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Old 15th Sep 2018, 9:18 pm   #1
'LIVEWIRE?'
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Exclamation Using a TV aerial to receive FM Radio!

Readers may wonder why I would need to do this, but I have been checking out a Hitachi SDT-400 Music centre recently, and, despite searching, I couldn't find a male to female adapter to connect my indoor FM aerial to the Hitachi, so I unplugged the aerial from my TV and connected it to the Hitachi. Despite the obvious mismatch between a multi-element UHF aerial and a VHF Tuner, I can receive a large number of FM stations, many in perfect hiss-free stereo, and in fact am listening to Classic FM as I type this.
The aerial, by the way, is on the roof and points toward the Oxford (Beckley) Transmitter about 20 miles distant. The reception by this method is so good that I'm thinking of fitting a splitter to my TV aerial lead so that it can, at least in the short term act as both a TV and FM aerial. If it works as well with my own Sony receiver as it does with the Hitachi, I would at least consider having an outside VHF aerial installed, although I've managed with an indoor ribbon aerial for over 40 years!
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Old 15th Sep 2018, 9:26 pm   #2
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Default Re: Using a TV aerial to receive FM Radio!

Reception using a TV aerial is often better than an indoor aerial simply because it's high up and not screened by walls. A proper aerial will give better results, but it's only worth paying for if you need it.
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Old 15th Sep 2018, 9:27 pm   #3
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Default Re: Using a TV aerial to receive FM Radio!

If the TV antenna is a UHF-type, I suspect that it's contributing little to the actual reception of Babd-II VHF radio signals and that most of these are actually getting picked up because the coax cable to the TV antenna itself is of low quality and the braid doesn't provide total screening of the central conductor.

[There was some truly horrendously poor "Low-Loss" coax produced in the 1980s/1990s, with only a few spindly strands of braid]
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Old 15th Sep 2018, 10:05 pm   #4
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Default Re: Using a TV aerial to receive FM Radio!

G6T, My TV aerial is only a year old, supplied & fitted in September 2017 by a reputable local aerial installer. The coaxial cable is a good quality properly screened type. I'm inclined to agree with Paul Sherwin as to why the reception is so good, especially as I live in a ground floor flat, so my indoor ribbon VHF aerial is only about 10ft. above floor level above a south-east facing window.
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Old 15th Sep 2018, 10:25 pm   #5
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Default Re: Using a TV aerial to receive FM Radio!

Is it not just driving half of a balanced input with the coax outer?
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Old 15th Sep 2018, 10:38 pm   #6
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Default Re: Using a TV aerial to receive FM Radio!

No, assuming a standard unbalanced 75 ohm input the screen will be earthed.
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Old 15th Sep 2018, 11:12 pm   #7
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Default Re: Using a TV aerial to receive FM Radio!

If the outer shielding braid of the co-axial cable has a high impedance to Earth at VHF, then the braid could be picking up a signal. Or if the braid is just not very good, then some VHF might be getting picked up on the inner core.

Either explanation is plausible. Whatever is happening, though, it's a fortunate accident and certainly shouldn't be relied upon in all circumstances.
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Old 16th Sep 2018, 9:44 am   #8
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Default Re: Using a TV aerial to receive FM Radio!

Both the Hitachi and my Sony Receiver (and the TV!) have standard 75 ohm aerial i/p circuits, so the braid is earthed. The coax. cable, however is quite long, about 2.5 metres inside the flat, and maybe 10M. or more outside, so it's conceivable that the braid is acting as an aerial, though this would still be grounded at the receiver end. As I said, it's not intended as a permanent solution (though if it works well, why not??), but merely a way to check the performance of the Hitachi M/C, which, being 40 years old, is fitted with a standard TV-type co-ax. socket, whereas my more modern Sony receiver is equipped with a male 75 ohm chassis socket, and I couldn't find an adapter to connect my indoor aerial to the Hitachi. Incidentally threads on almost any topic seem to generate a lot of replies, not in itself a bad thing, but sometimes seeming to make a simple issue/request seem very complicated!
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Old 16th Sep 2018, 10:20 am   #9
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Default Re: Using a TV aerial to receive FM Radio!

There's no reason not to use this as a permanent solution if it's adequate for your needs.
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Old 16th Sep 2018, 10:30 am   #10
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Default Re: Using a TV aerial to receive FM Radio!

Precisely so. This seems like a simple case of "if it works, use it". Doing so can't harm anything. The actual mechanisms involved aren't worth worrying about unless it stops working for some reason.
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Old 16th Sep 2018, 10:39 am   #11
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Default Re: Using a TV aerial to receive FM Radio!

Like I've always said, there's aerial theory and there's what happens in practise. And in my experience, there's very often a huge grey area between the two! Obviously, you make every attempt to 'go by the book' if funds and a physically practical solution are possible (that's what I try to do), otherwise if it works it works. It's about enjoyment factor, not appeasing the writings of a dusty 50s text book.

For example, my 'DAB aerial' is my pole, roof mounted vertical dipole FM aerial that doubles perfectly well for DAB reception. People on here have called it 'wrong'. How can that be so when there's no bubbling mud, and the resulting reception sounds like perfectly good digital reception? Answer: it's not wrong and I've saved money, complexity, maintenance and experienced hours of listening enjoyment.

I'm into hifi tuners at the moment and I often see the question, "What is the best tuner?". A common, 'clever dick' answer is, "The one connected to the best aerial". And although that is to a large extent true, I'd go further and say the one that is connected to the aerial that provides for your needs. Why complicate matters if 'simple' works? And trust me, I'm not a 'make do' kind of person, but logic should kick in at some point otherwise we'd all have large towers with various motor controlled, rotatable Yagi arrays on them.
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Old 16th Sep 2018, 11:11 am   #12
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Default Re: Using a TV aerial to receive FM Radio!

Quote:
Originally Posted by 'LIVEWIRE?' View Post
The reception by this method is so good that I'm thinking of fitting a splitter to my TV aerial lead so that it can, at least in the short term act as both a TV and FM aerial.
Rather than a splitter and the losses that will incur, a VHF/UHF diplex filter would be better.
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Old 16th Sep 2018, 12:17 pm   #13
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Default Re: Using a TV aerial to receive FM Radio!

Sounds a better idea, Terry, but when I typed 'Vhf/UHF diplexers into my search box, a message from Talk Talk 'Harmful Website Blocked' appeared - this referred to something called 'go.deepteep.com' whoever they are. CPC-Farnell list several such devices, but they are all attenuators, not what I really want.
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Old 16th Sep 2018, 1:10 pm   #14
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Default Re: Using a TV aerial to receive FM Radio!

Try Amazon and search for
Antiference UF21R UHF FM DAB Y Shaped Diplexer
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Old 16th Sep 2018, 3:05 pm   #15
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Default Re: Using a TV aerial to receive FM Radio!

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Sounds a better idea, Terry, but when I typed 'Vhf/UHF diplexers into my search box, a message from Talk Talk 'Harmful Website Blocked' appeared - this referred to something called 'go.deepteep.com' whoever they are.
That is bizarre!

Vision used to sell them - I got one for the new RF distribution system at the Dulwich museum. Vision very kindly ensured that it was aligned to cover down to 40MHz to include Channel B1 (as nobody uses Band I anymore, they don't normally worry about anything below Band II these days).

They shouldn't be too difficult to find because a lot of aerial systems diplex the outputs of the UHF and Band II aerials onto a single downlead so, obviously, another filter is required at the other end to split them again. Perhaps a local aerial installer might be able to help?

Something else you could look for is a CATV isolator. These are fitted where the cable from the street enters the house and pass RF but block any direct connection with the network, so there is no possibility of creating earth loops or feeding back dangerous voltages from faulty equipment. Most (but not all) have a separate output for FM and would do the trick.

Another alternative is another CATV product, an A-B switch. They used to be used a lot in the days before SCART connectors became common to select between the cable feed and the RF output of VCRs. Obviously, they are passive and work fine in reverse. (I'm assuming that you are not going to watch TV and listen to the radio at the same time!)

I used to have a couple kicking around but they almost certainly got skipped when we moved a couple of years back - downsizing from an Edwardian 4 bedroom house to a 1960's 2 bedroom bungalow isn't easy - particularly after accumulating 'stuff' for over 40 years there!
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Old 16th Sep 2018, 3:17 pm   #16
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Default Re: Using a TV aerial to receive FM Radio!

Quote:
Originally Posted by Nuvistor View Post
Try Amazon and search for
Antiference UF21R UHF FM DAB Y Shaped Diplexer
Or, for neatness, how about this?

A bit more expensive, though, and needs a 35mm backbox as well.
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Old 16th Sep 2018, 4:01 pm   #17
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Default Re: Using a TV aerial to receive FM Radio!

Hi,

At a tangent....

Back when I was living at home with my Parents in the 70's I used my parents unused band I and III aerial to feed my Quad FM1 tuner. This worked well and enabled me to get a strong Capital Radio signal in Rayleigh, Essex.

Although its characterised for band I and III it did a good job for band II. I figure if you were to plot the overall combined response of the two aerials it would show a reasonable response at band II frequencies.

Regards
Terry
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Old 16th Sep 2018, 4:53 pm   #18
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Default Re: Using a TV aerial to receive FM Radio!

Terry, there is a redundant TV/VHF diplexer similar to the MK one in that link, left over from when these flats were served by a communal aerial system. It's 52 years old, but should still be serviceable. I'd forgotten about that. All I would need to do is connect the cable from my TV aerial in place of the internal wiring, then use two extension leads, one terminated in a 75 ohm aerial plug for the TV, the other terminated in a 75 ohm line socket for my Sony receiver.
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Old 16th Sep 2018, 4:58 pm   #19
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Default Re: Using a TV aerial to receive FM Radio!

Just need to make sure it’s not a band1/3 +VHF FM type diplexer, 52 years 1966 VHF TV was the normal for BBC1 and ITV.
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Old 16th Sep 2018, 5:18 pm   #20
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Default Re: Using a TV aerial to receive FM Radio!

A simple check before and after should determine that.

If a variable attenuator is to hand, a more scientific method can be tried.
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