75 ohm terminals.

"David Paste" wrote in message
...
One question though: How dramatically does altering the length of the
Ts affect the tuning of the aerial? I tend to listen to R3 and Classic
FM which are at differing ends of the spectrum, so to tune to one
frequency would presumably affect the other? Not that I need to - my
reception is now actually /very/ good. In good reception areas, would
it be OK to tune the aerial to 98MHz i.e. in the middle of the 88 -
108 FM band?

The length doesn't effect it much for frequencies within the 88 to 108
range.

The calculated lengths are not going to be exact anyway when the aerial is
mounted indoors with all sorts of other metal objects nearby to effect it's
resonance.

Yes if you cut the aerial to optimize for one end of the band, say radio 2
at around 89MHz frequencies towards the other end of the band would suffer
poorer reception.

--

Brian Gregory. (In the UK)

To email me remove the letter vee.

On 10 Aug, 16:11, UnsteadyKen wrote:

Too bloody true, it's not so much the sound quality I object to

I do! Over-compressed, difficult to listen to. I suppose most of them
are set up with the idea that the listener will be in a car (with open
widows too!), or in a noisy workplace.

it is
the dismal bland programming, especially now that the Heart group seems
to be snapping up all the local independents in the East
Anglia/Midlands area and turning them into identikit clones.

Yeah, but this is symptomatic of a greater issue, I think. If everyone
has exposure to the same media, more money can be made by fewer
companies. Pop radio stations are just QVC for record labels, to me.
As much as the BBC annoys me at times, there are some seriously good
shows on there - variety and esoteric stuff, marginal interest stuff
(I still keep hoping they'll resurrect Sing Something Simple!).

The internet, of course, has been a boon to variety. Podcasts are a
great way to get good 'radio' shows!

On 10 Aug, 15:31, Jim Lesurf wrote:

To complicate matters, the answer will depend on the cable and the 'load'
(i.e. input to the tuner) since the optimum depends both on the inherent
radiation coupling of the antenna and the 'match' into whatever it is
conected to.

Well, you have reached and exceeded my understanding of these things.
Actually, I still have no idea what the impedance rating of a cable
refers to. It's not the resistance to DC current in the wire, that is
for sure, as impedance is an AC thing as far as I am aware. But what
does it mean? Is it per unit length of the cable? I don't think that's
right, either. Ah, for a little more education!

The wider you open the window, the more muck blows in. *:-)

LOL!

On Tuesday, August 10th, 2010 at 09:54:43h -0700, David Paste explained:

The internet, of course, has been a boon to variety. Podcasts are a
great way to get good 'radio' shows!

WNYC's "Radiolab" being a good example.

http://www.wnyc.ORG/shows/radiolab/

Or WBEZ's "This American Life" being another.

http://www.thisamericanlife.ORG/

Brian Gaff wrote:

it needs a balun/ transformer there.

In practice though, you can do all sorts of things and get away with it.

I couldn't bring myself to recommend the O/P just sucks it and sees after Bill's "that's what's wrong with this country" comment
;-)

I made the mistake of commenting to a total stranger thet the aerial
on his roof could not possibly work properly, because two feeders
were connected directly to it serving separate rooms.

His reponse was the colour was perfect on all the Freeview channels in both
rooms, and I obviously was talking through my arse, as indeed I must have been.

There's no justice.

--
Graham.

%Profound_observation%

On Aug 10, 8:12*am, Alan wrote:
On Tue, 10 Aug 2010 02:43:28 +0100, UnsteadyKen

wrote:
Here we stick with the a reversed coax Belling Lee type, requiring a
female connector on the FM downlead. Presumably this is to stop us
connecting the the radio aerial to the telly and vice versa.

I don't think I've ever come across that. The downlead on both FM and TV
aerials has required a male Belling and the FM and TV receivers have had
female Bellings.

Yes, some tuners have belling male RF inputs. Sometimes they're
recessed so you have to carve off the platic from the line connector
so it will go in the hole.

Bill

On Aug 10, 8:18*am, Andy Burns wrote:
Brian Gaff wrote:
it needs a balun/ transformer there.
In practice though, you can do all sorts of things and get away with it..

I couldn't bring myself to recommend the O/P just sucks it and sees
after Bill's "that's what's wrong with this country" comment ;-)

Oh dear, I was on my high horse. Sorry.

Bill

On Aug 10, 8:48*am, charles wrote:
In article ,
* *Mark Carver wrote:

On 10/08/2010 08:12, Alan White wrote:
On Tue, 10 Aug 2010 02:43:28 +0100, UnsteadyKen
*wrote:

Here we stick with the a reversed coax Belling Lee type, requiring a
female connector on the FM downlead. Presumably this is to stop us
connecting the the radio aerial to the telly and vice versa.

I don't think I've ever come across that. The downlead on both FM and TV
aerials has required a male Belling and the FM and TV receivers have had
female Bellings.
It's quite common for Japanese FM tuners to have female Bellings, I
think my Sony does, I can't remember for certain though.

It's a German idea, to the best of my knowledge

--
From KT24

Using a RISC OS computer running v5.16

This is nothing compared to the chaos when wallplates appeared on the
market with male for tv and female for FM/AM. When we get a call to
flats "No reception: new tenant" we get on the phone and explain that
they need a line connector and a magnifying glass to read the script
on the wallplate. Thios is a daily occurrance.

Bill

wrote:

This is nothing compared to the chaos when wallplates appeared on the
market with male for tv and female for FM/AM. When we get a call to
flats "No reception: new tenant" we get on the phone and explain that
they need a line connector and a magnifying glass to read the script
on the wallplate. Thios is a daily occurrance.

My lad's university accommodation had a female for TV and a male for FM,
(though there appeared to be nothing present on the FM socket). His room
wasn't a one off, his neighbours were the same

Fortunately I had come armed with a bag of 10 BL sex changers. The
block's warden had a box of 'VCR style' M-F fly leads in his office, I
bet they were soon used up !

In article
,
David
Paste wrote:
On 10 Aug, 15:31, Jim Lesurf wrote:

To complicate matters, the answer will depend on the cable and the
'load' (i.e. input to the tuner) since the optimum depends both on the
inherent radiation coupling of the antenna and the 'match' into
whatever it is conected to.

Well, you have reached and exceeded my understanding of these things.
Actually, I still have no idea what the impedance rating of a cable
refers to.

It refers to the 'inherent' behaviour of a length of the cable. Imagine a
*very* long length of cable. Now apply a voltage (potential difference)
between the wires at one end. This extracts some charge from one wire and
shoves it onto the other. (This is necessary for the wires to now have
different potentials.) This movement of charge, and the change in voltage
between the wires now 'ripples along the wires' at the speed of light.

The result is that a given applied voltage induces a current, and both
ripple out along the wires of the cable.

For any particular cable a given voltage will set up a specific amount of
current. The ratio gives you the 'characteristic impedance' of the cable.

If you now connect a load *with that resistance* at the other end of the
cable it will 'match' the cable. So when the voltage and current reach the
load, the voltage causes the load to demand the same amount of current as
now is flowing along the cable at the load. Result: All the conveyed energy
is 'eaten' by the load.

However if the load has the wrong impedance (i.e. not the same value as the
cable's) that won't work correctly. Some of the energy arriving at the load
'bounces' and is returned to the source. (In this case the antenna.) The
system then doesn't work properly.


It's not the resistance to DC current in the wire, that is for sure, as
impedance is an AC thing as far as I am aware. But what does it mean? Is
it per unit length of the cable? I don't think that's right, either. Ah,
for a little more education!

The cable will have an amount of capacitance per length, and inductance per
length. These do relate to the cable's characteristic impedance. But the
impedance is an inherent general property.

FWIW The UK tradition for domestic VHF and UHF is to use '75 Ohm' coaxial
cables. The reasons are somewhat blurred by the mists of time. :-) However
the 'natural' output impedance of a simple dipole tends to be in the region
of 70 - 95 Ohms. So the combination is a convenient one.

Professional RF/microwave/test systems in other uses may well use other
types of cable. So for example '50 Ohm' is common in lab gear. All very
awkard if you work in a field like TV or Audio (i.e. FM tuners, etc) since
you often have to have convertors, etc. Some DAB tuners also have used 50
Ohm, just to stir the pot a bit, I guess. 8-] Can all be a PITA. Some old
kit also uses weird and now obsolete types of connector. Presumably because
'It seemed a good idea at the time'. ;-

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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