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?

--
TOJ.

On 17/05/2022 15:02, The Other John wrote:
> 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?
>

If that co-ax is 40 years old, it is not 100% screened.

If any of it is exposed to the elements, the outer sheath will have long
perished and rain water will have ingressed into it.

a kink in the cable can cause a standing wave if its not rainwater ingress.

I'd personally put up a new aerial and new CT100/WF100 co-ax and be done
with it.

Getting 40 years out of a co-ax is very good going though and that cable
doesn't owe you anything :-)

On 17/05/2022 15:31, SH wrote:
> On 17/05/2022 15:02, The Other John wrote:
>> 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?
>>
>
>
> If that co-ax is 40 years old, it is not 100% screened.
>
> If any of it is exposed to the elements, the outer sheath will have
> long perished and rain water will have ingressed into it.
>
> a kink in the cable can cause a standing wave if its not rainwater
> ingress.
>
> I'd personally put up a new aerial and new CT100/WF100 co-ax and be
> done with it.
>
>
> Getting 40 years out of a co-ax is very good going though and that
> cable doesn't owe you anything :-)

Yes, when we moved into our last house in yr 2000, there's was a network
of aerial feeds to bedrooms that in inherited.

One room had virtually no signal on UHF Ch 66, and the channels in the
40s weren't too special. In the end I replaced the run with some CT-100,
all was fine, I stripped back sections of the old cable that were
outdoors. Horrible cheap coax, and most of the copper braid had turned
into green slime. The house was built in 1985, so the cable wasn't more
than 15 yrs old

Back to the case in hand. Pre DSO and DTT Reigate was a Grp C/D
transmitter. Post a photo of the aerial, some of us can tell whether
it's A or C/D by its 'look' !
In 2018 everything moved into Band IV, and the three PSB muxes (23, 26,
30) are in an SFN with Crystal Palace, though the three COMs (21, 24,
27) are not, though that shouldn't affect your reception either way.

On 17/05/2022 15:02, The Other John wrote:
> 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?
>

Get your bins out and have a look at the colour of the plugs in the ends
of the aerial boom. In theory (note - theory - Marky!) it should be red
for a group A, yellow for a group and one of a number of colours
including green, brown, and black if it is C/D or wideband.

Daft though it may sound, if you have an attenuator put it in the feed
to the TV. It is always possible with a 10ele shooting at a Tx 1.5m away
you may be getting co-channel interference from something much further
away. Likewise it is also possible you are overloading the tuner.

On 17/05/2022 15:02, The Other John wrote:
> 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?
>

The aerial and the cable need to be replaced. The new aerial should be a
log periodic, but not one of the little ones that are only about a foot
long. The cable should be CT100-type, copper foil/copper braid.

The aerial fixings will need to be replaced most likely.

Bill

The Other John wrote:

> 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:

Have you tried the spectrum scan at different speeds? or with smoothing options?

You have quite a slope on several of the muxes, I seem to remember getting
similar ... possible RTL AGC issue?

<http://andyburns.uk/misc/CH21-CH68.png>

On 17/05/2022 16:28, Andy Burns wrote:
> The Other John wrote:
>
>> 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:
>
> Have you tried the spectrum scan at different speeds? or with smoothing
> options?
>
> You have quite a slope on several of the muxes, I seem to remember
> getting similar ... possible RTL AGC issue?
>
> <http://andyburns.uk/misc/CH21-CH68.png>

You don't have a clear pattern of the gain always falling across the
muxes though. Three fall, two climb, and the rest are all over the place.

BTW, slopes across muxes always look horrendous when the scan limits are
far apart!

Bill

On 17/05/2022 16:21, williamwright wrote:
> On 17/05/2022 15:02, The Other John wrote:
>> 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?
>>
>
> The aerial and the cable need to be replaced. The new aerial should be a
> log periodic, but not one of the little ones that are only about a foot
> long. The cable should be CT100-type, copper foil/copper braid.
>
> The aerial fixings will need to be replaced most likely.
>
>

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.

Woody

harrogate three at ntlworld dot com

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

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

.....with al ?

On 17/05/2022 16:59, Mark Carver wrote:
> 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
>
> ....with al ?

Weird. The picture looks like copper but the description says "Al Foil".

--
Brian Gregory (in England).

On 17/05/2022 17:21, Brian Gregory wrote:
> On 17/05/2022 16:59, Mark Carver wrote:
>> 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
>>
>> ....with al ?
>
> Weird. The picture looks like copper but the description says "Al Foil".
>
Whenever I've used some I'm quite sure it's pure(?) copper ?

On 17/05/2022 18:04, Mark Carver wrote:
> On 17/05/2022 17:21, Brian Gregory wrote:
>> On 17/05/2022 16:59, Mark Carver wrote:
>>> 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
>>>
>>> ....with al ?
>>
>> Weird. The picture looks like copper but the description says "Al Foil".
>>
> Whenever I've used some I'm quite sure it's pure(?) copper ?

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

--
Brian Gregory (in England).

On Tue, 17 May 2022 15:31:50 +0100, SH wrote:

> If any of it is exposed to the elements, the outer sheath will have long
> perished and rain water will have ingressed into it.
>
> a kink in the cable can cause a standing wave if its not rainwater
> ingress.

From the chimney to where it goes through the wall is exposed facing north
west and a clip has pulled out of the wall so the coax hangs like 'J',
quite loose, not a kink.

--
TOJ.

On Tue, 17 May 2022 16:00:27 +0100, Woody wrote:

> Get your bins out and have a look at the colour of the plugs in the ends
> of the aerial boom. In theory (note - theory - Marky!) it should be red
> for a group A, yellow for a group and one of a number of colours
> including green, brown, and black if it is C/D or wideband.

I've had a look and it hasn't got coloured ends, just aluminium plugs.
Also I misrembered the size of it, it's a 10 element, not 18.

--
TOJ.

Mark Carver wrote:

> Brian Gregory wrote:
>
>> The picture looks like copper but the description says "Al Foil".
>>
> Whenever I've used some I'm quite sure it's pure(?) copper ?

Same here, but the braid says copper clad aluminium and the foil screen must be
the same by the description ...

On Tue, 17 May 2022 16:21:17 +0100, williamwright wrote:

> The aerial and the cable need to be replaced. The new aerial should be a
> log periodic, but not one of the little ones that are only about a foot
> long. The cable should be CT100-type, copper foil/copper braid.
>
> 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 :)

--
TOJ.

On Tue, 17 May 2022 16:28:42 +0100, Andy Burns wrote:

> Have you tried the spectrum scan at different speeds? or with smoothing
> options?
>
> You have quite a slope on several of the muxes, I seem to remember
> getting similar ... possible RTL AGC issue?

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.

--
TOJ.

On 17/05/2022 19:32, The Other John wrote:
> 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 :)
>
Well, by your report that's exactly what you may well have, and clearly
it isn't working !

On 17/05/2022 20:06, Mark Carver wrote:
> On 17/05/2022 19:32, The Other John wrote:
>> 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 :)
>>
> Well, by your report that's exactly what you may well have, and
> clearly it isn't working !

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)

On Tue, 17 May 2022 14:02:58 -0000 (UTC), The Other John
<nomail@home.org> wrote:
>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?
I know nothing about spectrum scanners, but your graph is completely
unbelievable with such cliff-edge drops and rises.
--
Dave W

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.
>

It looks to me as though it could be peaking about every 34 MHz. I
think that would correspond to half a wave for standing waves, and with
a velocity factor of about 66%, that would give me, I think, about 300cm
as the length of the feature in the cable you are looking for. I think
a multipath path distance would be about 900cm.

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.

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.

--
TOJ.

On 17/05/2022 19:32, The Other John wrote:
> On Tue, 17 May 2022 16:21:17 +0100, williamwright wrote:
>
>> The aerial and the cable need to be replaced. The new aerial should be a
>> log periodic, but not one of the little ones that are only about a foot
>> long. The cable should be CT100-type, copper foil/copper braid.
>>
>> 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 :)
>

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

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