QRZ! Ham Radio 5/QRZ Ham Radio Callsign Database - Volume 5.iso/digests/homebrew/940324.txt

Internet Message Format | 1994-11-13 | 15KB

Date: Thu,  3 Nov 94 04:30:35 PST
From: Ham-Homebrew Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Homebrew Digest V94 #324
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Ham-Homebrew Digest         Thu,  3 Nov 94       Volume 94 : Issue  324

Today's Topics:
                  40 - 70 MHz crystal filter design
                            antenna tuner
                             buying help.
                       FM Crystal Set (2 msgs)
                    Interdigital Filters (2 msgs)
                            Intermod Help!
                Program for desining low pass filters
                       Source of ferrite cores
                       Where does the power go

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policies or positions of any party.  Your mileage may vary.  So there.
----------------------------------------------------------------------

Date: 2 Nov 1994 14:46:15 GMT
From: [e-mail] (Bill Kirkland)
Subject: 40 - 70 MHz crystal filter design

Are there any articles or programs detailing design of crystal filters in the
40 - 70 Mhz range.


Bill Kirkland

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

Date: 02 Nov 94 09:13:00 -0500
From: [e-mail] (Bob Klug)
Subject: antenna tuner

Does anybody have plans for an easy-to-build antenna tuner?
I am new to the shortwave listening hobby.  For my birthday last year
my girlfried bought me a "boat anchor" --a Blaupunkt model 40103 AM/FM/
Sw radio & phonograph player that is probably 25 years old.  She got it
at a local flea market for $25.  I bought a 70 ft piece of stranded
copper wire for an antenna and hung it in my attic.  I get pretty good
reception, but I read Harry Helm's book on shortwave listening and he
recommends using an antenna tuner.  I got plans for one from Panaxis
but it involves winging 44 turns of wire around a core.  This will be
my very first attempt at building any equipment and I am afraid winding
44 turns of wire around a core and making 12 taps from it will be more
difficult for me to get working than I realize.

Can anybody offer me an easier-to-build model, or give me any other
advice or encouragement?  Thanks.


Bob Klug
---------
Fidonet:  Bob Klug 1:109/239
Internet: [e-mail]

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

Date: 28 Oct 94 19:58:28 CST
From: [e-mail]
Subject: buying help.

just by the goddammed coors light, and be done with it.

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

Date: 2 Nov 94 17:43:27 GMT
From: [e-mail]
Subject: FM Crystal Set

Ian Mitchell asked how the crystal set works in digest #323.

He correctly mentions that to receive FM it acts as a slope detector.  A slope
detector uses the selectivity curve of the tuned circuit to convert the FM into
AM which is then detected by the diode.  If all of the energy of the FM circuit
is below the center frequency (Fo) of the tuned circuit, then frequencies closer
to Fo will have higher amplitudes than lower frequencies.  This has the effect
of amplitude modulating the signal.  Below is a model of what the selectivity
curve of a single tuned circuit response looks like with Fo, Fc (the carrier of
the FM), Fmax (high freq for maximum deviation of FM signal), and Fmin (low freq
for maximum deviation of FM signal) shown.  The name slope detection comes from
using the slope of the Vout vs Vin curve as shown below.


               __|__
              /| |  \
             / | |   \
            /  | |    \
           /   | |     \
          /|   | |      \
         / |   | |       \
        /  |   | |        \
       /   |   | |         \
______/    |   | |          \_______
      |    |   | |
      |    |   | Fo
     Fmin  |  Fmax
          Fc

There is an error in Ian's schematic.  The diode detector MUST have a DC return
to ground.  Because of that I suspect that the .001 uF capacitor with L2 to
ground should be deleted.

Ray Mack
WD5IFS
[e-mail]

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

Date: 2 Nov 1994 01:57:45 GMT
From: [e-mail] (Jim WB5AOX)
Subject: FM Crystal Set

Ian, the described circuit is only a regular run of the mill AM detector.
I'd be interested in the results of such a circuit on FM, though since
broadcast FM is SO broad it might well detect usable audio with slope
detection.  Slope detection of FM works on the principle that you tune
to the "side" of an FM sig with an AM receiver and the frequency "wobbles"
of the FM carrier come across as amplitude variations in the receiver since
the signal strength is, in fact, varying as the frequency slides back and
forth in and out of the AM receivers bandwidth (VERY wide in the case of
similar crystal detectors with NO IF filtering).  The audio thus recovered
is not as loud as when using a good FM detector but if you have sufficient
audio gain it produces quite usable results.... years ago while in college
in the mid 1970's I homebrewed a simple walkie-talkie in a bud minibox
using a VHF engineering transmitter strip and a simple converter in front
of a garden variety AM protable transistor receiver.... it was so quiet
with no signal present I didn't need squelch, it was very stable, and I
could even separate fairly close (in frequency) repeaters so long as they
weren't PHYSICALLY close!  Wish I hadn't cannibalized it, that thing was
a kick to use in front of old timer appliance op hams.....
I also ( and you of course still can) have listened to many a 10 meter FM
QSO with a normal AM rx.   The trick is to tune in for maximum signal
strength, then tune off to the "side" of the signal slowly until the audio
becomes intelligible.  It usually takes some tinkering to get the best
audio, but if tuned properly it will produce surprisingly good audio.
That crystal detector circuit likely would be so broad...... it may work
fine since FM broadcast is on the order of 100 KHZ wide.  And if 2 stations
are fairly close to each other you likely know the result.... more than
one song at a time or none, depending on how far apart they are in
frequency.
Jim Devenport WB5AOX

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

Date: Thu, 27 Oct 94 09:29:02 -0500
From: Richard Trok <[e-mail]>
Subject: Interdigital Filters

FROM:[e-mail]

The program listing that you sent for Interdigital Bandpass Filters was
received incomplete. It ended at Line 930.
I am very much interested in this program and would appreciate it if you
could resend it.
Thanks
Rich  NI9S

___
 X SLMR 2.1a X

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

Date: Thu, 27 Oct 94 09:28:00 -0500
From: Richard Trok <[e-mail]>
Subject: Interdigital Filters

TO:[e-mail]
FROM:[e-mail]

The program listing that you sent for Interdigital Bandpass Filters was
received incomplete. It ended at Line 1320.
I am very much interested in this program and would appreciate it if you
would resend it.
Thanks
Rich  NI9S

___
 X SLMR 2.1a X

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

Date: 2 Nov 1994 01:40:04 GMT
From: [e-mail] (Jim Devenport WB5AOX)
Subject: Intermod Help!

Are you SURE of the "cellular" tower being the source of the interference?
if so, or if you know the main source of RFI and its frequency range, you
can knock the bad interference down 20 to 30 dB (WADS!) with the installation
of a simple coax notch filter.
For 800 MHZ (cellular), merely cut a piece of RG-58 to approx. 2 1/4 inches, put a bnc fitting on
one end, leave the other end open, and install it wit a tee fitting on your
HT ant connection, the jpole coax going to the other port of the tee.
For 450 MHZ, make the coax stub 6 1/4" long
for 150 MHZ, make the stub 18 3/4" long
The basic trick is to cut a coax stub to the 1/4 wave electrical length
so the coax will resonate at the offending frequency.  Since coax has a
"velocity factor" in that rf travels more slowly thru it than solid
copper wire or air, the velocity factor has to be "factored in".
RG58 and may other types of flexible coax has a velocity factor of .6667
so you first find the 1/4 wave length:
(example) 850 MHZ=  468 divided by 850; this is the half wavelength,
then divide by 2 to get the 1/4 length (or simply start by dividing the
desired freq into 234) , which should come out close to .275 feet or 3.3
inches, then multiply that by the velocity factor (3.3 X .67= 2.21 inches
or very close to 2 1/4 inches.  It helps to include the effective length
of the BNC tee at this UHF frequency range...
these make very effective notch filters but do have insertion loss,
especially at frequencies near the notch frequency.... however getting rid
of that much rfi may well outweigh any losses incurred.
73,
Jim Devenport

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

Date: 2 Nov 1994 16:46:06 GMT
From: [e-mail] (Ignacy Misztal)
Subject: Program for desining low pass filters

In <[e-mail]>, [e-mail] (Joe Mack) writes:
>In article <395rsv$[e-mail]> [e-mail] (Ignacy Misztal) writes:
>>I am looking for formula or at best a PD program to design low pass
>>elliptic filters. I am also looking for help with filters that have
>>all inductances the same.
>>

I forgot to say that these are transmitting filters made of coils and
capacitances.


Ignacy Misztal              Ham radio: NO9E, SP8FWB
E-mail: [e-mail]
University Of Illinois      1207 W. Gregory Dr., Urbana, IL 61801, USA
tel. [phone]         Fax: [phone]

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

Date: Wed, 2 Nov 1994 15:09:39 GMT
From: [e-mail] (David Stockton)
Subject: Source of ferrite cores

David Crooke ([e-mail]) wrote:
: My father (GM0RHP) is looking for a source of 4" long by 1/4" dia. ferrite
: core rods to build some fancy antenna. The only source he knows of is in
: California, USA - is there anywhere closer or am I best to just order them
: on plastic and have them pop them in the post in a jiffy bag?

: Dave


   I can probably help.  I may even have something suitable in my junk
box.  I've not seen your dad for some time.

  There IS life in the UK on this group!

    Cheers
              David  GM4ZNX

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

Date: Thu, 3 Nov 1994 02:57:29 GMT
From: [e-mail] (Gary Coffman)
Subject: Where does the power go

In article <3998nm$[e-mail]> [e-mail] (Guy Fletcher) writes:
>
>This is a rather different way of looking at the question,
>hence the new thread. Considered comments welcome.

You've said it much better than anyone else. The rest of us have
been trying to stretch other models to say the same thing, sometimes
without much success. If I may summarize, real power always flows
towards the load, any heating in the amplifier is the result of
loss of efficiency due to a poor load impedance at the amplifier
output terminals. All else is chimera.

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | [e-mail]
Lawrenceville, GA 30244     |                     |

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

Date: Mon, 31 Oct 1994 20:46:16 GMT
From: [e-mail] (Scott Dorsey)

References<[e-mail]> <39164j$[e-mail]>, <[e-mail]>
Subject: Re: THE LITTLE RAZOR BLADE RADIO (UPDATE)

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>In article <39164j$[e-mail]> [e-mail] (Burt Keeble) writes:
>>So far, the only sources of high carbon steel that I have found are
>>cutting implements (razor blades, carving blades, etc....).  I would
>>like a source that isn't potentially dangerous.
>>
>>Any suggestions?
>
>Chain saw bars, cold chisels, files, etc are all high carbon steel.

Cast iron isn't high carbon steel, but works well for a steel detector
anyway if you can get a polished section.  Still, I always had better
luck with copper oxide detectors myself (and copper oxide is everywhere,
unfortunately).
--scott
--
"C'est un Nagra.  C'est suisse, et tres, tres precis."

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

Date: Wed, 2 Nov 1994 15:05:52 GMT
From: [e-mail] (Zack Lau (KH6CP))

References<[e-mail]> <[e-mail]>, <[e-mail]>
Subject: Re: Where does the power go?

Gary Coffman ([e-mail]) wrote:

: Class AB1 amplifiers routinely achieve 65% efficiency from DC input
: to RF output in VHF TV broadcast service. Tubes certainly aren't
: 100% efficient, but that's not because of some output impedance
: resistor. It's because of contact resistance, back bombardment,
: and plain old I^2R losses in the tube structure. Every attempt
: is made to minimize these losses. Tube contact surfaces are silver
: plated, and made large, tube structure lengths are minimized, and
: suppressor grids are used in some cases. Flowing 12 amps at 8 kV
: can cause a tube, and cavity, to heat, but not 48 kWs worth.

8000V/12 amps*.35=233 ohms

Can you further break down these losses--how much is
due to to each factor?  I have to admit that I'm surprised
that contact losses would be worth mentioning, particularly
since they involve large, silver plated surfaces.  I use
cheap molex connectors with little tin plated contacts, and
they aren't significant in a circuit with involving 2 amps
at 12 volts (12V/2amps=6 ohms).
--
Zack Lau  KH6CP/1           2 way QRP WAS
                           8 States on 10 GHz
Internet: [e-mail]   10 grids on 2304 MHz

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

Date: Wed, 2 Nov 1994 01:59:06 GMT
From: [e-mail] (Gary Coffman)

References<[e-mail]> <[e-mail]>, <395svn$[e-mail]>
Reply-To: [e-mail] (Gary Coffman)
Subject: Re: THE LITTLE RAZOR BLADE RADIO (UPDATE)

In article <395svn$[e-mail]> [e-mail] (Burt Keeble) writes:
>
>Well, how do I make a copper oxide detector?   Maybe that would be a
>better component?

Think pennies. That green coating old copper pennies get is a copper
oxide.

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | emory!kd4nc!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | [e-mail]
Lawrenceville, GA 30244     |                     |

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

End of Ham-Homebrew Digest V94 #324
******************************