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TV Signal breaking up |
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#1 |
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Inactive Member
Join Date: Dec 2010
Posts: 17,902
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TV Signal breaking up
Recently noticed on some TV programmes recorded to my PVR parts of the signal have been 'breaking up'.
The PVR itself is a Humax Foxsat T2 new this year and the TV is fine, so i'm thinking the problem is at the aerial end. I have this type of aerial which is mast mounted outdoor on the roof; http://www.ebay.co.uk/itm/Mercury-12...item1e89e9c0fd The aerial is now 20 years old as will be the cable also. I thought about renewing the cable and seeing if that helps, but i also notice many of the more recent TV aerials are now like this; http://www.ebay.co.uk/itm/SLx-27884D...item5b063d6ded Is my 20 year old aerial simply a duffer and am i better off replacing with a new one similar to the above......or would just renewing the cable solve the problem? |
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#2 |
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Forum Member
Join Date: Oct 2004
Location: Buckingham
Posts: 28,534
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Which channels are having problems?
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#3 |
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Forum Member
Join Date: May 2004
Location: Reading
Posts: 27,884
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Quote:
Recently noticed on some TV programmes recorded to my PVR parts of the signal have been 'breaking up'.
The PVR itself is a Humax Foxsat T2 new this year and the TV is fine, so i'm thinking the problem is at the aerial end. I have this type of aerial which is mast mounted outdoor on the roof; http://www.ebay.co.uk/itm/Mercury-12...item1e89e9c0fd The aerial is now 20 years old as will be the cable also. I thought about renewing the cable and seeing if that helps, but i also notice many of the more recent TV aerials are now like this; http://www.ebay.co.uk/itm/SLx-27884D...item5b063d6ded Is my 20 year old aerial simply a duffer and am i better off replacing with a new one similar to the above......or would just renewing the cable solve the problem? ![]() If the aerial was cream crackered the TV as well as the Humax would be having problems - assuming they are both connected to the same aerial and you use the Freeview on the telly. It is possible for the signal to be marginal and for the TV to handle weak signals better than the Humax, though I've found my Fox-T2 has handled poor signals better than my TV usually. You should be able to determine if it is poor signal by looking at what signal strength the Humax gives for the affected channels. Anything above 40% should be OK, below 30% and you might have problems. Checking the cable and aerial would certainly be worthwhile. It is always possible the aerial has shifted position or rain has got into the terminal block causing corrosion. Similarly breaks in the cable insulation can let in the rain and degrade performance. Oh and despite what that eBay ad says there ain't no such animal as a "digital Freeview aerial" ![]() And another thing - one thing that pops up on DS from time to time is interference between HDMI and aerial cables. If you are using HDMI on the Humax try physically separating the leads and see if that helps. Some cheap and nasty leads are not as well screened as some so let in more garbage. Particularly some RF leads I've come across. |
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#4 |
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Forum Member
Join Date: Oct 2007
Posts: 5,007
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The first aerial you linked to is an 18 element yagi which has a typical gain of 14 to 15dB. If in good condition there is no reason to replace it.
The second one is a bunch of lies. It is not 48 element, no one makes 48 element aerials. It's a 12 element quad director aerial with probably less gain than the yagi. Someone has counted the elements 4 times. It will have more windage though and will be very lucky to last 20 years like the old one. Another lie is calling it a "digital" aerial. Aerials are actually analogue devices even when receiving digital signals. I would also question calling it a Freeview aerial as it will receive anything in its frequency range not just Freeview. |
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#5 |
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Inactive Member
Join Date: Dec 2010
Posts: 17,902
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Quote:
Which channels are having problems?
Quote:
I assume that as you have linked to a UHF aerial you actually have a Fox-T2 as a Foxsat is a satellite receiver so connecting it to a UHF aerial would be a bit of a waste of time
![]() Reason i got mixed up was i used to have that then flogged it to go to the T2 before it disappeared as 1)use Freeview more and 2)USB port enabling offloading which isn't on current model PVR's now (they don't like people saving stuff!!). Quote:
If the aerial was cream crackered the TV as well as the Humax would be having problems - assuming they are both connected to the same aerial and you use the Freeview on the telly.
It is possible for the signal to be marginal and for the TV to handle weak signals better than the Humax, though I've found my Fox-T2 has handled poor signals better than my TV usually. You should be able to determine if it is poor signal by looking at what signal strength the Humax gives for the affected channels. Anything above 40% should be OK, below 30% and you might have problems. Checking the cable and aerial would certainly be worthwhile. It is always possible the aerial has shifted position or rain has got into the terminal block causing corrosion. Similarly breaks in the cable insulation can let in the rain and degrade performance. Oh and despite what that eBay ad says there ain't no such animal as a "digital Freeview aerial" ![]() And another thing - one thing that pops up on DS from time to time is interference between HDMI and aerial cables. If you are using HDMI on the Humax try physically separating the leads and see if that helps. Some cheap and nasty leads are not as well screened as some so let in more garbage. Particularly some RF leads I've come across. Aerial condition appears ok but haven't been up on the roof.....just viewed from the ground. All the elements are there but without getting up on the roof i don't know if the connections are a bit dodgy. Maybe would be a good idea to replace the cable with new just as a belts 'n braces job? Quote:
The first aerial you linked to is an 18 element yagi which has a typical gain of 14 to 15dB. If in good condition there is no reason to replace it.
The second one is a bunch of lies. It is not 48 element, no one makes 48 element aerials. It's a 12 element quad director aerial with probably less gain than the yagi. Someone has counted the elements 4 times. It will have more windage though and will be very lucky to last 20 years like the old one. Another lie is calling it a "digital" aerial. Aerials are actually analogue devices even when receiving digital signals. I would also question calling it a Freeview aerial as it will receive anything in its frequency range not just Freeview. |
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#6 |
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Forum Member
Join Date: Apr 2006
Location: North Derbyshire
Posts: 41,774
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Quote:
The first aerial you linked to is an 18 element yagi which has a typical gain of 14 to 15dB. If in good condition there is no reason to replace it.
The second one is a bunch of lies. It is not 48 element, no one makes 48 element aerials. It's a 12 element quad director aerial with probably less gain than the yagi. Someone has counted the elements 4 times. Admittedly it's not a plain yagi with 48 elements, BUT the improved design of such aerials gives better gain and performance than a plain yagi. Going back to the 1960's fitting Antiferance TC-18's resulted in unwatchable pictures, fitting a J-Beam MBM-46 resulted in perfectly acceptable pictures - the difference in fringe areas is HUGE. The same applied to the later Antiferance XG-21's etc. |
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#7 |
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Forum Member
Join Date: Dec 2008
Posts: 2,494
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One further point about aerials, is tuning.
Unless it changed at digital switch over to a nationwide standard, different transmitters have transmissions in different bandwidths therefore it's not just the gain you need to look at but at what channel band the aerial is tuned for. eg It's no good getting an aerial tuned for channels 21-37 (Group A), if in your area Freeview is on channels 48-68 (Group C/D), as you will have a much lower gain at the channels your on. A wide band aerial gets around this but has a lower gain. It's also worth noting the reception quality of the area you're in as that dictates the amount of gain needed and you can have too much gain as well as too little. |
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#8 |
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Forum Member
Join Date: Dec 2011
Posts: 1,039
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White-Knight
You are making a good point there. In my area what you saying is the case. I had a Group A aerial, a 2 metre long one, left by the previous house owner, and it cuts off above about Ch 40 anything above that and it operates more as an attenuator than an aerial. Thus several multiplexes are missing completely. Essentially it's totally useless now. I got a much lower gain wideband aerial now and it performs well across the whole range of multiplex frequencies. It is much shorter as well. This may or may not apply to the OPs area. It needs looking into before making assumptions. |
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#9 |
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Forum Member
Join Date: Oct 2007
Posts: 5,007
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Quote:
While I agree about no need to replace the existing aerial (unless it's faulty), I would disagree with the rest of your post.
Admittedly it's not a plain yagi with 48 elements, BUT the improved design of such aerials gives better gain and performance than a plain yagi. Going back to the 1960's fitting Antiferance TC-18's resulted in unwatchable pictures, fitting a J-Beam MBM-46 resulted in perfectly acceptable pictures - the difference in fringe areas is HUGE. The same applied to the later Antiferance XG-21's etc. Conventional yagis are still available, it's just that the DIY sheds, Screwfix etc don't seem to sell them. |
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#10 |
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Forum Member
Join Date: Apr 2006
Location: North Derbyshire
Posts: 41,774
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Quote:
MBM-46 and XG21's were available in grouped versions. These modern aerials are mostly wideband with lower gain. Interesting that these modern quad director aerials are never used in professional applications, PMR etc.
![]() As for PMR etc. they are used as and when they are required, but as you're normally designing the system from scratch (and it almost always needs to be omnidirectional anyway) you design it accordingly, with good signal strengths. Quote:
Conventional yagis are still available, it's just that the DIY sheds, Screwfix etc don't seem to sell them. ![]() Standard yagi's are still easily available, both channelised and wide band. Gain of course isn't as low as it used to be, as the bandwidth has been reduced (increasing gain) due to the band reductions. |
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#11 |
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Forum Member
Join Date: Dec 2008
Posts: 2,494
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Quote:
As they only stock a very limited range, it makes sense to stock what gives them the best profit, and 'fits all occasions'
![]() Standard yagi's are still easily available, both channelised and wide band. Gain of course isn't as low as it used to be, as the bandwidth has been reduced (increasing gain) due to the band reductions. Some retailers I've spoken to have said they don't work well in the UK. Yet others swear by them - they're very high gain and I've viewed Freeview on one in a holiday cottage we went to for 2 weeks, and whereas I can't vouch for the technicalities as I don't know the strength in the area, although I believe it to be weak from talking to the cottage's owner, the picture from a consumer pov was fine. Looks like a very clever design to me a wideband yagi - with 3 yagis on the 1 reflector. DAT 75 for anyone who doesn't know what I'm talking about here: http://www.tlc-direct.co.uk/Images/P..._3/MXDAT75.JPG I was going to install one before I decided to go Freesat instead as there's an additional reception element you can add -The Boss, (I think you now choose it either with or without at the point of purchase rather than as an add on like it used to be), and with that gain is up to 31dB with 19dB in passive mode without. |
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#12 |
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Forum Member
Join Date: Apr 2006
Location: North Derbyshire
Posts: 41,774
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Quote:
Televes DAT's still cause a lot of controversy.
Some retailers I've spoken to have said they don't work well in the UK. Yet others swear by them - they're very high gain and I've viewed Freeview on one in a holiday cottage we went to for 2 weeks, and whereas I can't vouch for the technicalities as I don't know the strength in the area, although I believe it to be weak from talking to the cottage's owner, the picture from a consumer pov was fine. Looks like a very clever design to me - 3 yagis on the 1 reflector. I'm also suspicious of the relevant performances on vertical polarised transmitters (as most in the UK are vertical).But as with any aerial, gain comes from directionality - the higher the gain, the more accurately it has to be aligned (with dishes been the extreme example). I don't see how been in the UK makes any difference though, an aerial is an aerial
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#13 |
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Forum Member
Join Date: Oct 2007
Posts: 5,007
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Quote:
Televes DAT's still cause a lot of controversy.
Some retailers I've spoken to have said they don't work well in the UK. Yet others swear by them - they're very high gain and I've viewed Freeview on one in a holiday cottage we went to for 2 weeks, and whereas I can't vouch for the technicalities as I don't know the strength in the area, although I believe it to be weak from talking to the cottage's owner, the picture from a consumer pov was fine. Looks like a very clever design to me a wideband yagi - with 3 yagis on the 1 reflector. DAT 75 for anyone who doesn't know what I'm talking about here: http://www.tlc-direct.co.uk/Images/P..._3/MXDAT75.JPG I was going to install one before I decided to go Freesat instead as there's an additional reception element you can add -The Boss, (I think you now choose it either with or without at the point of purchase rather than as an add on like it used to be), and with that gain is up to 31dB with 19dB in passive mode without. |
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#14 |
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Forum Member
Join Date: Jun 2003
Location: Cheshire
Posts: 6,447
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This from the TLC site that was in White-Knight's link: Quote:
Televes I've used a tri-boom like this just once. It was on a job about 6 years ago. I showed the client a Log Periodic but he insisted on a "good" aerial, by which he meant just 'big'. It worked well enough, but like most Yagis it favours signals in the upper end of the frequency band. Televes don't seem to publish a gain curve for the aerial; or not one that I've found on a quick browse of their page for this aerial. DAT HD BOSS 790 Digital Aerial The Architecture of DAT HD antenna guarantees the RF characteristics in the UHF band. Based on the same concept DAT HD BOSS 790 is designed to optimize the performance of DTT reception in an environment with high 4G signals in UHF channels 61-69. For this, electrical parameters of BOSStech technology has been optimized. The DAT HD BOSS 790 has mechanical features that allow the folding of the structure and a fast tool-less securing system for the reflectors. High density mechanical design for optimal storage and shipment. When the BOSSTech device (located in its junction box) is powered (active antenna), it works automatically adjusting the level of the received signal to an optimum value, this is: if the incoming level is low, the device raises the level at its output; and on the contrary, if the incoming level is too high, decreases the level at its output. In other words, it is an intelligent device that self regulates the output level of the antenna to an optimum level. When the device is not powered (passive antenna) is completely transparent to the signal path. Do not worry about signal strength, just align the antenna and the Boss-Tech device will work for you. Made of aluminium for long life. F connector junction box Personally I think they're a bit of a gimmick. Normally with high gain Yagis the optimum gain is only achieved in a narrow frequency band towards the upper end of the frequency range. That's great if your local transmitter works at those frequencies, but less so if it doesn't. For example, if used for Crystal Palace where the muxes are at the bottom end of the frequency range the tri-boom would probably be outperformed by a simple Log Periodic with a small masthead amp. My own local transmitter is Winter Hill. That used to have the channels grouped at the upper end. But gradually they''ve been shuffled to the lower and mid regions. The plan from 2019 is for them all to be from C22 to C45. That will make high gain wideband aerials a poor aerial choice. I can see the appeal of the DAT HD 790 with the BOSS module. Big peak figures, a brutish "look at me" product, and the idea of some magic wizard gain amp that's supposed sort out the signal even if the DIY'er cocks up the install. What's not to like from an amateur's point of view? But it's really just a case of dumbing down. It's a bit of a laugh seeing the houses where the owners installed these. Massive "sail" aerial on a weedy bracket and usually not installed at the right height. Within a year they're often pointing in the wrong direction because the breeze pulled the bracket out. Meanwhile, contract Yagis installed for 20~30+ yrs are still pointing where they should. |
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#15 |
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Forum Member
Join Date: May 2005
Location: Redditch Worcs
Posts: 17,287
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Gain curves
http://aerialtests.weebly.com/dat75.html I have one - it was used pre-dso to get Sutton Coldfield (trees in the way) . Now use log40 in loft on Lark Stoke. |
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#16 |
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Forum Member
Join Date: Jun 2003
Location: Cheshire
Posts: 6,447
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Quote:
Recently noticed on some TV programmes recorded to my PVR parts of the signal have been 'breaking up'.
The PVR itself is a Humax Foxsat T2 new this year and the TV is fine, so i'm thinking the problem is at the aerial end. I have this type of aerial which is mast mounted outdoor on the roof; http://www.ebay.co.uk/itm/Mercury-12...item1e89e9c0fd The aerial is now 20 years old as will be the cable also. I thought about renewing the cable and seeing if that helps, but i also notice many of the more recent TV aerials are now like this; http://www.ebay.co.uk/itm/SLx-27884D...item5b063d6ded Is my 20 year old aerial simply a duffer and am i better off replacing with a new one similar to the above......or would just renewing the cable solve the problem? If Ch5 is breaking up then check out the other channels in the same mux group; PSB2 D3+4 carries ITV, Ch4 , Film4, ITV2, E4, More4 and some +1 channels. They should be similarly affected. Others here have touched on some of the causes of signal loss in general. To add to that, we've gone through 15+ years of channel jigging, first when analogue and digital co-existed. Then later at DSO, and then further reordering of the channel allocations to make way for new services and the 4G sell off of Ch61~68. There's more disruption planned too as successive Governments look to plunder the channel band for more telecoms sell-offs. The upshot of all of this is that aerials that were once well suited for local reception conditions are now "out of band". This applies as much to wideband aerials as it does to ones that are tuned to a narrower frequency range. So whilst aerials and cables deteriorate over time there's also a case of shifting goal posts as the channels have been repositioned. Aerials such as the SLx are a poor "blind" choice for that reason, and also because of the build quality. If there is such a thing as a universal aerial, then a DM Log Periodic comes about closest. One of those combined with a small masthead amp if required will see you through the reallocation of the channel groups and give equally good reception across the broadest range of transmission frequencies. Combine that with some WF100 cable and you'll be back in business. |
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#17 |
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Forum Member
Join Date: Jun 2003
Location: Cheshire
Posts: 6,447
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Quote:
Gain curves
http://aerialtests.weebly.com/dat75.html I have one - it was used pre-dso to get Sutton Coldfield (trees in the way) . Now use log40 in loft on Lark Stoke. |
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#18 |
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Forum Member
Join Date: May 2005
Location: Redditch Worcs
Posts: 17,287
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Quote:
That's handy, thanks. Still haven't seen an official curve from Televes though.
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#19 |
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Forum Member
Join Date: Jun 2003
Location: Cheshire
Posts: 6,447
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Any idea how much signal you were losing through the trees? FiL has same problem but isn't local to me so I can't get to site easily to meter. He is on satellite at the mo but considering going to Freeview. Thanks
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#20 |
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Forum Member
Join Date: May 2005
Location: Redditch Worcs
Posts: 17,287
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Quote:
Any idea how much signal you were losing through the trees? FiL has same problem but isn't local to me so I can't get to site easily to meter. He is on satellite at the mo but considering going to Freeview. Thanks
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#21 |
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Forum Member
Join Date: Dec 2008
Posts: 2,494
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@OP, Trees are even worse with digital terrestrial apparently.
If you're faced with trees, I'd consider sat if you can mount it to get a view over, which usually can be done given that sat dishes receive signals from above at an acute angle not straight out horizontally. |
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#22 |
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Forum Member
Join Date: Dec 2008
Posts: 2,494
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Quote:
Gain curves
http://aerialtests.weebly.com/dat75.html I have one - it was used pre-dso to get Sutton Coldfield (trees in the way) . Now use log40 in loft on Lark Stoke. It appears that if you're in a weak area, even the non Boss Aerial has significant gains (bearing in mind 1dB is a ten fold gain ie 8dB is 10 times stronger signal than 7dB). If you were to add the Boss version and around another 10dB or more, than would be maybe 19dB more than the log at the high end of the bandwidth. I know they used to sell a mounting kit for these for vertical polarisation btw. From Televes: http://www.televes.com/imagenfaqs/dat75bn.jpg The only caveat I ever had for the Dat 75 was my area is subject to very strong winds and obviously there's a lot to catch the wind with one of these.. However mounted properly in a more sheltered area in a weak reception area, I would think it's a good aerial to use. |
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#23 |
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Forum Member
Join Date: Apr 2006
Location: North Derbyshire
Posts: 41,774
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Quote:
(bearing in mind 1dB is a ten fold gain ie 8dB is 10 times stronger signal than 7dB). If you were to add the Boss version and around another 10dB or more, than would be maybe 19dB more than the log at the high end of the bandwidth.
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#24 |
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Forum Member
Join Date: Mar 2003
Location: S.West England.
Posts: 18,031
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Quote:
That's interesting Graham, thanks.
It appears that if you're in a weak area, even the non Boss Aerial has significant gains (bearing in mind 1dB is a ten fold gain ie 8dB is 10 times stronger signal than 7dB). If you were to add the Boss version and around another 10dB or more, than would be maybe 19dB more than the log at the high end of the bandwidth. I know they used to sell a mounting kit for these for vertical polarisation btw. From Televes: http://www.televes.com/imagenfaqs/dat75bn.jpg The only caveat I ever had for the Dat 75 was my area is subject to very strong winds and obviously there's a lot to catch the wind with one of these.. However mounted properly in a more sheltered area in a weak reception area, I would think it's a good aerial to use. Some of us did have such massive installations to get the pre-switchover freeview, but tbh have replaced it with a smaller low install for the digital relay since switchover for peace of mind. The changed service since switchover also meant our large installation was getting conflicting signals that made reception worse than before! We supplement our freeview lite service with freesat. Most people here have had sky for years (even before switchover) while since switchover even more have it while a significant number have opted for freesat. No cable tv option. |
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#25 |
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Forum Member
Join Date: Oct 2007
Posts: 5,007
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Quote:
Hm, so it appears that their quote of 19dB gain for the non Boss version is a lie.It also spears Boss is an amplifier with AGC. Must make alignment difficult if the strength does not change as you move the aerial. There are DAT75 look alikes around as well. Wonder how they compare. |
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