QRZ! Ham Radio 3/QRZ Ham Radio Callsign Database - Volume 3.iso/digests/homebrew/940013.txt

Internet Message Format | 1994-06-04 | 15KB

Date: Sat, 29 Jan 94 04:30:34 PST
From: Ham-Homebrew Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Homebrew Digest V94 #13
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Ham-Homebrew Digest         Sat, 29 Jan 94       Volume 94 : Issue   13

Today's Topics:
                    Antenna pre-amp design. Help!
                 Antenna Tuner Project Advice Needed
                              Crazy VFO
                 digital readout using freq counter?
                 Electronics parts stores in DC area
                 IBM-PC Shareware for PCB Photo work
              T-368 exciter successfully transistorized!
                want to build reciever for 108-137Mhz
                          XTAL source needed

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Archives of past issues of the Ham-Homebrew Digest are available
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We trust that readers are intelligent enough to realize that all text
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policies or positions of any party.  Your mileage may vary.  So there.
----------------------------------------------------------------------

Date: Wed, 26 Jan 1994 00:18:52 GMT
From: nic.hookup.net!paladin.american.edu!europa.eng.gtefsd.com!emory!rsiatl!ke4zv![e-mail]
Subject: Antenna pre-amp design. Help!
To: [e-mail]

In article <[e-mail]> [e-mail] writes:
> Can anyone here give me some advice on building an antenna pre-amp
>for working 4 - 24 mHz? Should I go broadband or switched bands? What about
>pre-filtering?

Normally, a preamp is unnecessary for the HF spectrum. The usual problem
is inadequate rejection of strong signals. However, if you've got an old
deaf receiver, like say a S-28, a preamp may help. You definitely want to
use a selective amplifier with good sharp tuned circuits. A triple ganged
circuit would be a good idea. Otherwise your preamp will operate in overload
most of the time.

> What are the advantages of designing one around bi-polar or mosfet?
>Can anyone contribute some tried and tested circuits for me to construct?

FETs would be the more popular choice. You can tap up on the selective
circuits for lighter loading, hence higher Q, with less problems with a
FET. The old MPF102 would work for this type of circuit, but it can
be driven rather easily into overload. A power VMOS FET like the VMP-4
may be a better choice. Run about 100 ma of standing current.

In looking through my collection of ARRL Handbooks, I don't find a
HF preamp until I go back to the 1962 edition. They have one using
a 6AK5 pentode. This should give you an idea of the apparent lack
of need for such circuits with more modern equipment.

If the problem is that you are using a small voltage probe antenna,
a FET configured as an emitter follower mounted directly on the
antenna may be used to transform the signal impedance down to
something more to the liking of the receiver and coax. Again run
enough standing current to avoid overload problems.

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

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Date: Sat, 29 Jan 1994 06:31:25 GMT
From: dog.ee.lbl.gov!agate!iat.holonet.net![e-mail]
Subject: Antenna Tuner Project Advice Needed
To: [e-mail]

[e-mail] (Bruce Pea) writes:

>I'm getting ready to put a dipole up and use ladderline to
>feed it. I'm going to need an antenna tuner so I can tune
>this wire across 160-10m.

>I thought building a tuner would be a nice winter project.
>Do any of you have a favorite tuner project you would like

"A *Balanced* Balanced Antenna Tuner", February 1990 QST, page 28.  Or
some variation on the idea of putting a 50 ohm balun on the INPUT of the
tuner, not trying to use a balun in the output to the line.

The above is a balanced L network -- with the inductance split between the
legs of the line, and the capacitance across the output.  You then feed
this with a current balun, like a large coil of coax, or the W2DU choke
balun, or even a good broadband transformer.

Another variation on this idea is the QRP Transmatch for Balanced Lines
found in my 1988 ARRL Handbook (maybe later editions too).  He doesn't
split the inductance, but does put the balun on the input, and keeps the
matching network floating.

In any case, avoid putting a toroid balun on the output when yoy're going
to feed a non resonant, reactive load such as a dipole used on all bands.
They are not designed for this, despite their almost universal use in
commercial tuners.  Another QST article, I can't remember where, documents
how badly they work under reactive loads.

I use two rotary inductors, a variable capacitor, and a coax balun
consisting of about 30 feet RG58 on a five-inch PVC pipe.  Works great --
solved a LOT of RF problems in the shack with a balanced open wire on
most HF bands.

John K0JD

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

Date: 28 Jan 94 23:39:26 GMT
From: sdd.hp.com!col.hp.com!srgenprp![e-mail]
Subject: Crazy VFO
To: [e-mail]

Roberto Valfredini ([e-mail]) wrote:

: I build a VFO ...
: The Vfo was performing good , after warming up for 20 minutes
: it was moving in a range of max 20  Hz.
: The frequency from power-on increase of 90-100 Hz.  ...

: Now the problem is  that if I put the vfo inside its metal box
: to make it usable and connecting the box itself to the ground of the
: vfo (as it should be )  etc etc ...  In a few words  putting it in its
: final state then it starts to become instable increasing or decreasing
: its frequency of more than 800 or more Hz and trying to drift also after
: more than 1 hour from power-up.

Is the oscillator's tank inductor a toroid or an air-wound solenoid
(cylinder)?  Air-wound solenoids radiate a large magnetic field which
can couple into nearby metallic objects, ruining the coil Q and
stability.  The smaller the metal box, the greater the problem.
Steel is especially bad.  If you are using an air-wound coil, try
using a larger box made of aluminum or copper-clad board soldered
together.

AL N1AL

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Date: Wed, 26 Jan 1994 01:17:03 GMT
From: gatekeeper.us.oracle.com!sgiblab!barrnet.net!netnews.synoptics.com![e-mail]
Subject: digital readout using freq counter?
To: [e-mail]

In article [e-mail], [e-mail] (Edward Pacyna) writes:
>
>The measurement principle is simple: the frequency of the VFO is counted and
>the frequency of the IF is added or subtracted from the VFO count

**** Here's another way.  You can use pre-settable counters, and instead of
presetting them to zero, you preset them to the two's complement of the IF
frequency.   That way, the count goes up from ( negative-of-the-if-freq )
through zero up to the actual frequency of interest.  This assumes high-side
injection of course.

    If you have a unit with different schemes for transmit and receive, then you
just arrange to preset the counter to one value for xmit, another for receive.
The scheme could even be expanded with diodes for bandswitching.

                                       - Jerry Kaidor, KF6VB

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Date: Thu, 27 Jan 1994 13:43:11 GMT
From: unix.sri.com!headwall.Stanford.EDU!agate!library.ucla.edu!europa.eng.gtefsd.com!howland.reston.ans.net!vixen.cso.uiuc.edu!uchinews!cs.umd.edu!ra![e-mail]
Subject: Electronics parts stores in DC area
To: [e-mail]

   I'm interested in starting a few electronics projects, but need to find
a good source of electronics parts.  Now don't tell me to go to Radio
Shack!  Their selection is *very* limited.  For example, I need a toroid
core to wind a transformer, but Radio Shack doesn't carry anything like
that.

   So, are there any *real* electronics stores in the Washington, DC area
that cater to electronic hobbyists?

-Dave, KA3QBQ
--
David Drumheller                  phone: [phone]
Acoustics Division, Code 7140       fax: [phone]
Naval Research Laboratory
Washington, DC 20375-5350   e-mail: [e-mail]

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

Date: Fri, 28 Jan 1994 01:49:00 GMT
From: news2.uunet.ca!iceonline!icebox![e-mail]
Subject: IBM-PC Shareware for PCB Photo work
To: [e-mail]

>I think you and anyone else interested would like Protel Easytrax.  I
>bought it when it was not ShareWare (Hay how was I to know two years
>later you could get it free).  I've run a few boards with it and had
>great success.  And you can throw a sheet of overhead projector film in
>your laser printer and save the trouble of having the gerber files
>plotted. (About $25 for a 8x10 film)
>--
>

And where would one be able to get Protel Easytrax from?  Is there a telephone
number or address that they can be reached at?

Jan Chojnacki VE7FJC
 -----------------------------------------------------------------------------
                            : If you eat a live toad first thing in the
 [e-mail]  : morning, nothing worse will happen to you all
                            : day.
                            : To you or the toad.
 -----------------------------------------------------------------------------

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

Date: Sat, 29 Jan 1994 06:52:59 GMT
From: dog.ee.lbl.gov!agate!iat.holonet.net![e-mail]
Subject: T-368 exciter successfully transistorized!
To: [e-mail]

I have had a military surplus T368 VFO/multiplier for some time.  I hooked
it to my old Heath DX60 when I first got back on the air about 5 years
ago, and it was a marvelous VFO -- far more stable than the mating HG10,
and cost $35 from Fair Radio Sales at the time.

If you're not acquainted with the unit, it has a 1.5-3 MHz PTO, a
mechanical digital readout, and doubler stages to cover 1.5-3, 3-6, 6-12,
and 12-24 MHz (they say 12-20, but the dial reads to 24; probably reflects
the ratings of the companion PA).  It's built like a tank, and the tuned
circuits in the multipliers track the PTO in typically elegant Collins
fashion.

Lately I have been building up Rick Campbell's R2 receiver, and have had a
5 watt transmitter for some time, built while I was trying to see if Rick
was going to provide kits!  When it became apparent that he was barely
able to keep up with circuit board requests, I made my own and went
forward.  Gradually, I realized that the old T368 would be a marvelous
general-coverage VFO -- it's built like a tank, far more stable than I
could ever construct.

Suggestions for transistorizing the PTO were made in Feb. 1989 QST
Technical Correspondence.  I adapted those ideas.  so far, so good.

I was on my own on the multiplier stages.  I chose to wire in JFET's,
using the locally-available NTE312.  One stage had a weird low-frequency
oscillation, but I cured it with a series RC network.  It worked! Then
just broadband output stages to boost the power up for those hungry
diode-ring mixers.

While I was at it, I added a tuning diode to the PTO for RIT and CW
offset.  I have two pots (found matching knobs at a local surplus house!)
and a switch added to the front panel, and a transistor switching
arrangement to select the correct pot when the transmitter is keyed.
Works well with full QSK.

Does this trip anybody's trigger?  Will happily provide more details if
interested -- not that I've done everything absolutely right, of course,
but like any experimenter, I just kept fiddling till it worked.

John K0JD

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

Date: 26 Jan 1994 22:51:31 GMT
From: news.ingr.com!b11!cmack.b11.ingr.com![e-mail]
Subject: want to build reciever for 108-137Mhz
To: [e-mail]

Ramsey sells a kit for an aviation-band receiver. It's in the 25-30 dollar
range.

Model AR-1
Ramsey Electronics
793 Canning Parkway
Victor, NY 14564
[phone]

The tuning is touchy - you might try a 10-turn pot to make it more manageable.
It only covers 118-135 Mhz - you could tune the LO to cover a different
range.
     Dan Kerl
     [e-mail]

I am not affiliated with Ramsey.

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

Date: Wed, 26 Jan 1994 20:12:26 GMT
From: mvb.saic.com!unogate!news.service.uci.edu!usc!elroy.jpl.nasa.gov!sdd.hp.com!col.hp.com!srgenprp![e-mail]
Subject: XTAL source needed
To: [e-mail]

Mike Stansberry ([e-mail]) wrote:

: I order my crystals from either International Crystal Mfg. (ICM),
: 1-800-426-9825, or Jan Crystals, 1-800-526-9825 (just noticed the
: similarity between those numbers, ...

9825 = "XTAL"

AL N1AL

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

Date: 27 Jan 1994 14:29:54 GMT
From: sdd.hp.com!spool.mu.edu!howland.reston.ans.net!usc!elroy.jpl.nasa.gov!newncar!csn!col.hp.com![e-mail]
To: [e-mail]

References <2i63gm$[e-mail]>, <[e-mail]>, <2i6pk8$[e-mail]>csn
Subject : Re: XTAL source needed

Stephen C. Trier ([e-mail]) wrote:
: Mike Stansberry ([e-mail]) wrote:
: : I order my crystals from either International Crystal Mfg. (ICM),
: : 1-800-426-9825, or Jan Crystals, 1-800-526-9825 (just noticed the
: : similarity between those numbers, ...

: In article <[e-mail]>, Alan Bloom <[e-mail]> wrote:
: >9825 = "XTAL"

: It can go a step farther.  426 = "ICM" and 526 = "JAN", so the numbers
: spell out 1-800-JAN-XTAL and 1-800-ICM-XTAL.  I wonder if the companies
: realized the similarity of their mnemonics when they chose them?

:         Stephen

Yeah, I figured out the letter to number conversion after I made that
first posting.

Mike, K0TER

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End of Ham-Homebrew Digest V94 #13
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