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Old 21st Aug 2019, 9:06 am   #21
Herald1360
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Default Re: Spitfire AM Transmitter Hum (Buzz)

It's not a modulator, clue's in the thread title

There is one in it of course......
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Old 21st Aug 2019, 6:56 pm   #22
space_charged
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Default Re: Spitfire AM Transmitter Hum (Buzz)

Oh yes, I know its not. I'm just trying not to use the "t" word. Suitably screened signal generators, modulated or not, are fine.
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Old 21st Aug 2019, 8:21 pm   #23
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Default Re: Spitfire AM Transmitter Hum (Buzz)

Quote:
Originally Posted by space_charged View Post
Oh yes, I know its not. I'm just trying not to use the "t" word. Suitably screened signal generators, modulated or not, are fine.
I will present the classic example. Have a look at this Statutory Instrument, as far as I know it is still in force.
http://www.legislation.gov.uk/uksi/1998/722/made

It is unusual, you might even say draconian, because mere possession of the item in question puts you on the wrong side of the law.
The item itself uses neither the T-word nor the M-word, it's a "Videosender" operating in the UHF TV band.

But isn't this much the same thing?

https://docs-emea.rs-online.com/webd...6b8093b7d2.pdf

The problem is there is not much scope for arguing what my intended use is, if I have already committed an offence by ordering the former and taking delivery.
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Old 21st Aug 2019, 9:26 pm   #24
Herald1360
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Default Re: Spitfire AM Transmitter Hum (Buzz)

Presumably whatever it is, it's not a videosender unless you connect it to a suitable aerial. The statutory instrument does talk about transmission rather than connection to the TV set. Otherwise anything with a RF modulator in it would be illegal.


As regards the legality of owning a Spitfire or WHY it's not a videosender and doesnt operate in the UHF TV band. AFAIK it's only illegal to use one not to own one.
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Old 21st Aug 2019, 10:12 pm   #25
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Default Re: Spitfire AM Transmitter Hum (Buzz)

Yes UK law is draconian. More or less, it says:

"thou shalt not emit electromagnetic radiation".

Except, that is, when you have a License to do so. Some devices are implicitly licensed, mobile phones, two way radios in approved bands, wireless routers and some remote control devices.

More exotic interpretation of the laws of physics tell us that we are emitting EM radiation just by not being at absolute zero and when we move (as in wave/particle duality). The list of other "violations" is extensive...

There are of course very good reasons for strict control of the EM spectrum and there would be chaos without it.
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Old 22nd Aug 2019, 9:39 am   #26
Hybrid tellies
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Default Re: Spitfire AM Transmitter Hum (Buzz)

Yes the laws concerning transmissions are very tight. Its just a pity they have not applied the same restrictions on emission levels from CFL,s, LED lamps, wall wort SMPS's Plasma TV'S etc which make the use of the AM bands impossible in many areas.
But if you choose the frequency of your pantry transmitter carefully there is very little chance of it being detected outside your house as the signal drops away into the high levels of noise at a very short distance from your house.

I use to be able to pick up my SSTRAN out as far as the end of our short drive. These days it disappears into the noise just outside the front door especially if the neighbours are using their ageing Plasma TV.
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Old 23rd Aug 2019, 4:01 pm   #27
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Default Re: Spitfire AM Transmitter Hum (Buzz)

I have the Spitfire transmitter using the switching power supplay. I never have any hum using battery powered radio. My earth is connected to the copper pipe of the main water tank.
I dont use the short antenna on its own that comes with it becuase it has poor efficiency in transmitting the RF signal. Instead I made an air core variable inductor with enamel copper wire winding on a 3" postal cardboard tube and giving the maximum inductanceof 1.4mH with about 10 tappings. You can also use ring- ferrite core inductor with tappings. The variable inductor is connected in series with the short antenna. I use a passive field meter and peak its reading at 1MHz or whatever the chosen transmitter frequency by trying different tappings. It makes day and night in difference in performance.
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