How do these work if only a 6 inch stub sticks out of the roof ?

To get a decent FM signal indoors I need a dipole of some sort
that is about 59 inches long, plus reflector and director.

I ask this because I am getting interference on 88.50 Mhz
from Rowridge, but not all the time. Earlier today it
was bad, but the other BBC FM stations were not affected.

When I drove into town, FM R2 on my car radio was fine,
but I don't know what transmitter it is picking up. No
interference at all. Strange.

I am midway between IOW and Wrotham.

On Sun, 11 Feb 2018 20:18:56 +0000, Andrew
wrote:

How do these work if only a 6 inch stub sticks out of the roof ?

To get a decent FM signal indoors I need a dipole of some sort
that is about 59 inches long, plus reflector and director.

I ask this because I am getting interference on 88.50 Mhz
from Rowridge, but not all the time. Earlier today it
was bad, but the other BBC FM stations were not affected.

When I drove into town, FM R2 on my car radio was fine,
but I don't know what transmitter it is picking up. No
interference at all. Strange.

I am midway between IOW and Wrotham.

Poorly is how they perform. Much better to have a telescopic antenna
that rises to about a quarter wave (75 cm). If you live in a poor
signal area with interfering transmitters coming in, a directional
antenna is the only answer, and you can't have that on a car.

How about DAB? That works 100% better than FM in a car.

d

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In article ,
Andrew wrote:
How do these work if only a 6 inch stub sticks out of the roof ?

Mine has a built in amplifier. Actually two - it uses a separate one for
DAB.

--
*Toilet stolen from police station. Cops have nothing to go on.

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

In article ,
Don Pearce wrote:
Poorly is how they perform. Much better to have a telescopic antenna
that rises to about a quarter wave (75 cm). If you live in a poor
signal area with interfering transmitters coming in, a directional
antenna is the only answer, and you can't have that on a car.

Not my experience. I replaced a wing mounted telescopic with a 'bee sting'
active type mounted on the rear of the roof - so longer feeders too. On
the same radio, it works slightly better than the telescopic. My guess
because the roof one has a decent ground plane.

How about DAB? That works 100% better than FM in a car.

That is my experience - but with a decent aerial too. Those windscreen
mount ones aftermarket ones being rubbish.

DAB round London is simply miles better reception wise than FM.

--
*Indian Driver - Smoke signals only*

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

In article , Andrew97d-
says...
How do these work if only a 6 inch stub sticks out of the roof ?

Because the stub aerial is mounted on several square metres of
reflector.
The car body acts as a ground plane.

I think many of these are helically wound, and some have amps in them. I've
often wondered how they can be good over such a wide bandwidth myself as
theoretically any wound component should have a narrow bandwidth or be very
bad at picking much up at all.
Brian

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"Andrew" wrote in message
news
How do these work if only a 6 inch stub sticks out of the roof ?

To get a decent FM signal indoors I need a dipole of some sort
that is about 59 inches long, plus reflector and director.

I ask this because I am getting interference on 88.50 Mhz
from Rowridge, but not all the time. Earlier today it
was bad, but the other BBC FM stations were not affected.

When I drove into town, FM R2 on my car radio was fine,
but I don't know what transmitter it is picking up. No
interference at all. Strange.

I am midway between IOW and Wrotham.

Really? Um in good signal areas it does but near to big buildings and hills
I notice that they tend to descend into boiling mud mode then switch to
another station.
With fm its the his and multipath distortion and weird whistles and
burbles that go up and down, often going back to mono gradually or abruptly
depending one supposes on the receiver design.

I ride in a lot of private hire cars and notice such things.
Very few have traditional aerials, many have the rubber duck and some
still use window heater aerials.
Brian

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Blind user, so no pictures please!
"Don Pearce" wrote in message
...
On Sun, 11 Feb 2018 20:18:56 +0000, Andrew
wrote:

How do these work if only a 6 inch stub sticks out of the roof ?

To get a decent FM signal indoors I need a dipole of some sort
that is about 59 inches long, plus reflector and director.

I ask this because I am getting interference on 88.50 Mhz
from Rowridge, but not all the time. Earlier today it
was bad, but the other BBC FM stations were not affected.

When I drove into town, FM R2 on my car radio was fine,
but I don't know what transmitter it is picking up. No
interference at all. Strange.

I am midway between IOW and Wrotham.

Poorly is how they perform. Much better to have a telescopic antenna
that rises to about a quarter wave (75 cm). If you live in a poor
signal area with interfering transmitters coming in, a directional
antenna is the only answer, and you can't have that on a car.

How about DAB? That works 100% better than FM in a car.

d

---
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Brian Gaff wrote:

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


I think many of these are helically wound, and some have amps in them. I've
often wondered how they can be good over such a wide bandwidth myself as
theoretically any wound component should have a narrow bandwidth or be very
bad at picking much up at all.


** Helical winding makes a short whip antenna resonant and so resistive across most of the FM band. The bandwidth is somewhat narrower than a regular 1/4 wave and the output signal lower pretty much in proportion to the length ratio.

Long range performance on stereo FM would be impossible were it not for the use of high powered transmitters equipped high gain antennas.




..... Phil

In article ,
Brian Gaff wrote:
Really? Um in good signal areas it does but near to big buildings and
hills I notice that they tend to descend into boiling mud mode then
switch to another station.

If you drive round a town with large high buildings deeply packed
together, and the FM transmitter some way off, you first get it switching
to mono then the signal fading. Centre of London ideal for this. DAB is
for some reason rock solid. On the stations I've listened to while trying
this.

With fm its the his and multipath distortion and weird whistles and
burbles that go up and down, often going back to mono gradually or abruptly
depending one supposes on the receiver design.

I ride in a lot of private hire cars and notice such things.
Very few have traditional aerials, many have the rubber duck and some
still use window heater aerials.

Given how much my aftermarket DAB aerial cost, I'm not sure a car maker
would pay that much. Aerials built into the screen are more a design thing
than the best performing.

--
*A conclusion is the place where you got tired of thinking *

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

On 11/02/2018 20:59, Don Pearce wrote:
On Sun, 11 Feb 2018 20:18:56 +0000, Andrew
wrote:

How do these work if only a 6 inch stub sticks out of the roof ?

To get a decent FM signal indoors I need a dipole of some sort
that is about 59 inches long, plus reflector and director.

I ask this because I am getting interference on 88.50 Mhz
from Rowridge, but not all the time. Earlier today it
was bad, but the other BBC FM stations were not affected.

When I drove into town, FM R2 on my car radio was fine,
but I don't know what transmitter it is picking up. No
interference at all. Strange.

I am midway between IOW and Wrotham.

Poorly is how they perform. Much better to have a telescopic antenna
that rises to about a quarter wave (75 cm). If you live in a poor
signal area with interfering transmitters coming in, a directional
antenna is the only answer, and you can't have that on a car.

How about DAB? That works 100% better than FM in a car.

d

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DAB is rubbish where I live, and I only want to find out why
88.50 (R2) from the IOW is regularly plagued with much more
hissing than usual, plus a buzzing and faint crackling too.
(But R1,3 and 4 were not afflicted the same way). It's
indoors FM reception that am interested in. I have a 3-element
fm aerial in the loft pointing at the IOW.

Awful yesterday, but today it is fine. It was only when I
went out at 2PM to check out Currys instant sale that I
noticed that my car radio picked up R2 FM without any
interference at all.