recommendations for a vertical FM omnidirectional aerial that canbe mounted at the bottom?

On Wed, 11 Jul 2012 21:10:29 +0100, "Ian"
wrote:

wrote in message
.. .
On Wed, 11 Jul 2012 18:21:59 +0100, Bill Wright
wrote:

wrote:

But all the OP was asking for was a "good quality vertical
omnidirectional FM dipole that can be mounted from the bottom rather
than in the middle as it will sit on top of a pole"!

His ambitions are clear from his other posts, and it is only sensible
to look at the whole picture.

You don't get a picture on FM radio.


I suppose I asked for that

I've got a picture on my FM radio. It's in a nice brown frame but the radio
is quite narrow and the picture often falls off.
Couldn't resist :-

Actually they do say that "the pictures are better on radio."

In article , Bill Wright
scribeth thus
Ian Jackson wrote:

All I can see is that he lives in a dodgy FM reception, asks advice on a
good-quality vertical omnidirectional FM dipole, and (later) that he has
found plans on the net for both the FM and DAB versions of the Slim Jim.
All the additional advice - although very interesting - is not really
helping him to find what he basically wants.

I wonder why no manufacturer has come up with a vertical quarterwave for
top-of-the-pole mounting. Such a thing would be useful.

Bill

I suspect that most all riggers would see that the UHF TV aerial should
sit up there. Consider one of these that has the long U shaped support
bracket be a bit awkward having that sticking up thru that?..
--
Tony Sayer

In article , Ian Jackson ianREMOVET
scribeth thus
In message , Bill Wright
writes
Ian Jackson wrote:

All I can see is that he lives in a dodgy FM reception, asks advice
on a good-quality vertical omnidirectional FM dipole, and (later) that
he has found plans on the net for both the FM and DAB versions of the
Slim Jim. All the additional advice - although very interesting - is
not really helping him to find what he basically wants.

I wonder why no manufacturer has come up with a vertical quarterwave
for top-of-the-pole mounting. Such a thing would be useful.

I'm sure they used have them on the Continent (usually in the form of
groundplanes, with four 1/4 wave radials) - essentially commercial
versions of this:
http://www.radiolocman.com/shem/shem....html?di=18847
I'm sure I've seen them the old 1960s catalogues - and even the real
thing.

I also found this, without radials:
http://www.magnumdynalab.com/fmantenna-st2.htm
which seems to be a 'proper' commercial domestic FM radio aerial.

Thats seems a shade Russ Andrews about it. A listener requiring good
clean reception would still be better off with a directional array like
a Yagi...



--
Tony Sayer

In article , Ian Jackson ianREMOVET
scribeth thus
In message , Steve Terry
writes
Ian Jackson wrote:
In message , Bill Wright
writes
Ian Jackson wrote:
In message , Ian Jackson
writes

As the FM band is centred on around 100MHz (3m), a quarterwave will
be around 1.m.
Someone nicked my 'point five'.
It should be, of course, 1.5m.
You've lost me somewhere.
100MHz = 3m.
1/4 wave = 3/4m = 750mm.
Allow for velocity factor and you get about 700mm.

It just goes to show that I can't divide 3 by 4!

Yes, the 1/4 wave is around 750mm. Yes, do a bit of shortening because
of the velocity factor being (say) 0.95ish - but as the centre of the
FM band is nearer 98.75Mhz, 750mm should be good enough. On these
matters, precision engineering doesn't worry me much.

You can widen the aerials bandwidth by bending over the top end of the
vertical, it's done on VHF airband aerials

You reckon? I can't say I've seen it described as such (or even seen it
done).

Me neither, and I can't quite see why that should do that either.
Got any examples around Terry?..
--
Tony Sayer

wrote in message
...

Actually they do say that "the pictures are better on radio."
Definitely.
"Hitch Hikers' Guide to the Universe" was so disappointing on television in
comparison to the radio version. The imagery of "Journey Into Space" on
radio was superb.

Regards, Ian.

tony sayer wrote:
In article , Ian Jackson
ianREMOVET scribeth thus
In message , Steve Terry
writes
Ian Jackson wrote:
In message , Bill Wright
writes
Ian Jackson wrote:
In message , Ian Jackson
writes
snip
You can widen the aerials bandwidth by bending over the top end of
the vertical, it's done on VHF airband aerials

You reckon? I can't say I've seen it described as such (or even seen
it done).

Me neither, and I can't quite see why that should do that either.
Got any examples around Terry?..

Amongst others, A43 set 230-270MHz UHF airband ground set,
12 inch copper plated sprung steel 1/4 wave whip with extra inch
on top folded back like a flattened letter P

I guess it works by widening the electrical length it also widens bandwidth
I would expect slight loss over a normal 1/4 at centre frequency

Steve Terry
--
Get a free GiffGaff PAYG Sim and £5 bonus after activation at:
http://giffgaff.com/orders/affiliate/gfourwwk

In message , tony sayer
writes
In article , Ian Jackson ianREMOVET
scribeth thus
In message , Bill Wright
writes
Ian Jackson wrote:

All I can see is that he lives in a dodgy FM reception, asks advice
on a good-quality vertical omnidirectional FM dipole, and (later) that
he has found plans on the net for both the FM and DAB versions of the
Slim Jim. All the additional advice - although very interesting - is
not really helping him to find what he basically wants.

I wonder why no manufacturer has come up with a vertical quarterwave
for top-of-the-pole mounting. Such a thing would be useful.

I'm sure they used have them on the Continent (usually in the form of
groundplanes, with four 1/4 wave radials) - essentially commercial
versions of this:
http://www.radiolocman.com/shem/shem....html?di=18847
I'm sure I've seen them the old 1960s catalogues - and even the real
thing.

I also found this, without radials:
http://www.magnumdynalab.com/fmantenna-st2.htm
which seems to be a 'proper' commercial domestic FM radio aerial.

Thats seems a shade Russ Andrews about it. A listener requiring good
clean reception would still be better off with a directional array like
a Yagi...

But - for omnidirectional reception - a directional aerial is not much
good without a rotator. For sheer simplicity, a single element vertical
(especially in an elevated position) usually suffices. Why do people
want to complicate things?!
--
Ian

In message , Steve Terry
writes
tony sayer wrote:
In article , Ian Jackson
ianREMOVET scribeth thus
In message , Steve Terry
writes
Ian Jackson wrote:
In message , Bill Wright
writes
Ian Jackson wrote:
In message , Ian Jackson
writes
snip
You can widen the aerials bandwidth by bending over the top end of
the vertical, it's done on VHF airband aerials

You reckon? I can't say I've seen it described as such (or even seen
it done).

Me neither, and I can't quite see why that should do that either.
Got any examples around Terry?..

Amongst others, A43 set 230-270MHz UHF airband ground set,
12 inch copper plated sprung steel 1/4 wave whip with extra inch
on top folded back like a flattened letter P

I guess it works by widening the electrical length it also widens bandwidth
I would expect slight loss over a normal 1/4 at centre frequency

The J-Pole - the American version of the UK Slim Jim - has a somewhat
narrower bandwidth than the Slim Jim. This is almost certainly because
the top of the Slim Jim is completely folded back on itself over its
entire length (at first glance, looking like a folded dipole). I assume
it effectively has a lower length-to-diameter ratio, and that gives it
the greater bandwidth. However, it certainly doesn't affect its
efficiency.
http://en.wikipedia.org/wiki/J-pole_antenna
--
Ian

On 10/07/2012 23:35, tony sayer wrote:
In ,
lid scribeth thus
On Tue, 10 Jul 2012 22:12:56 +0100, Ian Jackson
wrote:

In , Bill Wright
writes
Ian Jackson wrote:
In , Ian Jackson
writes


As the FM band is centred on around 100MHz (3m), a quarterwave will
be around 1.m.
Someone nicked my 'point five'.
It should be, of course, 1.5m.
You've lost me somewhere.
100MHz = 3m.
1/4 wave = 3/4m = 750mm.
Allow for velocity factor and you get about 700mm.

It just goes to show that I can't divide 3 by 4!

Yes, the 1/4 wave is around 750mm. Yes, do a bit of shortening because
of the velocity factor being (say) 0.95ish - but as the centre of the FM
band is nearer 98.75Mhz, 750mm should be good enough. On these matters,
precision engineering doesn't worry me much.

AIUI the OP is on a dominant site. A l/4 mounted on the top of the
pole is going to attract a lot of static or possibly even worse.

For safety it should have something like a l/2 coax stub across the
bottom to provide a DC path.


If Stephen is where I think he is in Northampton then that relay station
up there won't be that far away, mind possible overload;!...


If you're referring to Dallington Park with Freeview lite, I cannot get
it at all due to the fact that my house is actually higher than the Tx's
tip. Hunsbury hill is higher up than the Tx Mast is.

If you're referring to the FM & MW radio transmitted from Kings Heath,
I can use stub filters on the FM signals from Kings heath to attenuate
and balance it with Waltham, Copt Oak, Wrotham, Oxford, Sandy Heath,
Sutton Coldfieid, Daventry and Bow Brickhill.

On 11/07/2012 18:18, Bill Wright wrote:
Ian Jackson wrote:

He doesn't want terrible multipath on his local station though, which
is what he'd get if he nulled it out like that.

Let's face it, reception of FM in cars, which usually have (at best) a
foot long 45 degree aerial, is usually pretty good - provided the car
is in a reasonably open location. Sticking an even better aerial 30'
up on the top of a pole, is likely to provide even better reception.
Complicated technical considerations and state-of-the-art aerials are
unlikely to be necessary.

True enough, but if a dipole was deliberately aligned to null out the
signal from a particular transmitter, FM reception of that transmitter
would most likely be dreadful. Remember, the null off the end of a
dipole is theoretically as deep as, say, Maltby Colliery (that's very
deep).
However it can work fine for DAB! See
http://www.wrightsaerials.tv/article...sed-arrays.pdf

Bill

That is exactly what I anticipate having to do to pull in more muxes
from a distant tx such as Zouches farm or Crystal Palace rather than
getting the much "louder" national muxes only from much closer Txes at
Bow Brickhill or Daventry.