All posts by Dave Lindsay
Below are all of Dave Lindsay's postings, with the most recent are at the bottom of the page.
Steve e Boy: A directional aerial focuses signal in one direction. The "gain" is simply that with respect to an omni-directional antenna (or a, theoretical, isotropic antenna [dBi], but let's not go there). Gain is at the expense of "loss" in other directions.
So it is not the case that an omni-directional aerial is better, per se.
However, all TV signals come from one transmitting station and therefore one direction. Hence it is good practice to use a directional aerial as your aerial will be less sensitive. As a caravan goes to different locations, signal levels can vary.
See here for information:
TV Aerials for Boats and Caravans
The aerial shown in that link is a Blake DML26WB (other suppliers are available) and it is especially suited to touring for a number of reasons. Firstly, it is a log periodic which has roughly the same level of gain across all frequencies (yagis aren't as good on lower frequencies/channels). The elements are flat which should make them more rugged; most other logs have round elements. It has a bracket that allows it to be set on an incline which might help in some situations.
Use double-screened cable with a pure copper core (not clad copper) and copper foil with copper braiding such as Webro WF100.
Also have a variable amplifier to hand. This won't always be needed, but it may be useful in some locations.
It would also be useful to have a filter to protect against interference from 4G base stations which will come on the air in the next quarter. This might as well be fitted permanently and before any amplifier.
Your original question pertained to potential 800MHz 4G interference, but this depends on a variety of factors including where the 4G signal is coming from, how sensitive your aerial is in that direction and how strong the TV signal is to how strong the 4G signal is. The way to protect yourself is to install a filter and use good screened cable.
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Steve e Boy: I've had a look at the Status 550 aerial, you mention:
The NEW Status 550 Directional TV / Radio Antenna System | Status Antennas
It's a log, so that's good. However, a few things spring to mind:
The frequency range is given in the instructions as FM (88 to 108MHz), DAB (175 to 230MHz) and UHF (470 to 860MHz). So, as perhaps is to be expected, the 800MHz band that is to be used for 4G is part of its spec and will need filtering.
The fact that the aerial is designed to pick up FM, DAB and TV means that these frequencies are passed down the aerial lead (before being split within the amp). This could affect the type of filter you can use.
The filter needs fitting before the amplifier as the 4G signal can have an adverse effect on it. However, if you fit a filter that only allows through the frequencies for TV, it will prevent FM and DAB signals being passed.
As an example, see here:
UHF Bandpass filters, amplifiers for terrestrial TV
The filter seen in the photograph is a SAC AE5100 which says on its body that its pass-band (that is the frequencies it lets through) is 470 to 790 MHz. Obviously that will inhibit FM and DAB.
I'm not a professional, so don't know whether such filters are available that will pass FM, DAB, UHF TV (21 to 60) whilst blocking 800MHz 4G (UHF channels 61 to 69). If there is, then it will allow the aerial to be used for FM and DAB whilst being protected against potential interference from future 4G.
It may be worth contacting the manufacturer to see what it intends to do. Maybe it will produce a filter.
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The more 4G phones come into service the more the possibility of interference from them in close proximity to your receiver. The thing is that you won't know what is the cause if it is outside and it will be intermittent.
Ideally, aerial amplifiers should have 800MHz filters built-in, but this will be down to the manufacturers.
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Steve Flynn: Interestingly, Hannington's four former analogue channels were not within a single third of the band Group, but semi-wideband Group E so I guess this might be how come your aerial is an E.
I'm not a professional, so can only give you theory. Here are some example gain curves:
Gain (curves), Again
An aerial's gain is simply at the expense of "loss" in other directions. So a higher gain aerial focuses the signal into a narrower beam. The gain of yagi aerials drops off on lower channels hence they are less directional on lower channels than on higher ones.
However, your amplifier will increase the amplitude of the signals. Getting a higher gain aerial doesn't necessarily improve matters as it has a narrower acceptance angle. As you are trying to pick it up at the bottom of a drop, having your aerial receiving on a finer beam isn't necessarily a better thing because the quality may suffer. You can increase the amplitude of a signal with an amplifier, but if you don't have the quality (digits in order) then you might as well pack up. See:
Television Aerial Boosters / Amplifiers, Splitters, Diplexers & Triplexers
What sort of reception of the Hannington COM channels do you get? If it is poor at times, is it strong but poor quality?
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Dee : Some transmitters only carry the Public Service (PSB) channels which means that a small proportion of the population can only receive those channels.
It is down to the fact that the Commercial (COM) networks can pick and choose which sites they wish to transmit from. Being run for profit they pick the most lucrative. See here for an explanation:
Londonderry (Northern Ireland) digital TV transmitter | ukfree.tv - 10 years of independent, free digital TV advice
On the basis that you had to retune, we know that the transmitter you are using at your new address is not the same as that at your old one. At your old address it appears you would have been using Crystal Palace whereas a lot of the aerials in your new locality are directed to the Hertford relay transmitter, which is on the Bengeo Water Tower. This is one of the transmitters that only carries PSB channels.
Unless you can receive from a full-service transmitter then you won't be able to receive the Commercial (COM) channels which are those that you are now without.
I looked on Streetview (photos taken before switchover in April 2009) and spotted one Crystal Palace-facing aerial, so you might be in luck, particularly as the signal is now stronger after switchover. It might be worth having a look around to see whether others have Crystal Palace aerials - they will be facing south and horizontal (elements flat).
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Mike: ITV from Waltham is on C54 (737.8MHz).
The other alternative is to have the aerial unplugged for lower channels which will prevent it from finding the East Yorks & Lincs signal from Belmont. Get the aerial in at about 50% or C45.
Once you've done this, go to the manual function and add C29 (538MHz) which is COM4 (ITV3 etc) from Waltham.
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James: How many conservation areas is there a dense spread of population which would require a number of mobile base stations to cover them?
How many conservation areas allow installation of odious mobile phone masts?
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Couch Spud: It will change channel and therefore you will need to do a full retune. The same goes for PSB1 which carries BBC standard definition TV and BBC radio.
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Idris Martin: Because different frequencies are affected by objects in the path to differing degrees. Different frequencies radiate slightly differently from the transmitter.
You have a quality issue. The fact that it is OK on a sunny day suggests that there is vegetation somewhere in the path.
The terrain plot shows that the Purbeck Hills are in the way and so you have no where near line of sight. For that reason I think that a high-gain aerial is likely not to be the best device.
The higher the gain, the narrower the acceptance "beam". As you aren't anywhere near line of sight, you don't have anything to aim at. Rather, your objective is to pick up what you can.
As digital reception requires good quality (digits intact) a wider acceptance angle could perhaps give better results. It stands to reason that if the quality of the signal across a wider angle is better than across a narrower one then reception is better, even though a lower gain aerial has been used. You can increase the signal strength with an amplifier, but you can't repair its quality.
If it is a wideband high-gain aerial then it isn't "high" gain on the channels you are trying to receive as the gain of wideband yagi aerials drops off on lower channels.
As you have no where near line of sight then it might be worth trying turning the aerial a bit to see if it improves it.
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Wednesday 13 February 2013 9:50AM
Steve Flynn: At switchover we had a posting from someone off Grayswood Road who had lost access to Haslemere transmitter and therefore BBC South/ITV Meridian programming because of this. Understandably he wasn't happy because he wanted these regional services rather than the London ones. His location was on the fringes of the Haslemere transmitter and, evidently, its signal is no match at that location for Crystal Palace's.