All posts by Roy Barton
Below are all of Roy Barton's postings, with the most recent are at the bottom of the page.John Lindsay. Thank you for your answer. Can I assume that a wide band aerial would be a definite bad choice?. (I bought one just today **** )
I also purchased a Labgear aerial amplifier. In the blurb it states it is for terrestial digital TV DTT and radio T-DAB and no mention of DVB-T. Is it safe to assume that a MSA111 would not degrade the signal in any way. (Other than when it might be overloaded) ?
| link to this comment |
Roy Barton:
John Lindsay. I really do appreciate the detail in your answers. I have checked with the manufacturers of my wideband aerial (not yet fitted). It is a labgear LAB450/WS
Labgear
They say it is not a Yagi, but when pressed they said it was based upon a Yagi but having 3 booms they say it was strictly not a Yagi. They went on to say as regards a log periodic it would perform as well as a group A on channel 28 where we have the problem. Some local stockists only stock wideband, but one distributor offers just one item in Group A, and it less than 25% of the cheapest wideband. Labgear only manufacture wideband.
You have made it clear what I should do. I will try to get a refund on the wideband and fit the cheap group A on vertical polarisation. To me this seems to be an aerial jungle. I would appreciate your comment. LAB450/WS is it worth messing with? (BH217DX)
| link to this comment |
Roy Barton:
I nearly fell out of my chair when the distributor said their Group A aerial was only £6.99 plus VAT. I think it was trade price. He said all the installers use them. I am now confused what a log periodic is. I thought log periodic was the simple aerial with a single boom. (I thought that all aerials were Yagis... but what do I know?) There is so much complexity. I have left the TV on all day displaying signal strength and signal quality. All day long while sun was shining the signal strength was around 99 and the signal quality was fluctuating between 40 and 70. When the sun went down the signal strength dropped to 90 and the signal quality fell to the lowest reading of just 1 (that is the same as 0) but occasionally the signal quality bounces up to 10 or 14 for a minute or so before returning to 0.
This is all very curious. I really intend to experiment with V polarisation using the tri boom and the cheapy just out of interest. Unfortunately I won't be messing with the aerial on the roof as that is inaccessible without cherry pickers or similar. (Or a very light footed installer with good equipment.)
I suspect that the G4 being introduced to Southampton my be the culprit?
My signal has to pass through the pylons of thw national grid half a mile away and some large conifers... but these were never a problem.
| link to this comment |
Roy Barton:
I appreciate all the comments. For me the matter is a case of technical curiosity. For a couple of days now I have left the TV on monitoring signal strength and signsal quality. The problem only became evident a few months back and has gotten signifcantly worse over the last few weeks. Yesterday the signal quality was consistently good fluctuating a little around 40% to 60% for six hours or so. Then later in the day the signal dipped to zero returning hours later for periods of a an hour or so to 20% to 30%. (20% is the threshold for getting a good picture.) All this time signaal strength was 90% to 99% as opposed to signal quality.
This morning the signal strength started out at 90% but quality around 10% and soon the signal strength and signal quality both dipped to 0% and has stayed like this for four hours or so.
I have been checking the above results with a second TV and that gives good agreement.
I am not an expert but the above seems to be weather or atmosphere related. None of the observations were made in windy or rainy conditions.
We live in forest well away from traffic. There is not much in the way of buildings. There are the pylon wires between us and Rowridge.
As far as I know the neighbours do not seem to be having problems.
Later today I will start experimenting with different aerial arrangements.
I don't want to be a pain... My later posts are mainly driven by technical curiosity on this wonderful forum. I have a satelite dish installed which I have not used for years and if all else fails I will upgrade that with new kit that I have packed away.
| link to this comment |
I just tried some experiments with the new wideband aerial (£40 worth but £18 with the special offer) I also tried a very old simple aerial with 18 elements (that I had laying about) presummably group A. I get the impression that the old group A easily outperformed the wideband. (It was much easier to handle being less than a quarter of the weight.)
I was amazed to find the group A aerial being held out of any window pointing down to the ground in a any direction gave a good picture on CH28 (film4). (Our problem channel)
This test was carried out at 5.30PM.
I then checked on the main TV with the good signal strength meter still connected to the aerial on the roof that I have not disturbed.
ON switch on, the signal strength was 99% and the quality 99%. half an hour later the signal strength is still 96% and the quality is 96%
This is after signal strengths and signal quality of 0% or 1% for a whole 8 hours earlier today with perhaps jumping up to around 10% for the odd few seconds.
To my inexperienced mind this sort of inconsistency points to atmospherics (as mentioned by JB38. )
The fact that transistions from good to bad are so very clean makes me wonder if somebody is switching channels or transmitters on or off somewhere. When I spoke to the Freeview chap he hinted at some such possibility, but I did not really follow what he was saying.
During these initial trials the signal strength was so good I could not distinguish between V and H with these aerials.
But I removed the dipole from the wideband aerial and without any directors I think there was a slight improvement in V compared to H. The key thing here is that the simplest low gain aerial (ie the dipole_ gave a perfectly good picture (on a good day.)
I hope I am not boring people with these observations. I will stop if you want me to stop mentioning these anomolous results. Wide variations from day to day and hour to hour. Some periods of a signal on the weakest channel as beyond perfect, followed by periods of a signal that is reported as non existent.
After more than 50 years of owning TVs I have never come across this.
| link to this comment |
After some experimentation and lots of observations I have reached some tentative conclusions.. I dont really understand the underlying causes.
At our house Channels 21 22 24 25 & 27 are always rock steady with the TV reporting perfect signals 99% strength and 99% quality.
Channel 28 is sometimes rock steady for long periods at 99%/99% (perfect) Then after hours of perfect reception the signal can dip to 0%/0% (absent) and remain as such for hours. Or it will slide abruptly into wildly fluctuating signals varying rapidly between 20% to 80% quality sometimes when the signal strength is showing at 97% to 99%.
These changes seem to be at random. The changes are independent of observable weather.
There are tree branches in the line of sight but it is unlikely that much has changed in the winter months. The problem has only been evident over the last couple of months. (For the past few years signal interruption has been very rare.) I will check to see if the snow brought any branches significantly lower.
Other conclusions. While signal is wildly fluctuating the randomness has made it impossible to conclude for sure that V is better than H. (The above observations in this post refer to the old H aerial on the roof.) However the information available shows V is generably best for channels including 28. (All the neighbours have H.)
The randomness will make it impractical to get in an aerial rigger on our difficult roof to finally resolve the issue.
The great mystery is what is so different about channel 28 ???
The wideband aerial that I just purchased is obviously a waste of space. I cant understand why these expensive aerials are stocked in preference to inexpensive group aerials. (Is it a scam?)
I very much appreciate all the help from people on this forum.
I guess that if the problem persists I will dig out my new sat kit that I never found time to rig up.
Seems crazy as I finish this post the signal readings on channel 28 are rock steady at strength 97% and quality 99% and have been for the last hour. Crazy.
| link to this comment |
For the last 48 hours the signal strength and signal quality as registered by or TV has been pretty steady at strength 98% to 99%. tiny fluctuations of a 1% or 2% occurs extremely rarely. The pictre reception is perfect. So keeping my fingers crossed the problem that has seemed to get worse slowly over a couple of months may have cleared. Possbily somebody at Freeview may have sorted something out.
If the problem has cleared on a permanent basis I am faced with the embarrassing possibility that the problem occured at the connectors on the aerial splitter/amp situated right close to the TV.
If it was a connector fault then it was a very weird one as the signal fluctuated on a very random basis between perfcet and zero with much of the time giving readings between the extremes. All this without any physical disturbance of the cabling.
One possibility is that the connector had some minor corrosion. Copper oxide can act as a semiconductor and possibly the non-linear effect of this coupled to the non-linear performance of the TV signal meter (hinted at by Mazbar)may have interacted with minor variations in the signal strength resulting in extreme results.
Who knows perhaps the problem will return and make the speculation above in this eamil turn out to be rubbish.
However whatever the facts are the observations I have made (and reception dropping out) are very weird and defy understanding.
One positive thing from this is that given the help of the postings above I have gained some understanding of what digital TV transmission is all about.
I don't understand how a channel can transmit simultaneously both horizonatlly and vertically. Vector analysis would suggest that the result would be something like 45 degrees polarisation. (But what would I know? )
| link to this comment |
Interesting comment by JB38. In the hypothetical case where two signals were combined from two aerials through a (perfect) diplexer, the output signal power would be the two added together. This would be dependent upon the two signals being perfectly in phase. It is likely that they would be in phase in the case put forward.
The above is a non-practical arrangement to illustrate adding signals together in a cable. However adding electromagnetic signals together in space is somewhat different. In space it is possible to have phase differences and also polarisation differences. If we assume that there are no phase differences in signals from an H aerial and V aerial we are left with polarisation angle differences. This is where vector summing comes in. Two equal signals at 90 degrees add together should give a single signal at 45 degrees. Presumably the power in the resulting signal would be the sum of the two added together.
I dont think the above comments have anything to with my problem (hopefully now gone away because I wiggled the connectors a bit). However there is a chance that I have misunderstood the H & V polarisation issue and anybody reading this might put me right.
One thing about polarisation if we were talking about visible light, polarisation would effect reflections from surfaces. I expect polarisation of TV signals might effect differences in reflection off pylons, clouds etc.
As I finish this email I see that the signal strength/quality meter on the Sharp TV is still steady at 98%/99% and has been that for three days. Channel 28 now shows the same result as all the other transmission channels. (The screen presentation for signal quality on this TV is excellent but I do accept that it probably not very linear but it serves a purpose very well.)
Initially I was very confused. There are Transmission Channel numbers and Entertainment Channel numbers. (Not many people differentiate.)
| link to this comment |
Thanks Briantist. That MIMO link explains all. I did not realise that the signals on H and V were different. I now understand, different signals on H and V keeps them separate. (Therefore effectively doubling the bandwidth.)
With the V & H co-frequency concept it is easy to see how you can can obtain 100% signal strength and 0% quality. (IE the two polarisations interfere perfectly with each other.)
I can see the problem, if the receiving aerial is not perfectly H or V then there is potential for the different signals operating on the same wavelength to interfere. Worse still any reflectors such as pylons might change the polarisation (?) and that would result in cross channel interference.
I am surprised that mixing H & V on the same transmitter works as well as it does on the fringes.
I wonder if the H & V divide explains why my BBC HD channel changed from 51 to 101 when I retuned? Before and after I got perfect signal quality and pictures on BBC HD (and all the other entertainment channels other than those on transmission channel 28) Is BBC HD on channel 51 in H and 101 in V ???
The subject gets clearer every post. (But there is still lots to mystify.
| link to this comment |
Page 1
Saturday 16 February 2013 3:08PM
Wimborne
For years we had perfect reception at BH21 7BT. Over the last few months it has degraded. I recently rescanned all the channels and it was puzzling why BBC1HD should have moved from ch 50 to ch101. But tht is trivial compared to our real problem. As a qualified electronics engineer I can't understand why signal strength and quality for BBC on Channel 24 is 99% but signal strength of Film4 on channel 28 is almost non existent on a good day as measured by our sharp TV signal strnegth is high but n a bad day quality is down to 1% or no signal at all. I have advice that we should rotate our aerial so that is is Vertical polarisation. We have not tried it yet. WE are confused as the UKfree.tv website indicates that Rowridge is H. But there are clues that it might be also V. Any info on this is very confusing, probably because some info on your website is out of date.
Please clarify. Should we continue pointing at rowridge and rotate our aerial through 90 degrees so the dipoles are vertical? I guess we should be using a type A aerial. Would you confirm that a wideband aerial is not to be recommended for our location.