Alexanderson day

[Mike Watterson]

Connect a stereo modulator to big aerial, band limit the audio to 2.5KHz and only feed the left channel. Add a low pass filter. Use part of a 40KHz approx SMPSU to have 400W and feed long wire.
You'll have 38 kHz LSB. If the wire is matched, the voltage at the far end reaches many kilovolts, judging by people's experience doing 138 kHz Amateur band.

No idea what any Radio Regulator might think of it. Note most modern IC FM transmitters for phone/mp3 to FM radio do have the L+R base band, 19 kHz pilot and 38 kHz DSBSC L-R all on one pin feeding the varicap of the PLL FM LO, so accessible.

Maybe the MOD/USA/Russians might object. I don't know what frequencies the subs use.

Well, a loop will transmit a tiny amount at this band. It will inductively couple at a distance limited by power. So called (and pointless) wireless charging uses a low frequency.

A wireless charging mat needs a cable and psu anyway, so wastes energy and phone stops charging if you pick it up unlike coax power plug or USB. A cordless Kettle is just a high power version of a DECT phone charging cradle, a bit misnamed.

[Panrock]

Yes,  the old distinction between "induction" and "radiation". Looks like it really has to be a long wire then.

The old days, with long runs of above ground telephone lines, would perhaps have offered possibilities. ..

Steve

[Mike Watterson]

Yes,  the old distinction between "induction" and "radiation". Looks like it really has to be a long wire then.

For transmission. A one loop about 1/5th to 1/10th of a wave diameter has to be resonated and the voltages are awesome. HF transmitters with loops DO exist, and they use massive motorised vacuum capacitors absolutely at the remote loop. Multiturn loops are hardly used at all as the voltage on transmit when resonated, which is needed, is massive.

You can run loop cable around a room and drive with a 100W audio amp for hearing-aid audio induction reception.

Simplified version.
For reception it's easy to add gain and loop picks up much less E field, so local radiated electrical interference isn't much received. You are getting the H with the loop. it's only a 1/4 monopole against earth or a one wavelength diameter loop that is getting equal E & H, resonant to Electromagnetic waves.
So for reception as much turns as you can manage around a bookcase or window frame may beat 30 m of washing line, simply because there is less interference. Though a washing line with a low pass filter for the Alexanderson is maybe fine because it's at least half the frequency of any electronic ballast or SMPSU.
The 12V 1A SMPSU of a new satellite receiver wiped out all LW & MW in the house this week. Replacing it with a 12V 1.5A from an old ethernet hub worked (same plug and polarity). I'll try putting it in a metal box with a filter on mains first, then add filter on the O/P if that's not enough.

I've found PC PSUs with all the filter inductors replaced with wire links and capacitors omitted on the mains side RFI filters.

No regulator samples retail sales unless there are deaths.

[Panrock]

I've found PC PSUs with all the filter inductors replaced with wire links and capacitors omitted on the mains side RFI filters.

No regulator samples retail sales unless there are deaths.

(Going briefly OT)  What's your opinion of today's interference environment on Band I AM? Could it be worse now than it was in the old days with motor car interference?

Steve

[Mike Watterson]

You mean VHF 40 MHz to 70 MHz? Biggest interference that high is so called Ethernet over mains. In reality ultra wideband transmitters. The fastest ones probably create interference above Band II, Air Band. SMPSUs and Electronic Ballasts are hitting LW, MW and lower SW bands.

I do remember Band I TV 405 TV and the occasional evil vehicle. I did repair and sell some 405 TVs in 1971 as second sets. We actually had 625 Line Band I TV after we moved to Limerick and Clare in 1983. Never ever 405 in those areas, the Irish 405 closed about the same time as UK, in maybe 1985 and was only for areas that picked up UK TV in the 1950s. The local UHF only mast for Limerick City was later. The Band I TV on 625 closed about 1999 here, replaced by a mix of Band III and UHF. Analogue closed in 2012 only four years after DVB-t + H.264 trails started. All the SD channels used 264 from the start, so only imported UK TVs with HD DVB-t2 worked at all. Criminal levels of imports and sales of UK TVs from 2010 to 2013 that could only work as a monitor on a setbox.

VHF FM band II should have been extended with OIRT 65.8 to 74.0 and Japan 76-95, giving 65 to 88.5 extra instead of DAB, which is now obsolete duplication of DVB-t.
I think 42MHz, 50MHz and 70MHz approx are now Ham bands. I've not noticed any significant noise on 50MHz SSB with a roof top aerial

[Raditechman]

Pleased to report that I heard the transmission direct today in West London. Just using a long wire and SDR Play RSp2 and SDRuno software.

John

[Doodlebug]

Pleased to report that I heard the transmission direct today in West London. Just using a long wire and SDR Play RSp2 and SDRuno software.

John

Well done.
I used same SDR etc as you and also a AOR7030 receiver both with
40inch frame, 100 turns. Just a load of static near Ashby de la Zouch.
No sign of any signal.

[Raditechman]

    Here is a an display of the signal in West London Doodlebug, sorry you got static.

[Doodlebug]

I have been browsing the Alexanderson alternator transmitter web site and came across
this. It's a mechanical RX ! I don't really understand it at present but thought some here
would be interested in this amazing mechanical radio.

http://qrp.gr/technology/electromechanic...mechrx.htm

[Mike Watterson]

Oh, a long time since I've seen a mixer implemented with saturating cores. The mechanical aspect is obviously just the local oscillator source.
The mixer part with the special transformers is equivalent to a ring diode mixer using two regular audio transformers. Home made copper oxide rectifiers will work. Then the AC motor is simply a local oscillator. A simpler mechanical Local oscillator could be used.
The saturating core transformers are a kind of active device. You can use them as amplifiers. The two motors are active devices. You could use one. No need for the stepping motor. Even a DC motor with a rheostat to set speed driving a steel disc with slots or a rotor past a guitar pickup (or moving iron earpiece with the disc removed) will work as the Local Oscillator. The more pickup coils, the higher the frequency for same RPM.