HD signal strenght from CP

[charles]

and there was the JayBeam JBX5 - wideband yagi. Brilliant when dry, but droplets of rainwater sticking to the ends of the elements killed the higher frequencies.

[The Natural Philosopher]

No, its not that. Its just that RF is hard to calculate as the effect of unknown 'stray' components starts to dominate performance.

In my day te magic rule was "40db (gain) per (linear) inch", that being pretty much waht you could get out if an IF amplifier at 10.7MHz or indeed 455/460/470Khz.. without it getting unstable...

[Dave Plowman (News)]

It is to a sound engineer. ;-)

True.

[Dave Plowman (News)]

Think the cable is good - and it's not that old. Satellite stuff from Blake, and not cheap. The Blake log beam comes with a tail with an F plug fitted. Not really checked that. But the connection to my downlead was well wrapped in self amalgamating tape.

I did take a TV to where the aerial lead comes into the house. It is split there - one feed to the workshop - other to the DA.

Feeding the aerial direct to the TV did just about give an HD signal - but much lower signal strength and quality than all the other muxes.

The same TV from the DA shows much the same signal strength and quality.

One thing I did wonder about is some building work on the high street - perhaps a 1/2 mile away. With a couple of tower cranes. Although not directly between me and CP.

[tony sayer]

In article , Dave Plowman (News) scribeth thus

No very much doubt that would cause a problem at that distance with DTV..

[Dave Plowman (News)]

I'm pretty well convinced it is the aerial itself at fault. Any simple checks I can do on that before getting the ladders out? What should it read on a DVM resistance wise? Thinking about a poor connection to it.

The fault seems to be getting worse. The Drama channel was giving problems. Signal quality as on the TV menu flickering from 100% to poor - although strength staying at 100%

[Ian Jackson]

In message , "Dave Plowman (News)" writes

A UHF TV aerial 'driven' element is invariably a folded dipole - so a simple resistance test at the TV and of the coax should indicate a very low resistance (only a few ohms - the loop resistance of the coax).

[Dave Plowman (News)]

Wasn't sure if they included some form of balun that might confuse things

- thanks.

[Ian Jackson]

In message , "Dave Plowman (News)" writes

If there is a balun, it will probably be in the form of a series transmission line. Whatever's there. it's unlikely that there will be a DC open circuit between inner and outer. I'd have a quick measure first, and see what you get.

>

[Dave Plowman (News)]

Been using the sat receiver, but really must get to the root of this problem.

All three aerials, FM, DAB, UHF, have a quite short run from the roof terrace chimney stack into the room below. There, the FM and DAB are combined, and the UHF one split - one to the Freeview tuners used for radio (they all work just fine) and to the DA, which feeds an outlet in every room. All the splitters etc are quality ones with F connectors, from Blake.

Resistance measurements of all three are:-

FM 0.7 ohm. DAB about 3 MegOhm. ;-) UHF 2.0 ohm.

All three downleads are decent quality satellite co-ax and no more than a meter or so different in length. Only the UHF one has a connector between the measurement point and the aerial, as the Blake Log Beam comes with a fitted tail.

[Dave Plowman (News)]

Well there's a thing. Swapped the FM aerial for the UHF one, and results pretty well the same. So it would seem the UHF one is faulty. I'll get the ladders out tomorrow and take the UHF one down to have a look at it.

[Bill Wright]

Anything from open circuit to about 1ohm measured at the bottom of the downlead. It depends on the type of balun, etc. However the reading should be perfectly steady. It it varies it does suggest a fault.

That sounds more like CCI (unlikely) or overload by something out of band, or general signal overload.

Bill

>

[alan_m]

Are all unused outputs on your UHF splitter(s) either at the splitter or at the end of ALL your cables terminated in 75 ohms? If not you could have an impedance mismatch which can cause reflections effecting some frequencies more than others.

these can be used with belling lee coax type to f adapters

[alan_m]

Nearby 4G mast???

[Dave Plowman (News)]

Bit of an update. Since the set plugged direct to the aerial (no DA etc) was barely showing any signal on CH 30 (london BBC1 HD, etc) but 100% on everything else, I decided to get another aerial. Got a wideband log beam from Blake which is larger than the existing log beam, also from Blake, but perhaps 15 years old.

The tail on this aerial was much shorter than the original, so needed to extend the downlead. (Difficult to simply replace it)

So before extending it, I plugged a spare lead between the new aerial and a TV again moved close to the aerial. Success. 100& signal and quality on all channels.

Extended the downlead, and returned everything to normal.

Still no BBC1 HD. ;-(

Bypassed the DA, and success.

Thinking it might be overloading, removed the DA and got it beside the TV so I could see what it was doing. No CH30. Attenuated it so the TV was no longer showing 100% Still no CH30, and error rate too.

Fitted a passive splitter so I've got the TV in the main room and kitchen, and both fine on Ch30, and ordered up a new DA from Blake.

Old one was a Philex from TLC. No idea if that is a good or bad make.

Looks like I had more than one fault. Or perhaps 1 1/2.

[Andy Burns]

Thought original issue was with CH56?

[Dave Plowman (News)]

Yes - that too. Although CH30 more the pressing one.

[Dave Plowman (News)]

New DA arrived from Blake, so everything back to normal. 100% on everything and zero error rate.

Plugged the old aerial into the TV in the workshop - 1st floor, and on the right side of the house for CP, and got a strong signal on everything other than CH 30 and 55.

Doesn't seem possible to take it apart to look at the connections to the downlead.

I did say RF was a black art - to me. ;-)

[Andy Burns]

Got a USB TV tuner stick that can double-up as a poor man's spectrum analyser?

[alan_m]

As a matter of interest, which USB tuner?