On 17/05/2022 22:08, David Woolley wrote:
> On 17/05/2022 20:25, Dave W wrote:
>> I know nothing about spectrum scanners, but your graph is completely
>> unbelievable with such cliff-edge drops and rises.
>
> The sharp edges are the boundaries between digital multiplexes.  There
> is a very small one in the middle because there has to be a small
> separation between multiplexes.  The other ones are transitions to empty
> channels, where the fuzzy horizontal lines represent the system noise
> floor.
>
> Digital TV uses spectrum much more efficiently than analogue TV, so you
> expect a flat top for the multiplex and then a large fall off.
>

I'd say it's believable, but is presumably scanned quite slowly and
averaged so random fluctuations due to noise are almost illuminated.

Here's one done in a different way:
https://www.brian-gregory.me.uk/GDL/spectrumspy-2020_03_10__04_03_33.png

It has numerous spurious spikes all over the place.

--
Brian Gregory (in England).

On 17/05/2022 16:51, Woody wrote:
> Correct me if I am mistaken, but doesn't CT100 have an aluminium foil
> under copper braid? I have used WF100 (dual copper) from Screwfix for
> years.

The expression 'CT100' has been usurped by unscrupulous Chinese vendors,
but no, it really means copper/copper.

Bill

On 17/05/2022 16:57, Mark Carver wrote:
> On 17/05/2022 16:51, Woody wrote:
>>
>> Correct me if I am mistaken, but doesn't CT100 have an aluminium foil
>> under copper braid? I have used WF100 (dual copper) from Screwfix for
>> years.
>>
> Copper foil
>
> https://www.cablemonkey.co.uk/data-sheet?id_attachment=37103

Best to use foamed PE rather than semi-airspaced, as well.

Bill

On 17/05/2022 18:06, Brian Gregory wrote:

> Maybe different manufacturers use the CT100 label for slightly different
> things.
>

You're not kidding they do.

Bill

On 17/05/2022 19:32, The Other John wrote:
>> The aerial fixings will need to be replaced most likely.
> I was afraid you'd say that! None of the neighbours has got a log
> periodic and as we're only 1.5 miles from the TX a bit of wet string would
> probably work:)

Even close to the tx the directional properties of a log could be
helpful. Also a log has flat response across the band.

Bill

On 17/05/2022 19:37, The Other John wrote:
> I could try different speeds but that wouldn't change the big dip would
> it? There isn't a similar dip on the adjacent channels 26 and 27. The
> AGC was switched off for the scan.

In America your 'big dip' is called 'suck out'. The Americans often use
colourful expressions to describe mundane things.

Bill

On 17/05/2022 20:25, Dave W wrote:

>
> I know nothing about spectrum scanners, but your graph is completely
> unbelievable with such cliff-edge drops and rises.

No, that's pretty well what you get from a spectrum analyser, as long as
the front end isn't overloaded.

Bill

On 17/05/2022 22:19, The Other John wrote:
> Anyway it's been fine for
> years but just recently developed the breaking up and freezing but only on
> the mux on UHF24.

Me: Your aerial isn't working properly.
Customer: Hurumph! It's worked fine for the last thirty years!
Me: It isn't working properly now though, because a fault has appeared.
Customer: Hurumph!

Bill

On 17/05/2022 23:25, alan_m wrote:
> And probably work if the aerial is in the loft. A log periodic is an
> ideal physical package for loft installation.

No no no! Loft aerials last for ever! What about the poor starving
children of future aerial men?

Bill

On 17/05/2022 23:52, Brian Gregory wrote:

> Here's one done in a different way:
> https://www.brian-gregory.me.uk/GDL/spectrumspy-2020_03_10__04_03_33.png
>
> It has numerous spurious spikes all over the place.
>

It's nice though.
You can make the same spectrum look completely different by:
- Altering the scan bandwidth (makes a massive difference)
- Altering the scan speed
- Altering the start and stop frequencies
- Altering the dynamic range
- Setting 'hold maximum' or 'hold minimum'.

Bill

Le 17/05/2022 à 16:02, The Other John a écrit :
> I've recently been getting break-up and freezing on some Freeview channels
> even though I'm about 1.5 miles line of sight from the Reigate
> transmitter. The channels affected are all on the mux on UHF 24 and are
> mainly the Sky channels. I did a spectrum analysis using my RTL-SDR stick
> and it shows there's a massive dip starting on UHF23 and pushing 24 right
> down.
>
> The scan can be seen here: <https://www.dropbox.com/s/sh7b3fdyabnadll/
> Scan%20470.0-592.0MHz%20lounge.png?dl=0>
>
> The aerial is a standard 18 element yagi which might be group C/D as it
> was for Reigate analogue, although it could be group A if the previous
> owner used to receive Crystal Palace before Reigate opened. Either way
> what do you think would cause such a drop in the middle of the band?
> Nothing has been changed recently but the coax is over 40 years old, could
> it be causing some kind of cancellation due to standing waves or summat?
>
On your spectrum analysis there is at least a 5dB variation across each
channel.This denotes the mixing of ,at least, 2 signals.
Probably one from the aerial and the other from bad coaxial cable or
connectors.
Big reflections in the distribution can also produce such bad results.

On 17/05/2022 22:19, The Other John wrote:
> On Tue, 17 May 2022 20:14:59 +0100, Mark Carver wrote:
>
>> By the way, in which direction is the mast from you ?
>>
>> The reason I ask is the Tx antenna is cardioid towards the SSE, so
>> basically if you're north of the M25, don't expect too much reliable
>> signal (even at 1.5 miles)
> Roughly NNW, so I should be in the SSE lobe. Anyway it's been fine for
> years but just recently developed the breaking up and freezing but only on
> the mux on UHF24.
>
Ah, I know more or less where you are (I've probably used your road as a
rat run, when that bloody level crossing in the centre of Reigate has
had a mega queue). High up, with a good view to the south ?

Another factor is CCI from Rowridge, it transmits on 21, 24, 27 all at
250kW and Vert Poz (same as Reigate), so directionality on your new
aerial is important

On 18/05/2022 00:09, williamwright wrote:
> On 17/05/2022 23:25, alan_m wrote:
>> And probably work if the aerial is in the loft. A log periodic is an
>> ideal physical package for loft installation.
>
> No no no! Loft aerials last for ever! What about the poor starving
> children of future aerial men?

I once had a Vision(??) branded log periodic in my loft where the rod
elements were just a poor interference fit into the boom. Over time the
elements worked their way out of the boom - they moved by a good few cm.
I assume that it was hot/cold temperature cycling within the loft that
caused this so maybe they don't last forever without problems.

Earlier this year I lost my chimney mounted aerial in a storm (the cable
around the chimney stack failed) and I fitted a replacement Blakes group
K log periodic in the loft. This Blakes aerial has the same type of
construction as that Vision aerial so maybe I'll be checking it later
this year :)

https://www.blake-uk.com/aerials-tv-log/28-element-log-periodic-group-k-aerial.html

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

On Wed, 18 May 2022 00:08:13 +0100, williamwright wrote:

> Me: Your aerial isn't working properly.
> Customer: Hurumph! It's worked fine for the last thirty years!
> Me: It isn't working properly now though, because a fault has appeared.
> Customer: Hurumph!

:)

--
TOJ.

On Wed, 18 May 2022 08:24:47 +0100, Mark Carver wrote:

> Ah, I know more or less where you are (I've probably used your road as a
> rat run, when that bloody level crossing in the centre of Reigate has
> had a mega queue). High up, with a good view to the south ?

About 400 yds from the level crossing in a slight hollow and our road is
mostly used as a car park by students at the local college!

--
TOJ.

On Tue, 17 May 2022 23:25:39 +0100, alan_m wrote:

> And probably work if the aerial is in the loft. A log periodic is an
> ideal physical package for loft installation.

I've thought about that but the loft is so full of junk that I would have
to hire a skip first and empty it before I can get up there! :(

--
TOJ.

On Wed, 18 May 2022 00:09:34 +0100, williamwright wrote:

> No no no! Loft aerials last for ever! What about the poor starving
> children of future aerial men?

They can go from door to door selling yellow dusters! :)

--
TOJ.

On Wed, 18 May 2022 00:09:34 +0100, williamwright
<wrightsaerials@f2s.com> wrote:

>On 17/05/2022 23:25, alan_m wrote:
>> And probably work if the aerial is in the loft. A log periodic is an
>> ideal physical package for loft installation.
>
>No no no! Loft aerials last for ever! What about the poor starving
>children of future aerial men?
>
>Bill

They may have to re-train as fibre and ethernet installers.

Rod.

On Wed, 18 May 2022 00:02:23 +0100, williamwright
<wrightsaerials@f2s.com> wrote:

>On 17/05/2022 19:37, The Other John wrote:
>> I could try different speeds but that wouldn't change the big dip would
>> it? There isn't a similar dip on the adjacent channels 26 and 27. The
>> AGC was switched off for the scan.
>
>In America your 'big dip' is called 'suck out'. The Americans often use
>colourful expressions to describe mundane things.
>
>Bill

I expect they'd say that suck out sucks.

Rod.

On 18/05/2022 00:09, williamwright wrote:
> No no no! Loft aerials last for ever! What about the poor starving
> children of future aerial men?

For South facing aerials, they could go into the solar power business.
I'm sure a few solar panels between the aerial and the transmitter would
screen quite well.

On 18/05/2022 09:55, The Other John wrote:
> On Wed, 18 May 2022 08:24:47 +0100, Mark Carver wrote:
>
>> Ah, I know more or less where you are (I've probably used your road as a
>> rat run, when that bloody level crossing in the centre of Reigate has
>> had a mega queue). High up, with a good view to the south ?
> About 400 yds from the level crossing in a slight hollow and our road is
> mostly used as a car park by students at the local college!
>
Ah, OK, Rowridge is likely to be far less of a problem then !

On 18/05/2022 09:23, alan_m wrote:
> I once had a Vision(??) branded log periodic in my loft where the rod
> elements were just a poor interference fit into the boom.

There was a whole rash of these mebbe ten years ago.

Bill

On 18/05/2022 00:00, williamwright wrote:
> On 17/05/2022 19:32, The Other John wrote:
>>> The aerial fixings will need to be replaced most likely.
>> I was afraid you'd say that!  None of the neighbours has got a log
>> periodic and as we're only 1.5 miles from the TX a bit of wet string
>> would
>> probably work:)
>
> Even close to the tx the directional properties of a log could be
> helpful. Also a log has flat response across the band.
>
>

If the OP could find one, one of those flying bedsteads of years ago
would work very well in the loft.

On 18/05/2022 19:13, williamwright wrote:
> On 18/05/2022 09:23, alan_m wrote:
>> I once had a Vision(??) branded log periodic in my loft where the rod
>> elements were just a poor interference fit into the boom.
>
> There was a whole rash of these mebbe ten years ago.
>

Vision, based on Nottingham and formerly known as Grade, make aerials
for caravans and motorhomes.

On 18/05/2022 00:00, williamwright wrote:
> On 17/05/2022 19:32, The Other John wrote:
>>> The aerial fixings will need to be replaced most likely.
>> I was afraid you'd say that!  None of the neighbours has got a log
>> periodic and as we're only 1.5 miles from the TX a bit of wet string
>> would
>> probably work:)
>
> Even close to the tx the directional properties of a log could be
> helpful. Also a log has flat response across the band.

Log periodics probably more likely to stay directional when loft
mounted. My limited experience with loft mounted yagis suggests they can
be so detuned by damp roof tiles and felt that they end up almost
omnidirectional.

--
Brian Gregory (in England).