Oblong antenna

[gyn_paul]

I noticed in Brico yesterday that they are selling for about 89E a dinky little flat panel 'dish'. This is obviously designed primarily for the French freeview by satellite service, but I'm wondering if it might do service pointed at 28W? The spec on the back says it has a gain of 33db.

So my question is: for comparison, what is the aprox gain of a bog-standard 80cm eliptical dish?

 

p

[AnOther]

Unless referenced to frequency take manufacturers gain claims with a generous pinch of salt as the gain increases with frequency.

A typical value even for a standard 60cm mesh type Sky dish would be 37.50 dB at 11.75 GHz and an 80cm could be around 50dB. Note that 3dB is a doubling so a 60cm is already almost 2x as much as your Brico job claims.

Anything smaller or lower gain than 60cm is likely to give marginal performance. When it comes to antennas it really is a case of bigger is better.

€89 sounds pretty expensive too.

[Anton Redman II]

Typical 60 cm dish 37.5 as below :

http://en.wikipedia.org/wiki/Satellite_dish

Discussion on dish size for Astra 2 D

http://www.satcure.co.uk/2d/fprint.htm

Db measure varies with frequency which may be why it is rarely quoted

http://www.sdsdigital.co.uk/Visiosat-65cm-Fibreglass-SMC65-Satellite-Dish-pr-735.html but higher values than the 60 cms above.

I think you will struggle the dish using this particularly for BBC and ITV on Astra 2D.

Using an 80 cm conventional dish we lose Classic FM a couple of times a year in very heavy rain but I spent a lot of time and effort of setting up

[gyn_paul]

Sorry, should have said. Ref was to 12.5GHz. So 33db would be pretty average - poor for looking at 28w in the middle of France, wouldn't it.

Thought it was too good to be true.

 

Size is everything, after all !

p  

[Martin963]

[quote user="AnOther"] Note that 3dB is a doubling

[/quote]

I'm going to nit pick here -  sorry!

If these were "power dBs" I'd agree.   If you double the power of a transmitter you add 3 dB to its output.

But with reception we're dealing with "voltage dBs" so you need 6 dB of gain to double the received signal.

I'm no mathematician but that's what we were taught at Auntie's knee....

[AnOther]

You're right of course, they say use it or lose it and these days I'm so past it that I have to think about bl00dy Ohms law, [:'(]

3dB or 6dB, I'm sure the OP gets the idea though, owt for nowt [;-)]

 

[Martin963]

I feel particularly bad about nit picking as you're being so helpful on my Alice/Club Internet query!

You can tell I don't really understand the maths,   since I have to separate the two sorts of dB!!

[gyn_paul]

All I can remember is that zero level is 4 on a PPM, and 6 on a PPM is 8dbs higher.

And 6-and-a-half is the level at which the Engineer in Charge comes rushing into the studio and beats you about the head with a rolled up copy of the Radio Times for not paying attention to the levels !

 

p

[Théière]

Yeh but mine goes to 11 [;-)]

[Martin963]

....   and what about stereo?    (3 1/4 per leg).   And that old conundrum of M-3 or M-6!

There's a brilliant series of virtual PPMs here if you're nostalgic.

http://www.darkwood.demon.co.uk/PC/meter.html

[gyn_paul]

[quote user="Martin963"]....   and what about stereo?    (3 1/4 per leg).   And that old conundrum of M-3 or M-6!

There's a brilliant series of virtual PPMs here if you're nostalgic.

http://www.darkwood.demon.co.uk/PC/meter.html
[/quote]

 

My nostalgia reached such levels that I felt compelled to bid for (and eventually win) a Cranford Stereo pair in a lovely free-standing wooden case.....fantastic.

'course what I really want is a Pye Mk1 local radio desk, 2 x Thorens gram decks, a pair of Philips tape machines (can't remember the number, but there's one in the Broadcasting museum in Hilversum) and a 4038.

p

[Pierre ZFP]

[quote user="Théière"]Yeh but mine goes to 11 [;-)][/quote]

Geek moment ahead:

You know of course that the BBC iplayer volume control goes up to 11,  as a nod to Spinal Tap.

I love it when a Geek slips something through the corporate net [:D]

 

[gyn_paul]

[quote user="Martin963"]....   and what about stereo?    (3 1/4 per leg).   And that old conundrum of M-3 or M-6!

There's a brilliant series of virtual PPMs here if you're nostalgic.

http://www.darkwood.demon.co.uk/PC/meter.html
[/quote]

 

...Wasn't the M-3 v M-6 business really all about the BBC arbitarily settling on a standard and then expecting the rest of the world to just fall in behind?

I seem to recall there was something similar about VT bars-and-tone for line-up being 100% saturation (or rather something definitely <100% saturation). It's quite some years now since I lined up a VPR-2 and, as you see, it's all slowly disappearing into a foggy soup in the back of - what passes for - my brain !

p

 

[Théière]

[quote user="Pierre ZFP"]

[quote user="Théière"]Yeh but mine goes to 11 [;-)][/quote]

Geek moment ahead:

You know of course that the BBC iplayer volume control goes up to 11,  as a nod to Spinal Tap.

I love it when a Geek slips something through the corporate net [:D]

[/quote]

[:D][:D][:D]

[Martin963]

[quote user="gyn_paul"]

[quote user="Martin963"]....  

[/quote]

 

...Wasn't the M-3 v M-6 business really all about the BBC arbitarily settling on a standard and then expecting the rest of the world to just fall in behind?

I seem to recall there was something similar about VT bars-and-tone for line-up being 100% saturation (or rather something definitely <100% saturation). It's quite some years now since I lined up a VPR-2 and, as you see, it's all slowly disappearing into a foggy soup in the back of - what passes for - my brain !

p

 

[/quote]

Well one could argue that at the time when the BBC operated the one and only stereo tx in Britain (Wrotham Third Programme) someone had to set a technical standard!   M-3 meant that a pure mono source under-deviated the transmitter by 3 dB (assuming it was peaking fully) but protected all the mono feeds (the vast majority at that time) properly,  whilst allowing more stereo-material deviation than M-6.

Of course once you achieve full stereo in *all* your distribution chain M-6 is a better standard, as the tx (comme tu sais) takes 1/2 (A+B) for M and 1/2 (A-B) for S,   and as we discussed earlier these are voltage dB's so 1/2 does indeed equate to - 6 dB.

I never got on to video (too frightened by those TV whizz kids to leave the safety of LBH)......

I'm envious of your "real" PPMs,   presumably they came with suitable drive equipment....?

[gyn_paul]

Well it has a mains socket and a pair of XLRs on the back, and it peaks in a pleasing fashion when attached to the line out of my mixer so they work... but how accurate they are I cannot tell. *

I once shared a house with a chap on the 'A' course (we local radio chaps learnt most of it all by 'sitting by Nellie') and he came home one day with the photocopied sheet which was the instructions for lining up a PPM (adjusting the log and the law etc etc) on the bottom of which I noticed some wag had hand-written (before the photocopying): " if all else fails, tweak the mechanical zero". A motto which has stood me in good stead these 40 years!

p

* In a perfect world they'd be attached to a line out from my TV, thus allowing me to ring Pres. and complain with some justification that it's not my imagination, their trails are indeed 6db higher than the programmes ! Not so much of a problem with R4. Their most abiding sin seems to be leaving the GTS pot open thus allowing stray pips to leak onto the airwaves on the 1/4-hours. The other evening at 18.00 we had both Big Ben AND pips!  You see, standard slipping. Even at BH.

[Martin963]

Ah yes,  were those the PPM's that went to max when you turned the power OFF perhaps  (a la type B desk).

As you probably know,   on a World Service shift one night both the announcer and SM in Green Con were bored to somnolence by a very dull half hour tape.    Unfortunately the SM had primed Lily Bolero,  and had also contrived to forget to deselect Big Ben on an OS from previously.

By the time Lily Bolero and Big Ben had simultaneously got well into their respective and cacophonous stride the two so-called stalwarts and guardians of the BBC World Service were fully wide awake and able to enjoy - in all its glory - the arrival of the pips in the pause following the din of quarter-hour chimes accompained by Lily Bolero and before the hour chimes of our national horological treasure.   It all fitted together very nicely,  as indeed it would.

Radio 4 is sadly subject (since autumn 2006) to compression even on the DSat feed (although I wonder if it actually is something other than Optimod, as it doesn't behave in quite an Optimodish way in my view) so a lot of the level kinks are inded smoothed out.   But not all,   I doubt there's more than 6 dB of compression applied........