Anyone built the "li'l 7"?

[McIntyre]

Had the urge to build something "with valves" yesterday, dug out an old yellowed circuit for a 117L7 Phono oscilator and managed to find all parts in the junk box including the 117L7. After a few hours the oscillator was was doing its thing and I was quite amazed at the performance from a single valve. Interested in the valves characteristics I decided to get some further info from the internet (and here is where the story gets interesting) - there, from my google search, was my exact circuit claimed to be designed by one "Walter Heskes" and copyrighted 1996-1997!
See http://antiqueradio.org/lil7.htm The only difference is that C5 (which is C3 on my circuit) is 50pf in my circuit.

So what is the role of copyright wrt circuits? Looking through many older (late 50's) Practical Wireless circuits I have often noticed the same circuit (with minimal slight differences) used 2-3 times over, over a period of 5 years. Hopefully we are never at the point that no new designs and circuits using valves can be reached but what is the chance of two or more designers producing the same circuit with (all but one) identical values?

Getting back to the 117L7 (and transmitters in general) how does one "measure" the strength, performance and distance a transmitter can transmit?

Andrew

[paulsherwin]

I'm not surprised this design puts out a good signal. The 117L7 is an output tetrode, and if you can get it to oscillate, it'll chuck out a lot of power. You could build the circuit with a lot of other valves such as a 6V6, 6BW6 or EL84. This design will be illegal in most countries, including I believe the US where low powered microtransmitters are legal.

There aren't many fundamentally different designs of phono oscillator around. Most use a heptode such as a 6BE6, while a few use a triode heptode like an ECH81. These are really just adaptations of a superhet frequency changer, and *would* be legal in the US, though not the UK.

To be fair about the Li'l7, I think the authors are claiming copyright for the whole project (circuit, construction etc) rather than simply the circuit - in any case, claiming copyright is one thing, proving it is another

As for measuring the output, you can get some indication by the power used by the output valve, but there are many other factors including aerial matching, aerial locatiion, aerial size etc. Maybe one of the radio amateurs on this forum would like to contribute?

Best regards, Paul

[XTC]

As far as I know, copyright controls the right to copy, and circuit techniques which are not obvious and fulfill the other requirements would be protected by patent. The other applicable set of IP rights would be trade secrets, although, hardly in this case.

Looks like the Antique Radio authors have probably taken a long standing circuit and maybe tweaked it a bit, chased down sources of suitable parts and published their own write-up and circuit diagram. Copyright amounts to their right to control copying of the write-up.

I'd guess they'd get upset if the diagram and write up they've done was published elsewhere on the web and passed off as someone else's work. In particular, they'd be very upset if someone was making money off their work without their permission. However, they are encouraging hobbyists to build the set. Exactly what action they could take against infringers is another story.

As for xmitter performance. I believe you measure the power into a dummy load. After that the range will depend on the quality of the aerial system, the location and a host of other factors.

Pete.

[McIntyre]

Originally Posted by paulsherwin

This design will be illegal in most countries, including I believe the US where low powered microtransmitters are legal.

Well honestly I have to admit that i don't know SA regulation regarding this. I know my home town doesn't have full time policing of this, they only come down here a couple of times a month for routine inspection (as if knowing when they come amounts to reall "raiding" of pirates ). Anyway the MW is no longer domestically used in my area - the last MW station quit broadcasting in 1996.

I have experimented with length of aerial and found 10 centimetres covers an area of aprox 20 meters which is sufficient. Don't imagine such a basic circuit will cover more than a few hundred metres max?
Andrew

[techno]

Hi

To get an aproximate check of output power try a
PR-12 bulb connected via 0.1 uF to the rf o/p socket.
With the bulb being brightly illuminated your o/p should
be in the range of 1-3 watts.
Keeping your aerial short to 10cm will keep your signal fairly local.
With a 1/8 wavelength at 1.6Mhz and a suitable ATU your signal will radiate over a 30 mile area.

Regards Techno

[XTC]

Andrew,

A problem with homebrew transmitters is that they can churn out harmonics which interfere with other users of the spectrum. It would be worth sweeping across the shortwave bands to make sure that this circuit is only producing the frequency it's supposed to.

Pete.

[McIntyre]

Originally Posted by XTC

Andrew,

A problem with homebrew transmitters is that they can churn out harmonics which interfere with other users of the spectrum. It would be worth sweeping across the shortwave bands to make sure that this circuit is only producing the frequency it's supposed to.

Pete.

Thanks that was one of the first things I did - used a normal domestic SW receiver. I've actually cut the aerial back even further so it doesn't transmit further than a radius of about ten metres. As I will really only use the oscillator very infrequently I don't think I will be interfering with anyone else.

And speaking of harmonics i have picked up (before) my neighbours land-line portable phone in the MW (can't remember exact frequency). I actually spoke to him about it. I thought it to be a bit bizarre - don't know if this happens often on portable phones?

Well at least now SA's original only independent station (from the 30-70's - until they were bought out by the previous SA government, no surprise ) has the air again on the exact same frequency in the MW - I've got hours of original broadcasts on miles of 1/4 tape - http://www.lmradio.org/ I imagine that LM was the equivalent of a Luxembourg to you UK people.

Andrew

[XTC]

In the UK (this may be an international standard), older cordless phones work duplex on 1.7 to 1.8 MHz and 48MHz. The lower RF they use is just off the HF end of the medium wave band and I wouldn't be surprised if MW went down that far on some radios. I forget what their power was (10mW seems right) but they could be picked up a couple of hundred yards away.

That was the sort of thing I was thinking about when I mentioned that harmonics might be a nuisance to other users.

There was no commercial radio in the UK until the 80s and Radio Luxembourg was a way of evading that. There were also pirate radio stations on ships around the coast from the early 60s. Radio Caroline was one.

I believe that before WWII Radio Normandie made commercial broadcasts to the UK.

LM Radio sounds like the same idea.

Pete.

[paulsherwin]

Originally Posted by McIntyre

Well honestly I have to admit that i don't know SA regulation regarding this. I know my home town doesn't have full time policing of this, they only come down here a couple of times a month for routine inspection (as if knowing when they come amounts to reall "raiding" of pirates ).

I imagine the SA law enforcement authorities are pretty busy and have better things to do than close down carefully run microtransmitters. That's certainly the case here, where even big commercial pirate stations manage to operate. Your main risk of attracting police attention will be if you cause problems for your neighbours, who then complain. As Techno said, if you couple the Li'l7 design to a proper matched longwire aerial the signal will cover tens of square miles, but you aren't going to do that are you

Best regards, Paul

[McIntyre]

Originally Posted by paulsherwin

I imagine the SA law enforcement authorities are pretty busy and have better things to do than close down carefully run microtransmitters. That's certainly the case here, where even big commercial pirate stations manage to operate.

Best regards, Paul

No I don't think there are any pirate stations in SA. SA quit shortwave in the late 60's opting for FM only. It was at that stage that foreign countries were pumping in so called "anti-apartheid" propaganda on the SW band. No domestic services are offered on SW or MW- except Radio Sonder Grense (Afrikaans services), on SW at night in the 90 m band, which are beamed at our neighbour countries Afrikaans Speakers. Modern receivers from the late 60's onwards only included FM. SW receivers across the Republic, during this era where directed at previous colonies on our borders in an attampt to destabalise them through preaching disatisfaction and the usual propaganda.


There is really nothing of value during daylight hours - I can pick up Radio France INternational, BBC world services, Voice of America. During the afternoon SW starts to become saturated with Indian and Chinese broadcats (don't know who they are aimed at?), and later at night North and West African countries can be received. Nothing spectacular. Oh there are two MW stations at night - 702 talk radio and Radio Kansel (Radio Pulpit) - a Christian Station.

Andrew

[McIntyre]

Originally Posted by XTC

There was no commercial radio in the UK until the 80s and Radio Luxembourg was a way of evading that. There were also pirate radio stations on ships around the coast from the early 60s. Radio Caroline was one.

I believe that before WWII Radio Normandie made commercial broadcasts to the UK.

LM Radio sounds like the same idea.

Pete.

LM Radio was originally run by a British guy named David Davies who worked at both Radio Normandie (pre-war) and for a period of a few months at Luxembourg.
LM used to play music which was deemed undesirable and immoral by the SA government - viz some of Elvis' songs, music and performances by many "Black" musicians and the Beatles etc - really anything happy sounding! Strangly enough LM was run by Portugal (of all places) in their (ex)-colony of Portugal-Mozambique. LM actually used the same "Evening prayer" at the end of their days transmissions which was used by Radio Normandie.

That's actually how you identify Export UK radios to SA, if on the tuning dial a station is marked "Lorenzo Marques" then it can be anywhere between 1935-1948, and "LM radio" is usually post-1950.

Andrew

[brightspark]

Originally Posted by McIntyre

Thanks that was one of the first things I did - used a normal domestic SW receiver. I've actually cut the aerial back even further so it doesn't transmit further than a radius of about ten metres. As I will really only use the oscillator very infrequently I don't think I will be interfering with anyone else.

And speaking of harmonics i have picked up (before) my neighbours land-line portable phone in the MW (can't remember exact frequency). I actually spoke to him about it. I thought it to be a bit bizarre - don't know if this happens often on portable phones?

Well at least now SA's original only independent station (from the 30-70's - until they were bought out by the previous SA government, no surprise ) has the air again on the exact same frequency in the MW - I've got hours of original broadcasts on miles of 1/4 tape - http://www.lmradio.org/ I imagine that LM was the equivalent of a Luxembourg to you UK people.

Andrew

I am the person behind the LM Radio website and am also putting together a radio series commemorating the station which closed down 30 years ago this October. I would appreciate receiving any recordings wich could help me make an first class series. I have all transcription facilities and would be happy to transfer from any media to CD and return originals.

Chris

[brightspark]

I am the person behind the LM Radio website and am also putting together a radio series commemorating the station which closed down 30 years ago this October. I would appreciate receiving any recordings wich could help me make a first class series for broadcast in S Africa later this year. I have all transcription facilities and would be happy to transfer from any media to CD and return originals.

Chris
curator@lmradio.org

[mikelect]

Ot Closed