freeview uk in sandyford/leopardstown signal update

timetunnel

i'm having a hit or miss at the moment.
some days have bbc and itv muxes but after a while they start to fade.
have tried two types of aerial group A and wide band.
sometimes get channel 22,24 or 44.
i purchased a mastercare digital aerial tester. it comes preset with channels 21 -68.
the signal must be between 36 to 70 dBuV anything outside of these ranges it shows low or high.
the signal my LG television must be receiving must be below the 36.
and it gives a signal on the television display of 60% + and picture but overtime it goes.
was thinking do i need to go higher with the aerial or is there something more i could do.
open to all .
thanks timetunnel

watty

Connect two or four indentical aerials, spaced correctly, with equal length cable via "splitters" (f-connector type) used as combiners.

Or give up and get a dish.

timetunnel

its more of a hobbie , i like messing around with things.since i was a kid with the old black and white tv. i use to love trying to tune in channels from the old aerial
i have a 1.2 meter dish motorised, freesat from my old sky dish, ntl. i like having all options. it keeps my brain alive. are you around the sandyford /leopardstown area and are you receiving a good signal

watty

Then read


http://www.directivesystems.com/STACKING.htm
http://www.iw5edi.com/ham-radio/?stacked-yagi-antennas,90
and
http://www.i1wqrlinkradio.com/ccarray/click.php?id=26

Have fun.

No, I'm other side of Ireland. See here http://www.wattystuff.net/amateur/the-shack/

championc

I'm in Ballinteer. I used to have decent BBC's and ITV's from Divis but I thought my masthead amp blew so I replaced it. When I bought the new amp, I also got a new LNB for my old Lenson Heath 1m dish which I hadn't used for years so I now use it for the Beebs. I'm looking at buying a Panasonic G20B set so I'm back fixing my Aerial again and re-checking all connections because the new amp (FTE) isn't looking as good as the old one (Triax) so I'm re-checking everything.

I've a Wolsey Lacuna meter but it needs re-charging so hopefully I'll get some readings this weekend.

Are your signal strengths taken before or after the masthead amp ? I have the amp in my attic so I can check either. What signal levels should I be looking at ?


C

Timetunnel is pointed to the Blaenplwyf transmitter in Wales which may be difficult at Ballinteer.

Divis dtt is only low power now and not scheduled to go high power untill the endo of 2012.
When it does ,you will have reliable UK freeview at Ballinteer if you've had good analogue which is likely there from my knowledge of the area.
Nice bit of height and northerly unhindered aspect!

timetunnel

that's a good question from championc .
would you be better putting the meter before the master amp.
was hopeing to get on roof as soon as my wife goes jogging.
to see if i can increase signal.

championc

Spending the evening listening to Leeds match - far more important !! I purposely left my amp in the attic so I could chop and change things rather than going up on the roof. So cable comes straight from my Triax 100 into the attic


C

yes use the meter at roof level before any amp-just the meter to the aerial on a short cable untill peaked.

Blaen and preseli should be very strong today ahead of an advancing weather front.So be aware of that.

championc

What db level is needed for a good signal and what would the max noise levels be ? I got an FTE Amplifier which has 3 amp settings - 26, 33 or 40 db's


C

championc

Does anyone know what could affect the display of UTV on ch 24 from Divis. I can see C4, BBC2 and BBC1 and according to my signal meter, the signal strength for UTV is comparable to the other channels but I get nothing on screen.


C

watty

use lowest setting that makes little difference. The higher settings are to drive longer coax.

too high a setting will overload either the TV tuner or the amplifier

championc

Thanks Watty

What signal in db's should be I expecting before the masthead amp. I seem to be getting low 20's


C

mullingar

watty wrote: »

Then read


http://www.directivesystems.com/STACKING.htm
http://www.iw5edi.com/ham-radio/?stacked-yagi-antennas,90
and
http://www.i1wqrlinkradio.com/ccarray/click.php?id=26

Have fun.

No, I'm other side of Ireland. See here http://www.wattystuff.net/amateur/the-shack/

Good links watty, but more designed for Ham Radio stuff.

Do you have any other good links on stacking Group A (orB) Yagi UHF aerials?

The best I found for UHF stacking are these:

http://www.atechfabrication.com/reception_solutions.htm

http://www.bobmerritt.com/dtv/dtv.htm


Televes also make a mast mounted stacking combiner/amplifier thingy, Televes 5006

www.televes.com/hojastecnicas/103758.pdf

watty

The "rules" in terms of spacing are the same.

take centre frequency.. say 600MHz,
so wavelength in m = 300/600 = 0.5m

You can simply scale dimensions for 144MHz or 430MHz to 600MHz.

Assuming Horizontal polarisation
(Rotate assembly by 90 degrees for vertical)
Anyhow if we take as rule of thumb that closest distance in vertical is 1 wave length and in horizontal it's 25% more then

vertical space is 0.5m and horizontal is 0.62m
More spacing may increase gain, change bandwidth and side lobes

The old rule was to stack at 2/3rds of the boom length.
A group A SR18 is 1.9m long. 2/3rds is 1.2m

This will give largest gain (3dB max).

You need two poles maximum about 1.5m long. Space these on your mast pole at maximum of 1.2m - (2 x height of aerial bracket).
Mount two aerials upright from top cross bar and two aerials hanging down from lower cross bar such as spacing of actual aerial booms is 1.2m
use shelly clamps.


Horizontal polarized

Aerial 1<-----1.5m -----> Aerial 2
                |     ^
		|     1.2m
		|     
		|     v
Aerial 3<-----1.5m -----> Aerial 4

Note the two poles are NOT 1.2m apart as the mounts of the aerials add about 15cm x2 = 0.3m

You can then experiment with adjusting spacing which makes a huge difference to side-lobe pickup. Minimum of 0.5m vertical and 0.62m horiozontal

If the aerials are vertically polarised then you can mount the aerials directly to cross poles spaced 1.5m apart on the mast and the aerials 1.2m apart on poles.

All coax must be same length, multiple of 1/4 wave is good.

Use three high quality exterior F-connector splitters as combiners:
Combiner A
1__
2__> ---1+2

Combiner B
3__
4__> ---3+4

Combiner C
1+2__
3+4__>--- 1+2+3+4

mullingar

^^ Great post;)

Interesting about the old rule of thumb, but I found this link:

http://pages.cthome.net/fmdx/stackant.htm

For optimum -performance, stacked antennas must be properly spaced. If you do not space vertically and horizontally stacked antennas more than ½ wavelength apart, they will adversely load each other. Loading is caused by the elements of one antenna re-radiating some of their received energy into the element of the other antenna, with consequent reinforcement and cancellation of fields and voltages. 0ptimum and minimum spacing is 0.94 and 0.60 wavelength, respectively, at the lowest frequency received. Spacing exceeding one wavelength reduces the performance of the stack.

Im sure it would make a lot more sense to you who is obviously a fanatic on the subject, what do you think?

The link is suggesting that the distance between the aerials should be (for Group A from NI) channel 21 = 470Mhz = 638mm x .94 = 599mm between aerials

watty

You must NOT space them LESS than a certain amount or they load/detune each other.

Think about it. Aerials on two nearby chimineys will have same signal if one or other aerial is removed. The issue is to add the signals in phase.

If you do not space vertically and horizontally stacked antennas more than ½ wavelength apart, they will adversely load each other

Too close and you detune and lose gain.
Too far and phase match is harder and side lobe performance is worse.



The spacing does depend on aerial gain/pattern. The half wave is dipole only.

mullingar

watty wrote: »

You must NOT space them LESS than a certain amount or they load/detune each other.

Think about it. Aerials on two nearby chimineys will have same signal if one or other aerial is removed. The issue is to add the signals in phase.



Too close and you detune and lose gain.
Too far and phase match is harder and side lobe performance is worse.



The spacing does depend on aerial gain/pattern. The half wave is dipole only.

Agreed that too close will de-tune and too far will cause all sorts of mis-matching.

Televes recommends 1.45m with their stacking combiner as linked to on a previous post. 1.45m = around 3x wavelengths.

If you had a clean sheet to stack a pair of Gp A aerials, what brand of extra high gain aerials would you use?
What would you use to combine the signals?
and what distance would you use to maximise around ch25 (half way between ch21 and ch 29 for post DSO in NI) = 503mhz or 596mm

watty

I'd use 4 x SR18A from Blakes.

3 x Quality outdoor F-Connector Splitters as combiners.

Crimp compression type plugs
PF100 coax
Group A mast amp about 1.2m to 2m below the last combiner.

mullingar

And if only 2 x Blake 18a's are used, what distance would you "suggest"?

watty

Then the side by side only applies instead of having a Quad (square).

You get half the signal of course.

mullingar

watty wrote: »

You get half the signal of course.

Do you?

I've read that a 2x stack vs single does not gain double results. You might gain only 3dB's (+50%) gain. I dont recall the exact reasons for this loss

Halving a quad will probably loose 2-2.5dBs' (-35%).

I was wondering what you would consider to be the best distance between a 2x stack to maximise the gain vs any potential headache.

Edit; I googled your Blake SR18A, it has a max gain of 13 dBd (cant find the gain curve). Other GpA's brands have 14-16dBd's (Triax/Antiference/XB16A) , this is a 2-3 dBd increase. Any reason for the preference of the Blake's?

Anecdotedly the twins here made a very noticeable difference to presely analogue reception at the same height as a single aerial of the same quality.

watty

3dB = twice the signal. It's a Log scale.

How much you lose having a Twin vs a Quad depends on your combiner losses. With "perfect combiners" it's 3dB.

0.5dB is very little as it's a log scale.

With Tweaked spacing, you get substantial interference rejection, that is not affected by combiner losses.

Since the limit is not amplifier noise any more but Atmospheric / Cosmic / Interference noise pickup, you can in reality be 6dB better off in SNR with a Quad or 3dB better on SNR on Twin compared with single even if combiner loss is 1.5dB on Twin and thus 3dB on Quad as the SNR is more important than absolute signal.


Noise versus Frequency showing that at UHF combiner losses will attenuate noise and Signal equally

If your mast PreAmp is 3dB NF or better, then at 600MHz loss on the combiners isn't important. A really good Grouped LNA (Mast amp) might be less than 1db.

championc

Watty, I have a Triax 100 mounted horizontally and I have a small cheapy (contract 10 element type) mounted vertically for RTE's from Clermont Cairn.

Is there any rule with having these any particular distance apart ? Both feed using separate cables into an A / E Combiner


C

watty

Opposite polarisations don't interact as much, so that is not so critical.
Grouped mast amp on the Triax 100, 1.5m below it, and then coax to combiner.


Aerials in general want 300/(MHz) meters spacing minimum.



Insane Example
Don't try this at home

championc

Watty, to get back to one of my earlier questions, if I have 25db before my amp and then add an FTE Masthead amp and set it to 40db, does this mean I should now have 60db + (allowing for some losses) at the TV ?

And at what db level gives you a decent picture ?


C

mullingar

championc wrote: »

Watty, to get back to one of my earlier questions, if I have 25db before my amp and then add an FTE Masthead amp and set it to 40db, does this mean I should now have 60db + (allowing for some losses) at the TV ?

And at what db level gives you a decent picture ?


C

Im not an expert on this field, but the dB gain cannot be used to work out if the signal is adequate or not.

TV's need an input of [I believe] 50-100dBuV. Its Voltage that important!

To get this voltage all depends on 2 things. The amount to uV your aerial pulls in and the amount this signal is amplified. (Amplifiers also amplify noise!!)

You wont know without a proper meter



Edit:

Just use a decent DVB-T box's tuning menu.

Most of them have 2 signal levels, signal quality (how much noise in the signal) and the strength. This strength meter will tell you if its strong enough. Make sure its not set too high though!

watty

In fact even signal level is misleading nowadays with very low noise tuners and especially digital systems.

The "level" is an approximate guide. Too much and you get distortion which Digital can't cope with at all compared to analogue. Too little and the there isn't enough noise margin.

10% to 90% is OK on "strength" meter if "quality" is 60% to 100%. Though different sets display the "quality" (Digital SNR, Signal To Noise, Eb/No, BER, Bit Error Rate) differently.

What matters on Digital systems is "quality" (SNR). If when the signal level is within reasonable limits the quality is poor, then unless there is a faulty amplifier (or LNB on Satellite) you need more Aerial (higher, bigger or both) or bigger dish (Satellite). Fiddling with Amplifiers, cables, LNBs, Tuners etc has only a marginal effect on quality as long as the signal level is within a very wide acceptable range.

As Mulligar says

I'm not an expert on this field, but the dB gain cannot be used to work out if the signal is adequate or not.

dB gain on the Amp or dB loss on Cable / splitters or dB Gain of aerial are only of use if you know what the actual signal level is.

You don't.

You maybe don't know how much loss the cable has, so adjust the gain of amp to put the Onscreen signal level in the middle, or with analogue start at minimum and increase just past where the noise (snow) stops getting less or can't be seen. Do not turn up higher as that make it more prone to distortion and interference.

The theory actually is that you add enough aerial for the "field strength" of the raw signal. The mast amp then is actually to cancel out the loss of the distribution system (feed cable from aerial to TV, with connector losses and possibly two way passive split (add 3dB to 4dB gain on amp) or 4 way passive split (add 7dB to 10dB to gain on amp). To feed many TVs you need an indoor distribution amp.)

championc

watty wrote: »

dB gain on the Amp or dB loss on Cable / splitters or dB Gain of aerial are only of use if you know what the actual signal level is.

You don't.

Hi Watty

I believe I DO. I have a Wolsey Lacuna Terrestrial Signal Meter. I cannot get any readings yet from the Divis Digital so all I'm working from right now is the Divis Analog frequencies and I'm getting 22-25db for Channel 4 directly from the Triax 100 (before the cable feeds into a FTE Masthead Amp). Unfortunately the Meter will not measure the Noise level and I understand that if I amplify signal, it is amplifying both good and noise.


C

watty

Exactly.

That's why an amplifier is only to "cancel out" all the losses AFTER the aerial, not to make the signal "better". Only "more aerial" makes the signal better.

22dB on it's own only makes sense as a Gain or loss.

either it's 22dBu (i.e. dB relative to 1uV, or about 100x one microvolt) or -22dBm which usually assumes an 75 Ohm or 50 Ohm and is relative to 1 mW usually.

dB are ALWAYS relative to something.

You are measuring signal on a high gain aerial. Not the actual Field Strength

Measuring noise is more complicated than level and depends on type of signal and bandwidth. Only very expensive gear measures noise on Analogue. The "quality" meter on Digital gear isn't a real noise measurement (SNR or Eb/No). It's actually just a measurement of how many errors are detected in the digital data stream. That can equally be from distortion/overloading, faulty software, faulty electronics or Interference or slightly wrong receiver parameters as actual real (usually presumed Gaussian) noise.

See http://www.ocarc.ca/coax.htm
Pick RG6 (minimum for TV and at UHF not much different to TX100, PF100), any better cable is a bonus.
Pick 600MHz as representative
Pick meters
Enter actual length (I entered 20m about 60ft)
Pick 1.5:1 SWR
Power only matters for Transmitters

Total Loss of Decent cable 20m long 5.011dB
Add 1dB per connection (can be 0.2dB)
so 7dB.

40m RG6 is 9.9dB @ 600MHz
@2GHz (limit of Sat IF) it's nearly 20dB, RG59

But the main difference of cheap spider web coax and double screen (foil +solid braid) is ingress of Interference, noise and egress of signal (with cheap cable the head amp can oscillate like a transmitter as it "hears" its own output).

Amp must be about 1m to 1.5m below aerial to avoid the Aerial picking up signal leaking from amp, connectors or cable.


Skinny RG59 is 5.5dB @ 600MHz but picks up too much noise.