Buying a used COMM

[res]

I want to buy a used COMM that is working (with all the accesories needed)
It is not going to be mounted i n a plane, it´s only for my home. I´d prefer
a better price than a newer one, so an old COMM could be accepted.
Thanks

Iñaki

[Mark Astley]

Do you mean a handheld or panel-mount unit? Do you actually need to
transmit or do you just want to hear ATC? Generally speaking, a good used
handheld will be easier to deal with than an old panel-mount. Yes you could
probably pick up an old Narco MK12 on e-bay for $5 but you'll need to track
down an antenna, rig up a power supply, etc. But if all you want to do is
listen in on traffic, the cheapest solution is to go to RadioShack and pick
up an air band radio. You can get a decent one for about $20. Note: unless
you're close to a ground station or have line of sight, you're only going to
hear one side of the conversation.

cheers,
mark

"res" > wrote in message
...
> I want to buy a used COMM that is working (with all the accesories needed)
> It is not going to be mounted i n a plane, it´s only for my home. I´d
prefer
> a better price than a newer one, so an old COMM could be accepted.
> Thanks
>
> Iñaki
>
>

[Ron Wanttaja]

On Thu, 22 Jan 2004 09:35:18 -0500, "Mark Astley"
> wrote:
>
>>I want to buy a used COMM that is working (with all the accesories needed)
>>It is not going to be mounted i n a plane, it´s only for my home. I´d prefer
>>a better price than a newer one, so an old COMM could be accepted.
>
>Do you mean a handheld or panel-mount unit? Do you actually need to
>transmit or do you just want to hear ATC? Generally speaking, a good used
>handheld will be easier to deal with than an old panel-mount. Yes you could
>probably pick up an old Narco MK12 on e-bay for $5 but you'll need to track
>down an antenna, rig up a power supply, etc.

If it's just for listening, the antenna can be just a bit of wire. Radio
Shack sells a couple of nice little 12V power supplies for running auto
accessories. Any 8-ohm speaker should work. You'll need the pinout for
the radio. You might be able to get by without a rack, if you can solder
wires directly to the radio connector.

I did this with my Narco Escort 110, back when the frequency standards were
tightened and I had to replace it. Just a nice evening's project, unless
you want to build an enclosure so it looks purty.

Mark's right, though, if your sole reason for it is to listen to traffic,
buy a cheap airband radio. Mine was an addition to an collection of old
instruments in my office, so it was just an added fillip to get it running.
Rarely turn it on, unless we have visitors with kids. I live with
line-of-sight to a nearby uncontrolled field, with the downwind traffic
about a quarter-mile away and 500 feet above me.

Got an old Mark IV coffee-grinder I'm half interested in firing up, but now
we're getting into some high voltage....

Ron Wanttaja

[Andrew Boyd]

Ron Wanttaja > wrote:

> the antenna can be just a bit of wire.

the trick is to cut it to the right length.

Might I suggest a "marconi antenna"? Do a google on it,
it's just a vertical piece of wire, cut to 1/4 wavelength,
with a horizontal ground plane underneath.

What's 1/4 wavelength? Well, from high school physics we
fundamentally we know that

V = F * Lambda

Where V = velocity, F = frequency, Lambda = wavelength

Using grade 8 algebra, divide both sides of the equation
by (non-zero) F to isolate Lambda gives:

Lambda = V / F

Assuming that radio waves move at the speed of light,
We know that V = 3 x 10^8 meters per second, and let's
use a nominal F = 120 Mhz or 120 x 10^6 = 1.2 x 10^8

Therefore Lamda = 3 / 1.2 = 2.5 meters. Therefore
1/4 wavelength would be 0.625 meters or around 24.4 inches.

Keep in mind, though, I'm just a dumb airshow pilot -
check with Jim about this. He builds these in his sleep
from welding rod.

--
ATP http://www.pittspecials.com/images/oz_inv.jpg

[G.R. Patterson III]

Andrew Boyd wrote:
>
> He builds these in his sleep from welding rod.

He only uses welding rod for the deluxe models. Coat hangers are fine for the
bottom of the line. :-)

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

[Jim Weir]

Which is the theoretical length of an infinitely small diameter wire antenna.
For antennas made out of REAL materials (like brass welding rod) you wind up
with a Finagle Factor that approximates somewhere between 90 and 95% for rod
between 1/8" and 1/4". In general, I recommend somewhere around 22.5 inches for
the bottom end of the band (around 120 MHz.) or so, and an inch shorter for the
dead center of the band at 127.5 MHz.

Jim



->Therefore Lamda = 3 / 1.2 = 2.5 meters. Therefore
->1/4 wavelength would be 0.625 meters or around 24.4 inches.
->
->Keep in mind, though, I'm just a dumb airshow pilot -
->check with Jim about this. He builds these in his sleep
->from welding rod.



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[Jim Weir]

Did an April article back when I was writing for Private Pilot on the advantages
of the "co-tanger antenna".

Jim


"G.R. Patterson III" >
shared these priceless pearls of wisdom:


->
->He only uses welding rod for the deluxe models. Coat hangers are fine for the
->bottom of the line. :-)




Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[G.R. Patterson III]

Jim Weir wrote:
>
> Did an April article back when I was writing for Private Pilot on the advantages
> of the "co-tanger antenna".

Jim, whatever happened to that guy that was going to get all your old articles
on-line for you? If that fell through, give me a shout at the reply-to address.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

[Jim Weir]

WE started on it last week. Give him a couple of weeks and we'll see what
happens.

Jim


"G.R. Patterson III" >
shared these priceless pearls of wisdom:

->
->
->Jim Weir wrote:
->>
->> Did an April article back when I was writing for Private Pilot on the
advantages
->> of the "co-tanger antenna".
->
->Jim, whatever happened to that guy that was going to get all your old articles
->on-line for you? If that fell through, give me a shout at the reply-to
address.
->
->George Patterson
-> Great discoveries are not announced with "Eureka!". What's usually said
is
-> "Hummmmm... That's interesting...."

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com