On 03/02/2018 11:43, RJH wrote:
On 03/02/2018 06:25, Phil Allison wrote:
Andrew wrote:

----------------


The irritating chattering and buzzing that affected 88.50 Mhz
disappeared after a few hours. Mystery.

The worst of the hissing must have been my loft-mounted FM 3 element
horizontal aeriel because the cap that seals the connectors is
missing. The humidity levels in the loft vary with the seasons and
weather, being ventilated and the connectors needed a good clean
with some wire wool.


** Loft mounting is still essentially an indoor antenna with all the
associated drawbacks.

The antenna is close to multiple sources of interference in the house,
has no line of sight over other roofs and whenever the roof material
becomes wet, it acts like an RF shield.


Being in the loft, it's likely to be a lot larger than an indoor aerial,
Â*purpose built for the job (although maybe not the best choice here),
and have a better aspect.

So, while far from perfect, likely to work better than an indoor aerial.

I lashed one up in my old house - went from practically nothing to 100%
on all channels (according to the Freeview box's meter)

Didn't know about the RF shield bit.

My 15-element external group C/D TV aeriel blew down in 2000 so I
tied it up inside the loft, pointing at Midhurst, but the roof
trusses mean it is pointing slightly downwards. While the freeview
signal strength is not brilliant it picks up all the channels that
I watch.

The only channel I cannot get, is the one that Midhurst doesn't even
provide - BBC4 HD. It seems that the people who watch CBBC during
the day are more 'entitled' to an HD channel even though it stops
at 7PM, leaving unused bandwidth that could have been shared
with BBC4 which only starts at 6PM.

When the weather improves I might put up an external log periodic
aeriel and try and pick up Hannington instead, but where I am is in
a bit of a hollow to the north of the South Downs but with
line-of-sight to Midhurst. Hannington is double the power of
Midhurst but I am outside it's normal range.

On 03/02/2018 06:25, Phil Allison wrote:
a low gain 3 element antenna the signal level has always been marginal - at best.

Well, to be honest, my trusty old 1978 AIWA 7400 had a signal strength
meter and I could get 80%+ deflection from both Rowbridge on the
IOW to the South West and almost the same from Wrotham to the North
East over in Kent, but that route has the North Downs in the way.

Both these transmitters are 250Kw and about 50 miles away.

On 03/02/2018 12:27, Andrew wrote:
On 03/02/2018 06:25, Phil Allison wrote:
a low gain 3 element antenna the signal level has always been marginal
- at best.

Well, to be honest, my trusty old 1978 AIWA 7400 had a signal strength
meter and I could get 80%+ deflection from both Rowbridge on the
IOW to the South West and almost the same from Wrotham to the North
East over in Kent, but that route has the North Downs in the way.

Both these transmitters are 250Kw and about 50 miles away.

Please!!! It is Rowridge, not bridge. Sorry but it jars my OCD.

--
Graeme Wall
This account not read.

In article ,
Andrew wrote:
When the weather improves I might put up an external log periodic
aeriel and try and pick up Hannington instead, but where I am is in
a bit of a hollow to the north of the South Downs but with
line-of-sight to Midhurst. Hannington is double the power of
Midhurst but I am outside it's normal range.

A log beam is actually a rather low gain aerial. With a very good DP, so
best for where multi-path is a problem. Which I don't think affects
digital as much as analogue.

--
*INDECISION is the key to FLEXIBILITY *

Dave Plowman London SW
To e-mail, change noise into sound.

RJH wrote:

-----------

** Loft mounting is still essentially an indoor antenna with
all the associated drawbacks.

The antenna is close to multiple sources of interference in the house,
has no line of sight over other roofs and whenever the roof material
becomes wet, it acts like an RF shield.



Being in the loft, it's likely to be a lot larger than an indoor aerial,
purpose built for the job (although maybe not the best choice here),
and have a better aspect.



** I have used full size antennas indoors, firstly for local FM and later for VHF digital TV. Moving the same antenna outdoors, with little increase in height, made a *very dramatic improvement* in overall results.


So, while far from perfect, likely to work better than an indoor aerial.


** Oh *that* kind of indoor antenna - contraptions with a pairs of telescopic rods are woeful excuses for antennas in even in good signal areas and with DTV.


..... Phil

Andrew wrote:

-------------

Phil Allison wrote:

a low gain 3 element antenna the signal level has always been marginal - at best.


Well, to be honest, my trusty old 1978 AIWA 7400 had a signal strength
meter and I could get 80%+ deflection from both Rowbridge ....


** Unfortunately, signal meters on FM tuners are not made to any sort of standard. Some will hammer over with next to nothing coming in and give owners a false impression of how "powerful" their tuner is.

Reality is, nothing makes up for having a weak or marginal signal coming from the antenna.



..... Phil

In article , Andrew Andrew97d-
scribeth thus
On 03/02/2018 06:25, Phil Allison wrote:
a low gain 3 element antenna the signal level has always been marginal - at
best.

Well, to be honest, my trusty old 1978 AIWA 7400 had a signal strength
meter and I could get 80%+ deflection from both Rowbridge on the
IOW to the South West and almost the same from Wrotham to the North
East over in Kent, but that route has the North Downs in the way.

Both these transmitters are 250Kw and about 50 miles away.

Actually there're at 125 kW per plane of polarisation thats to say 125w
in the vertical and 125 horizontal.

And they aren't totally ommni-directional either in what they do
radiate.

Still a decent 3 or more element aerial up in the clear outside with a
decent feeder and tuner should be quite good....

A very good tuner is the Denon DENON TU-260L can pick them up on e-bay
for around 20 quid - there sorted...
--
Tony Sayer

In article , Andrew Andrew97d-
scribeth thus
On 02/02/2018 09:34, Jim Lesurf wrote:
The use of the term "most" noted. :-)

The point here is that "most" simply accepts that "some" may do so, and
they will be the instances someone will them find gives them a problem.
Thus - perhaps - asking for advice. Even "a few" when many thousands were
made can mean some will.

But - as per my first posting - the stats indicate that an antenna or
downlead degraded by water, birds, etc is more likely. Followed by some
other change in reception conditions - change in multipath, or a new TX in
the same tuned RF band, etc.

Jim


In article , Brian Gaff
wrote:
I'd not say the drift is the cause. Most receivers of the vintage noted
are pretty good. As its changed over time far more likely to be aerial
related. Brian

The irritating chattering and buzzing that affected 88.50 Mhz
disappeared after a few hours. Mystery.

The worst of the hissing must have been my loft-mounted FM 3 element
horizontal aeriel because the cap that seals the connectors is
missing. The humidity levels in the loft vary with the seasons and
weather, being ventilated and the connectors needed a good clean
with some wire wool. All ok now, though still some hiss which I
never used to get with my old AIWA 7400. I should have kept it,
it had a signal strength meter which showed an obvious reduction
when there were aeriel issues.

I've been looking at this site :-

http://aerialsandtv.com/fmanddabradio.html

And I didn't realize that I could have an external vertical
half-wave dipole that would work quite well for FM and DAB,
since Rowbridge has mixed polarity.

Its not quite that simple a dipole if vertically mounted is 0 dB Gain
and will only collect half what's radiated a much better be is a 3 or
more element Yagi extra gain and discrimination against unwanted
multipath etc...

The reason I avoided having an external FM aeriel before was
because we have a large flock of rooks locally who patrol all
the bird tables. They are big birds and seem to like bouncing
up and down on aeriels.

Airgun...
--
Tony Sayer

tony sayer wrote:

----------------


Both these transmitters are 250Kw and about 50 miles away.


Actually there're at 125 kW per plane of polarisation thats to say 125 w
in the vertical and 125 horizontal.


** Interesting.


And they aren't totally ommni-directional either in what they do
radiate.


** Nothing like omni-directional, in fact.

Broadcasters are not interested in communicating with ETs or high flying aircraft so *beam" the available power towards the ground and the horizon - much like a light house beams its lamp.

To do this multiple antennas are mounted in a vertical line, phased to create a narrow vertical beam with a wide horizontal pattern. Such a set up boosts the apparent power of a given transmitter by a factor of 10 or more.

The real RF power behind an advertised "250kW" station is likely to be 10 or 20kW. Saves heaps on the power bills.


Still a decent 3 or more element aerial up in the clear outside with a
decent feeder and tuner should be quite good....


** Yes, once mounted up high, the roof and everything under it disappears far as the antenna is concerned.



..... Phil

In article , Phil
Allison scribeth thus
tony sayer wrote:

----------------


Both these transmitters are 250Kw and about 50 miles away.


Actually there're at 125 kW per plane of polarisation thats to say 125 w
in the vertical and 125 horizontal.


** Interesting.


And they aren't totally ommni-directional either in what they do
radiate.


** Nothing like omni-directional, in fact.

Broadcasters are not interested in communicating with ETs or high flying
aircraft so *beam" the available power towards the ground and the horizon - much
like a light house beams its lamp.

Yes indeed. But the Horizontal plane of cover isn't quite "Ommni"
especially on large square or rectangular support masts like the
original FM Station here at Wrotham in Kent. Several tiers of Alan Dick
Spearhead arrays are used..

http://tx.mb21.co.uk/features/wrotham/mixedpol.php


Just because a Transmitter says its "x" kW does not mean that it is in
all directions. Some TV relays are very directional.

To do this multiple antennas are mounted in a vertical line, phased to create a
narrow vertical beam with a wide horizontal pattern. Such a set up boosts the
apparent power of a given transmitter by a factor of 10 or more.

The real RF power behind an advertised "250kW" station is likely to be 10 or
20kW. Saves heaps on the power bills.

Yes it does..


Still a decent 3 or more element aerial up in the clear outside with a
decent feeder and tuner should be quite good....


** Yes, once mounted up high, the roof and everything under it disappears far as
the antenna is concerned.



Yep!, no substitute for Height...


.... Phil



--
Tony Sayer