Loft aerial upgrade

[davecooper]

I have had a backup aerial in my loft for many years due to occasional problems with the roof aerial. Currently it is a small log periodic which actually works surprisingly well although reception on some independent channels can be a bit hit and miss at times.
Anyway, I want to change this for something with better performance but which will still fit in my quite small loft. Realistically, the maximum length would be 1200mm, width about 300mm and a fairly compact reflector if it has one. Luckily, I can cradle mount it if required as my loft has cross beams at waist height.
I am in south Cumbria and use the Winter Hill transmitter which works well for my loft orientation. I have looked at a few aerials but don't know where to place most importance, ie. transmitter group, gain, directionality, front to back gain etc etc. Any advice would be welcome. This aerial will never be used outside so resistance to the elements is not an issue. Thankyou.

 

[Old Salt]

I am in a premier inn in newcastle and the signal is crap. Get a dish and freeview telly.

 

[Lucid]

I have had a backup aerial in my loft for many years due to occasional problems with the roof aerial. Currently it is a small log periodic which actually works surprisingly well although reception on some independent channels can be a bit hit and miss at times.
Anyway, I want to change this for something with better performance but which will still fit in my quite small loft. Realistically, the maximum length would be 1200mm, width about 300mm and a fairly compact reflector if it has one. Luckily, I can cradle mount it if required as my loft has cross beams at waist height.
I am in south Cumbria and use the Winter Hill transmitter which works well for my loft orientation. I have looked at a few aerials but don't know where to place most importance, ie. transmitter group, gain, directionality, front to back gain etc etc. Any advice would be welcome. This aerial will never be used outside so resistance to the elements is not an issue. Thankyou.

Your current aerial is a small Log Periodic, you said. Logs are always wideband, but how big that band is has changed over time. Originally it went from channel 21 up to channel 68. (Each channel number is a progressively higher frequency in megahertz.) The aerials have coloured markers on their ends. A ch21-68 wideband would have a black marker.

When they sold off the 800MHz range then the new TV range went from 21-60. This is known as a T Group wideband. The end marker would be black also. Then they sold off the 700MHz range, so we now have aerials going from ch21~49. These are K Group widebands. The coloured marker is white or grey.

The reason for telling you this is so you can gauge how well your aerial is doing at pulling in signal.

First, it's in a loft, so the signal has to penetrate the roof tiles and maybe even pass through an adjacent loft. When the tiles get wet they block more signal too. Second, if this is a small Log Periodic - about 12~15" / 30~40cm long rather than the 36"~54" / 1~1.3 m for a normal-sized Log - then it's going to pull in less signal. Finally, if it's covering the full 21~68 range then what signal it does pull in will be spread over a much bigger range than one of the narrower band Logs.

What all this means is that you could go for a new Log Periodic - full size - and be pretty confident you'll get more signal. Have a look at the DM Log from Aerials & TV LINK This will hit the mark for your size limits. Scroll down the page to the graphs. There's one that compares the DM Log against a mini Log. The DM Log gives you more gain right the way through the range.

If you want more gain than this then you're going to move away from wideband aerials into the narrower frequency range of the Group A aerials. It's Group A because its reception is concentrated on the bottom half of the new 21~49 frequency range. That matches the transmissions from Winter Hill now all the channel shuffling is over.

Since the aerial is focused on a much smaller frequency range, all the reception power is concentrated. This means that the aerial should have higher gain.

From the ATV site again, they have a graph for one particular aerial, but versions of it for the various band coverage ranges.

The black line is the old ch21-68 wideband. The grey line is for the smaller range of the K group aerials. You should be able to see that the grey line sits higher than the black from ch21 through to the now defunct ch53. That means more signal. In this case, about 1.5dB more.

The red line if for a Group A version of this 18-element Yagi. The 'hump' in the gain curve is a bit more pronounced. Compared to the Group K aerial, the gain advantage rises from about 0.5db through to around 3dB extra. Do bear in mind that the gain curves and predictions are for the aerials that ATV sells. They've tested ones from various manufacturers. Some were good, others mediocre or poor. The point here is that if you buy from say Screwfix or some online retailer, it's very likely that the aerials won't perform to the same standard.

For loft installations, ATV recommends its XB10A. This crossbeam (XB) aerial has a lot more gain than the DM Log, however, the reflector is going too be wide for you. It's almost 60cm wide.

 

[davecooper]

Thanks for the reply. I have had some recent correspondence with ATV with respect to an outside aerial and will be ordering a Yagi18A once I am able to fit it. I didn't want to ask them further questions about a loft aerial as it seemed a bit cheeky having not yet ordered anything from them.

Your reply however has helped no end and it would seem that I can just about accommodate a Log36 aerial, which going by the graphs would give me the best rise in gain for the aerials I can use.

 

[Harry Bloomfield]

All modern TVs have Freeview. How will a dish help without a satellite receiver?

Many modern TV's, include a built in sat receiver - three of mine include one.

 

[davecooper]

The issue is access to the roof aerial. We have a family of seagulls on the roof which become very aggressive if you get near them and as they are a protected species there is not much we can do about them at the moment. Add to that the fact that you have to get accross flat roofs which are like skating rinks given the slightest bit of moisture, getting to the aerial is not the safest of activities.

I don't want a dish as I replastered my living room last year and took the opportunity to bury coax and speaker cables in the walls. As my TV is in the middle of a wall, I don't want satellite cables showing.

 

[Old Salt]

All modern TVs have Freeview. How will a dish help without a satellite receiver?

Freesat then if your being picky

 

[Lucid]

Whether or not a better loft aerial will help we don’t really know. I would be putting my money on fixing the roof aerial.

BIB In this case I don't believe that's true.

All else being equal, we can take a pretty accurate educated guess. Where there's an existing small Log, a larger Log of equal or better quality will pull in more signal.

Read through the OP. All the clues are there.

 

[Rodders53]

Lucid has explained it all very well and there's not much I can add really.

Exactly where in South Cumbria matters a tad. The Local TV Preston mux beam uses frequency channel 40 which not in Group A. But many a group A aerial will still have enough gain for that, if you are predicted to receive it. A grouped aerial should give extra gain over a T or W wideband or even K (the new wideband for 21 - 48 UHF TV) for Winter Hill. However they are probably all too large to meet your size limitations.

If Julian has advised a Yagi 18A for outside installation then I'd be concerned a log 36 in the loft still won't have enough gain (albeit it will be a dB or two higher than currently). But if the signals are clean enough a low-gain (masthead amplifier) could be considered? It is what is done outside in marginal reception areas with suitable directional antennas. I'd consider trying one with the existing loft aerial before getting the log 36 and maybe still using it.

NB Antenna location within a loft may well need careful positioning to receive all frequencies equally well. Higher/lower crabbed left/right and fore/aft. Bits of string, fishing line and cable ties can be used to support an aerial in a loft (just nothing metallic like copper wiring).

 

[SUNRAY]

Understandable. But if you used decent coax such as WF100 you could repurpose it for satellite signals.

Unless it's a particularly long cable run, any 75Ω coax will normally be fine, I had one running on ~15m of PSF1/7 (~3mm no foil) for several years.

 

[Rodders53]

Unless it's a particularly long cable run, any 75Ω coax will normally be fine, I had one running on ~15m of PSF1/7 (~3mm no foil) for several years.

Ah the exception that proves the rule
BBC spec PSF1/7 https://www.canford.co.uk/Products/36-329_CANFORD-VCM-M-CABLE-BBC-PSF1-7-Cream was unlikely to have been intended for use at UHF TV frequencies (450-850 MHz).

With a spec stating 6dB loss per 100 metres at only 10 MHz I hate to think what its loss was at 100 MHz let alone higher! You must have had a very strong signal where it mattered not that a good chunk was lost en route via such cable. Impedance may not have been all that important, either, in that case.

The good thing about BBC spec coax was that it was a very close weave braid (95% cover in the spec) so had excellent screening, of course. Interference screening is the main reason we recommend all copper double screened RF cables are used.

In this thread's location situation with the current loft aerial working at the digital cliff edge every little counts so WF100 or similar low loss spec would be strongly advised (6dB/100m at 100 MHz, 15dB/100m at 600 MHz, and 20dB/100m at 1 GHz),

 

[Harry Bloomfield]

Unless it's a particularly long cable run, any 75Ω coax will normally be fine, I had one running on ~15m of PSF1/7 (~3mm no foil) for several years.

I ran most of our TV cables in the mid 80's, when the house had a back to brick refurb. Antenna down to loft, then on to living room, where I have a distribution amp, from where the rest of the rooms in the house are fed. I used the then standard brown cable, poorly screened, with no foil, throughout, and all indoors.

The only part to be renewed, has been the drop from the chimney, into the socket in the loft.

 

[Rodders53]

Mid-1980s brown UHF coax cable was likely pretty good quality. Stuff went downhill later on. If you have a scrap length remove some of the outer to see how well it is screen covered?.

https://www.aerialsandtv.com/knowledge/cable-connectors-and-leads/the-three-main-types-of-coax-cable Justin states

Traditionally everyone used "Low Loss CoAx" for virtually all TV (and FM radio) aerial cable and years ago much of the CoAx on the market was of pretty reasonable quality with high percentage screening cover. The vast majority of low loss Coaxial cable sold these days is absolute rubbish.

 

[davecooper]

I have just found some info on the ukfreetv website that might explain the problems I am having. The only channels I have ever had problems with are Quest and Yesterday. Reception on these is variable, getting worse in the evening. The freeview channel predictor on ukfreetv shows the optimal transmitter for these two channels as being Lancaster. However, Quest+1 is shown as Winter Hill. I checked the reception for Quest and Quest+1 today, there was no reception for Quest, perfect for Quest+1. So is this my problem?
Although my aerial is pointed at Winter Hill, is it managing to pick up some signal from Lancaster?

I was concerned about the quality of my down cable but reading the latest posts, it seems mine may not be too bad. It is 1980's brown coax and looks well screened.

 

[Rodders53]

ukfreetv is awfully out of date and was never that reliable. Ignore it.
Use the Freeview prediction tool and specify the (S)erved and (M)arginally served numbers that gives.
Those numbers will indicate if reception is predicted to be variable under certain weather conditions (or not).

Lancaster is a transmitter broadcasting all 6 multiplexes the same as Winter Hill does as a Main transmitter.
It was one of the 81 original low power DTT sites back from the turn of this Century, so some say it is a 'main transmitter' now (though MB21 suggests it is still an off air relay rather than a line-fed 'daughter' site).

Quest+1 (LCN 70) is broadcast on Ariva A --- freq ch 31 from WRH Horizontal, and f.ch 28+ from Lancaster, Vertically polarised.
Quest (LCN 12) is on Arqiva B --- f.ch 37 WRH and 22+ Lancaster.

So different frequencies and different polarisations.
The log periodic in the loft is better than most at rejecting cross-polar signal and especially signals coming from 'behind' it. Depending on where you are exactly... nearby postcode of shop, pub, church etc.,. would help confirm. So it's probably not a wrong transmitter issue? Although if Freeview predicts good Lancaster reception it may be worth pointing it that way in Vp to use it?

It's often possible to use a TV metering to display the transmitter frequency/channel info to check what is being used. How depend on TV brand often enough.

Manual tuning will ensure only the transmitter your aerial points at is tuned in (that will only be necessary if the receiver has mis-tuned)?

Your issues are all related to near digital cliff edge reception with the added unknowns of wind and rain affecting thing due to foliage between transmit and receive.