BT DTR-T4000 strange loss of signal

Julien Helme

New Member
I'm in the NW Winterhill region and have good signal on all muxes most of the time.
Just one temporary mux 7 (ch55 - 746MHz) randomly drops to 0% on signal and quality and then jumps back to 85% signal and 100% quality.
I've even seen it alternate once every second from zero to 100%, zero 100% as I look at the screen.
The RF signal is looped through to my TV which shows a consistant level at all times so I assuming that my cables are ok and it's the DTR-T4000 that is sensitive to this lower powered mux for some reason.
Speaking of which I've made my own flyleads out of WT100 cable (the same as my downlead) at only 50cm long and the connectors are a good tight fit so I'm ruling out any cable issues.
Things from other posts I've tried
1. 6db Attenuator.
2. Different leads - RF and HDMI
3. Software reset from maintenance mode.
etc etc.
I wouldn't mind but the only channel that matters in this world (BBC4 HD......oh and maybe Quest HD ) is on that mux and I record a lot from that channel.
Any other suggestions but be most welcome.
Thanks.
 

Ezra Pound

Well-Known Member
If you don't need to use an attenuator on the main muxs then adding a 6db attenuator for Com7 won't help, Com7 is transmitted at a much lower power as it is
 

Rodders53

New Member
Location?
COM7 is a single frequency network and may suffer from distant transmitter interference, particulary under certain weather conditions or in some locations. Check your interference prediction numbers at freeview.co.uk/corporate/detailed-transmitter-information
BTW what does you meter show for the other received frequencies?

WRH main muxes are 100kW erp and now all in group A frequencies except COM7 (23 kW = -6dB approx) and some of the local TV muxes. Old Winter Hill C/D aerials won't perform very well at group A but some (notoriously the Triax Unix 52 C/D was identical to the wideband version).

It's possible that trees / wet leaves moving are causing interference (leaf size matching the high frequency wavelength).

Where is the aerial (roof, loft, room)? Do you know make and model, and whether grouped or definitely wideband? How old is it? Is there any amplification involved (other than that in the Humax when it passes signals to internal tuners and to the TV loop out socket).
Have you checked COM7 / signal levels on the TV when aerial goes direct rather than via the Humax?
 
OP
J

Julien Helme

New Member
Thanks for the replies

"If you don't need to use an attenuator on the main muxs then adding a 6db attenuator for Com7 won't help, Com7 is transmitted at a much lower power as it is" - Indeed - I only mentioned it to avoid people suggesting it as a fix as I have quite a strong signal.

It is a two floor house chimney mounted aerial with no obstructions or trees.
Single down lead straight to the only TV in the house. WT100 cable.
Don't know if it is a wideband or not but going off the signal strengths mentioned below. I havn't felt the need to investigate further. It is an old one but as all of the good muxes which are now in group A, are OK and I'm getting 90% on ch55, I'm assuming it's wideband ish. Even if it was C/D I don't have any problems with the group A muxes
Good muxes 95% signal strength, 100% signal quality.
Mux 7 90% signal strength, 90% signal quality.
When the mux 7 drops to zero on the Humax, the TV still shows a good 90% signal strength as I mentioned. And when the Humax is flicking between 0% and 90% like a madman as sometimes happens, the signal on the TV remains constant.
Predictions for my post code.
winterhill.jpg

Can't get an obstruction prediction map as there is a coding error on the website
I can't really believe that tropospheric ducting or any other natural phenomenon would cause a full drop to zero % though?
 

prpr

Well-Known Member
Time to get your spectrum analyser out then.
Failing that, wait till next June and the problem will fix itself.
 

Black Hole

May contain traces of nut
When the mux 7 drops to zero on the Humax, the TV still shows a good 90% signal strength as I mentioned. And when the Humax is flicking between 0% and 90% like a madman as sometimes happens, the signal on the TV remains constant.
To me, this is a red flag that there's something wrong with the Humax rather than the reception path. On other Humax units (HDR-FOX in particular), there is a "hidden service menu" which provides access to a signal test on individual tuners. If there is such a thing on the DTR, it is worth running the test on COM7 (the troublesome one) for each tuner.
 

Rodders53

New Member
Location (approx, village or suburb name to gauge how close to WRH you are)?
Predictions are for <1% of time interference in all points of the 100m x 100m prediction square. So that's not the issue.

Must say I'd not heard of WT100 cable but after Googling: it's all copper (silver plated!) and made by a Korean company called Withwave and seems to have a decent enough spec.

Have you checked for a new mobile phone transmitter pole, or upgrade to one, coming on line in your area that might be causing interference? Check on the RestoreTV website (used to be AT800). restoretv.uk/diagnose-your-problem/

In your shoes I'd be doing a number of tests...
Measure all muxes 'as is', 95%-90% you say above. (That seems a very high level to me.)
Insert 6dB attenuation and repeat the numbers.
Try greater attenuation if you can 10-18dB as a test/sanity check. A 2-way splitter is 4dB attenuation on each leg.
IIRC 75-80% is the 'ideal' strength on most Humax Freeview PVRs' tuners?
Try a room / set top aerial perhaps (moving the Humax to another room if necessary to do so)?
Or even on a neighbour/friend relative's aerial?

90% quality on COM7 suggests some data corruption (bit errors) that's usually correctable; likely caused by something such as unwanted reflections from objects or trees, or perhaps signal overload? {Note it's the overall RF total going into the front-end amplifiers that can cause overload and inter-modulation corruption that appears as harmonics affecting only some multiplexes.}
 

Black Hole

May contain traces of nut
IIRC 75-80% is the 'ideal' strength on most Humax Freeview PVRs' tuners?
I'm not sure where you get that idea from. There is no published specification for what strength = 100% actually means, what headroom there is, nor what minimum level is required. I normally recommend strength should read less than 100% because the "meter" tops out at 100 so a reading of 100 could mean 200.
 

Rodders53

New Member
I'm not sure where you get that idea from. There is no published specification for what strength = 100% actually means, what headroom there is, nor what minimum level is required. I normally recommend strength should read less than 100% because the "meter" tops out at 100 so a reading of 100 could mean 200.
Reading various forums. Empirical data and long experience with such.

100% signal means all sorts of things on different devices however. Many Panny TVs are post agc and error correction so 10/10 is the normal.

Humax are not post agc as far as I can tell so... My advice stands.

You are just super argumentative and sometimes come over as aggressively patronising BH.
 

Black Hole

May contain traces of nut
You are just super argumentative and sometimes come over as aggressively patronising BH.
You made a statement which needs backing up with facts. Maybe you just don't like being challenged.

IIRC 75-80% is the 'ideal' strength on most Humax Freeview PVRs' tuners?
"Ideal"? Reference?
Empirical data and long experience with such.
So your opinion rather than body of fact then. If you had said so I wouldn't have questioned it.
 

MartinLiddle

Super Moderator
Staff member
Certainly my aim when tuning most models of Humax PVR, based solely on my experiences, is to aim for a signal strength below 85%. However that rule of thumb doesn't seem to work for the Aura based on other peoples experiences.; I can't yet comment personally on the Aura because despite getting delivery notifications on two consecutive days quoting specific time slots, nothing has turned up yet.
 
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