Using an Aurora as a pantry TV transmitter.

[mark pirate]

I would like to broadcast from my Aurora to my 405 line TV collection, using some set top aerials for reception.

I only need to receive a good signal of say a twelve feet radius, I have an old valve based signal booster (as yet untested) that could be used, but what would be an appropriate aerial for transmitting?

Mark

[Brigham]

Twelve 45 mc/s vertical folded dipoles evenly spaced around a 30 foot rod secured to a suitable chimney should get out all right. Make sure the Aurora is set for Ch.1, and don't open the door to strangers, no matter how hard they knock!

[Herald1360]

^^^WHS^^^

The shortest piece of wire that works at the range you want. Anything vaguely resonant or efficient will radiate far too well!

[Studio263]

I'm sure that in the Aurora manual it specifically says not to attempt to broadcast the signal. This is possibly because it is full of harmonics and you may find yourself getting into trouble.

You will need some sort of filter on the output at the very least if you want to try this, I'd go for the CH.1 setting as this makes the design and layout that much easier.

[KeithsTV]

I can confirm the RF output is full of the odd harmonics of the channel selected. These are present to well above the top of the UHF TV band (860MHz). Some of the Band 1 channels have harmonics in Band 3 so creating a Band 1 & Band 3 set up the channels have to be carefully chosen.

One possibility for a filter is a triplexer for combining/splitting FM, DAB and UHF signals. I uses a couple of these in my aerial distribution system and it seems to work very well.

Keith

[mark pirate]

I had not thought about harmonics, I do have a few filters/splitters to try.
It will be a much easier setup than running a wired distribution system to all my sets, but I don't want to the signal to cause any problems to my neighbours!

I will experiment with it in my workshop using my Sony 9-90UB to get the signal to the required level without travelling too far.

I expect a compromise will be necessary to compensate for the less sensitive sets.

I will report my findings soon.

Mark

[Radio Wrangler]

The nasty thing about odd harmonics, is that they coincide with overtone modes of antennae cut to resonant lengths, so you don't even get any selectivity from the antenna. You have to do all the hard work with a filter on a transmitter.

I would be careful about the signal strength. Tellies were never very sensitive, but there are people now trying to set new distance records in what was once the old band I TV frequency assignment, and they are using high gain directional beams into very low noise receivers. Strange signals get spotted and reports passed along through various bodies t Ofcom. Don't trust a TV as an indicator of what might get noticed.

David

[Alex728]

Originally Posted by Radio Wrangler

I would be careful about the signal strength. Tellies were never very sensitive, but there are people now trying to set new distance records in what was once the old band I TV frequency assignment, and they are using high gain directional beams into very low noise receivers.

David

those bits of Band I that are not allocated to amateur use are still recognised by the EBU, CEPT and national Communications Ministries as a broadcast band, but today it is generally only used in the UK for studio to transmitter links and longer range outside broadcasts (as wide band FM analogue audio), by smaller community radio stations.

48.30 MHz is a common allocation for this purpose which I think is near the sound channel for one of the Band I channels.

If someone put up such a TX up in Ipswich they'd cut straight across ICR-FM, whatever they were sending would go out on Band II as well and I've very quickly get a panicked mobile phone call from the station management asking me what on earth is happening. I'd have then (with a very heavy heart, having formerly been a pirate myself) to make a formal report that would go to Ofcom.

I appreciate the hassle of stringing coax everywhere, but I do wonder (especially as cheap baluns are widely sold at CPC etc) and computer network cable can apparently operate to 1000 MHZ if this could evolve into a project to emulate the old "British Relay" type systems using twisted pair cable?)

Hard wiring the sets may be a hassle, look on the bright side, no extra power consumption, no incomming interference and (the best bit) you can relax knowing that the knock on the door is only the takeaway!

[murphymad]

Hi This is all very interesting, and it would be very nice to have a local transmitter to run 405 line TV's from, BUT I doubt that all the TV's would work up to the expected picture quality due to differing designs and types of sound and vision recievers (TRF/Superhet) within the recievers in your collection. This being presumed by the very low power nature of the TX needed.
The problem of Harmonics is a real one, and should not be brushed under the carpet. It could end up annoying many people around you without you ever knowing.

Directly connecting the aerials back to an isolated distribution system is the best way forward. This has recently been done at the Vintage Wireless Museum.

Also to consider is the problems encountered when more than one TV is on at any one time in the same room. You would not expect to have any problems, but patterning and strange issues have surfaced when we have set up BVWS TV displays that you just would not expect.
The Marconi VT53/73DA will act as a transmitter and run another couple of TV's without any aerials connected quite well as the internal screening is awful. It should have an earthed aerial system, but in most people's vintage setup this is not the case.
The TV's were never designed to be close to another TV and most people who had no need for two sets close together, neither could they afford it!

Don't just connect all of the aerial coax together using splitters, that will do nasty things as well.

The installation up at the Museum is an "ideal" solution, but costly and requires equipment.
I will follow that setup for my 405 signal distribution in the Murphy Museum (when I get that far).
Think back to the 1000 TV's running in London, they did it with many separate amplifiers and modulators and miles of cable.
They would have had to comply with all regulations and not become a source of radiated signals.

Mike...

[Heatercathodeshort]

I have an AURORA in what I call my 'museum' feeding an old Rainbow Band 1 distribution amplifier [1950] and 6way splitter. One of the outlets is fed to an old Band 3 loft aerial positioned on a top shelf and the signal is just strong enough to feed hand held portables and small screen [2-6"] receivers placed below the aerial on lower shelves for display. The modern 8 way amplifier feeds UHF signals via the R.F. modulator to UHF receivers. It is a very low level signal and living in a rural location, have not had any problems. I never open the door to strange men in white coats. Time will tell.. John.

[HamishBoxer]

As I value my ham licence think I will stick to hard wiring.

The last time a man in authority knocked on my door it was from council planning department, over my Tennamast and that caused me enough hassle and expense.

[Radio Wrangler]

Ah, yes... in cases of infringement of the wireless telegraaphy act, they do have authority to remove ALL radio equipment from the offending premises and destroy it.

David

[HamishBoxer]

Oh yes, they certainly would not hesitate.

[Heatercathodeshort]

I presume this also applies to pantry transmitters used for rebroadcasting radio to old receivers? My television signal is so weak it refuses to leave the building! I have had more R.F. leak from professionally installed aerial distribution systems. J.

[mark pirate]

After a little bit of experimentation I have found using an old UHF aerial connected to the aurora does not have much range!
Transmission is improved however, by fitting a the rod aerial from a DAB radio, which conveniently screws on to the F connector on the Aurora, this gives a range of around five feet using my Sony 990UB as the test set, running on it's rod aerial.

I certainly think that this limited power (the RF output of the Aurora is 76dBµV (6.3mv) typical into 75 ohms, should not cause any interference to my neighbours, although I will dig out my old 405 signal booster and see if it can give the desired range.

Otherwise I will have to go down the hard wired route to feed nearly 20 sets!

Mark

[Heatercathodeshort]

The system I use only feeds the receivers directly below the Band 3 aerial. If I place items anywhere else, even on the lower shelves I get practically nothing! I'm not worried about this very small 'leakage'. Everything else in the museum is hard wired. John.

[Alex728]

what about a "leaky feeder?" I'm no RF expert but believe that its essentially a "coax wiv 'oles in it". you might need to get the holes separately from the coax but a few OM's have told me this arrangement is used to let RF into certain parts of a building but not beyond its boundaries especially for student radio stations and the like..

[Heatercathodeshort]

Oh no! This sounds like an 'Oxygen free' co-ax story Alex. Life really is too short..J.

[AC/HL]

It's used in tunnels for radio communications.