[SADXA] First Demonstration of Radio by Marconi Dec. 12th, 1896
W7EXG (Bill)
W7EXG at q.com
Tue Dec 13 23:24:13 EST 2016
Thanks Mike and Ted.
Here are some more interesting aspects on Marconi's Transatlantic Radio
Propagation.
As an Electrical Engineer, I find it interesting, if not amazing, that the
1901 receiver was created prior to the Fleming valve - tube invention and
thus there was NO electronic diode element - everything in receiver was
passive.
The RF detector used a mechanical element called the COHERER Detector. It
consisted of a metal tube, filled with loose metallic particles with a
metallic plug on each end. The end-to-end resistance is high due to loosely
packed particles. However, when a voltage is applied, the metal particles
cling to each other between the ends, and create a low resistance path. By
noting the change in current flow, or resistance, the voltage can be
detected. Marconi used a RF step up voltage transformer in his receiver, to
increase the sensitivity of the Coherer detector.
One drawback of the Coherer detector was that once the metallic particles
cohered, the tube needed to be tapped, to return the filings back to their
loose and high resistance state. So, Marconi built a mechanical tapper, to
tap the tube automatically after signal detection.
Apparently, there was no 30WPM with the repeated letter S.
To think about the sensitivity of the RF detector, we know an S9 Signal is
referenced as a 50uV signal into 50 ohms at receiver. This IS a strong
Signal. So my guess is Coherer might have been responsive to 100uV, or 0.1
mV. The Transformer might have stepped this voltage to 1mV.
The Spark Gap Transmitter was developed by later-to-be tube Inventor
Fleming, and run by a 30kW alternator. Thus powerful gap energy was coupled
to the transmitting antenna. Maybe received signal was 40/9??
There are some doubts about Marconi's timing and wavelength used. It is
documented that the time of transmissions was 11:30am to 2:30pm Newfoundland
time. If true, then it is unlikely the reported 850kHz signal (AM band)
would travel 2000 miles. If the times are correct, it is more likely higher
frequencies propagated from the spark gap, and were the frequencies being
detected?
I have also seen some recent articles of people constructing Coherer
detectors. It might be fun to play with them, and see what their actual
sensitivity might be. They are truly just metal filings in a tube with metal
plugs on each end.
As we all know, everyone is trying to push the envelope in Amateur Radio.
Perhaps a WAS with ONLY passive detector receivers, [such as the Coherer
Detector] should be an ARRL Award? This may stimulate better inventive
passive element detectors. There is some value in this, since electronic
detectors are at risk during high levels of radiation.
I suspect the FCC won't let us build a 30kW Spark Gap generator for our
Transmitters.
Thanks again for your comments.
Best 73s,
Bill W7EXG
-----Original Message-----
From: SADXA [mailto:sadxa-bounces at mailman.qth.net] On Behalf Of W0LTL - Mike
Zonnefeld via SADXA
Sent: Monday, December 12, 2016 11:55 PM
To: sadxa at mailman.qth.net
Cc: MikeZW0LTL at aol.com
Subject: Re: [SADXA] First Demonstration of Radio by Marconi Dec. 12th, 1896
Nice!
73
Mike
W0LTL
In a message dated 12/12/2016 10:29:06 P.M. Pacific Standard Time,
ted at teddowning.com writes:
A great answer, Bill. Merry 12 December.
Ted w7key
> On Dec 12, 2016, at 5:29 PM, W7EXG (Bill) <W7EXG at q.com> wrote:
>
> Hi Ted,
>
> In the spirit of your DX spot questions, here is my response.
>
> On another December 12, but in year 1901, Marconi succeeded in sending
the
> first radio transmission (estimated at 850kHz) 2000 miles across the
> Atlantic Ocean, from England to Newfoundland. This disproved detractors
who
> told him that the curvature of the earth would limit transmission to 200
> miles or less.
>
> His message was Morse-code signal letter "S"
>
> Thus December 12 is actually a GREAT DAY for Amateur Radio, since it was
on
> this DAY in 1901, when "some type" of ionospheric reflection was proven,
> suggesting world wide DX was possible.
>
> Fortunately the FCC was not involved yet, so no call Sign was required.
> However, rumor has it, that Marconi's WANTED TO HAVE the first amateur
radio
> call, so his 1 by call was -- S. In that context, Marconi WAS the 1st
> Amateur Radio Operator, and 1st DXer on Dec. 12, 1901. This is an
amazing
> 1st.
>
> Since 2000 mi at 850kHz clearly was a nighttime propagation, the
propagation
> reflection was off the F layer.
>
> However, the transmitting system consisted of a dipole, driven by an
> induction coil and a spark gap.
>
> I am guessing that the spark gap still radiated energy at frequencies way
> ABOVE the MUF at the time, and some of that high frequency energy escaped
> into space -- and is still out there.
>
> If the universe is curved with a circumference of 115 Light Years to THIS
> DATE, I suggest listing tonight on 20m or higher frequencies, about
> midnight, for ... ... ... ...
>
> But, be sure your using one of those whiz-bang SDR receivers with a noise
> floor below absolute temperature.
>
> My DX Spot for Dec 12, IS NOT FOR TODAY, BUT mainly FOR TONIGHT, so you
> still have a chance at this rare DX event!!
>
> If you hear radio Station with call sign S, give him a call.
>
> Might be hard to get a confirmation, but you might check LOTW anyway. It
> will take awhile for S to hear your call and get it in the LOTW data
base,
> however.
>
> Be wary of bogus "S" stations.. who may be pretending to be "S". This is
> always an issue for us DXers.
>
> Pile-ups.. well YES!. Since I just put S on the DX Cluster forecast for
> tonight, I suspect the pile-ups might be intense.
>
> Good luck and good DX! And Mainly ... Have Fun!!
>
> 73s,
>
> Bill W7EXG
>
> -----Original Message-----
> From: SADXA [mailto:sadxa-bounces at mailman.qth.net] On Behalf Of Theodore
> DOWNING
> Sent: Monday, December 12, 2016 8:48 AM
> To: Southern AZ DX Association E-Mail Reflector
> Subject: Re: [SADXA] First Demonstration of Radio by Marconi Dec. 12th,
1896
>
> Now that's a DX spot for sure! Was it today? Darn it, What call sign?
What
> frequency? I doubt there will be a pile up. :-)
>
> Ted
> w7key
>> On Dec 12, 2016, at 8:28 AM, W7EXG (Bill) <W7EXG at q.com> wrote:
>>
>> Dec. 12, 1896:
>>
>> First demonstration of the radio:
>> Marconi demonstrates his radio set to the public, today -- on Dec. 12th
> in
>> 1896
>>
>> 73s,
>>
>> Bill W7EXG
>>
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