Question Help interpreting Freeview coverage results

oldmanhouse

Active Member
Hi folks. Some Freeview channels I like to watch (4Seven, 4Music) have recently moved from ARQ B to ARQ A. Unfortunately for me, the reception I get for ARQ A is non-existent, whereas ARQ B was good.

In an effort to determine if there's any hope of improving my setup sufficiently to receive reliable signal from ARQ A, I've run the official Freeview coverage checker and the Wolfbane tool too. My aerial is pointing to the Heathfield transmitter. You can see the results from my actual postcode in the screenshots attached, but if anyone would be so kind as to take a look, you could use this address near to my location: 2, RH15 9XB.

A bit of information about my setup. Items in blue are things I've installed, those in purple were here when I moved in.
  • TV in living room is a Panasonic TX-L50B6B, with built in Freeview HD tuner
  • Flylead is made up of WF100 cable
  • Coaxial socket / wall plate is screened type (Labgear)
  • There's a Labgear UHF amplifier in the loft, looks pretty old. There were connections to the bedrooms, all of which I've unplugged as not needed.
  • Aerial is mounted on a pole, externally on the side of the house
  • Cabling between aerial/amplifier/coaxial socket is an unknown entity. It doesn't look like WF100, but I'm not sure what it is.
  • AT800 filter installed between aerial and amplifier (near amplifier)
Based on the Freeview coverage results, ARQ B should be have slightly better signal than ARQ A but that's not been my experience at the TV.

Perhaps also worth mentioning that although I don't watch anything from SDN much, the signal strength/quality isn't very good (<50%), but I still receive
a watchable picture.
 

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mikej

Well-known Member
The first thing to check is whether or not the channel move actually happened, because many of the changes due in April/May onwards have been postponed due to the current coronavirus crisis. Have you definitely lost the channels ?

Are you able to determine what type of aerial you have by it's appearance ? It may be that you can get an aerial more suited to the frequencies you're currently receiving. It looks like the Wolfsbane predictor suggests your channels occupy the range 41-52 and the Freeview checker says 41-47 so there is obviously a small discrepancy there, however Wolfbane's recommended Group B aerial looks like the most suitable option for you at the moment according the graph at the bottom of this page and it should also cover the 41-52 range, depending on which site is more up-to-date. Be sure to check what the ultimate plans are for your transmitter, as it's possible that further channel changes could be due in the coming years.

Replacing all the coax from aerial to TV could be a wise move, particularly if the house is fairly old and the installation dates back to when the house was built. Replacing the aerial and coax were one of the first things I did when I moved into my (1970s) house, when I discovered that the TV reception was poor.
 

A1944

Active Member
Looking at the Freeview transmitters page for Meridian:
it appears that the channel coverage at Heathfield changed from 41-52 to 40-47 in July 2018, so it would seem that the Wolfbane details are two years out of date.

Also, I note that the Wolfbane graphic shows the Mux names as still including "1, 2, A, B, C, D" whch I thought were removed from use at DSO nearly 10 years ago.
 

Rodders53

Distinguished Member
Heathfield - if that's the transmitter the aerial(s) are pointing at is now and was a group C/D transmitter, needing wideband when DTT started but is now a group B site. Many group C/D work ok at the lower frequencies and one famous aerial (Triax Unix 52) was the same aerial described as C/D or Wideband.
But not all do.
Heathfield adopted its current frequencies in July 2018. All 6 multiplexes transmit at the same 20kW erp on frequencies 40 SDN, 41 BBC A, 43 Arq A, 44 D3&4 , 46 COM6 and 47 BBC B (HD).

Wolfbane predicts 50 dBuV/m at 10m agl with clear line of sight and that number will apply to all 6 muxes. Aerial gain: say 8 dB (a small aerial/log periodic), 10 metres of cable and termination loss: say -3dB so 55dbuV at a set. Ideal is 45 to 65 dBuV so bang in the middle. No amplifier needed.

A large aerial might give 10-12dB of gain at best but that would only make the number 57-59dBuV.

An amplifier will increase the signal sent but invariably adds a touch of noise. Over-amplification can cause problems of too much signal = overload with symptoms not unlike a lack of signal (and often high strength variable/poor quality on tv metering).

I'd recommend losing the amplifier as a test as the first step. (At the same time find out the model / gain of the Labgear amp and post that here.) Use the TV meter to check all 6 muxes received (also double check they are the correct frequencies tuned in, not from another transmitter!).

Removing unused connections from an amplifier gives no advantage. They are isolated from one another. Fitting 75 ohm terminations outlets is recommended. Normally not needed on most domestic installs except with unused very high level outputs (intended for further passive splits on very big homes).

(Midhurst is an alternative suggested by Freeview with similar interference numbers; possibly slightly bett). 39dBuV for the 3 10kW muxes and 42 for the 20kW ones. It is also line of sight.)

Freeview numbers are about interference from other UK and continetal transmitters. Based on a %age of locations in the prediction square (100m x 100m sides) that are (S)erved = interference for <1% of time and (M)arginally served = interference for 1% to 50% of time. Your numbers don't look too bad but suggest you could have issues during steady high pressure weather events on the COM muxes.
 

A1944

Active Member
The first thing to check is whether or not the channel move actually happened, because many of the changes due in April/May onwards have been postponed due to the current coronavirus crisis.
According to the clearance schedule for 2020, no changes were planned for Heathfield this year.
 

Rodders53

Distinguished Member
AT800 filter.
May also be worth trying with that removed as well as the amplifier - it will give a 3dB signal loss
(Blake aerials website wrt LTE).
 

oldmanhouse

Active Member
Thanks for all the responses, loads of information for me to dig into! The signal changes have definitely happened @mikej, there was a simulcast of 4Music on ARQA and B for a while but this got switched off early June.

The Wolfbane tool confused me as we're definitely not receiving anything on the channels it mentions, so must be out of date as you say @A1944. We're definitely receiving on 41-47 from Heathfield.

I've been trying a few of your suggestions @Rodders53. Removing the AT800 filter made a positive difference and has restored enough signal on CH43 (ARQA) to get a watchable picture. Although it is only registering as 10% signal quality and 30% signal strength on the tuner's meter, so it seems to be borderline.

I removed the amplifier (Labgear MSA241 UHF/FM, 10dB gain) from the setup, by using a coax coupler to join the input (from aerial) and output (to TV) cables. This had a noticable negative impact on the signal quality and strength for all channels and caused CH43 to drop off again, so I have reconnected it. I'm only using 1 output from the amp, which leaves the other 3 unused so will look at getting some coax 75ohm terminators if it may help.

I kept an eye on signal levels throughout yesterday. I was getting 10% signal quality on CH43 yesterday morning but I also checked later in the afternoon and it had jumped up to 60-70%. Then, in the evening, inexplicably, I lost CH41 (BBC A) which is very unusual. Now this morning BBC A is back and ARQA is back to 10%.

I've not been able to identify which Group my aerial belongs to @Clem_Dye @mikej. Visually, it looks identical to all my neighbour's so I expect it dates from about 1995 when these houses were built. The only difference with mine is that a previous occupant has gone to the trouble of mounting the aerial on a taller mast, so it is a bit higher up than my neighbour's (who use satellite). Access to the aerial is very difficult and would involve getting scaffolding (a problem I've encountered for gutter/soffit maintenance too) so replacing it or even inspecting it, or pointing it at a different transmitter is cost prohibitive.

Options available to me would be replacing the coax cabling inside the house. The lead from the aerial looks like RG6 to me (plastic air gapped dielectric, tin foil shielding, silver coloured braiding) so I would love to replace that, but can't get up the aerial to do so. I could cut it off as it comes into the loft, but having a coupler might degrade the signal more than changing the cable type may help?

The lead from the amp to the living room looks a bit better quality. Plastic dielectric but the braiding is copper at least. Replacing this with WF100 is do-able but not sure how much difference this would make.

Another option is trying a loft aerial. With this I'd at least be able to point it where I want, and get the right type (wideband, group K, etc)
 

Clem_Dye

Distinguished Member
A loft aerial is worth a try if outside access is difficult, but an outside installation is going to be your best bet. Tinkering with what you have now might bring some marginal gains, but won’t yield anything substantive, I think.

Clem
 

mikej

Well-known Member
@oldmanhouse On my (fairly new) Labgear distribution amp, a special termination was only required on the 'full' output (which can be used for a passive splitter) and not on the other unused connections.

From the instructions for mine... " Please Note: If the “FULL” power socket is not being used it must be terminated with the 75Ω terminator supplied."

It might be worth seeing if you can get hold of the instructions for yours online ?

If you currently have an external TV aerial on a long pole and the neighbours all have external aerials, then I wouldn't even bother trying a loft aerial personally but, as with some of the other things you mentioned (changing coax etc), it might be a case of trying it and see what happens.

If I was in your position, I would replace as much of the internal coax as I could and if the current aerial really is inaccessible (and not safe for a DIYer like me to get to), then I'd consider paying someone to replace the coax between aerial and amp and either realign the current aerial or replace it. If your distribution amp is really old, then replacing that would be another option, but obviously not guaranteed to solve your problem.

@Rodders53 has highlighted some further changes to Freeview coming later this month, so be sure to check that information, as some channels will be lost and some may be on the move again.
 

Rodders53

Distinguished Member
Don't bother with 75 ohm terminators - they will make so little difference it's not worth the time and trouble.

The cable description is similar to some air-spaced CT100 cable I have so may not be as poor as imagined. RG6 cable loss-wise is very similar to WF100 cable.
Some use copper-coated steel, and similar less-desirable materials for the screen and braid - mainly giving problems when masthead amplifiers and DC voltages are needed and/or when damp gets in...

Foam filling is desirable to prevent water wicking along and into the indoor kit, but air-spaced works well for UHF signals.

Cables generally don't have a major loss over the lengths used in domestic installs see Coaxial Cable Specifications WF100 CT100 WF65 RG6 But dodgy / poorly made connections often do. It is worth the time to inspect and re-make all those you can get to easily.

I'd need signal level and quality readings on all 6 mux frequencies to aid diagnosis conclusions. BUT I really think your 1995 aerial will be a grouped C/D of a design such that the group B frequencies are significantly attenuated. ATV aerial gain tests : all the gain curves - A.T.V. Poles, Brackets, Clamps & Aerials (contract or yagi 18 style).

Trees in the line of sight can cause variable reception though, with the size of leaves affecting certain wavelengths(= frequencies) more than others. So consider what your aerial would 'see' and if there is something obstructing its view?

The only solution to a C/D with poor response in group B is a new aerial (and cable at the same time) though.

A 25 year old aerial and its cable is likely to be near end of life anyway. (The average life - some will be more others less - was always said to be around the 10-12 years mark.)

An higher gain (perhaps masthead type) amplifier might be worth a punt? Although the usual caveat of amplifying a poor signal just gives you bigger poor signal. Splitters, amps and diplexers - A.T.V. Poles, Brackets, Clamps & Aerials

Mains high gain amplifier - A.T.V. Poles, Brackets, Clamps & Aerials has 18dB of gain (10dB more then yours = 10x the signal out cf now).
Mast head amp "universal" 1 way - A.T.V. Poles, Brackets, Clamps & Aerials is variable 7dB up to 22dB. Proception make 1-way masthead amps with 27dB, fixed, gain.

Now having a high gain amp in the loft rather than as close to the aerial as possible is not ideal - but may be worth a shot? If you can get it as close to where the aerial cable enters the building.

The alternative is to buy a larger style group B aerial and try it inside the loft... but roofing materials or gable ends will reduce the signal (-10dB is a common rule of thumb). Much, much more if pointing through a row of terraced party walls.
 

A1944

Active Member
Oddly enough, trees don't always cause any noticeable effects, even when you might expect them.

I am 25 miles from Crystal Palace, with a 50 foot rise in that direction only a few hundred yards away. Within 50 feet of my aerial is the start of a 300 yard area of solid woodland (mainly oaks), on a raised area of ground, with the treetops well above the height of the aerial (which is at the top of a 16 foot pole fixed at chimney level).

Despite all that I notice no change in signal level between Summer and Winter.
 

oldmanhouse

Active Member
Ah yes, I did make some notes about the signal levels. Here we go:

Channel (UHF)NameSignal prior to 4G filter removal (%)Signal after 4G filter removal (%)
40SDNQuality: 90-100
Strength: 60
Quality:100
Strength: 60
41BBC AQuality: 80-90
Strength: 50
Quality: 90-100
Strength: 50
43ARQ AQuality: 10
Strength: 20
Quality: 10
Strength: 40
44D3&4Quality: 20-30
Strength: 40
Quality: 40-50
Strength: 40
46ARQ BQuality: 80-90
Strength: 60
Quality: 90-100
Strength: 60
47BBC B HDQuality: 90
Strength: 60
Quality: 90-100
Strength: 60

I didn't note down numbers when removing the amp, but it was a definite drop, and then there was the instance where (without any changes) BBC A dropped down to 0-10% and ARQ A up to 60-70% (quality).

Thanks for the suggestions regarding the amp and aerial, will have a look over the ATV website this evening.

It has occurred to me the 4G filter removal could be a red herring if by unplugging it I fixed a poorly seated connection. Also, I've changed the coax plugs on both leads connected to the amp. They seemed OK but I made them up again with some new connectors I had spare from making my flylead.
 
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Rodders53

Distinguished Member
It has occurred to me the 4G filter removal could be a red herring if by unplugging it I fixed a poorly seated connection.
The filter specs say they have an insertion loss; and that's reflected in the numbers - prove it by reinserting before the amp.

Your Panny is a 2012/13 model year I think??

My GT60 plasma is 2013 and its signal strength/quality metering has something to be desired/unusual.
I lived in Lowestoft when DSO happened and the powers transmitted increased tenfold (by 10dB). My set's metering is from 0 to 10 not in percent. It showed 10/10 both before and after the power change - except for the local TV multiplex for Norwich that I wasn't meant to receive which was lower and somewhat variable.
Wolfbane predicts 49dBuV/m at my old address so pre DSO it would have been 39dBuV/m.
I was using a Televes DAT45 with margin raising device (masthead amplifier) - an overall claimed 16 dB gain. So 65 dBuV post and 55 dBuV pre DSO at my TV set.
So my plasma metering was probably post the automatic gain control of the tuner as it remained the same.

Whether your LCD set is the same metering system or not I don't know. My newer Panny LCD (2016 model year) is not the same metering as my Plasma TV, and in %.

But your strength numbers are generally low and I'd want to see much higher.


Labgear MSA241:
I can't find that model.
MSA242 has 4 outputs. UHF in, VHF/FM/DAB in. With 8dB gain per port.
It also has the ability to feed +12V over coax to a masthead amplifier.
Is there a plastic box on the mast under your aerial?

If yes then perhaps the masthead amp inside that box, or the power feed from the Labgear has failed (or detected a short circuit on the output cable and cut off)? This is a bit of a long shot though
 

TJT1

Member
I wonder if it's possible that OP has an inadvertent quarter wave open cct. stub skulking about on his aerial system causing a notch at or around CH 43?
This is also a long shot and just thinking out loud really and I am prepared to crash and burn.
 

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