QRZ! Ham Radio 4/QRZ Ham Radio Callsign Database - Volume 4.iso/digests/homebrew/940286.txt

Internet Message Format | 1994-11-13 | 16KB

Date: Tue, 27 Sep 94 04:30:36 PDT
From: Ham-Homebrew Mailing List and Newsgroup <[e-mail]>
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Subject: Ham-Homebrew Digest V94 #286
To: Ham-Homebrew


Ham-Homebrew Digest         Tue, 27 Sep 94       Volume 94 : Issue  286

Today's Topics:
                  Can combine two 50MHz Tx signals?
                      High Voltage Screen Supply
                    Interdigital filters (3 msgs)
                 Need Help: measuring coil resistance
                                Pspice
                 Reuse surface mount parts? (2 msgs)
                  Specs: "RCA 400  40341"  "2N6485"
                      WTB: a few NE561 pll chips

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Archives of past issues of the Ham-Homebrew Digest are available
(by FTP only) from UCSD.Edu in directory "mailarchives/ham-homebrew".

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: Mon, 26 Sep 1994 12:28:47 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!gatech!wa4mei!ke4zv![e-mail]
Subject: Can combine two 50MHz Tx signals?
To: [e-mail]

In article <[e-mail]> [e-mail] (Alan Cooney) writes:
>Greetings:
>
>I'm looking for your suggestions on combining two or more six meter
>signals.  These are in the 100 milliwatt range, and are relatively
>closely spaced (100-200 KHz).  I need a broadband solution (untuned)
>if possible, so that the transmitter frequencies can be varied within
>a few hundred kilocycles or so without altering the need for a 'tune up'.
>
>What the heck is this for, you ask?  I work for a company that builds
>remotely controlled models for the movie industry.  We use six meter
>RC equipment with one power amp and antenna per RC 'channel', and that
>can add up to a rack of power amps and a field of antennas for a given
>shoot.  We'd like to be able to combine at least two signals before
>amplification -- to cut the number of amps and antennas we have to fuss
>with.

Ahem. If you really mean the 6 meter amateur band, I want the name
of the company. Using amateur radio for commerical gain is still
illegal.

If you mean commercial frequencies near 6 meters, then the way to
get around the rack of amps and field of antennas is to use Wilkinson
combiners on all the transmitters and feed them into a single linear
amplifier. Make sure the amp is really linear though. One that will
pass a broadcast TV signal will work. A low band CATV master distribution
amplifier would be a good choice. That can then feed a single antenna.

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, 26 Sep 1994 18:39:45 +0000
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!news.sprintlink.net!demon!ifwtech.demon.co.uk![e-mail]
Subject: High Voltage Screen Supply
To: [e-mail]

Harry W3IIT wrote
>
> I'm looking for a reference to a high voltage screen power supply for an RF high power amplifier.
>I'd like a shunt regulated supply so that it has a low impedance and preferrable variable voltage
>around 300 to 400 volts or so. I know that basic regulators can be made using VR tubes but I'm
>looking for something more robust and with some adjustment capability.

There are two in the _VHF/UHF_DX_Book_ (from ARRL) which were designed
for 4CX250/350s and similar. They use op-amp regulation with either
bipolar or power MOSFET shunt elements, and are well proven designs with
good protection against short-circuits and flashover. Regulation is
+-100mV or better - more than you'll ever need.

I've had a similar MOSFET design running for about 3 years which also has opto-
coupled overcurrent shutdown. There's a new PCB for this 'in beta' which will be
configurable for voltages from 200 up to about 600, in any grounding configuration,
and should be a universal retrofit for existing screen supplies using VR tubes and zener
stacks. More details later...

(Excuse the boost for the book, but that's where several of us assembled a lot of good
information that wasn't easily available anywhere else.)


 73 from Ian G3SEK               |  Editor,  _The_VHF/UHF_DX_Book_
 Abingdon, England               |
 [e-mail]       | "In Practice" columnist for RadCom (RSGB)

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

Date: 26 Sep 1994 12:05:00 GMT
From: ihnp4.ucsd.edu!swrinde!howland.reston.ans.net!math.ohio-state.edu!jussieu.fr!news-rocq.inria.fr!univ-lyon1.fr![e-mail]
Subject: Interdigital filters
To: [e-mail]

 Hi !

 Does anybody out here have any design formulae to build narrow-band inter-
digital filters ?
 Typically, I need a filter centered on about 1297 MHz with more than 90 dB
insertion loss at 1291 MHz. The French SHF repeater shift is - 6 MHz.

 Thanks,
 Vincent

--
F1RCS - Worldwide Friendship through Amateur Radio
ENST, Ecole Nationale Superieure des Telecommunications, Paris

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

Date: 26 Sep 1994 13:21:58 GMT
From: news2.near.net!usenet.elf.com!rpi!marcus.its.rpi.edu![e-mail]
Subject: Interdigital filters
To: [e-mail]

Elendir ([e-mail]) wrote:
:  Hi !

:  Does anybody out here have any design formulae to build narrow-band inter-
: digital filters ?
:  Typically, I need a filter centered on about 1297 MHz with more than 90 dB
: insertion loss at 1291 MHz. The French SHF repeater shift is - 6 MHz.
    Wow, holy unloaded Q batman!

    anyway, there supposedly is a design program out there that
was published... I think it's written in basic.  I don't have it
personally though.

            -L


--
Lance Lascari WS2B <[e-mail]> Senior EE @ Rensselaer Polytechnic Inst.
Mount Greylock Expeditionairy Farce Secret agent #52,342

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

Date: Mon, 26 Sep 1994 12:32:47 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!gatech!wa4mei!ke4zv![e-mail]
Subject: Interdigital filters
To: [e-mail]

In article <366ddd$[e-mail]> [e-mail] (Elendir) writes:
> Hi !
>
> Does anybody out here have any design formulae to build narrow-band inter-
>digital filters ?
> Typically, I need a filter centered on about 1297 MHz with more than 90 dB
>insertion loss at 1291 MHz. The French SHF repeater shift is - 6 MHz.

Ouch! That's tough. To get that much rejection, your insertion loss on
the desired receive channel is going to be really high, probably as much
as 10 db. I doubt that will be acceptable. You should stick to standard
cavity notch duplexers instead.

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, 26 Sep 1994 17:15:05 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!news.cs.utah.edu!cs.utexas.edu!howland.reston.ans.net!europa.eng.gtefsd.com!ceylon!news2.near.net!zcias2.ziff.com!tomkreyche.zdlabs.ziff.com!user@network.
Subject: Need Help: measuring coil resistance
To: [e-mail]

Dear homebrewers,

I'm working on a commerical seismometer (for measuring distant earthquakes)
and don't understand some coil phenomena.

The instrument has an coil of very fine wire (about #44) wound on a hollow
plastic core, probably >> 5000 turns, about 1.5 inches in diameter.
Horizontal earth movement causes this coil to move in and out of a strong
magnet, which generates a changing voltage.

If I remove the magnet and measure the coil resistance, it shows a rock
steady 48.1 k ohms.

With the magnet in place around the coil and with the coil locked so it
can't move, the coil resistance bounces slowly betwee 47.6k and 48.5k.

The measurements are made at a stable room temperature using a fluke 75
multimeter. I imagine the meter works by running a small current though the
DUT and measuring voltage across a resistor, so naturally any change in
current in the DUT will play hell with the measurement.

Why does the resistance appear to change with the magnet in place? Is it
simply due to very small thermal movements, even though the coil is locked?
or is something else going on, like changes in the earth's magnetic field
or something more mundane?


Thanks, Tom KG6YJ

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

Date: 27 Sep 94 00:19:19 GMT
From: [e-mail]
Subject: Pspice
To: [e-mail]

>Do any of you use pspice on a Mac?  I downloaded a copy but am unable to
>get it to run.  My system crashes..with a bad F-line instruction message.
>Any ideas?
>Thanks...John

It requires an FPU to run and I dont think you have one.

mail me direct if you want to talk about it!

Kevin Purcell, N7WIM / G8UDP      [e-mail]     206/649-6489
Seattle dBug Mac Developers SIG organiser

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

Date: Mon, 26 Sep 1994 13:01:21 +0000
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!agate!howland.reston.ans.net!news.sprintlink.net!demon!ifwtech.demon.co.uk![e-mail]
Subject: Reuse surface mount parts?
To: [e-mail]

> Fred McKenzie ([e-mail]) wrote:
> >
> : If ordinary solder (63-37 tin-lead) is used, the lead can almalgamate with
> : the silver that is fired onto the component.  The result is that you can
> : no longer solder to it.  You must use something like a "silver-saturated"
> : solder, or the appropriate solder paste.  (Note:  this is not the same as
> : "silver solder", which has a much higher melting point.)
>
... or to put it another way, ordinary solder dissolves the silver out of the
plating on the component. Obviously this phenomenon only affects ceramic-bodied
compnents such as Rs, Cs and Ls. ICs and other devices with solid metal
legs can be resoldered for as long as they hold together :-)

> Wow, I never heard that before.  We use standard tin-lead solder all the
> time around here for soldering SMT devices.

Well, yes - ordinary solder is OK for first-time use of components, but
each repeated application to reclaimed components (and that includes 'cleaning'
old solder off them) makes the ceramic-metal connections less reliable.

I never re-use chip Rs (they only cost pennies), and always suspect the
joint continuity of re-used chip Cs.

Regarding the hot air / blowtorch method of stripping boards, GM4ANB recommends
doing it over a bowl of cold water. If the components (ICs in particular) are
sealed as they should be, they'll benefit from the immediate cooling.


 73 from Ian G3SEK               |  Editor,  _The_VHF/UHF_DX_Book_
 Abingdon, England               |
 [e-mail]       | "In Practice" columnist for RadCom (RSGB)

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

Date: Mon, 26 Sep 1994 12:22:14 GMT
From: ihnp4.ucsd.edu!agate!howland.reston.ans.net!gatech!wa4mei!ke4zv![e-mail]
Subject: Reuse surface mount parts?
To: [e-mail]

In article <[e-mail]> [e-mail] (Alan Bloom) writes:
>Fred McKenzie ([e-mail]) wrote:
>[Re: soldering surface-mount devices]
>
>: If ordinary solder (63-37 tin-lead) is used, the lead can almalgamate with
>: the silver that is fired onto the component.  The result is that you can
>: no longer solder to it.  You must use something like a "silver-saturated"
>: solder, or the appropriate solder paste.  (Note:  this is not the same as
>: "silver solder", which has a much higher melting point.)
>
>Wow, I never heard that before.  We use standard tin-lead solder all the
>time around here for soldering SMT devices.

Heh, heh, maybe that's why Tektronix gear is so much more reliable.
They used to include a little role of silver bearing solder in
every instrument so the tech could fix it right.

(In the old days that was because of the silver bearing contacts on
their ceramic terminal strips, but it applies to modern SMDs too.)

It's true that using ordinary solder can cause the silver to leach
out of the contacts on SMD components. That can lead to connection
failures. That's primarily an issue with leadless SMDs like caps
and resistors. It doesn't apply to leaded ICs. Their leads are
tin plated, and solder fine with ordinary solder.

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: 26 Sep 1994 11:26:01 -0400
From: newstf01.cr1.aol.com!newsbf01.news.aol.com![e-mail]
Subject: Specs: "RCA 400  40341"  "2N6485"
To: [e-mail]

My meager selection of data books do not have any information on the the
following:

RCA 400  or  40341 (device has both of these markings)


2N6485  which is a tiny metal cased 6-pin device.

The RCA device was pulled out of a "50 MHz oscillator" purchased at a
hamfest for $1.  The thing was cold soldered (no wonder it didn't work).

The other device was pulled from a PC board of some type.

Thanks for any answers for these two--I would like to use the RCA device
at two meters if it is rated for that high a frequency.

72,73, jim n0oct

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

Date: 26 Sep 1994 13:51:09 GMT
From: ihnp4.ucsd.edu!usc!howland.reston.ans.net!math.ohio-state.edu!magnus.acs.ohio-state.edu!csn!jabba.cybernetics.net!cybernetics.net![e-mail]
Subject: WTB: a few NE561 pll chips
To: [e-mail]

Am trying to build a project requiring a Signetics NE561.  I am unaware
of any substitute with the same set of features.  Can anyone spare 2-4
pieces from their old parts bins?

Thanks, Jeff

--
Jeff Brown                 [e-mail]

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

Date: Mon, 26 Sep 1994 17:43:08 GMT
From: ihnp4.ucsd.edu!dog.ee.lbl.gov!news.cs.utah.edu!cs.utexas.edu!howland.reston.ans.net!EU.net!sun4nl![e-mail]
To: [e-mail]

References <[e-mail]>, <[e-mail]>, <[e-mail]>rtj
Subject : Re: Reuse surface mount parts?

In <[e-mail]> [e-mail] (Ian G3SEK) writes:
>Regarding the hot air / blowtorch method of stripping boards, GM4ANB recommends
>doing it over a bowl of cold water. If the components (ICs in particular) are
>sealed as they should be, they'll benefit from the immediate cooling.

Is that true? I fear that the temperature shock is likely to cause
micro-cracks in the plastic body.

Geert Jan

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

End of Ham-Homebrew Digest V94 #286
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