AM receiver convert to ATC receiver

[Joerg]

Once upon a time, before Led Zep, I built a super-regenerative receiver that
used an acorn valve for the RF gain, a 958 if I remember correctly, a
Jackson air-spaced variable capacitor with a knob connected directly to its
1/4" shaft, and a small air-spaced coil wound from chunky silver-plated
copper wire. I connected it to the 144 MHz 'ground-plane' aerial I'd
installed on a pole at the end of the garden of our family house and found I
could tune-in to BBC television sound which, in those days, was AM (possibly
around 44 MHz in Band I).

I thought this was a great facility ... until I switched the telly on
downstairs and noticed the dreadful interference on the picture of BBC1. Of
course, it was my receiver that was causing it. Then I looked outside and
realised the distance between my ground-plane and our TV aerial was greater
than the distance between it and a load of aerials on other houses. Ooops!

I think I got away with that one, but I learned a bit of a lesson about
super-regen (or just regen) receivers that have the aerial connected
directly to the detector, not via an RF amp.

At least you didn't get zinged. When I built my first receiver with
controlled feedback (to set the BW) the structure was such that the cap
for the feedback had to ride between two points on plate level. Meaning
250VDC or so. No problem I thought since the knob was bakelite and would
certainly isolate that. Fired it up, connected earth and antenna,
reached for the feedback and *OUCH*. I had forgotten the minor detail
that the bakelite knob did not have a recessed set screw.

 

[Phil Allison]

"christofire"


( 10k post deleted)

respect

** Learn to bloody TRIM !!



...... Phil

 

[Archimedes]

Hi Wayne

I dont see any problem using that kit to listen to ATC.
When I go to the AP on Friday, I will be there with my regen receiver
listening to ATC - and I will be 500 meters from the active runway.
Cheers

 

[Claude]

"Bob Monsen"


** Firstly - I am very impressed that you accepted my comments in the
spirit they were intended.

A rarity on usenet - my congrats.




** Capture effect is almost entirly due to the " limiting " that occurs
in the IF amplifier stages.

Unlike AM, the IF stages of an FM receiver are normally operated very
heavily into overload ( ie gross amplitude clipping ) so the weaker of two
( IF frequency FM signals ) is completely over-whelmed by the stronger
e - which them becomes the only signal present at the FM detector.

There is even a Wiki about it:

http://en.wikipedia.org/wiki/Capture_effect


This feature was seen as a BAD idea for aircraft radio comms - it being
preferable to have something more like a telephone party line, so the
weaker voice could still be heard and even if not read clearly, the pilot
or ground controller could ask for a repeat of the message.

This got screwed up once at Tenerife and two jumbo collided as a result.

http://en.wikipedia.org/wiki/Tenerife_disaster#Communication_misunderstandings




...... Phil

Egad boy, Tenerife was a series of sequential bad decisions and the captain
not wanting to listen to his co-pilot. There was never a radio lock out,
only a pilot brain lock out. The pilot of one of the aircraft was paranoid
of missing his take off because weather was such that he would not be able
to leave until the next day so every word he hear his brain misinterpreted.
Unfortunately once a VHF aircraft radio press to talk is activated it locks
everyone out!!! You can't yell breaker breaker, well ok you can but you
won't be heard. This is why I gets real nervous in a high traffic area, I am
always afraid that the chatter won't allow me my turn to transmit. .

This all gets a bit muddled when the military are able to use VHF harmonics
in the UHF range. I don't know if it is only for distress beacons ( 121.5
Mhz harmonically picked up on 243 Mhz) or if they can do it on other freqs?

Claude

 

[Claude]

If a malfunctioning DTT set-top box can radiate enough to set off a SARSAT
and call out air-sea rescue, I have little doubt what a regen receiver is
capable of if it goes anywhere near the relevant frequency, especially if
connected to an antenna cut for one of the aero bands. See
http://www.telegraph.co.uk/news/mai...ml&sSheet=/portal/2006/01/15/ixportaltop.html

I wonder what they charge for vexatious call-outs!

Chris

Which probably explains why the new 406 EPIRB transmits to the satellite at
406 Mhz which is ( I believe ) in a protected area of the spectrum. I do
agree with you, the power involved is less than 5 watts ( not a researched
number) so any hack fooling around with a transmitter in that range could do
funny stuff. One new fail-safe feature is active on 406 EPIRBS is that the
satellite is listening for an embedded digital signal that identifies the
EPIRB. Each device has a unique identifier and the first thing a SAR station
does is call the registered owner on the phone. If you own such an EPIRB
please ensure that it is properly registered.

While I am here , anyone out there have plans for a functional cell phone
jammer that could jamm all 4 protocols to within 50 feet or so? I have seen
theoretical papers ( Google) but would like to know if any hobbyist has
ever built a successful one?

Claude
Montreal

 

[Claude]

It is illegal in every country in the world, and your little 'prank'
could cost someone their life.


--
http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm

Ok last post on the subject. They are NOT illegal everywhere, many
businesses and restaurants use them. I just don't know to how many uV/m they
are restricted.

What follows is in no way directed at others in this group who I find
helpful and friendly. I am just going to blow my steam valve off at this
particular responder

Aw crap I just saw the name on the reply, forget everything, I don't exist.
You are right the woman next door who stops mid stride in her driveway while
taking the garbage out to check her emails on her crackberry will surely
need an ambulance. Just to make sure all of the airwaves are safe I will
wrap tin foil around all of my electronic devices right now. I hope that
you are a minuscule exception to this groups usual civility.

Notwithstanding your possibly strange reaction I have been convinced to back
off the project.

Claude
Canada.

 

[Michael Black]

Not in the U.S. they don't... at least not without attracting a lot of legal
trouble for themselves.

And useage is no indicator of legality.

Most people who talk about wanting to jam cellphones don't have a clue
about what's involved or the rules governing the radio frequencies. Since
they don't know about the laws, if they felt a need to jam cellphones
likely they'd jump at the chance if offered a jammer. And of course, it
being illegal there are always people willing to supply the product, they
likely can make money from it. At the very least, little competition.

I don't doubt that some places in North America have cellphone jammers.
That doesn't make the legal. I have no doubt in other parts of the world
that some places use jammers; they may be "allowed" through lax laws, or
just lack of man power to track them down.

There may be places where they are legal, but having written that I find
it harder and harder to imagine it. Not because there might be some
countries in the world where they care less about radio frequencies, but
that cellphones have become so commonplace that they can't be treated like
the "wild west" of the early days of radio.

Michael