been getting a few pixellations in certain weather conditions on one MUX...turns out its the one that 'stands alone at 800MHZ appx, with all the rest at 300 Mhz,.
..aerial is original analogue one, so its not unexpected..
Got reasonable signal strength and an amp, so its more a question of getting narrow beamwidth over the band, than getting the last DB out.I can null out what is probably a co cahnnel interfere by rotating e existing aerial, but then the main mux goes bad on me.
TV installer offered me an expesnive thing covered in bow ties for 30 quid..is a log periodic better? I cant seem to find polar diagrams of a buggered wideband yagi versus a log periodic anywhere.
Don't forget that beamwidth is inversely proportional to gain i.e. high gain = narrower beamwidth (in one or both planes)
A log periodic will be wider band but lower gain. The Yagi is the best bet. The bow tie structures are designed to give as wide a bandwidth as possible with high gain (bandwidth being impedance bandwidth presented to the telly by the antenna, or pattern bandwidth being minimal change in pattern (and hence mainlobe gain) against frequency).
On Tue, 6 Jul 2010 19:45:52 +0100 someone who may be "Duncan Di Saudelli" wrote this:-
It is the best bet in some circumstances. However, if a log periodic, or indeed a bit of wire hanging out of the aerial socket on the television [1], is enough to get a good picture then these are the best bet. Much less to be blown about by the wind.
is not what Mr Philosopher asked for, but it is a good start.
As it says at
"The fact that one of the dipoles can be resonant for any part of the broadcast band means that Log Periodics have a pretty flat signal gain curve. They also have a tight polar response (i.e. they are less likely to pick up signals you don't want), a decent "cross polar rejection" and low wind loading. Finally Logs have good suppression of impulse noise which can be a cause of intermittent blocking and freezing on digital signals. Manufacturers have been known to claim that Log Periodics short this noise out to earth, but it's just as likely that the aerials' tight polar response just means they`re less likely to pick it up in the first place !
"Unfortunately Logs have a relatively low gain figure and the they're only available in wideband. Thus they are only really suitable for areas with a fairly good signal, though the Log 40 is OK for medium signal strength areas as well. Apart from this Achilles heel the Log is one of the best antennas, particularly for digital, which is why we use them wherever possible, as do the broadcast authorities, for both receiving and transmitting."
[1] I have seen one of these get perfect digital signals from a transmitter that is of high power and near enough.
300 would be lower than channel 21 which is at 474MHz!
Not polar, but quite decent comparisons here:
formatting link
you can get enough gain out of a log, then they are nice because they are very flat in response right across the the full band. However if you are in a marginal or poor reception area, then a yagi may be a better bet.
Also remember that any water in the coax will have the biggest hit at the top of the band, so it may not just be the aerial. (I had very odd performance where I was losing individual channels in a mux rather than the whole mux, that turned out to be a dodgy 10m bit of low loss from the mast to the splitter - replaced with CT100 and all was well).
Sudbury now and post switchover is group E which are a bit harder to find (although the site above has some).
A decent 18 element yagi should do. I am about 35 miles line of site south of sudbury, and I have a triax 18 element yagi (the Antifeerance trucolour, or blake would be equally good) that I have knobbled to be a group E using the Bill Wright hacksaw method! I have that feeding one of Andy's Proception variable gain amps, and then a passive splitter. Rock solid performance across all the muxes all year round.
You need to be a little careful with amplification on Sudbury, because the analogue levels are quite a bit higher than the digital, and you don't want to drive the amp over the edge (I had to push the analogue levels close to 99 dBuV to get acceptable digital on all muxes)!
I am only ten miles NW, and signal is good. Its that the QUALITY on the MUX2 is sometimes crap. Not always, just sometimes. So its likely another transmitter somewhere screwing things up, over the horizon.
I did try the camper vans antenna..that's a short XB type. that worked pretty well.
Mmm. That favors the log then..its pretty low gain at 'analog' freqs. I have only modest gain - its a distribution amp, not a mast head. Thats in here, in upper storey office. cable is about 5 meters of high grade satellite up to it so up two meters and along about 5 meters..antenna is almost over my head.
As I say, I am more trying to reject the unwanted than get massive gain on the wanted.
I cant quite work out what is co channel to the MUX2. Only the dover stuff is anything like in the same direction..unless I am getting reverse pickup from the north west. or over the horizon stuff from the continent.
All the STBS show the same issue..if its on one, its on all, and so unless the actual distribution amp is overloading, its not that. The fact that only certain muxes - usually just the one - get it, also points to it being a specific piece of interference over a narrow band,.
They all show good signal level/crap signal quality when it happens, too. There is some degradation of quality shown on the diagnostics on other channels, but one is always worse then the bad MUX to work but then others degraded.
I think I'll just try a log40, and see if it makes it any better.
It only happens half a dozen days on the year, usually when there is a smashing film on ITV2,3,4 etc..sigh.
and let us know the figure quoted for Field Strength (dBuV/m) and the recommended aerial type.
If you can use a log I would as the response is flat and directional (no stray lobes). The Vision (super)log40 is a good aerial but as you have it in the loft it may be a bit light in gain. It's also a bit heavy for tail mounting (which it must be) so it's a bugger to keep the nose up.
As you may already have found, roofing materials appear to be perfect notch filters at random mux frequencies. Following the good advice of pro installer Bill Wright on uk.digital.tv I put my (v large) loft aerial with the nose about an inch away from the felt, it seems to minimise weird effects that seem to creep in when the aerial is in the middle of the loft.
Ah, ok - the output of sudbury is "shaped" so as not to end up upsetting the folks off to the right of the north sea. From NW of the transmitter, I would expect you to be able to get MUX 2 twice - once on Chan 54 from the main transmitter, and again at 68 from the B transmitter. The output from B is however much higher, but attenuated to toward the east). Muxes
1 and 4 are attenuated to the west - but if you are sufficiently to the north that ought not bother you.
At the moment the analogue and digital channels are very closely spaced. So in the run of channels from 47 to 51 you get ITV, Mux3, 2, 6, and then BBC1 all slap bang against each other.
The moderate gain of the log would seem like the best bet then. The other difficulty with high gain yagis is that while they become more directional, they also seem to acquire odd lobes of sensitivity on their polar response, which can mean you pick up some unexpected things!
(I used to have a high gain aerial pointed at crystal palace, that managed to pull in a couple of muxes quite well from Bluebell hill - nearly 90 degrees of axis)
Well if you are looking at the chan 68 copy, then nothing in that direction other than perhaps Dover - that has mux 1 on 68, but only at 1kW
If what is on one its on all? (interference, complete loss of signal etc)
Its a possibility - remember you have analogue channels at 250kW compared to at best about 8kW for the muxes. If the amps output is saturated, it could be dancing all over different bits of the spectrum.
Have you got a plug in attenuator you could put in line with the aerial as a test?
Is there a pattern to when you get problems? Weather, time of day etc?
Could be high pressure causing a "lift" - bringing in co channel from the continent or a transmitter like dover that is usually too low power to matter.
With tricky problems like that, its very hard to get far by trial an error without test equipment I found.
In article , The Natural Philosopher scribeth thus
A log as many have stated is very flat on response across the bands but low gain. However a wideband Yagi is a bit of a misnomer as by its nature its a rather >narrowband< device.
What I think you need to do is to get the aerial outside, now I'm sure thats not really a problem even to try and see for a while. Remove any unnecessary amplification in case of cross mod that -might- be occurring unless you've checked that on a spectrum analyser.
I don't know just how you expect to find the diagrams of a buggered aerial anywhere unless you know just how buggered it is;!..
Next time your in Gods chosen City Cambridge, go and see Clint at Martin Gibbs in Milton road just near what's known as Mitchams corner and ask him what he recommends and take his advice tho take a cheque with you or cash he's a bit olde world with these new card things;!.
I suspect that if the upper MUX is causing trouble at Ch. 68 the old group B is failing very badly at that frequency. In the loft there are prolly standing waves and other nasties which are overall causing further problems.
How do you know for certain that its external interfereres?.
Where you are you should get excellent signals.
Ever tried Taccy instead?. Or Freesat even its very good indeed......
Well as we're using an old aerial thats group B its possibly going the sod up the higher numbered channels..
Been very few this year so far..
Indeed sometimes this seemingly straightforward TV reception does need an analyser and quite some know how and sadly thats rather lacking among the aerial frigging community I've noticed...
Its prolly lack of flatness of signals across the spectrum . Can be caused by poor aerial mounting, wrong or poor choice of aerial, unnecessary or poor amplification, cable problems etc..
BBC ONE:698167000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:600:601:4167 BBC Parliament:618000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:205:421:17024 BBC Red Button:698167000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:0:0:4479 BBC TWO:698167000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:610:611:4231 BBC THREE:698167000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:0:0:4351 BBC FOUR:618000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:0:0:16832 BBC NEWS:698167000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:640:641:4415 BBC World Sv.:618000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_3_4:FEC_AUTO:QAM_16:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:0:440:18304 ITV1:754000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_2_3:FEC_AUTO:QAM_64:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:520:521:8257 ITV2:754000000:INVERSION_AUTO:BANDWIDTH_8_MHZ:FEC_2_3:FEC_AUTO:QAM_64:TRANSMISSION_MODE_2K:GUARD_INTERVAL_1_32:HIERARCHY_NONE:530:531:8325 ITV2
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The problems I had were on ITV2+1 and whatever else is on the same MUX.
754Mhz by the look of it. If that's what the second column means. I used to occasionally get sandy heath, and I think I once got a second set of MUX2 but not recently. And the sandy heath stuff has gone now I have the aerial pointed straight at sudbury..sandy is almost 90 degrees off beam.
yes..teh analogue one when pointed about 30 degrees off, netted me sandy heath quite decently!
yes. on occasion, any or all of the above.
Since its all behaving itself tonight, no. But I doubt it is that. I am on the edge of the 'medium' signal area shading into the low' areas.
almost always at night. usually between sunset and midnight. Cant quite pin weather itself down. but its NOT when its raining. Wind maybe..trees on the horizon waving? dunno.
I suspect so. I am not as au fait with UHF as VHF, but I spent a year with a big yagi developing an FM tuiner. Could pull in loads of stuff - got Milan once. Lots of eastern European stuff.
yerrs. I'd LURVE a spectrum analyser.£3500+ for a basic decent 0-1Ghz.
Its well clear of the chicken wire and thatch bit. It's got a whole house wing roof all to itself, apart from the FM pointing at right angles at tacky.
Cant get tacky at all mate. Its crap on FM as it is. Sandy heath is the only other option, and that's definitely on the edge. Trouble with freesat is the number of receivers I would need. we have 7 TVS here. In fact I have ten distribution outputs in all .. getting satellite to them all would be tricky.,
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