plexiglass

[Tony Morgan-2]

How about making our own Hex Key covers?

Tony W7GO


----- Original Message -----
From: "Ron D'Eau Claire" <[hidden email]>
To: <[hidden email]>
Sent: Sunday, July 09, 2006 11:32 AM
Subject: RE: [Elecraft] plexiglass


The trick is often in cutting or drilling it cleanly and squarely without
melting or scratching it, and in polishing the edges. The nice thing about a
place like Tap Plastics is you take a template or dimensions to the store
and in a few minutes you walk out with nicely cut, polished and even drilled
materials ready to use! They'll even glue up assemblies requiring more than
one piece.

It's a great service! I'd be very surprised it was only available on the
west coast of the USA. If so, I suspect it's a business someone could do
very well with in our do-it-yourself culture.

Ron AC7AC




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[Ron D'Eau Claire-2]

Alex wrote:

In my reading about green radios I can't afford (but want anyway) and  
in various readings I've heard that detecting the 455-kHz LO of a  
superhet isn't all that hard, and that for instance in countries that  
require a radio license, they use such techniques to check if people  
in their houses have radios (or TVs) that they're not on record of  
having licenses for! And, in a lot of the military radios, the  
shielding is VERY good so that detection is much harder to do.

----------------

That's true for some tens of feet around for unshielded vacuum-tube radios
that used fairly robust local oscillators. In countries where a license for
a receiver is required, authorities sometimes located receivers by driving
up and down streets with special listening vans. They could often hear the
local oscillator if they were quite close to the receiver's location.  

Local oscillators don't radiate well. The antenna input to the receiver is
tuned to the signal frequency, well off of the L.O. frequency, so it and any
antenna doesn't radiate much. It's the same for TV's; There's virtually no
radiation from the antennas.

What receiver DOES radiate well enough to be heard for miles around -
sometimes around the world - is a regenerative detector without an RF stage
to isolate the detector from the antenna. In that case, the detector (when
oscillating in autodyne mode for CW reception) is oscillating on the same
frequency the antenna circuit is tuned to, and well-coupled to the antenna!
Vacuum tube regenerative detectors might produce a watt or more of RF, and
solid state detectors can produce 10s or 100s of milliwatts.

In the late 1920's and early 1930's, before superheterodynes became popular
for Ham use, the QRM from oscillating regenerative detectors was a very
serious problem on many Ham bands. Armstrong (who invented both the
regenerative detector and the superheterodyne circuit the Elecraft receivers
use) wrote open letters to Hams that were published in journals like QST
begging them to add RF amplifiers ahead of their regenerative detectors.

That's still true today for people using vintage designs from that era, but
they are relatively few in number and we're assaulted by so much other RFI
(read the recent thread on digital RFI) that they're seldom noticed.  

Ron AC7AC

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[Vic K2VCO]

Alexandra Carter wrote:

> I've heard that detecting the 455-kHz LO of a superhet
> isn't all that hard, and that for instance in countries that require a
> radio license, they use such techniques to check if people in their
> houses have radios (or TVs) that they're not on record of having
> licenses for!

Here in Fresno, there's a billboard that detects the FM station to which
car radios passing it are tuned, and summarizes the data for marketing
purposes.

I always switch to AM when I see it.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[zeke7237]

I've seen the detector van driving around the neighborhood in Dunoon
(Argyle) in Scotland when I was there courtesy of the USN. They also
used to run a commercial showing a nuculer family sitting around the
warm glow of the telly .. when the cops break down the door and drag
away dad, the VO comes in "Have you renewed your television license?"

On 7/9/06, Alexandra Carter <[hidden email]> wrote:
> In my reading about green radios I can't afford (but want anyway) and
> in various readings I've heard that detecting the 455-kHz LO of a
> superhet isn't all that hard, and that for instance in countries that
> require a radio license, they use such techniques to check if people
> in their houses have radios (or TVs) that they're not on record of
> having licenses for!
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[N2EY]

In a message dated 7/10/06 4:40:39 PM Eastern Daylight Time,
[hidden email] writes:


> , they use such techniques to check if people  
> in their houses have radios (or TVs) that they're not on record of  
> having licenses for!

Bit of history:

Way back about 100 years ago, there was little or no regulation of radio - or
"wireless telegraphy" as it was known then.

With only a few short-range experimental stations on the air, there was
little need for regulation, but as radio technology and popularity improved, the
need for rules was obvious.

Here in the USA, various legislation was proposed by the parties involved,
mostly the Navy and commercial wireless companies such as Marconi and
Telefunken. This was 1910, before the FCC, ARRL, broadcasting, or the Titanic disaster
that resulted in much more comprehensive regulation of radio.

Their model was the telegraph legislation. Why not just extend the rules
written for wire communication to wireless? It had been done for the telephone,
why not for radio?

The proposed rules did not differentiate 'receiving station' from
'transmitting station'. The commercial folks liked the idea of licenses for all stations
because it would help keep people from listening in.

A few interested amateurs/experimenters and organizations had gotten
themselves involved, however. One of them was Charles Stewart of St. David's, PA,
representing the Wireless Association of Pennsylvania. He argued that there was a
vast difference between wired and wireless, and that the 'waves come upon us
whether we bid them or not'. Also involved was the Radio Club of America.

Because of these efforts the legislators were convinced to only license
transmitting stations in the USA.

But the UK and most other countries had no Charlie Stewart, and they licensed
both receivers and transmitters. When Paul Godley went to England in 1921 to
listen for American amateurs on 200 meters, he needed a license for the
receiver. Since he wasn't British, he could not be issued a license, and a British
assistant actually held the receiving license.

Charlie Stewart became 3ZS and was one of the founders and vice presidents of
the ARRL. He passed away in February 1936, the same month as HPM and Mrs.
Maxim.

St. David's is right next to Wayne, where I live. I think I have located his
house, too.

---

The use of "detector vans" is lampooned in a Monty Pyhton skit, in which a
man tries to obtain a license for his pet bee named Eric.  


73 de Jim, N2EY
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[k6dgw]

Subject was "pexiglass"

John D'Ausilio wrote:
 > when the cops break down the door and drag away dad, the VO comes
 > in "Have you renewed your television license?"

Yes indeed, and a little frightening for us Colonists, what with all
that "pursuit of happiness" babble and all.  However, the radiation from
the TV comes primarily from the parts that make the screen light up with
a raster (if it's a CRT, and then, of course it probably was) ... fairly
high voltage sharp-edged signals with lots of harmonics ... and they do
radiate, at least for many tens of meters, on very predictable
frequencies.  The LO's are still pretty weak and generally below the noise.

Connection to Elecraft:

1.  I can't hear the K2 LO on my wide-band service monitor with the
input connected to the K2 antenna connector or laying next to the power
cable so I assume the NSA can't either

2.  Elecraft products do not have CRT's associated with them so no one
is likely to break down your door on that account while you're on the air.

3.  When transmitting with my K2, it is my sincere desire that
*everyone* can hear me.  (OK, that 'connection' is a little weak)

There was one thread some time ago that began with an Elecraft question
that slowly morphed into dentistry (don't ask me how). This one has
covered transparent plastic, tools to work with it, advisability of
using it, sources of plastic, war (that was a big jump, no?), military
radio equipment, frozen battleships made of ice (not sure how that
happened), TV police, and at least one Urban Legend.  I wonder how far
it will continue.

N0SS:  A friend agreed to fix the Mitrek repeater and controller
problems that filled my workbench, and I'm back to fixing the KPA100
problem that resulted from the attempt to fix the 40m parasitic problem.
  Stay tuned.

Fred K6DGW
Auburn CA CM98lw
K2 4398
KX1 897
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[Geoffrey Mackenzie-Kennedy-2]

Alex NS6Y wrote:

> In my reading about green radios I can't afford (but want anyway) and  in
> various readings I've heard that detecting the 455-kHz LO of a  superhet
> isn't all that hard, and that for instance in countries that  require a
> radio license, they use such techniques to check if people  in their
> houses have radios (or TVs) that they're not on record of  having licenses
> for! And, in a lot of the military radios, the  shielding is VERY good so
> that detection is much harder to do.

---------------------------------------------------------

In 1940 the SWBC radio for use by passengers, on the ship that was used to
evacuate a bunch of us youngsters to Africa, was put into a solid locked
metal box. I believe that this was to prevent U-boats detecting any
radiation from the receiver, most likely a superhet. The loudspeaker was
outside of the box and there must have been an external antenna. Maybe
overkill or wishful thinking.

73,
Geoff
GM4ESD



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