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Richard L
Guest
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 Posted:
Fri Jan 21, 2005 2:13 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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In message <1106251629.948649.307460@z14g2000cwz.googlegroups.com>
"wrightsaerials@aol.com" <wrightsaerials@aol.com> wrote:
But if you're snipping bits off a quarter-wave stub, you can't be
certain you've found the right length until you've gone past it.
From a practical point of view, I've always preferred the
half-wave stub, shorted at the end. You can make the short by
experimentally pushing a hatpin through the cable at successive
points to locate the spot which kills the frequency of interest.
--
Richard L.
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DAB sounds worse than FM
Guest
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Mark Carver
Guest
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| Posted:
Fri Jan 21, 2005 3:40 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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DAB sounds worse than FM wrote:
| Quote: | Mark Carver wrote:
One advantage is that it's very cheap (just off cuts of co-ax and a
bit of soldering) to try :-)
I take it this is a short-circuit quarter-wave stub?
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No, open circuit
| Quote: | What do you connect to what? That is, what do you connect each end of
the inner conductor to and what do you connect each end of the outer
conductor to?
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See page 4 from Bill's web page
http://www.wrightsaerials.tv/Resources/VHF%20Interference.pdf
However, as Richard L has suggested elsewhere in this thread, a half
wave stub might be an easier option. Same connection details, except
it's twice as long as a quarter wave, and the end is short circuited. |
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Arthur
Guest
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| Posted:
Fri Jan 21, 2005 3:41 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver <markcarver@onetel.com>
wrote:
| Quote: | I used one with success to reduce a strong TV carrier (UHF E31) that
was splashing
across on a much weaker one (E34). It didn't impair the level of the E34
carrier noticably,
and the E31 carrier (also wanted) was still usable. That's a 24 MHz
range in 550ish MHz.
I suppose scaling that down to the OP's problem in Band II might be
expecting too much ?
One advantage is that it's very cheap (just off cuts of co-ax and a bit
of soldering) to try :-)
I've also used it successfully for Band I and Band IV TV signals, but I |
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.
Arthur |
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tony sayer
Guest
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| Posted:
Fri Jan 21, 2005 4:31 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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In article <opskx7yqzzilotte@home2.mshome.net>, Arthur
<Arthur@nospam.com> writes
| Quote: | On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver <markcarver@onetel.com
wrote:
I used one with success to reduce a strong TV carrier (UHF E31) that
was splashing
across on a much weaker one (E34). It didn't impair the level of the E34
carrier noticably,
and the E31 carrier (also wanted) was still usable. That's a 24 MHz
range in 550ish MHz.
I suppose scaling that down to the OP's problem in Band II might be
expecting too much ?
One advantage is that it's very cheap (just off cuts of co-ax and a bit
of soldering) to try :-)
I've also used it successfully for Band I and Band IV TV signals, but I
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.
Arthur
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We had to get one of these done recently to "notch" out an FM TX from an
RX on the same site 800 kHz apart!.
Works very well, made by aerial facilities www.aerial.co.uk
Cost around 480 squids IIRC;)
--
Tony Sayer |
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DAB sounds worse than FM
Guest
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| Posted:
Fri Jan 21, 2005 5:09 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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Mark Carver wrote:
| Quote: | DAB sounds worse than FM wrote:
Mark Carver wrote:
One advantage is that it's very cheap (just off cuts of co-ax and a
bit of soldering) to try :-)
I take it this is a short-circuit quarter-wave stub?
No, open circuit
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Ah well, I had a 50% chance of getting it right. :)
It's surprisingly effective innit. At first, you look at the frequency
response in Figure 8 on page 4 and you think it's going to negatively
effect the the signals on all the other channels too much.
As well as adding a stub filter, I still think David should get a Yagi,
though, because if he wants to hear how good FM can be then the extra
5dB gain relative to a dipole can't hurt, and I think he mainly listens
to BBC network stations, so I assume they'll all come from the same
transmitter.
BTW, what is the effect / how much loss is caused by not using a balun
to connect a dipole to coax?
--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info
Find the cheapest Freeview, DAB & MP3 Player Prices:
http://www.digitalradiotech.co.uk/freeview_receivers.htm
http://www.digitalradiotech.co.uk/dab_digital_radios.htm
http://www.digitalradiotech.co.uk/mp3_players_1GB-5GB.htm
http://www.digitalradiotech.co.uk/mp3_players_large_capacity.htm |
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davidrobinson@postmaster.
Guest
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| Posted:
Fri Jan 21, 2005 5:33 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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Arthur wrote:
| Quote: | On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver
markcarver@onetel.com
wrote:
I've also used it successfully for Band I and Band IV TV signals, but
I
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.
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We're only about 3 miles from Sandy Heath. I'm not worried about the
tuner - it's the distribution amplifier (not bought yet) that I suspect
would be overloaded, which would give nice cross mod of BBC 3CR and
Chiltern all across the FM band.
All I can do is try. When I have something in place, I'll come back and
seek advice if the problem manifests itself. I've read Bill's excellent
article, and will try both 1/4 and 1/2 wave stubs first to try to solve
the problem.
Thanks for all the advice everyone.
Cheers,
David.
P.S. suggestions for suitable DA with good headroom where no gain is
required would be gratefully received. |
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Arthur
Guest
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| Posted:
Fri Jan 21, 2005 6:29 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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On Fri, 21 Jan 2005 11:31:21 +0000, tony sayer <tony@bancom.co.uk> wrote:
| Quote: | We had to get one of these done recently to "notch" out an FM TX from an
RX on the same site 800 kHz apart!.
Works very well, made by aerial facilities www.aerial.co.uk
Cost around 480 squids IIRC;)
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Yes, they make very good ones - silver plated inside.
Arthur |
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Mark Carver
Guest
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| Posted:
Fri Jan 21, 2005 6:48 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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DAB sounds worse than FM wrote:
| Quote: |
As well as adding a stub filter, I still think David should get a Yagi,
though, because if he wants to hear how good FM can be then the extra
5dB gain relative to a dipole can't hurt, and I think he mainly listens
to BBC network stations, so I assume they'll all come from the same
transmitter.
|
I think not, unwanted locals are from Sandy Heath, wanted nationals from
Peterborough ?
| Quote: | BTW, what is the effect / how much loss is caused by not using a balun
to connect a dipole to coax?
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Oooh, you're almost into chaos theory there I think ? |
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Marky P
Guest
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| Posted:
Fri Jan 21, 2005 7:25 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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On 21 Jan 2005 04:33:27 -0800, "davidrobinson@postmaster.co.uk"
<davidrobinson@postmaster.co.uk> wrote:
| Quote: | Arthur wrote:
On Fri, 21 Jan 2005 07:39:48 -0000, Mark Carver
markcarver@onetel.com
wrote:
I've also used it successfully for Band I and Band IV TV signals, but
I
think it's asking a bit much for this to work with closely-spaced,
relatively narrow-band FM signals in Band II.
I would suggest that if the transmissions are sufficiently spaced in
frequency for a stub to be effective, the FM tuner should itself have
sufficient selectivity and dynamic range to work without the stub.
We're only about 3 miles from Sandy Heath. I'm not worried about the
tuner - it's the distribution amplifier (not bought yet) that I suspect
would be overloaded, which would give nice cross mod of BBC 3CR and
Chiltern all across the FM band.
All I can do is try. When I have something in place, I'll come back and
seek advice if the problem manifests itself. I've read Bill's excellent
article, and will try both 1/4 and 1/2 wave stubs first to try to solve
the problem.
Thanks for all the advice everyone.
Cheers,
David.
P.S. suggestions for suitable DA with good headroom where no gain is
required would be gratefully received.
|
What is the distribution amp for? Are you planning to feed multiple
tuners? If so, it may be possible just to use a passive splitter with
very little loss in signal. This way you shouldn't get overload from
Sandy. I would recommend a 4 element aerial at least if this was the
case. If you plan on pointing it Peterborough (which from where you
are is roughly in the same direction as Sandy?) you should get a
perfect signal, at least when it's up & running again!)
Marky P. |
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DAB sounds worse than FM
Guest
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| Posted:
Fri Jan 21, 2005 7:39 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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Mark Carver wrote:
| Quote: | DAB sounds worse than FM wrote:
As well as adding a stub filter, I still think David should get a
Yagi, though, because if he wants to hear how good FM can be then
the extra 5dB gain relative to a dipole can't hurt, and I think he
mainly listens to BBC network stations, so I assume they'll all come
from the same transmitter.
I think not, unwanted locals are from Sandy Heath, wanted nationals
from Peterborough ?
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No, I meant that the BBC network FM stations (Radios 1-4) will all be on
the same transmitter.
| Quote: | BTW, what is the effect / how much loss is caused by not using a
balun to connect a dipole to coax?
Oooh, you're almost into chaos theory there I think ?
|
In other words, it's not particularly important?
--
Steve - www.digitalradiotech.co.uk - Digital Radio News & Info
Find the cheapest Freeview, DAB & MP3 Player Prices:
http://www.digitalradiotech.co.uk/freeview_receivers.htm
http://www.digitalradiotech.co.uk/dab_digital_radios.htm
http://www.digitalradiotech.co.uk/mp3_players_1GB-5GB.htm
http://www.digitalradiotech.co.uk/mp3_players_large_capacity.htm |
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Mark Carver
Guest
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| Posted:
Fri Jan 21, 2005 7:48 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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DAB sounds worse than FM wrote:
| Quote: | Mark Carver wrote:
I think not, unwanted locals are from Sandy Heath, wanted nationals
from Peterborough ?
No, I meant that the BBC network FM stations (Radios 1-4) will all be on
the same transmitter.
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Ah sorry, yes.
| Quote: | BTW, what is the effect / how much loss is caused by not using a
balun to connect a dipole to coax?
Oooh, you're almost into chaos theory there I think ?
In other words, it's not particularly important?
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Oh yes it can be, it's just not easily calculatable. |
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Richard L
Guest
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| Posted:
Fri Jan 21, 2005 9:31 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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In message <Iu8Id.90$e4.55@newsfe4-win.ntli.net>
"DAB sounds worse than FM" <dab_is@low.quality> wrote:
| Quote: |
No, I meant that the BBC network FM stations (Radios 1-4) will all be on
the same transmitter.
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You're confusing this with DAB. The BBC network FM stations are
not all on the same transmitter. But they're all at the same site.
;-)
--
Richard L. |
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DAB sounds worse than FM
Guest
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Googolplex
Guest
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| Posted:
Mon Jan 24, 2005 10:48 pm Post subject:
Re: Is this an FM aerial? Where did it come from? |
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davidrobinson@postmaster.co.uk wrote:
There's one of those (but longer) in a house in the next village from me... |
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