How much stock do the professional installers place in the CAI aerial 
benchmarking scheme? I receive DTT from Reigate 6 miles away, which seems to 
be powered by an AA battery, plus I'm in a dip behind some trees. Installers 
hate my site and won't guarantee anything when quoting.

I'm willing to stick up my own aerial. I've installed my own dish, used 
reasonable PF100 cables etc, carefully cut/ crimped/ fed around careful 
radii etc on corners, and kept away from noisy sources. I'm about to migrate 
to a multiswitch and a quattro LNB etc for better satellite distribution 
with triplexing plates.

So, looking at the CAI aerial benchmarking document online, do the lower 
numbered standard aerials have better gain properties, particularly in 
wideband (needed for Reigate)? I see the cheapo Screwfix stuff have plenty 
of "category 3" aerials, supposedly high-gain, but I note these are the 
minimum standard and have less gain really than "category 1" aerials. Or 
have I musunderstood?

I do appreciate there's much more to installing aerials than this - I've 
followed this group for a while - but as no-one seems to want to come near 
my site with any guarantee I'm prepared to take the risk of doing this 
myself.

Advice would be gratefully received.

Thanks,

Basil.

"Basil"  wrote in message 
news:WIudnWmJup8FhtXVnZ2dnUVZ8hednZ2d@posted.plusnet...
> How much stock do the professional installers place in the CAI aerial 
> benchmarking scheme?

The score must depend on how much a company pays them!  They certainly don't 
go inspecting a lot of the installations.
Too many cowboys fitting aerials now, even those apparently approved.

Rob wrote:
> "Basil"  wrote in message 
> news:WIudnWmJup8FhtXVnZ2dnUVZ8hednZ2d@posted.plusnet...
>> How much stock do the professional installers place in the CAI aerial 
>> benchmarking scheme?
> 
> The score must depend on how much a company pays them!  They certainly don't 
> go inspecting a lot of the installations.
> Too many cowboys fitting aerials now, even those apparently approved.
> 
> 
The DAT 75 is a Standard 1 Wideband aerial, but the Mast passes through 
the aerial between the elements. This us usually frowned upon by any 
good installer with any other aerial. How this passes is strange...

Glenn...

"Basil"  wrote in message 
news:WIudnWmJup8FhtXVnZ2dnUVZ8hednZ2d@posted.plusnet...
> How much stock do the professional installers place in the CAI aerial 
> benchmarking scheme? I receive DTT from Reigate 6 miles away, which seems 
> to be powered by an AA battery, plus I'm in a dip behind some trees. 
> Installers hate my site and won't guarantee anything when quoting.
>
> I'm willing to stick up my own aerial. I've installed my own dish, used 
> reasonable PF100 cables etc, carefully cut/ crimped/ fed around careful 
> radii etc on corners, and kept away from noisy sources. I'm about to 
> migrate to a multiswitch and a quattro LNB etc for better satellite 
> distribution with triplexing plates.
>
> So, looking at the CAI aerial benchmarking document online, do the lower 
> numbered standard aerials have better gain properties, particularly in 
> wideband (needed for Reigate)? I see the cheapo Screwfix stuff have plenty 
> of "category 3" aerials, supposedly high-gain, but I note these are the 
> minimum standard and have less gain really than "category 1" aerials. Or 
> have I musunderstood?
>
> I do appreciate there's much more to installing aerials than this - I've 
> followed this group for a while - but as no-one seems to want to come near 
> my site with any guarantee I'm prepared to take the risk of doing this 
> myself.
>
> Advice would be gratefully received.
>
> Thanks,
>
> Basil.
>
>
>

The only aerials I use which are CAI benchmarked is the log periodics from 
Blake. I wouldn't take too much notice of the benchmark scheme for aerials. 
I rate it highly for cables though.

Basil wrote:

> So, looking at the CAI aerial benchmarking document online, do the lower 
> numbered standard aerials have better gain properties,[...]
> 
> Advice would be gratefully received.

You need to read the Benchmarked Aerial 'Guidelines' Document:
http://www.cai.org.uk/downloads/Guidelines%20for%20the%20use%20of%20Benchmarked%20Aerials.pdf

-- 
Andy

>
> You need to read the Benchmarked Aerial 'Guidelines' Document:
> http://www.cai.org.uk/downloads/Guidelines%20for%20the%20use%20of%20Benchmarked%20Aerials.pdf
>
> -- 
> Andy

That PDF is what I read before I posted, hence the observation that many of 
the advertised aerials supposed "high-gain" characteristics are not in line 
with the guidance in that document. My example is a Screwfix-advertised 
Labgear aerial with a supposed 16.5 dB gain. It has a category "3" rating. 
Category "3" is appearently the minimum standard in the document and has the 
LEAST gain.

Thus is there any surprise that this appears contradictory? That's why I 
asked for some guidance. The general feedback would seem to be to not follow 
that PDF's scheme. Isn't this rather poor that the industry can't agree with 
it's own professional bodies? Shouldn't the advice be clearer?

Basil

Basil wrote:

> That PDF is what I read before I posted,

OK, but your question "So, looking at the CAI aerial benchmarking
document online, do the lower numbered standard aerials have better gain 
properties, particularly in wideband" suggested that you'd only been 
looking at the products list.  The table in the guidelines document 
clearly sets out minimum gains in dBd for each standard for each of the 
main bandwidth groups. For Group W products the minimum gains at each 
end of the band are:

- standard 1: 10 - 12 dBd
- standard 2:  7 - 10 dBd
- standard 3:  5 -  8 dBd
- standard 4:  7 dBd (flat).

> hence the observation that many of the advertised aerials supposed 
> "high-gain" characteristics are not in line with the guidance in that
> document. My example is a Screwfix-advertised Labgear aerial with a 
> supposed 16.5 dB gain. It has a category "3" rating. Category "3" is 
> appearently the minimum standard in the document and has the > LEAST
> gain.

Quite revealing, isn't it?  It's possible, though probably not very 
likely, that the product mentioned has enough gain to make it into 
standard 2, yet the advertised gain is 16.5 dB (note no reference 
stated).  Draw your own conclusions.  The benchmarking test provides the 
submitting manufacturer or vendor with detailed test results, but 
they're not under any obligation to publish them.  Everybody still seems 
to quote a single gain figure and if this bears any relationship to 
reality it will be at (or towards) the top of the band for a Yagi-type 
product.  Some surreptitiously quote the gain in dBi which of course 
gives an instant 2.15 dB boost for the unwary.  Others seem to use the 
dBWSCC scale (dB relative to wet string in coal cellar).

> Thus is there any surprise that this appears contradictory? That's why I 
> asked for some guidance. The general feedback would seem to be to not follow 
> that PDF's scheme. Isn't this rather poor that the industry can't agree with 
> it's own professional bodies? Shouldn't the advice be clearer?

What advice?  The guidelines document is mostly explanatory, rather than 
advisory.  Advice is in the CAI codes, and in the DTG R-books - the 
latter available at
http://www.dtg.org.uk/retailer/publications.html.

It's a shame if the scheme is being discredited.  A lot of effort went 
into setting it up (yes, I was involved), and into ensuring that 
accurate measurements were made.  Originally all the testing was done by 
Schaffner, on a specially-built 40 m test range at their Broadwood test 
site near Dorking.  Gain testing was by the substitution method, using a 
BBC log-periodic (itself calibrated at NPL) as the reference antenna.
Testing has since transferred to NPL itself.

Bear in mind that UHF coverage, for the most part, is 
interference-limited, rather than noise-limited.  Forward gain alone is 
not the only consideration and benchmarking also checks radiation 
pattern and cross-polar discrimination.

Can a standard 3 product be called high-gain?  Certainly it can if 
compared with the wideband 'contract' aerials that were in common use 
before  DTT got started.  I remember attending a meeting at Crown Castle 
(Warwick) around 1997-98, at which they presented the results of gain 
measurements on various aerials available at the time.  From memory, 
typical gains of contract wideband Yagis (so-called) were around 0 to +3 
dBd at channel 21.  One specimen even had less than 0 dBd gain at that 
frequency.

HTH
-- 
Andy

On Jun 8, 1:43 am, Andy Wade  wrote:
> Basil wrote:
> > That PDF is what I read before I posted,
>
> OK, but your question "So, looking at the CAI aerial benchmarking
> document online, do the lower numbered standard aerials have better gain
> properties, particularly in wideband" suggested that you'd only been
> looking at the products list.  The table in the guidelines document
> clearly sets out minimum gains in dBd for each standard for each of the
> main bandwidth groups. For Group W products the minimum gains at each
> end of the band are:
>
> - standard 1: 10 - 12 dBd
> - standard 2:  7 - 10 dBd
> - standard 3:  5 -  8 dBd
> - standard 4:  7 dBd (flat).
>
> > hence the observation that many of the advertised aerials supposed
> > "high-gain" characteristics are not in line with the guidance in that
> > document. My example is a Screwfix-advertised Labgear aerial with a
> > supposed 16.5 dB gain. It has a category "3" rating. Category "3" is
> > appearently the minimum standard in the document and has the > LEAST
> > gain.
>
> Quite revealing, isn't it?  It's possible, though probably not very
> likely, that the product mentioned has enough gain to make it into
> standard 2, yet the advertised gain is 16.5 dB (note no reference
> stated).  Draw your own conclusions.  The benchmarking test provides the
> submitting manufacturer or vendor with detailed test results, but
> they're not under any obligation to publish them.  Everybody still seems> to quote a single gain figure and if this bears any relationship to
> reality it will be at (or towards) the top of the band for a Yagi-type
> product.  Some surreptitiously quote the gain in dBi which of course
> gives an instant 2.15 dB boost for the unwary.  Others seem to use the
> dBWSCC scale (dB relative to wet string in coal cellar).
>
> > Thus is there any surprise that this appears contradictory? That's why I> > asked for some guidance. The general feedback would seem to be to not follow
> > that PDF's scheme. Isn't this rather poor that the industry can't agree with
> > it's own professional bodies? Shouldn't the advice be clearer?
>
> What advice?  The guidelines document is mostly explanatory, rather than> advisory.  Advice is in the CAI codes, and in the DTG R-books - the
> latter available athttp://www.dtg.org.uk/retailer/publications.html.
>
> It's a shame if the scheme is being discredited.  A lot of effort went
> into setting it up (yes, I was involved), and into ensuring that
> accurate measurements were made.  Originally all the testing was done by> Schaffner, on a specially-built 40 m test range at their Broadwood test
> site near Dorking.  Gain testing was by the substitution method, using a> BBC log-periodic (itself calibrated at NPL) as the reference antenna.
> Testing has since transferred to NPL itself.
>
> Bear in mind that UHF coverage, for the most part, is
> interference-limited, rather than noise-limited.  Forward gain alone is
> not the only consideration and benchmarking also checks radiation
> pattern and cross-polar discrimination.
>
> Can a standard 3 product be called high-gain?  Certainly it can if
> compared with the wideband 'contract' aerials that were in common use
> before  DTT got started.  I remember attending a meeting at Crown Castle
> (Warwick) around 1997-98, at which they presented the results of gain
> measurements on various aerials available at the time.  From memory,
> typical gains of contract wideband Yagis (so-called) were around 0 to 
> dBd at channel 21.  One specimen even had less than 0 dBd gain at that
> frequency.
>
> HTH
> --
> Andy

As someone who has only bought one aerial in his life, my only goal
was to buy a "branded" one which was the right group and had the
appropriate likelihood of good gain.

Bill Wright seemed to recommend Antiference, so that's the way I
went.  If I hadn't read here, I might have gone "fancy" and thought
that a DAT-45 or -75 "looked good", so I avoided them.

Other than Antiference, Blakes seem well recommended.  I guess once
they do the job, quality of build is essential as it is up there in
the elements for many years to come.

Matt