QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/files/qrp/archives/current.txt/text0007.txt

Text File | 1994-11-27 | 5.8 KB | 144 lines

=>
=>All,
=>
=>leaving for NC for a few days.. will be on the air (hopefully)
=>while driving..bungey corded the MFJ20mSSB in the car with a Ham
=>Stick.. hooked up my Radio Shack ignition noise filter (couldn't
=>operate the MFJ in the car before because of engine noise..
=>amazingly with the RS in line using the Cigarette lighter..seemed
=>to work when I tested it out).

The cigarette lighter jack should not be used to operate ham equipment.
Run fused power leads directly to the battery using heavy-guage insulated
cable through the firewall.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Randall Rhea                                        Informix Software, Inc.
Client Services Engineer                              [e-mail]

From [e-mail]  Tue Jul  5 13:09:21 1994
Return-Path: <[e-mail]>
    id KAA03934; Tue, 5 Jul 1994 10:04:30 -0700
Date: Tue, 5 Jul 1994 10:04:30 -0700
Message-Id: <[e-mail]>
To: [e-mail]
From: [e-mail]
Subject: LM386 noise?
Sender: [e-mail]
Precedence: bulk

On 07-04-94  [e-mail] wrote to  [e-mail]:

 > I've just put together an audio amplifier using a LM386N (date code
 > 7636) and using earphones it has a rather loud background hiss.  Is
 > this normal?

Depends on what you mean by "rather loud."

POSSIBILITY... do you have the right load on the input?

POSSIBILITY... your headphones are very efficient and you're hearing the noise
floor to a greater degree than you would with a speaker.  Solution:
attenuating resistors in the output line to the headphones!

Not many ham references talk about this, but it is a common practice in audio
equipment.  A headphone is more efficient than a speaker, plus you're listening
with the things right in your ear.  The resistor just puts the headphone
efficiency more on a par with a speaker, so that for about the same volume
setting you get about the same perceived audio level.

I first discovered this with a hi-fi setup as a kid.  Why did I hear more noise
when attaching the phones to the speaker output than I did thru the headphone
jack?  Because the phone jack had 100 ohm attenuating resistors, thus swamping
the noise and making you turn up the volume higher so the s/n ratio of the
output amp is decent.  100 ohms would be appropriate for such a moderate power
hi fi amp (25 watts/channel).  For our needs, probably less.

You could also have oscillations and such, but had to take this opportunity to
point out this little-known problem.

* John Seboldt...Mpls, MN... :      The joint chiefs of staff:      *
| Amateur radio K0JD...      :  General Confusion and Major Error   |
* [e-mail]       :            ("Car Talk")              *

 -> Alice4Mac 2.3 E QWK Eval:05Mar94

From [e-mail]  Tue Jul  5 13:24:03 1994
Return-Path: <[e-mail]>
    id KAA04179; Tue, 5 Jul 1994 10:20:07 -0700
Date: Tue, 5 Jul 1994 10:20:07 -0700
Message-Id: <[e-mail]>
To: [e-mail]
From: [e-mail]
Subject: "Balanced" L Nets?
Sender: [e-mail]
Precedence: bulk

On 07-05-94  [e-mail] wrote to [e-mail],

 > I believe that there is a similar article in one of the antenna
 > compendiums that goes through a bit more analysis (than Lau's article)
 > of this type of design (balun in front of unbalanced L-network).
 > Although the L-network looks unbalanced, the balun forces it to be
 > balanced - and using one inductor, rather than two, greatly simplifies
 > the design.
 >
 >         I don't know if this really works - in a quick read-thru of
 > the article it seemed that something was missed in the theoretical
 > discussion - I really should go back and dig into it more deeply.  But
 > I agree with John, give it a try, it is a MUCH simpler design.
 >
 >         - Jeff, WA6AHL

It might be a "pretty" good scheme overall, but SOMETHING must be unbalanced if
you really are a perfectionist.  After all, phase delays in AM broadcast
networks are finagled via various different L and C values in the lines to
different towers.  You might have current 180 degrees out of phase, but voltage
not.

Which may be fine for simple dipoles

* John Seboldt...Mpls, MN... :      The joint chiefs of staff:      *
| Amateur radio K0JD...      :  General Confusion and Major Error   |
* [e-mail]       :            ("Car Talk")              *

 -> Alice4Mac 2.3 E QWK Eval:05Mar94

From [e-mail]  Tue Jul  5 13:51:02 1994
Return-Path: <[e-mail]>
    (1.38.193.5/16.2) id AA28725; Tue, 5 Jul 1994 13:50:33 -0400
From: [e-mail]
X-Mailer: America Online Mailer
Message-Id: <[e-mail]>
To: [e-mail]
Date: Sat, 02 Jul 94 10:07:31 EDT
Subject: Z-match tuner article
Sender: [e-mail]
Precedence: bulk

I wrote:

 > I'm also building a Z-match (recent issue (late 93?) of Communications
 > Quarterly).  Nice thing about the Z-match is that it requires no balun
 > to run coax, random wire or balanced feed line.  We used one at FD
 > built by WN9V, and it too will match darn near anything.

John Seboldt <[e-mail]> asked:

^Can you track this down further?  My current dilemma is coming up with ONE
^design that really works for either balanced or unbalanced.  For example, my
^balanced version of W1FB's "Simple Resonant ATU" has the link wound in the
^middle; this is less than optimum for unbalanced....

I found the article, it is Winter 1994 Communications Quarterly "A Single
Coil Z-Match Antenna Coupler" by T. J. Seed, ZL3QQ, page 99.  There are quite
a few diagrams and drawings (drarwrings?) and I don't have access to a
scanner.  If you can't find the mag near you, maybe we could work something
out

Good Luck!

72 (+/- 1) Jim N0OCT