But normally a vertical dipole cut for FM will do both bands.

ah, an 1/8th wave dipole ;-)

You mean a full wave dipole ? :-) (Band II used at Band III)

Yes - suffering from " aged-related" confusion.

--
From KT24 - in drought-ridden Surrey

Using a RISC OS5 computer

In article . com,
Mark
Carver wrote:

Jim Lesurf wrote:

I don't disagree with any of that, but my practical experience is
that a vertically polarised FM (Band II) dipole responds very well
to Band III DAB signals.

The point to be careful of here is the meaning of "very well". :-)

[snip]

You're quite right Jim, it's all too easy to fall in to, shudder,
"spiney's world" :-)

shudder :-)

A couple of years ago I acquired a DAB tuner, I simply tried connecting
the Band II dipole to it. I was amazed that it pulled in four distant
(30 miles) muxes, none of which are intended to serve my area. I
constructed a 'lashed up' Band III dipole and mounted it at the same
height as the Band II, the results were no better, and one mux was
actually worse. Moving it around made little to no difference. The DAB
tuner has a bar graph signal strength display. These muxes read about
4-5 bars out of 15 on the display. Needless to say my own local DAB
muxes are off the scale regardless of aerial, or even damp string.

I have been impressed by just how reliable DAB reception can be even for
signal levels far below those needed for decent FM reception. It also seems
to me to be significantly more resistant to impulse interference. It
confirms the ideas behind the orginal development of DAB to provide very
reliable and robust data linkage and overcome the practical problems of FM.
Quite a nice demo of the effectiveness of the comms techniques employed.

This makes it all the more frustrating that I am now in the process of
perparing to install UHF distribution around the house - mainly to get
sound radio via 'Freeview' and (I hope!) bypass both our local FM reception
condition problems and the 'quart in a pint pot' of BBC DAB. The DAB RF
signal and tuner are fine... shame about the BBC's attitude to the content.
:-/

However at least the piped UHF/DTTV will also provide sound from the TV
stations as well, which will be useful at times. BBC4TV often have good
concerts. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"charles" wrote in message
...

Yes. Of course if the DAB signals are weak you need a proper DAB aerial.
But normally a vertical dipole cut for FM will do both bands.

ah, an 1/8th wave dipole ;-)

How's that then?

Bill

"Mark Carver" wrote in message
ups.com...
A couple of years ago I acquired a DAB tuner, I simply tried connecting
the Band II dipole to it. I was amazed that it pulled in four distant
(30 miles) muxes, none of which are intended to serve my area. I
constructed a 'lashed up' Band III dipole and mounted it at the same
height as the Band II, the results were no better, and one mux was
actually worse. Moving it around made little to no difference. The DAB
tuner has a bar graph signal strength display. These muxes read about
4-5 bars out of 15 on the display. Needless to say my own local DAB
muxes are off the scale regardless of aerial, or even damp string.

There are lots of unknowns of course, for starters I doubt either the
'proper' Band II or my lashed up Band III dipoles are a perfect match
at any of the considered frequencies, whether they're supposed to be in
band or not.

Consider the situation at the head-end of a largish TV/radio distribution
system. We desire FM and DAB reception. Field strength for all signals is
good. The place has line-of-sight to high powered transmitters. If we
install separate FM and DAB aerials we need to pass each set of signals
through bandpass filters and then combine them, or we need to use a
diplexer. Because of the absolute necessity for preventing the VHF signal
levels from being unneccessarily high, we will need to attenuate the aerial
signals. Now you might think that this could be done with greater finesse if
the two sets of signals could be attenuated separately, but in fact this is
rarely the case.So I just got fed up of using two aerials, two attenuators,
two bandpass filters and a combiner, when one aerial one bandpass filter and
one attenuator worked just as well.

In the early days of DAB I would use a DAB yagi, then find that I was
attenuating the signal much more than I was attenuating the FM signal. The
difference in attenuation counters the isolation of the bandpass filters or
diplexer to some extend (well, to the extend of the difference in
attenuation, of course) so theoretically there could be phasing issues,
resulting in response dips across the DAB band.

I must stress though, that if DAB signals are required that have low field
strength, there is no alternative but to use a good DAB aerial.

Bill

"charles" wrote in message
...
In article ,
Bill Wright wrote:

"Mark Carver" wrote in message


[Snip]

So I just got fed up of using two aerials, two attenuators, two bandpass
filters and a combiner, when one aerial one bandpass filter and one
attenuator worked just as well.

What about unwanted 'out of band' signals when you do it that way? From
un-attended police stations, for instance.

It's certainly necessary to have a good look at the territory around 150MHz.
In a city I would try to leave the analyser on 'store' for an hour, although
that is no protection against the ham with a 200W 2m rig in his car.

In practice I would only use the 'one aerial' technique in areas of very
high FM and DAB field strength, so there will be a 12dB or 18dB attenuator
in the aerial feeder, which gives a lot of protection against transmissions
from the nearby streets. After all, the system should be able to stand a
narrowband signal 15dB above the broadcast signals without any problem.

On systems where there are very long cable runs it's essential to attenuate
the lower frequencies at each repeater (equalisation or 'slope') --
otherwise the repeaters can get very bad indigestion if the local ham cranks
up his burner!

Did you see that thing I wrote for 'Television' a few years ago about the
problems caused by local FM transmitters (pirates and RSLs)?

Bill

In article ,
Bill Wright wrote:

[Snip]

Did you see that thing I wrote for 'Television' a few years ago about the
problems caused by local FM transmitters (pirates and RSLs)?

No, I stopped seeing it whan I left Auntie. I have come across the those
sort of problems myself.

--
From KT24 - in drought-ridden Surrey

Using a RISC OS5 computer

On Fri, 11 Aug 2006 19:14:45 +0100, "Bill Wright"
wrote:


"charles" wrote in message
. ..
In article ,
Bill Wright wrote:

"Mark Carver" wrote in message


[Snip]

So I just got fed up of using two aerials, two attenuators, two bandpass
filters and a combiner, when one aerial one bandpass filter and one
attenuator worked just as well.

What about unwanted 'out of band' signals when you do it that way? From
un-attended police stations, for instance.

It's certainly necessary to have a good look at the territory around 150MHz.
In a city I would try to leave the analyser on 'store' for an hour, although
that is no protection against the ham with a 200W 2m rig in his car.

In practice I would only use the 'one aerial' technique in areas of very
high FM and DAB field strength, so there will be a 12dB or 18dB attenuator
in the aerial feeder, which gives a lot of protection against transmissions
from the nearby streets. After all, the system should be able to stand a
narrowband signal 15dB above the broadcast signals without any problem.

On systems where there are very long cable runs it's essential to attenuate
the lower frequencies at each repeater (equalisation or 'slope') --
otherwise the repeaters can get very bad indigestion if the local ham cranks
up his burner!

Did you see that thing I wrote for 'Television' a few years ago about the
problems caused by local FM transmitters (pirates and RSLs)?

Bill

I wanted to set up a pirate station once. I was all ready to jump in
& buy a transmitter 'till someone told me that I lived on the doorstep
of the blokes who monitor dodgy radio stuff (Baldock, Herts) & I would
be switched off & locked up in seconds :-(.

Marky P.

On Fri, 11 Aug 2006 21:06:28 GMT, Marky P
wrote:

I wanted to set up a pirate station once. I was all ready to jump in
& buy a transmitter 'till someone told me that I lived on the doorstep
of the blokes who monitor dodgy radio stuff (Baldock, Herts) & I would
be switched off & locked up in seconds :-(.

Marky P.

I used to work for the G.P.O. (telephones) back in the sixties and I
had great fun running 10 watts on medium wave.

It stopped all of a sudden when I heard someone in the same building
saying that he was on overtime that night to catch a local pirate....

Oh those men in green vans...