FAO: Aerial experts

[Mr_WhiteUK]

Hi there, I'm pondering whether or not to install a new aerial, the old one is a bit decrepit, it can't pick up channel 5, the rest of the channels are ok, but I think they could be better.

The cabling and connectors are old and had it, and it's not a very good install by who ever did it.

It goes into the wall, into the bedroom, where the cable has a connector on it, then there is a hole drilled through the floor and ceiling of the living room, with another cable going through that, and a connector on both ends, which is then connected to the cable in the bedroom using blu-tac since the connectors that end have had it, and they decided to just use blu-tac instead of fixing them.

I'm 32 miles from the Sandy Heath, pointing south west, and I don't really think the current aerial is up to it.

So I'm going to install a Dat 75, in the hope it'll be able to pickup freeview.

Now here is the question.

I need the Dat 75, the installation kit (6ft pole, 9 inch wall bracket, bolts, plugs, V bolts, cable, clips & coax plug) and there is another thing which I'm not sure if I need or not, which is the Televes DAT45/75 Margin Rising Device.

Which is a signal amplifier, yes?

Would I need this, and if so, which power supply would I need?

Televes Power Supply Unit (Twin) ?

I found the Dat 75 manual, and it looks like the margin rising device plugs into the normal output on the Dat 75, then you plug your cable into the output of the margin rising device, into the house, which then goes into the psu, and then the output comes out of the PSU, correct?

Now the question is, do I need a margin rising device?

And also, what connectors will i need?

What socket is on the aerial/margin rising device, female?

So I'd need a male to plug into that, male on the other end to plug into the PSU, then another male to male cable to plug from the PSU into the TV, correct?

Also, I found a guide on how to fit a connector, since I've never been very successful at doing so

http://www.satcure.co.uk/tech/fconn.htm

http://www.satcure.co.uk/tech/plugs.htm (Half way down the page)

Do they look ok to you guys? and am I correct in thinking that the braided copper is just flat against the outside of the cable and just touching the connector?

Which connectors will I need? there is one of these http://www.tvaerials.com/product.asp...id=75&product= included with the installation kit, will I need another one to connect to the PSU, since it says it has F connectors, and then one of these http://www.tvaerials.com/product.aspx?productid=673 to connect from the PSU to the TV?


Help will be appreciated, thanks

[HeadBanger]

I have installed the DAT75 with the MRD so can answer some of your questions but first of all you need to determine what sort of aerial you need from http://www.wolfbane.com/cgi-bin/tvd.exe? here for digital and/or
http://www.wolfbane.com/cgi-bin/tva.exe? for analogue. These will tell you your signal strength in dBuv and what type of aerial you need.

If you over amplify an already good signal you can cause the tuners (analogue and digital) to overload. The general rule of thumb is to ensure that you don’t end up with more than 80dBuv of analogue signal (at TV / freeview box) and aim for 75dBuv. An analogue signal that is too strong will cause digital to breakup regardless of the digital signal’s strength and interference (herringbone haze) on analogue. When calculating the signal at the TV you will also need to include signal loss from the cable. Take -0.2dBuv per metre of coaxial cable you have run (so 10m cable would equate to -2dBuv of signal loss).

Regarding the DAT75; it is very high gain (approx 12.5dBuv at UHF channel 21 rising to a max of 18.8dBuv at channel 67) wideband aerial (i.e. it receives all UHF channels 21-69). The MRD just clicks in the DAT (12v supply reqd) and will give a further gain of 12-13dBuv over all frequencies so the overall gain will be +31.8dBuv at channel 67. This combination is only needed where the signals are extremely weak and wideband reception is also needed. However, you may not even need a wideband aerial so you need to check this first (along with the predicted signal strengths). If you re-post with your results we can help you further.

[Mr_WhiteUK]

Thanks for the help, here are the results:

Digital:


Analogue:



Like I said, I'm 32 miles (33 according to that site) from sandy heath, and the traditional freeview websites say I can't even get one channel, which is why I looked at the Dat 75.

I should be able to get freeview with that, since I'm within the range of the transmitter, and I'm not sure what obstacles are in the way, so for the money I thought I might as well look at the Dat 75, since I think I'm far away enough to use it?

Thanks again for the help

[HeadBanger]

OK so you need group A (channels 21-37) for analogue and E (channels 35-68) for digital so if you intend to watch both analogue and digital then you do indeed need a wideband aerial. Using the DAT75 with MRD will give you a digital signal of:

Est signal 31 dBuv
DAT75 gain 18.8 dBuv (estimated max at channel 67)
MRD gain 13 dBuv
Cable loss (2 dBuv) (for an estimated 10m)
At Freeview 60.8 dBuv

This is more than adequate and should provide you with all channels free of any breakup. However, the DAT75 with MRD may provide too much gain on analogue (which causes problems on digital) as follows:

Est signal 55 dBuv
DAT75 gain 14 dBuv (estimated max at channel 31)
MRD gain 13 dBuv
Cable loss (2 dBuv) (for an estimated 10m)
At TV/Freeview 80dBuv

You may get away with it but if you have problems with your digital reception you will need an attenuator to reduce the strength. I think the DAT75 will be overkill for your situation though. It’s also a huge, ugly beast but it is great for really poor signals (mine is just 22dBuv on digital and I get all channels + no break up with it!).

I think that the DAT45 with MRD would be a better bet as you will end up with 59dBuv on digital (still fine) and a safer 78dBuv on analogue (which still maybe too high).

Finally, make sure that you run new CT100 (or better) coaxial cable as it rejects signal interference much better than your bog standard coaxial.

Hope this helps.

[Mr_WhiteUK]

Thanks for the advice, if I did get the Dat 75 and I got too much gain, would an attenuator affect the quality at all?

Or could I just turn off the MRD?

What would happen to the freeview if I had too much analogue gain?

And would the Dat45 definitely do the job factoring in any losses from obstacles or anything like that?

And since you've fitted a 75, could you clarify how many and what connectors I need, would it be 2 F to connect the aerial to the psu and one F To male coaxial cable to connect from the PSU to the tuner?

The cable with the installation kit is this stuff, http://www.tvaerials.com/product.aspx?productid=551

Is that not good enough?

Also, someone told me you get the MRD included with the Dat 75, which would save me £13, is that true? is it included with the 45?

Thanks again

[Bearded_Malc]

I have a DAT75 with MRD too (and CT100 cable). My figures from wolfbane are 29dBuV/47dBuV. I don't have any problems with analogue but that may depend on the STB. The DAT75 is a bit of beast but impressive or am I compensating for something However, what I did do is use a wide dia pole and use 2 chimney brackets so it is held rock solid.

An attenuator should not introduce any noise since it is a passive device (ok resistors have noise but it is minimal compared with amplifiers). My DAT75 did not come with a MRD which I have to buy separately. MRD as well as being an amp also improves impulse noise immunity, hence the name.

[Mr_WhiteUK]

My chimey is too short and small too use as a mounting, and it's in the wrong place to mount the aerial.

So I have to use a wall mounting on the side of the cottage towards the front.

Do you think the stuff in this kit will be up to it?

http://www.tvaerials.com/product.aspx?productid=287

6ft x 1.25" pole and a one piece wall mount, I can always go for the Dat 45 but I will only save like a tenner if I do.

This is my basket, anything missing?

[SamRadford]

Apart from its massive size, weight and wind load, the DAT75 is also very directional, making it more difficult to align correctly. And if it's not aligned correctly, you'll get less signal. Frankly, I can't see the point in causing problems for yourself when a DAT45 will do the job perfectly well.

As for your shopping list, the 1.25" pole will not be substantial enough. A 9" bracket certainly isn't going to be large enough by itself.

I don't like cheap aluminium TV plugs - I always use nickel-plated brass.

I don't like cheap "clothes line" fly leads. Better to make up your own with spare cable and plugs.

Make sure the 'F' connectors are the correct size for your cable. Many shops try to make you believe that "one size fits all".
See notes here:
http://www.satcure.com/accs/page7.htm#fconn

Make sure the power supply can provide enough current for the Televes MRD (90mA).

Don't forget cable and wall clips.

Edit: and mast caps to prevent wind howl:
http://www.satcure.com/accs/page2a.htm#clamp

[SamRadford]

And cable ties. (Don't use PVC tape to hold the cable to the mast. It just falls off and leaves the cable flapping!)

[HeadBanger]

I’m not familiar with the Televes PSU (I power my MRD from a Triax DDU) but I would think you will need four screw on F connectors (one taking cable in [and powering MRD], two for outputting cable to your wall 2 TVs) and one F connector to connect the coaxial to the aerial. Both the aerial and the MRD may well come with these anyway.

If are going to run 2 TV’s off the PSU you are effectively splitting the signal so I think you will lose another appx 4dBuv (unless it has further an internal amp) – check what the loss is. If you only need to run one TV get a PSU with one TV out instead. I think you can buy the DAT45 with the MRD pre-fitted – not sure about the DAT75 though.

I mounted my aerial on a 12ft high by 2” wide alloy pole and used 12” wall brackets (screwed in with 6 x M10 bolts). Yes the aerial works if you disconnect the PSU but then you will lose all of the 13dBuv of gain plus you’ve then wasted £27. Better just to buy an attenuator (£5ish) if needed.

Good luck!

[Mr_WhiteUK]

Do you think the Dat 45 would do the job even considering any set backs? I'd be annoyed if I got it and it didn't perform 100% and did exactly what I want it to, considering there is only £12 difference between buying the 45 and the 75, I'd feel happier with the 75.

And would the 45 cope being split between three TVs in the future, which I may want to do.

As for the mounting, the aerial won't even have to clear the house since where it's mounted is exactly where it'll need to be pointed, according to my caclulations and looking at where all the other big aerials are pointing, so there won't be a huge amount of wind on it, plus it's only an 1850s cottage, so it's not very high, so not a huge amount of wind even clearing the roof, the aerial doesn't even weigh 5kg, a 1.25" pole has the integrity to support that, surely it's just the mountings which are important?

I can always buy a few more mountings if it shows any sign of stress.

The aluminium connectors etc are no biggy, they're just in there incase I want to connect it to other TVs in the future.

The PSU is a Televes PSU designed for use with their MRD, so I assume it has enough power.

The cables they sell all seem to be the same, so I assume the F connectors they sell will fit?

Do you think the cable supplied with the installation kit is good enough?
http://www.tvaerials.com/product.aspx?productid=551

Cheers

[Bearded_Malc]

The point I made about my chimney mounting equals applies to wall mounting. Rather than 1 mount, 6ft pole and DAT75, get 8ft pole and 2 mounts. Put the second mount 2ft below the first. The bottom of pole is now clamped totally solid and the longer poles are larger diameter giving less movement at the aerial.

[Mr_WhiteUK]

Do you think it's still necessary even on such a vertically challenged house?

Since I'll really only need -2ft of pole to get the aerial in the right poisition, I just went for that one since it works out a fair bit cheaper buying the installation kit rather than everything seperately.

If it needed more support, I would expect an extra support on the 6ft pole would do the job, since it's really not going to be exposed to the elements to the degree most aerials would be.

I hope I don't sound arrogant, but it's just that it'll be protected by the house from two directions, minimal wind from one direction, and only really be exposed in the direction it's aiming, I can literally pull my self into my upstairs bedroom window by standing on a milk crate to give you an idea of how short the house is, and there aren't any obstacles it needs to be raised above, so it's not going to be at the altitude of harsh wind.

[Bearded_Malc]

OK, fair point which I had missed. In most cases, especially with the large size of the DAT75 a firm pole is a good idea but in your case it probably doesn't matter.

Sorry to throw a spanner in the works here but if I interpolate your info on location (without hard evidence) you live somewhere near ELY??

If that is the case I installed a TV for a friend a few months ago on the north west side of Ely town. I was surprised that despite the relatively clear path, very high power and Group A analogue class of Sandy Heath that the best analogue and digital signals were actually received from Tacolneston in Norfolk.