All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Malcolm Wood: If you're reading this, I've just read the article you provided a link to written by Bill Wright about phased arrays. Have you tried it out and are you in business?
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kaz: The downside to using Hastings is that the three COM channels (from Heathfield these 42, 44 and 41) are on the same channels as used by the transmitter in Eastbourne on the South Cliff Tower which, like Bexhill, is PSB only. So it may be the case that these are now wiped out, or at least intermittant at your mother's location.
Getting the desired sub-regional BBC and ITV is possible when picking up from Hastings, albeit starting to get more costly. A second aerial could be installed on Bexhill with diplexer (which combines signals from the two). It is unfortunate that Bexhill is horizontal as a single aerial would have worked for both otherwise (because they're in the same direction). As I say though, this is getting costly with the extra aerial and diplexer, and is not forced to work, what with the Eastbourne PSB transmitter being co-channel with Hastings' COMs.
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What was observed with the channels being available one day and not on another is what can happen with digital reception. It may be that when these services were picked-up, the signal level was "just" above (or a "bit" above) the threshold required (by the receiver) and that now it is "just" below that threshold. The difference in levels between the two may be small, but the effect is stark (which is digital reception for you).
Signal levels vary all the time due to the weather etc. Had the level been "quite a lot" above the threshold, a reduction of the level experienced could have still left it above the threshold and therefore it would have continued to work and your mother would have noticed nothing.
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Steven Moore: You have posted on the page for the Torquay Town transmitter, yet C57 is that of its parent, Beacon Hill.
If your aerial is vertical and points to Torquay Town transmitter which is on the roof of Walden Point on St Luke's Road South then the problem is that your box is incorrectly tuned.
If your aerial is horizontal and points to Beacon Hill, then perhaps you have too much signal. See this page for an explanation and remedy in this case:
Freeview signals: too much of a good thing is bad for you | ukfree.tv - independent free digital TV advice
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kaz: Following on from what I said about the signal level dropping just below that needed, it does make me wonder whether a signal booster may improve matters. Signal boosters aren't the be all and end all and can have a negative outcome depending on the circumstances.
jb38, as the expert, perhaps you can advise as to whether a signal booster may be worthwhile here, particularly if a replacement aerial for Heathfield is not likely.
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Jarzembowski: There are two transmitters that are not far off being in line with one another from your location. As such, I suggest that the most likely answer here is that your receiver has tuned to the wrong one.
The two transmitters are (along with UHF channel numbers):
Whitehawk Hill @ 283 degrees (adjacent to Brighton Racecourse)
PSB1 (BBC One etc) C60
PSB2 (ITV1 etc) C53
PSB3 (BBC One HD etc) C51 (if applicable)
COM4 (ITV3 etc) C57
COM5 (Pick TV etc) C56
COM6 (Yesterday etc) C48
Newhaven @ 264 degrees (Harbour Heights on the west side of the Ouse)
PSB1 C50
PSB2 C43
PSB3 C40
Based on what you've said, there are two things that make me think that your aerial is directed at Whitehawk and not Newhaven (albeit that there is just 20 degrees difference):
- Only Whitehawk carried Freeview before switchover, so if you were receiving it then, that is the transmitter you were using.
- Newhaven only carries PSB services now (see above). Thus if COM channels are being received, they must be from Whitehawk. You have only identified PSBs as being a source of poor reception.
Bring up the signal strength screen whilst on BBC One and it should tell you that it is tuned to C50 (Newhaven) or C60 (Whitehawk). I suspect that it is tuned to Newhaven instead of Whitehawk for PSBs.
How you solve this problem depends on how well designed your receiver is. If it has manual tuning, then this will be much easier to accomplish.
During the automatic tuning procedure it scans UHF channel numbers (frequencies) 21 to 69. Have the aerial unplugged up until it is passed those channels used by Newhaven. Plug the aerial in when it gets to 61% which should coincide for about C51 (so just after Newhaven highest channel). The scan may go fast with the aerial unplugged.
Once you've done this, then go to manual tune and tune to UHF channel 48 to add COM6. You will probably need to do the same for PSB3 which is on C51, if your receiver is a HD one. You may find that ITV1 is missing, in which case also do a manual tune on C53.
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Martin: As geoff says, check that it is tuned to Whitehawk and not Rowridge.
If it is, then the simple workaround is to unplug the aerial for the first 40% of the scan. This will miss out low channels (frequencies) used by Rowridge, but will scan higher ones used by Whitehawk.
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Martin: If you do find that it is tuned to Whitehawk, then I suggest that you get a 20dB variable attenuator.
For example (other outlets and sellers are available):
VARIABLE ATTENUATOR TV SIGNAL REDUCER 20dB 3 5 6 9 10 12 15 18 DIGITAL FREEVIEW | eBay
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Nick: I wonder if there is a notch in the Sudbury COMs antenna in your direction. Hence you aren't getting the full benefit of the 100kW. I think this because you said that you could get the 14kW signals occasionally.
Thus, maybe the strength of those signals is significantly weaker than the PSBs and this is contributing to desensitise your receiver which is in turn making it insensitive to the COMs.
With this in mind, I wonder if you need to boost the strength of the COMs only. A spectrum analyser would obviously show you instantly if they are there, but weaker than the PSBs.
Before trying what I've outlined below, you could perhaps try attenuating the signal to see whether the strength of the COMs increases, even if not enough to put it above the threshold to give you a picture.
This may or may not work as you will obviously be reducing all signals and not just the PSBs.
Or: If you were to use a Group C/D bandpass filter, this would remove all but C/D channels and hence remove the PSBs. You could then experiment by seeing what can be picked up. Then try amplifying it.
Obviously, as KMJ,Derby says, the siting of the aerial may be a factor. With little or no signal it is difficult to know whether the aerial is being aimed in the right direction. Remember that the PSBs are a Single Frequency Network with Rouncefall, so going by those signals may be a red herring.
If you successfully get the COMs from Sudbury, having amplified them (and them only), then you need to diplex the output of the amplifier with another feed containing the PSBs, either from Sudbury or Aldeburgh. Your former analogue Group B aerial may be of use here if you decide to receive PSBs from Sudbury.
Bear in mind that in the future, additional COMs may come on the air using channels between 31 and 37 and likely as not using the same or similar quasi-national network. So you may have to change again if you want to pick them up. How you do it now may affect how easy any future change might be.
A diplexer which splits at C51 will allow you to have the output of the amplifier (whose input is filtered to allow C/D only) *and* either Sudbury or Aldeburgh PSBs (which needn't be filtered) going to your receiver.
I assume that the C/D filter on the input of the amplifier might be needed to prevent any nasty effects by boosting the PSBs (even though they will be subsequently filtered by the diplexer.
As I might have said before, I'm not a professional and am just putting my thoughts forward based on what I understand. I would appreciate comments by the professionals on what I've proposed and how likely they think this might be an effective solution.
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The message at the top of this page does say that Sudbury is "liable to interruption" which does suggest that engineering work is ongoing. Maybe it will be worth waiting to see if reception of the COMs is possible on completion before adjusting your aerial arrangement.
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Sunday 1 July 2012 9:09PM
Nick: The PSBs from Sudbury and Rouncefall operate as a Single Frequency Network (SFN). This means that they use the same channels and therefore the aerial might pick up some signal from one transmitter and a bit from the other. So the result is the sum of the two at the point where the aerial is.
Rouncefall doesn't carry the COMs, so orienting an aerial based solely on the PSBs could lead to a not-so-accurate aiming of the aerial.
The only possibility I can think of is that the COMs are more restricted (than the PSBs), perhaps because to prevent interference on the Continent.
What strengths do you get on the PSBs from Sudbury?
If you can't get the Sudbury COMs, then in order to get Angia regional programming, you could perhaps have another aerial on Aldeburgh. The channels allow diplexing with Dover. Rouncefall is 39 degrees clockwise of Dover, so this is probably too far off beam for the aerial you have to pick it up.