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Old 23rd March 2006, 06:29 PM   #11
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Location: North Derbyshire
Quote:
Originally posted by johnthedoctor
Nigel, I already knew that radio was available from sat dishes but assumed it was DAB quality so dismissed it.

I can get a good analogue radio signal from a satellite dish? I'm not so keen if it's digital and has to go through a DAC, the aerial is to get the full benefit of my AKAI tuner.
No, it's not analogue from satellite, it's digital - but it's digital of better quality than the analogue FM transmissions - the satellite transmissions are the highest radio quality available in the UK. I'm glad you've dismissed DAB - too low a quality and completely pointless!.
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Old 6th May 2006, 05:19 PM   #12
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Dear Dr J.
You can easily try to connect an fm dipole (the T antenna for indoor use) at your antenna input.
If the reception is good. you can use the circular aerial on roof; if not you need a Yagi antenna, more elements, more gain and more directivity (you should use an antenna rotor for aim pointing).If you have multipath you can use two yagi one vertical and one horizontal coupled via an impedence combiner.
Another solution is an helicoidal antenna (only one) and you can receive whatever kind of polarisation you want.
Consider DIY , internet is plenty of antenna project.

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cicero32
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Old 6th May 2006, 05:34 PM   #13
AndrewT is offline AndrewT  Scotland
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Hi John,
I used a roof mounted circular FM aerial when in Knutsford. I will never repeat that exercise. Too low a signal level leading to noise and birdies. Quad FM4 tuner.
Even 300ohm ribbon some 15feet lower down and inside the brick building gave a stronger signal.

Go for a 3 element yagi pointed at the source with most frequencies you want to listen too. You could go for more elements but costs more and might need a stronger pole & fixing.

Nigel or anyone else who has the data,
can you give comparative details of the digital sources available to UK listeners? DAB, Freeview Radio, Satellite Radio, FM's digital source (14bit companded down to 10bit?).
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Old 6th May 2006, 06:56 PM   #14
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Thanks for all the replies, I now have a plan. The local fitter with a shop front won't fit my rotator, some gubbins about insurance blah blah but I'm sure I can find a cowboy fitter (ie. cheap) to do it for me.

As low loss sat cable can also make good speaker cables I'm now looking to source a reel, solid copper, full copper foil shield etc. Two birds, one stone. (I hope.)
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Old 6th May 2006, 10:13 PM   #15
tvi is offline tvi  Australia
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Heres a nice map that links to lists showing the polarisation used by the BBC in various areas.
BBC Map ]

If you have a local ham radio group maybe they can help with the rotator installation issues, hopefully someone there can also tell you the max load for the rotator so you won't over stress it with something like this
Click the image to open in full size.

Regards
James

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Old 7th May 2006, 01:30 AM   #16
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Nowt that big.

A 3 element, that's all. All the fitter has to do is get it horizontal and pointing almost North, that'll do.
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Old 7th May 2006, 01:53 PM   #17
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I built a 'J-pole' for FM use,and with a decent tuner (my Sansui TU-717) it *rocks!* Simply the best antenna i've used so far for recieving FM,and I even have it mounted at ground level (the "tail" is stuck into the flower-bed outside my window!) I can already hear distant stations (LPFM's too.) from all over the place,and if I put it up on the roof i'm sure it would be alot better.
The feedline is ~20 feet of RG-8x from RadioShack.
Measuring and soldering the pipe isn't too hard,Tuning it was a bit tricky,but it really performs well,and is quite low-noise.

If you're up to soldering up some pipe,i'd recommend it..it's cheap to build too.

http://www.hamuniverse.com/jpole.html

The only drawback is that it's 3/4 wavelength tall.
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Old 7th May 2006, 03:36 PM   #18
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I think I'll be OK with my 3 element, my brothers FM ribbon is working well in his loft at a similar height to my roof. For BBC radio best reception is from the Holme Moss transmitter which surprised me as it's on the other side of the Pennines.

I only listen to 2 stations, R2 and R3. Adverts annoy me too much to bother with commercial stations. R3 seems to be playing more jazz and world music now, some nights it has my jaw dropping and they don't use much compression if at all.

I've found a source for the cable, how do these specs look? I'll be wanting to make speaker cables and interconnects from it as well.

http://www.cybermarket.co.uk/ishop/923/shopscr3294.html

Take no notice of the pic, they've used it for all their sat cables.
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Old 7th May 2006, 03:39 PM   #19
AndrewT is offline AndrewT  Scotland
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Hi Digital,
I notice that for 100Mhz the connection points are 70mm (23/f) up from the j bend and only 67mm (22/f) apart.
How critical to reception performance are these dimensions?

Where the coax is prepared for the connection, should the bared core be the same length as the stripped screen (each about 40mm long)?
Or would it be better to have a short core and long screen leg?
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Old 7th May 2006, 08:40 PM   #20
infinia is offline infinia  United States
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The J pole antenna is actually a 3/4 wave vertical polarization antenna with a gamma match. The gain is quite good (6 dB over a that of a 1/2 wave dipole) but BW is fairly narrow, mostly used in transmitter applications. The feed point is called a gamma match and is easily tunable if desired. The connections can be built so the tap points can be adjusted up or down. The antenna is an unbalanced design so a choke is needed to keep the shield from radiating. A few turns of the coax in a ferrite core can be used to keep shield currents down.
http://www.hamuniverse.com/jpole.html
referring to the link given previously
B= 1/4 wave this is the ground point. Open ckt at the end rotated 90 deg is a short circuit by definition.
A= 3/4 wave
D= sets the Q of resonance(can be moved out for wider BW)
gamma match is tuned for SWR or return loss
D+2C = gamma match adjustable to maximize return (SWR) loss at desired freq.
another link
http://www.pcs-electronics.com/en/pr...p?sub=antennas
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