QRZ! Ham Radio 5/QRZ Ham Radio Callsign Database - Volume 5.iso/digests/homebrew/940305.txt

Internet Message Format | 1994-11-13 | 9KB

Date: Sun, 16 Oct 94 04:30:21 PDT
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Subject: Ham-Homebrew Digest V94 #305
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Ham-Homebrew Digest         Sun, 16 Oct 94       Volume 94 : Issue  305

Today's Topics:
               Looking for MPF102 replacement (2 msgs)
                        Q: VLF antenna design
                  Screen Voltage Protection Circuit

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

Date: Fri, 14 Oct 1994 21:45:59 GMT
From: [e-mail] (J.D. Cronin)
Subject: Looking for MPF102 replacement

I have a few projects in mind that use a MPF-102 for pre-amps on
2-meters and 440.  Are there any newer parts that have better gain
or less noise?  The Motorola RF Device book doesn't list substitutes
for the MPF102.

73...Jim  N2VNO

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

Date: 15 Oct 1994 17:47:44 GMT
From: [e-mail] (Han Kim)
Subject: Looking for MPF102 replacement

Dana Myers ([e-mail]) wrote:
> In article [e-mail],  [e-mail] (J.D. Cronin) writes:
> >
> >I have a few projects in mind that use a MPF-102 for pre-amps on
> >2-meters and 440.  Are there any newer parts that have better gain
> >or less noise?  The Motorola RF Device book doesn't list substitutes
> >for the MPF102.

> I'd recommend the J308/309/310 family for 2m/70cm pre-amp use.  A J310
> is certainly superior to an MPF102 in these applications.  However, you
> may need to adjust the circuit to the different specs of the J310 (have
> a look at the data sheets).  A 2N4416 is essentially identical to an
> MPF102, and may be easier to find.

The data sheet I have says a Siliconix U310 (Is this the same device as
J310?) 16dB of common-gate power gain at 105MHz and 11dB at 450MHz. The
noise figure is 2.7dB at 450MHz. I think this is certainly better than
the MPF102. There is also an improved version of MPF102 (MPF106, I think).

But still, this may not be the best choice for preamp circuits. Usually
MOSFETs are superior to J-FETs at higher frequency, and at 440
it would be so difficult to find a cheap J-FET that gives the gain and
NF as a MOSFET would. I usually recommend a dual-gate MOSFET for preamps
when some people might have a few in their part bin. I think the good old
40673 has been phased out but there are still plenty to choose from, like
3SK40, 3SK45, 3SK48, 3SK51, 3SK72-74, 3N204, 3N211, etc. These in general
will give you 20dB or more of gain and 2dB or less of NF in general up to
300MHz. I like 3SK72, 3SK73, or 3SK74 most, because they are rather
inexpensive and available in small microdisk package which is easier to
work with than TO-18, 72 or 92 package. 3SK72 is mostly used in TV or
FM radio, whereas 3SK74 has been found on many ham-gears from Japan.
(I think I first saw this first in my old IC-730 front-end mixer.)
There is a very good example of a dual-gate MOSFET preamp in recent
ARRL handbook.

If you have to buy something new, then I say go for a GaAsFET. There are
several types you can get for less than 5 buck a piece. A GaAsFET has
much better NF especially at 440. The handbook has several plans on this,
too.

Han                      KB9BQO / HL1AMS

> ---
>  * Dana H. Myers KK6JQ, DoD#: j | Views expressed here are      *
>  * [phone]               | mine and do not necessarily   *
>  * [e-mail]      | reflect those of my employer  *
>  * "Antenna waves be burnin' up my radio" -- ZZ Top                *
--
Han Seok Kim                          | [e-mail]
Wave Propagation Lab.                 | (217) 333 - 4406
Univ. of Illinois at Urbana-Champaign | Linux - to die for

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

Date: 15 Oct 1994 14:23:39 GMT
From: [e-mail] (Wolfgang von Hansen)
Subject: Q: VLF antenna design

Hi everybody!

First of all I want to apologize for my bad english regarding the technical
terms--but being a beginner to antenna design implies not knowing all the
words correctly.

I need some information on how to build a VLF antenna. It shall receive
signals at 10-14kHz with an omnidirectional characteristic. It should also
be quite small [<=1ft] in size.
Currently I am thinking of two ferrite bars (?) which are arranged
orthogonally. What I need to know is how to calculate the resonant circuit.
I also need infos on how to build a simple amplifier and connect the
antenna to it. A transformation of the signal to other frequencies is not
necessary.

Thaks in advance,

Wolfgang
--
[e-mail] | Gurus use `cat >a.out' instead of gcc
float o=0.075,h=1.5,T,r,O,l,I;int _,L=80,s=3200;main(){for(;s%L||
(h-=o,T= -2),s;4 -(r=O*O)<(l=I*I)|++ _==L&&putchar(*((--s%L?_<L?--_
%6:6:7)+"World! \n"))&&(O=I=l=_=r=0,T+=o /2))O=I*2*O+h,I=l+T-r;}

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

Date: 15 Oct 1994 14:02:10 -0400
From: [e-mail] (ELLS22)
Subject: Screen Voltage Protection Circuit

My 4-1000A Amp project is moving forward sloooooly but surely. I need
ideas on a sane, simple and safe (for me and the tube) interlock so that
screen voltage can't be applied if the plate voltage is not present. It
seems to me that I have to sense the 5KV directly, decide that it is or is
not there and lock in/out the screen voltage. The circuit also has to
react quickly in the event of Plate Voltage failure.

Any ideas would be appreciated. Remember I'm old, still understand 12AU7s,
and need all the help I can get.

Thanks
WA6CWV, Russ Ellsworth, Boise Idaho

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

Date: Fri, 14 Oct 1994 16:19:41 GMT
From: [e-mail] (Chuck Horvat)

References<[e-mail]> <36sb2i$[e-mail]>, <[e-mail]>
Subject: Re: Homebrew Antennas for cordless phones

In article <[e-mail]> laforest.snowcrest.net (Dale LaForest) writes:
>From: laforest.snowcrest.net (Dale LaForest)
>Subject: Re: Homebrew Antennas for cordless phones
>Date: 7 Oct 1994 07:59:54 GMT

>Does anyone know if the range of cordless phones can be extended by adding
>a long wire to the end of the antenna?

>This digitial cordless phone uses 900 mhertz frequency... and should the
>antenna be any particular length to optimize its effectiveness?

>I'm wondering because I heard that digital cordless phones might have up
>to 4 times the range of standard cordless phones...(700' max), ... so I'm
>wondering if a 1/2 mile range is possible?

>thanks

>Dale LaForest
>e:mail at

>[e-mail]
>[phone]

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

Date: 15 Oct 1994 20:45:43 GMT
From: [e-mail] (Richard Karlquist)

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References<[e-mail]> <[e-mail]>, <[e-mail]>
Subject: Re: Fractional turns on toroids?  Use two (or more) cores...

In article <[e-mail]> [e-mail] (Greg Dermer) writes:
>but you CAN get fractional turns. Though theoretically
>possible at any frequency, it's practically limited to frequencies where
>laminated or tape-wound cores are used.  Drill a hole through the core and
>run one turn through it so that that turn only links part of the flux in
>the core.  Voila, a partial turn.
>
>
>It's a real drag trying to drill a hole in ferrite, though. ;)
>
Instead of drilling a hole, use two ferrite cores next to each other.
Wind the windings thru both cores, and the fractional tap would
be passed thru the gap between the two toroid cores.  maybe try filing
a notch in both cores to pass the tap.

attempt at an ascii drawing:
---------------------
    __     __       |
   /  \   /  \      |
--| ----+| ---------- winding  (one turn shown, tap gives 1/2 turn)
   \__/ | \__/
   ^    |    ^
 core  tap  2nd core

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End of Ham-Homebrew Digest V94 #305
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