[SADXA] First Demonstration of Radio by Marconi Dec. 12th, 1896

[W7EXG (Bill)]

HI Ron,

This is an excellent article.  Very Interesting read with nice references. 

It will prove to be very helpful. 

Yes, I plan to build a Coherer and Experiment with it as well.  I would like
to build a Coherer receiver, to understand the difficulties of the Coherer
structure and use. 

Yes, in electronics as you know, pre-biasing to near threshold has always
been a technique, but not without issues. But I agree.. If it can be biased
to within 1 mV or Threshold, and the next 1 mV triggers it, who is going to
complain. The I/V characteristics of the device will be interesting. I am
guessing the repeatability of the I/V curves will be the issue.  

Thanks again for the reference. 

Bill W7EXG




-----Original Message-----
From: SADXA [mailto:sadxa-bounces at mailman.qth.net] On Behalf Of Ron Jones
Sent: Friday, December 16, 2016 8:28 AM
To: 'Southern AZ DX Association E-Mail Reflector'
Subject: Re: [SADXA] First Demonstration of Radio by Marconi Dec. 12th, 1896


Bill,
 Thanks so much for taking time to write such an informative note. Great
stuff, to be sure.
I have a link to an old IEEE paper with some more technical details about
Marconi's receiver(s). 
https://www.ieee.ca/millennium/radio/radio_differences.html
It is a great read. 

Your comment about 1.5V being WAY too high:

"I think 1.5V activation voltage is WAY too high, for activating the Coherer
from a DX signal. Activation voltage must be in the 1mV to 10 mV range MAX
as I suggested in my last email.  S9 is 50uV. 20/9 would be 500uV, and 40/9
would be 5mV, if you get my drift!! We might be able to actually get these
signal voltages, with a 1.5kW Spark Gap Transmitter, and step up transformer
at the receiver's front end, per Marconi. "

 is spot on. I wonder if you were to "bias" the coherer to just before it
conducts it may increase its sensitivity so an extra half mV would do the
trick. It would take a delicate adjustment, and would only sort of work,
but, hey, it was really hard for him and it took many tries to have success.

One last thing, I have a very high Q loop antenna that has tons of "voltage
gain" due to the "Q rise in voltage" phenomena with tuned circuits. I am
going to play with it and a home brew coherer and see if I can get any
detection with a nice strong signal. But, that project will be on hold till
after the holidays.

One other last thing, your comment about some of the Coherers may have
actually been diodes due to dissimilar metals, poor contact, etc. is alluded
to in the attached article. I think that is a valid observation.

Great stuff!!

And, yes, I did the rusty razor blade detector as a kid who was fascinated
with the magic of radio....and that magic is still there.  

73
Ron K7RJ

Hi Ron, 

I actually did see this article, and it does have value. But, the author was
suggesting 1.5 V across the Coherer, and was placing the receiver only a few
feet away from the Spark Gap Transmitter. 

I did not reference this article, as I was looking specifically for an
actual recreation of DX propagation with the Coherer, of at least 500 or so
miles, not a few feet.  Be interesting to find someone who has actually done
this. 

Maybe Ted is right.. Perhaps no one has recreated this feat, with similar
equipment. 

I think 1.5V activation voltage is WAY too high, for activating the Coherer
from a DX signal. Activation voltage must be in the 1mV to 10 mV range MAX
as I suggested in my last email.  S9 is 50uV. 20/9 would be 500uV, and 40/9
would be 5mV, if you get my drift!! We might be able to actually get these
signal voltages, with a 1.5kW Spark Gap Transmitter, and step up transformer
at the receiver's front end, per Marconi.  

So really, I would like to build some type of Coherer detector what will be
activated by 1mV or less. We are dead in the water, if this cannot be
achieved. I think that is the challenge. I am hoping someone, other than
Marconi, has already done this. Hopefully there might be some reference that
fully explains the Coherer, including activation voltages. Most articles
just generally describe the Coherer.

Fleming invented the "Thermionic Valve" in 1904, so interested in Passive
detectors such as the Coherer quickly faded. 

I think its time to rethink passive non-crystalline detectors!! The outcome
might be impressive in view of today's knowledge and technology. 

I wondered why Marconi did not consider dissimilar metals, which would have
a work function and potential barrier diode type junction. I am sure he was
well aware of this function, but maybe did not appreciate the significance
of the potential barrier, or junction, at the time? 

I remember using a rusty razor blade and a needle for a detector, as a kid,
to hear a local AM radio station. 

I did see an article where mercury was later used in the Coherer, instead of
iron filing. However, some now think this WAS simply a dissimilar metal
junction diode with the metal end plugs.  This should have been recognized
by Marconi. Maybe they discovered it did not need to be tapped!! That would
certainly be an improvement. Hi Hi.    

Thanks for your input and thoughts. 

Best 73s,
Bill W7EXG

-----Original Message-----
From: SADXA [mailto:sadxa-bounces at mailman.qth.net] On Behalf Of Ron Jones
Sent: Wednesday, December 14, 2016 12:37 PM
To: 'Southern AZ DX Association E-Mail Reflector'
Subject: Re: [SADXA] First Demonstration of Radio by Marconi Dec. 12th, 1896

I stumbled on a web page describing a homebrew coherer. I only scanned the
page, but it looks like a really cool project that falls into the "just
because you can" category, and what better reason do we need? 

http://www.sparkbangbuzz.com/els/coherer-el.htm

Ron K7RJ
 

______________________________________________________________
SADXA Website http://www.sadxa.org

SADXA mailing list
Home: http://mailman.qth.net/mailman/listinfo/sadxa
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:SADXA at mailman.qth.net

This list hosted by: http://www.qsl.net
You can support qsl.net: http://www.qsl.net/donate.html