What is best, wideband or grouped aerials diplexed?

But surely "bigger is better" - you must be able to charge more for a
monster Yagi than for two smaller logs, even if the picture is worse ;-).

That, of course, is why there are so many unneccessarily huge aerials on
the roofs of Britain.

Bill

This thread has just buggered up my thinking. I was about to install a
wideband aerial since I don't get all the Freeview channels from my group A
aerial pointing to Craigkelly. On checking the transmitter info for
Craigkelly, the recommend a group K/W aerial which seems to be a reduced
band wideband aerial (if that makes sense). Does your dislike of wideband
aerials also apply to a group K/W?

I had a look at the Antiference web site and they don't appear to make a
group K/W. Any others that you would recommend?

Archie

"Archie" wrote in message
k...

But surely "bigger is better" - you must be able to charge more for a
monster Yagi than for two smaller logs, even if the picture is worse
;-).

That, of course, is why there are so many unneccessarily huge aerials on
the roofs of Britain.

Bill

This thread has just buggered up my thinking. I was about to install a
wideband aerial since I don't get all the Freeview channels from my group
A aerial pointing to Craigkelly. On checking the transmitter info for
Craigkelly, the recommend a group K/W aerial which seems to be a reduced
band wideband aerial (if that makes sense). Does your dislike of wideband
aerials also apply to a group K/W?

I had a look at the Antiference web site and they don't appear to make a
group K/W. Any others that you would recommend?

Archie

Hmm . . . Bit of a bugger isn't it? There's nothing made, and I doubt if it
would be much better than a W if there was. You only need 21-42 and that
wouldn't be so bad, but a 21-53 aerial wouldn't be any better than 21-68.
Unfortunately the gain of a yagi falls through the floor at bandwidths
greater than 10% of centre frequency. Well, it does at the ends of the band
covered anyway. The directivity is very poor as well. Personally I'd use a
log periodic, knowing that it wasn't ideal. Wideband yagis tend to be crap
at the bottom end, which doesn't help you at all.

Bill

On Sun, 7 Jan 2007 02:35:50 -0000, "Bill Wright"
wrote:


"Archie" wrote in message
. uk...

But surely "bigger is better" - you must be able to charge more for a
monster Yagi than for two smaller logs, even if the picture is worse
;-).

That, of course, is why there are so many unneccessarily huge aerials on
the roofs of Britain.

Bill

This thread has just buggered up my thinking. I was about to install a
wideband aerial since I don't get all the Freeview channels from my group
A aerial pointing to Craigkelly. On checking the transmitter info for
Craigkelly, the recommend a group K/W aerial which seems to be a reduced
band wideband aerial (if that makes sense). Does your dislike of wideband
aerials also apply to a group K/W?

I had a look at the Antiference web site and they don't appear to make a
group K/W. Any others that you would recommend?

Archie

Hmm . . . Bit of a bugger isn't it? There's nothing made, and I doubt if it
would be much better than a W if there was. You only need 21-42 and that
wouldn't be so bad, but a 21-53 aerial wouldn't be any better than 21-68.
Unfortunately the gain of a yagi falls through the floor at bandwidths
greater than 10% of centre frequency. Well, it does at the ends of the band
covered anyway. The directivity is very poor as well. Personally I'd use a
log periodic, knowing that it wasn't ideal. Wideband yagis tend to be crap
at the bottom end, which doesn't help you at all.

Bill

So, when a wideband is said to have a gain of, say, 16.5dB (in the
case of the Televes X43) would that be up the top end of the band?
This particular aerial describes itself as being CD/W. Which is odd.

Marky P.

Bill Wright wrote:

Hmm . . . Bit of a bugger isn't it? There's nothing made, and I doubt if it
would be much better than a W if there was. You only need 21-42 and that
wouldn't be so bad, but a 21-53 aerial wouldn't be any better than 21-68.
Unfortunately the gain of a yagi falls through the floor at bandwidths
greater than 10% of centre frequency. Well, it does at the ends of the band
covered anyway. The directivity is very poor as well. Personally I'd use a
log periodic, knowing that it wasn't ideal. Wideband yagis tend to be crap
at the bottom end, which doesn't help you at all.

Archie's problem won't end after DSO. In fact current spread of DTT from
Craigkelly is 33-42, after DSO it'll be 21-49.

Current
http://www.dtg.org.uk/retailer/tx_cscot.html

Post DSO
http://www.tellyaerial.34sp.com/ta.php/rrc

Although ERP will rise from 2kW to 50kW, which will help.


--
Mark
Please replace invalid and invalid with gmx and net to reply.

"Marky P" wrote in message
...
So, when a wideband is said to have a gain of, say, 16.5dB (in the
case of the Televes X43) would that be up the top end of the band?

They might be quoting the maximum gain, which is likely to be about three
quarters or seven-eighths of the way up the band covered.

This particular aerial describes itself as being CD/W. Which is odd.

Some firms make an A, a B, and a wideband, which they call a CD/W. These
often perform reasonably well in CD but very badly on 21 - 30.

Antiference now don't make a TC18B. The present product claims to cover 21
to 53, but actually it doesn't work properly below 27. The product works as
well on 37 to 53 as the old model though.

Bill

On Sun, 7 Jan 2007 11:49:02 -0000, "Bill Wright"
wrote:


"Marky P" wrote in message
.. .
So, when a wideband is said to have a gain of, say, 16.5dB (in the
case of the Televes X43) would that be up the top end of the band?

They might be quoting the maximum gain, which is likely to be about three
quarters or seven-eighths of the way up the band covered.

This particular aerial describes itself as being CD/W. Which is odd.

Some firms make an A, a B, and a wideband, which they call a CD/W. These
often perform reasonably well in CD but very badly on 21 - 30.

That's good then, as I got one quite cheap off ebay to use up the top
end :-)


Antiference now don't make a TC18B. The present product claims to cover 21
to 53, but actually it doesn't work properly below 27. The product works as
well on 37 to 53 as the old model though.

Bill

"Alan Pemberton" wrote in message
erve.co.uk.invalid...
OK, so in a nutshell, by stacking/baying two log perodic arrays you:

- lose bandwidth
Only if the two aerials are pointing in diferent directions, something that
would only be done for transmission. If they are pointing in the same
direction they remain in phase (as regards signals from the direction
they're pointing) right across the band. It's best to set up phasing on the
highest used channel, then check across the band.


- gain gain (!)
It's hard to gain more than about 3dB in practice.

- gain (or lose) directivity, depending.
With the two aerials pointing in the same direction and correctly phased all
that happens is that a series of response notches appear all round. Their
angles depend on the spacing between the two arrays, and the frequency. I
have a chart somewhere showing the spacing needed to notch out specific
angles. In practice if the spacing is correct for a particular angle on a
middle channel it's near enough for the others.

One snag with logs is that the forward lobe is very wide, and I suspect that
this is why they sometimes give disappointing results in urban locations,
where there are large buildings behind and in front. The wide forward lobe
lets in the dreaded 'double bounce' signals -- the absolute killers as far
as ghosting is concerned. I had an absolute bloody nightmare with this 20
years ago in central London. The site was a flat roof with C Pal to the
south and the PO tower and a large rectangular slab of a building to the
north. To the south, just next to CP was another large flat sided building.
There was one very strong ghost. We went so far as to erect a chicken wire
screen on a frame behind the aerial, and it had no effect whatsoever. In the
end I concluded that the reflected signal was a double bounce, from
something behind onto the block to the south, then back to us. It was
totally intractable and almost seemed as if it was a transmitted fault,
which of course wasn't the case. I've often wished since that I'd tried two
aerials at opposite ends of the roof (max angular distance as seen from Tx)
because I wonder if this would give a sharp notch a fraction of a degree
from the Tx direction. Phasing would have been tricky but possible I think.

In a difficult reception area (for instance the middle of Rotherham, using
Crosspool, surrounded by big buildings, field strength rather low) stacking
two logs gives a significant improvement in BER; more than the slightly
stronger signal would indicate. I can only assume that this is due a general
reduction in echoes, general local low level interference, co-channel
signals, etc.

Bill

Hmm . . . Bit of a bugger isn't it? There's nothing made, and I doubt if
it would be much better than a W if there was. You only need 21-42 and
that wouldn't be so bad, but a 21-53 aerial wouldn't be any better than
21-68. Unfortunately the gain of a yagi falls through the floor at
bandwidths greater than 10% of centre frequency. Well, it does at the ends
of the band covered anyway. The directivity is very poor as well.
Personally I'd use a log periodic, knowing that it wasn't ideal. Wideband
yagis tend to be crap at the bottom end, which doesn't help you at all.

Bill

I see what you mean with the low frequency reponse of a group W aerial.
There doesn't seem to be too much info out there on gain.frequency graphs
but I found one he- http://www.antiference.co.uk/9graph.gif

I wonder why on many of the information sites for digital TV reception they
suggest using a group K aerial when no one makes them.

There aren't too many LP aerial around but I found a couple. A Maxview
ALP28W (7.8 bd gain) and the Blake DML26WB (8.62db gain). Are there any
better ones out there?

Archie

"Archie" wrote in message
k...

Hmm . . . Bit of a bugger isn't it? There's nothing made, and I doubt if
it would be much better than a W if there was. You only need 21-42 and
that wouldn't be so bad, but a 21-53 aerial wouldn't be any better than
21-68. Unfortunately the gain of a yagi falls through the floor at
bandwidths greater than 10% of centre frequency. Well, it does at the
ends of the band covered anyway. The directivity is very poor as well.
Personally I'd use a log periodic, knowing that it wasn't ideal. Wideband
yagis tend to be crap at the bottom end, which doesn't help you at all.

Bill

I see what you mean with the low frequency reponse of a group W aerial.
There doesn't seem to be too much info out there on gain.frequency graphs
but I found one he- http://www.antiference.co.uk/9graph.gif

I wonder why on many of the information sites for digital TV reception
they suggest using a group K aerial when no one makes them.

There aren't too many LP aerial around but I found a couple. A Maxview
ALP28W (7.8 bd gain) and the Blake DML26WB (8.62db gain). Are there any
better ones out there?

We have settled on the Blake after much experimentation with Vision,
Antiference, et al, but we've had a big disappointment because we had one
snap off recently. The boom snapped near the clamp. Not good at all, and
I'm hoping it isn't going to be a regular occurance.

Bill

We have settled on the Blake after much experimentation with Vision,
Antiference, et al, but we've had a big disappointment because we had one
snap off recently. The boom snapped near the clamp. Not good at all, and
I'm hoping it isn't going to be a regular occurance.

Bill


Thanks Bill

Do you think that the gain is OK for a distance of 32km from Craigkelly?

Archie