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Labgear Tri-Boom Mast Digital Aerial (or similar)



 
 
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  #11  
Old September 27th 18, 09:10 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 7,332
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

Brittle plastic engineering again.
Brian

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"Bill Wright" wrote in message
news
On 26/09/2018 19:38,
wrote:
First post - I have a TV aerial that looks the same shape as the Labgear
Tri-Boom Mast Digital Aerial -
https://www.screwfix.com/p/labgear-t...l-aerial/60215

The topmost part of the rear reflector (?) wobbles by about 25mm as it
appears to rotate at its connection point to the main horizontal
component. The aerial feeds a splitter/distribution box and we are
getting an intermittent broken picture on one of the two TVs that it
supplies.

Is the loose part likely to be the cause of the problem, can it be
taped/cable tied still or does the aerial need to be replaced?

Many thanks

Martin

The make of aerial most prone to losing the top half of the reflector is
also prone to water getting into the junction box and then down the coax.

Bill



  #12  
Old September 27th 18, 09:12 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 7,332
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

Cable or aerial?
Brian

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Note this Signature is meaningless.!
wrote in message
...
On Wednesday, September 26, 2018 at 8:29:46 PM UTC+1,
wrote:
On 26/09/2018 19:38,
wrote:
First post - I have a TV aerial that looks the same shape as the Labgear
Tri-Boom Mast Digital Aerial -
https://www.screwfix.com/p/labgear-t...l-aerial/60215

The topmost part of the rear reflector (?) wobbles by about 25mm as it
appears to rotate at its connection point to the main horizontal
component. The aerial feeds a splitter/distribution box and we are
getting an intermittent broken picture on one of the two TVs that it
supplies.

Is the loose part likely to be the cause of the problem, can it be
taped/cable tied still or does the aerial need to be replaced?

Many thanks

Martin


The make of aerial most prone to losing the top half of the reflector is
also prone to water getting into the junction box and then down the coax.

Bill


Any suggestions for a better quality replacement?
Many thanks


  #13  
Old September 27th 18, 09:20 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 7,332
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

I suspect in that area almost anything is OK for digital. The first aerial
was either not of the right sort, ie bandwidth wise, cheap and nasty or not
fitted correctly!
You need an expert to make an aerial not work 12 miles away from a main
station, a real talent in fact.
Brian

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----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

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Note this Signature is meaningless.!
"Bill Wright" wrote in message
news
On 26/09/2018 21:31,
wrote:
On Wednesday, September 26, 2018 at 9:14:47 PM UTC+1,
wrote:
On 26/09/2018 20:58,
wrote:
Postcode CV7 7EP, I believ the transmitter is Sutton Coldfield, I have
a picture of the current aerial but don't think I can post it here? The
upper and lower 'rear reflectors' Each have 5 horizontal bars if that
helps with identification (its the same shape/style as the labgear unit
I mentioned and has yellow parts on each end of the rear element that I
mentioned and on the main horizontal body.
Thanks


Weirdly I did a bit of signal surveying in that area years ago. You
aren't far from having line-of-sight to Sutton C. about 12 miles away. A
log periodic will work fine.

But first check the obvious. Water in the cable, loose connections,
faulty splitter, faulty wall plate, damaged cable, faulty flylead (wall
to TV cable), etc. I take it there's no aerial amplifier in use?

Bill


Thanks - the feed from the aerial goes into a Wolsey WPS100/1 then into a
Remotelink A280D.


Seems a bit over the top. Have you tried removing/bypassing the
WPS100/100? Or at least turning the gain up and down? How is it powered by
the way? Is it powered or is it just an expensive attenuator?

I'm wondering if the Wolsey amp if powered is overloading the Remotelink
amp and maybe even the TV set. You have between 18 and 33dB gain. That
could be far too much.


If go go for the 'long periodic'


log periodic. That's because they are made from tree trunks (ignore that;
I'm a bit ****ed)

are there any other elements to the specification? Is there a particular
make that you would recommend? A daft question but will that be okay for
digital - my first aerial that was fitted by Digital*ave (specialist)
wasn't.

Everything is OK for digital. Forget that.
https://cpc.farnell.com/blake-uk/bla...ial/dp/AP03352
Or ring ATV Sheffield, ask for Justin, mention my name.
http://aerialsandtv.com/

Bill



Thanks




  #14  
Old September 27th 18, 09:59 AM posted to uk.tech.digital-tv
charles[_2_]
external usenet poster
 
Posts: 783
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

In article , Brian Gaff
wrote:
I suspect in that area almost anything is OK for digital. The first
aerial was either not of the right sort, ie bandwidth wise, cheap and
nasty or not fitted correctly! You need an expert to make an aerial not
work 12 miles away from a main station, a real talent in fact. Brian


sound terribly like the aerial rigger I cam across whose letterhead read
"Specialist in poor signal reception". He'd succeeded perfectly at a house
100 m from a local relay by putting a pre-amp on the aerial!

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
  #15  
Old September 27th 18, 01:42 PM posted to uk.tech.digital-tv
Jeff Layman[_2_]
external usenet poster
 
Posts: 797
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

On 27/09/18 04:08, Bill Wright wrote:

Everything is OK for digital. Forget that.
https://cpc.farnell.com/blake-uk/bla...ial/dp/AP03352
Or ring ATV Sheffield, ask for Justin, mention my name.
http://aerialsandtv.com/


Looks good. But how do you tell the difference (if there is any)
between different log periodics? The following are all similar prices,
although somewhat more expensive than the Blake. Is there any practical
difference if they are for loft mounting, rather than being outside?

https://www.amazon.co.uk/AERIAL-LOG-PERODIC-36-ELEMENT-TYPE/dp/B01L62DT7G/ref=sr_1_4?ie=UTF8&qid=1538046869&sr=8-4&keywords=log+periodic+aerial

https://www.amazon.co.uk/36-Element-Log-Periodic-Aerial-Pre-Wired-F-Connector/dp/B016MWH5O8/ref=sr_1_5?ie=UTF8&qid=1538046869&sr=8-5&keywords=log+periodic+aerial

And this is perhaps smaller, but seems to get good reviews (if you
believe Amazon reviews...):
https://www.amazon.co.uk/Raptor-LTE-Periodic-Digital-Antenna-silver/dp/B016Y90NLQ/ref=sr_1_6?ie=UTF8&qid=1538046869&sr=8-6&keywords=log+periodic+aerial

--

Jeff
  #16  
Old September 27th 18, 02:49 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,952
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

On 27/09/2018 09:59, charles wrote:
In article , Brian Gaff
wrote:
I suspect in that area almost anything is OK for digital. The first
aerial was either not of the right sort, ie bandwidth wise, cheap and
nasty or not fitted correctly! You need an expert to make an aerial not
work 12 miles away from a main station, a real talent in fact. Brian


sound terribly like the aerial rigger I cam across whose letterhead read
"Specialist in poor signal reception". He'd succeeded perfectly at a house
100 m from a local relay by putting a pre-amp on the aerial!


Charles, I think enough time has passed for me to tell this tale. When I
first went to Visnews at Park Royal the situation was that the
120-outlet distribution system had had the problem of very low signal
levels at the ends of the (very long) rows of padded outlets. The system
had been planned using a series of extremely optimistic and unrealistic
assumptions. The maintenance guys had called in the local rigger who
removed the 18 element aerial and fitted the very largest aerial made by
Antiference, an XG21/A. This gave little or no improvement so they added
a masthead amplifier. This was with clear line of sight to Crystal
Palace, which was oh, about eight miles away? Both the masthead amp and
the main distribution amp (which was in any case woefully inadequate)
were driven into severe cross mod. At this point the rigger threw in the
towel and cleared off.

Bill
  #17  
Old September 27th 18, 03:04 PM posted to uk.tech.digital-tv
Bill Wright[_3_]
external usenet poster
 
Posts: 2,952
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

On 27/09/2018 13:42, Jeff Layman wrote:
On 27/09/18 04:08, Bill Wright wrote:

Everything is OK for digital. Forget that.
https://cpc.farnell.com/blake-uk/bla...ial/dp/AP03352

Or ring ATV Sheffield, ask for Justin, mention my name.
http://aerialsandtv.com/


Looks good.* But how do you tell the difference (if there is any)
between different log periodics? The following are all similar prices,
although somewhat more expensive than the Blake. Is there any practical
difference if they are for loft mounting, rather than being outside?

https://www.amazon.co.uk/AERIAL-LOG-PERODIC-36-ELEMENT-TYPE/dp/B01L62DT7G/ref=sr_1_4?ie=UTF8&qid=1538046869&sr=8-4&keywords=log+periodic+aerial


https://www.amazon.co.uk/36-Element-Log-Periodic-Aerial-Pre-Wired-F-Connector/dp/B016MWH5O8/ref=sr_1_5?ie=UTF8&qid=1538046869&sr=8-5&keywords=log+periodic+aerial


And this is perhaps smaller, but seems to get good reviews (if you
believe Amazon reviews...):
https://www.amazon.co.uk/Raptor-LTE-Periodic-Digital-Antenna-silver/dp/B016Y90NLQ/ref=sr_1_6?ie=UTF8&qid=1538046869&sr=8-6&keywords=log+periodic+aerial


They are all OK, but the short one has slightly less gain.

Log periodic aerials have two parallel booms, usually close together.
These booms together form a transmission line. A series of half wave
dipoles are attached to the booms, each dipole having one quarter wave
section fixed to Boom A and the other to Boom B. Each dipole (except two
or three; see later) are tuned to a frequency within the range required
for reception or transmission, and are fixed in order of resonant
frequency along the two booms. Each dipole is connected in opposite
phase to its neighbours. The two booms are connected together
electrically at the low frequency end of the aerial. The feeder cable is
connected across the two booms at the high frequency end. The feeder
often runs inside one of the booms to its low frequency end, where the
aerial is fixed to the mast. Running the feeder inside the boom that is
connected to the feeder’s screen seems to reduce the need for
balance/unbalance conversion. The dimensions and spacing of the two
booms is designed to produce an impedance of approximately 75Ω. For
these reasons log periodics don’t seem to need a balun.

And the extra two or three dipoles? One is just slightly longer than
would be resonant at the lowest operating frequency and then there’s
another one or two that are shorter than would be resonant at the
highest operating frequency.

Each element of a log periodic is longer or shorter than its neighbour
by a fixed ratio, and the inter-element spacing also increases or
decreases by a fixed ratio. The inter-element spacing is generally a
quarter wavelength of the adjacent dipole’s resonant frequency, or a bit
less.

The smaller the ratio of the lengths of adjacent dipoles the higher the
gain. A large ratio will lower the gain but increase the bandwidth for a
given number of dipoles. Just as the yagi is inherently narrowband the
log is inherently wideband. Almost all logs sold in the UK for UHF TV
reception are wideband in that they cover all the channels used for TV
broadcasting. However Vision Products have a ten-dipole product that
covers Channel Group A only. The gain as you might expect is slightly
better than that of a ten-dipole log designed for all channels.

For a given frequency only a small zone along the boom of the log
periodic is active. The zone is centred on the dipoles that are at or
near resonance at that frequency. Consider two adjacent dipoles,
somewhere about half way along the boom. The incoming signal is in the
middle of the frequency range of the aerial, so the two dipoles are
approximately resonant and are therefore in the active zone. Feeder
reversal and the distance between the two elements gives a phase shift
of 360° between them. In other words, for a signal coming from the
‘front’ of the aerial (only) the signal on the two dipoles is additive
if it is collected from the front of the boom-cum-transmission line.
This is why log periodics are directional, and why the feed-point is at
the sharp end. It’s possible for three or even four dipoles to work
together in this way. A smaller ratio between the lengths of adjacent
dipoles means more dipoles are near resonance for a particular
frequency, which is why the gain is higher for such an aerial. There are
two things that prevent the dipoles that are shorter and longer than the
resonant ones from playing much of a part in reception. One is that they
aren’t resonant and the other is that the spacing between them does not
produce the 360° of phase shift that is essential for the aerial to have
gain and directivity. The spacing between the directors on a yagi can be
varied widely (and often is to help feeder matching) but with a log
periodic the spacing has to be much more closely defined, and has to
take into account the velocity factor of the twin booms. (Velocity
factor is the speed of radio transmission in anything other than free
space; for instance feeder cable or aerial elements.)

If only a few dipoles are active, why does a typical log periodic have
as many as twenty? It’s because the more dipoles there are (for a given
ratio between the lengths of adjacent dipoles) the greater the range of
frequencies the aerial will receive. This is simply because the range of
the lengths of the dipoles is greater.

The active zone shifts with frequency, and you can easily find the
active zone of a log periodic for a given frequency. Monitor the signal
output of an aerial at that frequency using a meter or spectrum analyser
and get hold of one end of each dipole in turn. This will de-tune that
dipole. When the signal level drops you’re holding one of the active
dipoles.

If a log periodic is compared with a yagi of the same size it’s very
much a case of horses for courses. The yagi will have much better gain
if it’s a grouped one, but if it’s wideband its gain at the lower end of
the band might be no better or even a bit worse than that of the log
periodic. The main advantages of the log periodic are that the response
is very flat right across the band and that the directional
characteristics are also maintained at all frequencies. This is where
the wideband yagi falls down.

The log will have a far better front-to-back ratio than the equivalent
yagi. This means that it is better at rejecting signals from the rear.
However the front lobe (the ‘acceptance angle’) of a log is much wider
than that of a grouped yagi, or of a wideband yagi when used on the
higher channels. This means that if it’s necessary to receive from two
transmission sites that aren’t co-sited but are within fifteen or twenty
degrees of each other the log can work well.

When it comes to rejecting unwanted signals from the side there isn’t
much in it when the polarisation is horizontal, but when it’s vertical
the log wins hands down.

Log periodics aren’t just used for UHF TV. Some DAB aerials are logs,
and logs are widely used for VHF TV, HF (short wave), and for direction
finding.

Bill

  #18  
Old September 27th 18, 05:26 PM posted to uk.tech.digital-tv
[email protected]
external usenet poster
 
Posts: 6
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

On Wednesday, September 26, 2018 at 7:38:05 PM UTC+1, wrote:
First post - I have a TV aerial that looks the same shape as the Labgear Tri-Boom Mast Digital Aerial - https://www.screwfix.com/p/labgear-t...l-aerial/60215

The topmost part of the rear reflector (?) wobbles by about 25mm as it appears to rotate at its connection point to the main horizontal component. The aerial feeds a splitter/distribution box and we are getting an intermittent broken picture on one of the two TVs that it supplies.

Is the loose part likely to be the cause of the problem, can it be taped/cable tied still or does the aerial need to be replaced?

Many thanks

Martin


Wow - many thanks for the variety of helpful responses. Following Bill's recommendation I’ve been in touch with ATV today - I've photographed the entire installation and sent the images along with questions for Justin tomorrow with a commitment to buy any equipment they suggest to solve the immediate problem and bring the installation to the best possible situation.. The knowledge that ATV (and companies like them) provide is essential for people like me, I’m keen to support them even though B&Q etc may be cheaper.
Martin
  #19  
Old September 27th 18, 06:28 PM posted to uk.tech.digital-tv
charles[_2_]
external usenet poster
 
Posts: 783
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

In article ,
Bill Wright wrote:
On 27/09/2018 09:59, charles wrote:
In article , Brian Gaff
wrote:
I suspect in that area almost anything is OK for digital. The first
aerial was either not of the right sort, ie bandwidth wise, cheap and
nasty or not fitted correctly! You need an expert to make an aerial not
work 12 miles away from a main station, a real talent in fact. Brian


sound terribly like the aerial rigger I cam across whose letterhead
read "Specialist in poor signal reception". He'd succeeded perfectly
at a house 100 m from a local relay by putting a pre-amp on the aerial!


Charles, I think enough time has passed for me to tell this tale. When I
first went to Visnews at Park Royal the situation was that the
120-outlet distribution system had had the problem of very low signal
levels at the ends of the (very long) rows of padded outlets. The system
had been planned using a series of extremely optimistic and unrealistic
assumptions. The maintenance guys had called in the local rigger who
removed the 18 element aerial and fitted the very largest aerial made by
Antiference, an XG21/A. This gave little or no improvement so they added
a masthead amplifier. This was with clear line of sight to Crystal
Palace, which was oh, about eight miles away? Both the masthead amp and
the main distribution amp (which was in any case woefully inadequate)
were driven into severe cross mod. At this point the rigger threw in the
towel and cleared off.


I can trump thatb with the BBC pavilion at the Royal Welsh Showground,
Aerial ok, but then fed into a two outlet DA from which about a dozen
sockets were fed in a ring! Of course, the electrician who installed it
was a cousin of one of the BBC Welsh Governors

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
  #20  
Old September 27th 18, 06:31 PM posted to uk.tech.digital-tv
charles[_2_]
external usenet poster
 
Posts: 783
Default Labgear Tri-Boom Mast Digital Aerial (or similar)

In article ,
Bill Wright wrote:

[Snip]

Log periodics aren't just used for UHF TV. Some DAB aerials are logs,
and logs are widely used for VHF TV, HF (short wave), and for direction
finding.


There used to be a big HF one on the Chinese Embassy in London. The World
Radio & TV Handbook once carried an advert for an HF Log where the elements
looked over a foot in diameter

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle
 




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