All posts by Jonathan
Below are all of Jonathan's postings, with the most recent are at the bottom of the page.jb38, thanks for the advice. No signal booster involved at the moment; I have a variable attenuator on order and will report back once I have tried this out.
To other readers can I recommend the article "Freeview signals: too much of a good thing is bad for you" which Brian pointed another questioner to shortly after my question. Very interesting reading and quite counter intuitive.
| link to this comment |
Follow up to my posts of Wednesday 28 September 2011 10:15PM and Thursday 29 September 2011 9:40AM (lost all multiplexes except C53 on 28 September; OX4 4EY but view of Beckley blocked; wideband high gain pole mounted aerial).
I got a 0-20dB variable attenuator. Playing with (is it 20dB at fully clockwise or fully anticlockwise?) certainly had an effect but nothing simple. Turns out that the signal quality is far more strongly affected by the exact position of the aerial drop cable than anything else.
Trial and error eventually led to a position where I could get the three high power multiplexes (C53, C57, C60) but nothing else. I'm a bit reluctant to fiddle any more until I have a slightly better idea of what I'm meant to be doing...
All thoughts appreciated!
| link to this comment |
Thanks to everyone for the many answers!
To clarify a few things:
(1) I am not exactly sure what my aerial is; it was replaced by Oxford Aerials in January 2010 and at the time improved our signal on both analogue and digital. My description as wideband high sensitivity may be wrong. There is no amplifier involved, however.
(2) Our view of Beckley is blocked by a combination of a gently rising hill and a pair of enormous beech trees. Historically our reception has been highly seasonal as leaves come and go on the beech trees.
(3) The coax drop lead is split at the attenuator, and also has a female-female converter to let me use two male-male leads. The leads are perhaps best described as "cheap" and may not be well screened.
(4) Originally I found it hard to see any pattern in anything when adjusting the variable attenuator. Later it became clear that this was because both the signal strength and quality readings changed as I lifted up the attenuator to twiddle it and put it down again. I have now found a position where the attenuator sits on a wooden cabinet and I can turn the knob in a reasonably reproducible way.
(5) The attenuator is as shown at AERIAL CABLE VARIABLE ATTENUATOR COAXIAL RF-TV FREEVIEW | eBay and I have been unable to locate any instructions.
(6) With the attenuator in its "stable" position I find that signal strength goes down on the multiplexes on 53, 57 and 60 as I turn it anticlockwise, but it varies remarkably little for what is suppose to be 20dB (e.g. from 45% to 30% over the full range). The signal quality on 53 and 57 is at 100% over the whole range; the quality on 60 is low and highly variable at fully anticlockwise and high and highly variable at fully clockwise.
(7) No other multiplexes are visible at either end of the range of the attenuator. I am doing a clean install from factory settings in each case.
(8) Removing the attenuator entirely (keeping the female-female adaptor in) greatly reduces signal strength and quality on all three multiplexes.
I am struggling to find an interpretation of all this that makes much sense. My best interpretation so far is that I have WAY too much signal so that even after 20dB attenuation I still have too much signal. (OX44EY)
| link to this comment |
OK, I'm making more progress. Key thing was to insert the attenuator directly into the wall socket rather than the middle of the drop lead. I have it turned fully anticlockwise which I am interpreting as maximum attenuation (this gives the largest signal strength, which is counter intuitive, but I am assuming that the signal strength is so high that even at 20dB it is overloading the system, and so the strength reading can be counter-intuitive).
I have now gained channel 55, one of the four slightly lower power multiplexes. I am now getting signal quality of 100% on 53, 55, 57 and 60. Still missing 51, 59 and 62, but very little there I care about. I may try attenuating still further to see if that brings the final channels in.
| link to this comment |
Given the success so far I have just ordered a 24dB fixed attenuator, which can be combined with my existing 0-20dB variable attenuator to give me a huge range. Will report back once this arrives.
| link to this comment |
Chris.SE, A reasonable question but I can't find the receipt for my aerial - I only have the email booking the visit which is how I know the fitter and date.
I have, however, applied a telescope to the problem, and can see the black junction box reasonably clearly. There seem to be four groups of text:
W 10 AB 1 CD/W
Channels 21/58
This junction box must be installed face down (or something to that effect)
CAII/AB 011
(I'm least certain about the top line where the text seemed slightly damaged).
It would appear to be a Yagi with 9 secondaries shaped like very flat Xs and two tilted reflectors.
| link to this comment |
Yet another update: my aerial is almost certainly a Vision 48 element as shown at Vision 48 Element High Gain TV Aerial
When installed (replacing an old C/D I think) this greatly improved reception of the outlying multiplexes on C29, C34 and C68. I can see it would be somewhat over the top for current conditions.
| link to this comment |
Stephen, the Humax Fox T2 should have the ability to handle this automatically if you do a full restart
menu -> settings -> installation -> factory default
You will need your security code, but if you haven't set this it will still be the default 0000
This will do a complete scan; when it finds the signals from both transmitters it should ask you which to select as your primary transmitter, offering Oxford as the default choice.
If that fails then try manual tuning, either as jb38 suggests or using the manual tune mode on the Fox T2 where you can tell it which channels to look at.
| link to this comment |
jb38, my fox t2 does give channel numbers as it scans; possibly different software versions are different on this? It also scans the whole range twice, and picks up different channels on the two scans, which could make your method a bit tricky; I don't know what the difference between the two scans is.
Returning to my own saga, I got the 24dB attenuator, and inserting that wiped out the signal entirely. In some ways this is a bit of a relief (a big enough attenuator should eventually do this), though it doesn't fit very sensibly with the behaviour of my 0-20dB variable attenuator.
More annoyingly, on returning to my variable attenuator the signal was not as good as before. My guess is that this is because I moved the fly lead in the process and the system is still very sensitive to that position. Various people have suggested that this could be due to a poorly shielded fly lead picking up signal, either directly or rebroadcast by the down lead (the installers didn't replace the coax below the loft when they installed the new aerial, so the condition is unknown; looking at it in the loft it seems old but sound enough).
Anyway my next set of plans involves (1) getting a better fly lead, and/or (2) trying an attenuator in the loft when the new coax from the aerial joins the down lead - this has F connectors so I can't use my existing attenuator family.
| link to this comment |
Page 1
Wednesday 28 September 2011 10:15PM
Oxford
Based in Oxford with a pole mounted wideband high gain aerial (no direct view of Beckley from ground level due to Rose Hill being in the way).
Yesterday I could receive all the multiplexes on my Humax HDR-Fox-T2, though some of the low power multiplexes were poor quality.
Today I did a hard restart (reset to factory settings and reinstall from scratch). I can get PSB1 on C53 (33% signal 100% quality) but that is all. Not a sniff of any other multiplex. Tried your reset procedure; didn't help.
All thoughts much appreciated.