QRZ! Ham Radio 5/QRZ Ham Radio Callsign Database - Volume 5.iso/digests/homebrew/940075.txt

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

Date: Sun, 27 Mar 94 04:30:31 PST
From: Ham-Homebrew Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Homebrew Digest V94 #75
To: Ham-Homebrew


Ham-Homebrew Digest         Sun, 27 Mar 94       Volume 94 : Issue   75

Today's Topics:
                 Antenna Tuner Project Advice Needed
                        Component Databooks  ?
                   G4WIM TV transmitter components
                                 Info
                  Noise figure/transistors (2 msgs)
                   RF VHF/UHF Preamp Design Params.
                              subscribe
                      V/UHF VSWR meter. Design ?

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Problems you can't solve otherwise to [e-mail].

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
herein consists of personal comments and does not represent the official
policies or positions of any party.  Your mileage may vary.  So there.
----------------------------------------------------------------------

Date: 26 Mar 1994 08:51:03 -0500
From: hp81.prod.aol.net!search01.news.aol.com![e-mail]
Subject: Antenna Tuner Project Advice Needed
To: [e-mail]

In article <[e-mail]>, [e-mail] (John
Seboldt) writes:

LOOKing for winter ATU project?

I have had excellent results with my SPC transmatch from ARRL handbooks.  A
very interesting design was in Oct '92 (I think) 73 mag that was essentially a
low pass filter: two floating variable inductors with a variable cap to ground.
 Good luck!

JimN0OCT

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Date: 26 Mar 1994 08:57:03 -0500
From: hp81.prod.aol.net!search01.news.aol.com![e-mail]
Subject: Component Databooks  ?
To: [e-mail]

In article <2mrqbu$[e-mail]>, [e-mail] (Jukka Peltomaki)
writes:

Harris (the people who make op amps) also have a software selection guide much
like Motorolas.

Good luck!

jimN0OCT

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Date: 26 Mar 94 07:40:24 GMT
From: [e-mail]
Subject: G4WIM TV transmitter components
To: [e-mail]

The components you need

>        MC145151P2 (Motorola)  and
>        M67715 (Mutsubishi).

are available from Mainline Electronics in England, France and Luxembourg.
Their contact details are:

England:
    Mainline Electronics
    Manor Court
    The Ford, off Little Glen Road
    Glen Parva
    Leicester LE2 9TL
    England
    tel: [phone]/777648
    fax: [phone]
France:
    Mainline Electronics
    2 Chemin Du Bois Roux
    69300 Caluire
    France
    tel: [phone]
Luxembourg:
    Le Radio Amateur
    20 Route De Burange
    L-3429 Dudelange
    Luxembourg
    tel: [phone]

The english prices are MC145151 - 11.90 pds and M67715 - 59.95 pds.

Alternatively, you could contact the author. His address is:

    Tim Forrester, G4WIM
    24 Corran Close
    Dallington
    Northampton NN5 7AL
    England
    tel: [phone]

--
Andy Rutter, g8hck

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Date: 27 Mar 94 05:22:09 GMT
From: [e-mail]
Subject: Info
To: [e-mail]

HELP
QUIT

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Date: Sat, 26 Mar 1994 03:54:32 GMT
From: ihnp4.ucsd.edu!swrinde!sgiblab!cs.uoregon.edu!reuter.cse.ogi.edu!netnews.nwnet.net!bach.seattleu.edu!quick!ole!ssc!fylz!eskimo![e-mail]
Subject: Noise figure/transistors
To: [e-mail]

In article <[e-mail]>,
 <[e-mail]> wrote:
>Hi,
>
>        Here's a design question. I am looking at the front-end RF amp
>which uses a 2N3904 and asking myself if I were to replace this with a
>transistor with a lower noise figure, say a 2N5179 or BF689, will I see
>any improvement? Is this mod worth pursuing? How much improvement can I
>expect to see here?
>
>        Tks.
>
>Daniel
>


In general, low noise transistors have the most beneficial effect at
higher frequencies.  If your RF amp is working at about 10 MHz or less,
you probably won't notice much improvement.  Above that, a simple test
is to listen to the noise with the antenna connected, but no signal
present.  Disconnect the antenna and see if the noise drops.  If it
does, then the limiting factor is the noise from the antenna, and not
the noise generated in the front end transistor.  If it DOESN'T drop,
then a lower-noise transistor is called for.

You can get real fancy with noise figure measurements if you want, but
for ordinary ham purposes, this test will tell you what you want to
know.


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

Date: Sat, 26 Mar 94 19:20:54 GMT
From: btree![e-mail]
Subject: Noise figure/transistors
To: [e-mail]

In article <[e-mail]>, Bill Turner <[e-mail]> wrote:
>In article <[e-mail]>,

[ request for low noise considerations deleted ]

>In general, low noise transistors have the most beneficial effect at
>higher frequencies.  If your RF amp is working at about 10 MHz or less,
>you probably won't notice much improvement.  Above that, a simple test
>is to listen to the noise with the antenna connected, but no signal
>present.  Disconnect the antenna and see if the noise drops.


Close, but not quite right.  Disconnect the antenna and replace it
with a decent terminating resistor.  Then check the amount of noise
being produced by the receiver.

The reason for using a dummy load instead of just disconnecting
the antenna is that some RF amplifiers have a tendency toward
instability when their inputs are not terminated.  The instability
can cause the amplifier's noisiness to appear to either increase
or decrease, primarily as a result of changes in gain in the stage.

BTW, turn off the AGC when doing the test if you want reliable
results.

Best regards,

Bob Hale   [e-mail]

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

Date: Sat, 26 Mar 1994 19:57:55 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!pipex!sunic!psinntp!psinntp!arrl.org![e-mail]
Subject: RF VHF/UHF Preamp Design Params.
To: [e-mail]

Dick Boley ([e-mail]) wrote:
: If you read articles on the construction of RF preamps they
: spen words on bypassing & shielding and claims of gain and
: noise figures. What they do not say is what contributes
: to these claims. Is it the tap point on a coil, a bias resistor,
: obviously the device, or is it some arcane combination.

: The ARRL Handbook has several preamps for home construction.
: The text mentions several transistors and some coil variations.
: It never explains how to "tune" the peramp for best gain and/or
: noise figure and the relationship to the various active devices.

As far as I can determine, the professionals stick the devices into
test fixtures, hook up a very expensive low loss transmatch to the
input, and tune it till they figure out what the best noise figure
is.  Then they subtract out the tuner loss, look at the settings,
and tell you the optimum input impedance to use.  There are also academics
who will attempt to predict noise figures, based on various physical
parameters.  Maximum gain is pretty simple, you match the input and
output impedances with a minimum of loss.  It is often difficult to
get maximum gain while using the impedance that uses gives the best
noise figure.

The fly in the ointment is stability--generally you don't want a
amplifiers to oscillate.  Thus, you have yet another set of impedances
to deal with, but this set has to cover all frequencies in which the
device might oscillate.  In my opinion, a smart designer is like a
good chess player.  He has a bunch of parts (like the pieces he has
left) and comes up with the best solution he can.  A computer is a
great help, but even modern day computers don't win chess games all
the time.  What people usually learn in engineering school is the
rules of the game, and perhaps a little strategy. Tough engineering
problems often aren't solvable by brute force--some wise guy will
think of an elegant solution missed by the "experts."

: I would like to build a basic preamp and start "playing around".
: However, I would like to have some reasonable expectations on
: what to play with and what to expect.  Any source for info in'this area ??

--
Zack Lau  KH6CP/1           2 way QRP WAS
                           8 States on 10 GHz
Internet: [e-mail]   10 grids on 2304 MHz

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

Date: 26 Mar 94 16:56:08 GMT
From: [e-mail]
Subject: subscribe
To: [e-mail]

subscribe
subscription

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

Date: Sat, 26 Mar 1994 05:42:52 GMT
From: ihnp4.ucsd.edu!swrinde!sgiblab!cs.uoregon.edu!reuter.cse.ogi.edu!netnews.nwnet.net!bach.seattleu.edu!quick!ole!ssc!fylz!eskimo![e-mail]
Subject: V/UHF VSWR meter. Design ?
To: [e-mail]

<[e-mail]>
<[e-mail]>
Organization: Eskimo North (206) For-Ever


Somebody makes a great VHF/UHF SWR meter which Radio Shack sells for
$39.95 and another unnamed company sells for about twice that - same
meter, only the name has been changed to increase the profit.

I've had one for a couple of years.  Works great.

W7LZP


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

Date: 25 Mar 1994 21:40:01 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!noc.near.net!hopscotch.ksr.com![e-mail]
To: [e-mail]

References <2maf72$[e-mail]>, <[e-mail]>, <[e-mail]>
Subject : Re: Converting CB to 10 meters

[e-mail] (Jeffrey Herman) writes:
>In article <[e-mail]> [e-mail] (William Freeman USG) writes:
>>    Note that it's probably not worth converting a CB to 10m
>>*unless* the CB is an SSB model.

>Not True! Keying the driver stage and adding an simple BFO to the receiver
>would give you a neat CW xcvr.

A mighty poor one, though.  First, an AM detector usually makes a lousy
product detector (hey even if it's just beeps, it should sound good); second,
you have a 6Kc bandpass instead of 3Kc, for twice the noise.

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End of Ham-Homebrew Digest V94 #75
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