Combined FM/DAB aerial

[tony sayer]

In article , Dave Plowman (News) scribeth thus

BBC Nationals 4 kW .. Heart, Capital, Magic, LBC 2 kW...

Something rather odd there...

[Andy Hall]

So that's how they scale the roofs without a roof ladder - using their spurs.

[Andy Hall]

thus

Presumably a local fill-in....

[Frank Erskine]

That's because you don't readily notice ærials which don't have birds perched on them. :-)

[Dave Plowman (News)]

Is that the power of the fill in transmitters for South London? If so they certainly don't appear to go so far as the others above.

[tony sayer]

In article , Dave Plowman (News) scribeth thus

Thats what the BBC claim...

[Dave Plowman (News)]

Just as an update I've played around with this most of yesterday and concluded it's the DA that's faulty. Although not sure exactly what the fault is.

I changed the DAB aerial back to the FM one - mounted vertically.

There are four tuners - two DAB, two FM, fed via a DA.

DAB now fine - FM noisy. Aerial horizontal DAB poor FM fine.

With the aerial vertical plugging the aerial direct to any tuner - fine. Horizontal - FM fine but DAB marginal on only one of the DAB tuners - other one fine.

So either the DA is faulty - although it appears to be increasing the signal level - or one of the tuners is *transmitting* a nasty back up the line?

I'm rather lost with RF. ;-)

[tony sayer]

In article , Dave Plowman (News) scribeth thus

What make and model of amp is it. I suspect that its overloading what with where you live etc Dave...

[Andy Hall]

I had one at one point that developed some fault that caused it to start oscillating at around 350MHz. The net result was that there was a lot of apparent noise and crud on FM and again on the lower channels of UHF (i.e. Crystal Palace). Higher UHF channels were OK. It took an installer with a rectum paralyser (sorry spectrum analyser) to detect this. Amplifier was swapped and all was well.

If one of the tuners is doing something, then turning devices off in sequence should find it.

[Dave Plowman (News)]

Thing is these problems are recent - it all used to work just fine. But I tried a plug in attenuator (6dB) which made no difference.

The DA is a Mini4 made by Fringe Electronics and is pretty old.

So I popped out to TLC and got this one:-

has done the trick.

[Dave Plowman (News)]

I'm wondering if the DA itself is hooting. Not got anything here that can check those sort of frequencies. My 'scope does go up to 100 megs, but I'd not know what to look for. It does show noise with the input shorted, though.

[Andy Hall]

Exactly.

I don't have the high signal issues that Tony alluded to - it was the DA that was taking off. This was creating wideband crap as well as interference but also it was still kind of working. Of course it may have been that it was providing no gain as opposed to some gain.

[tony sayer]

In article , Dave Plowman (News) scribeth thus

Fine must have been something really odd with it.

A bad case of electrickery flowing uphill perhaps;)...

[tony sayer]

In article , Dave Plowman (News) scribeth thus

Wonder if somewhere there is a line powering switch thats been put on by mistake?...

[Dave Plowman (News)]

There is indeed an internal one but it was off - and to make sure I checked the aerial socket.

I'll take it into work on Friday and look at it on the spectrum analyser there. Or to be truthful ask one of the engineers to do it. They tend to be pretty hot on RF - lots of radio mics and walkie talkies etc to fix.