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## :database:electronics:Communications:Circuits:

Article Reference: CFDC9D65A310CF47

### impedance matcher

Date: 17 Mar 1996 21:00:25 GMT

Original Subject: Re: Impedance matching

```Workshop (workshop@pcm.co.za) wrote:
> Hi there
> This is to all those who know anything about impedance matching!
> I have a circuit using a ne602 ic.The input impedance is is quoted
> as bieng 1.5k.I have a Phillips application note (AN1993)
> that uses this ic.The input to the mixer of the ic is from a 50 ohm source.
> The 50 ohm source has been matched to the ic by the following circuit.

>                    To pin 1 of
>                       |  mixer
>                       |
>                 |-----------
>                 |          |
>                 |          |
>                === 47p     |
>                ===         ()
>                 |          ()0.28uH
>   To 50 ohm ____|          ()  To pin 2 of mixer
>    source      ===         ()         |
>                === 220p    |          |
>                 |          |          |
>                 |          |          |
>                 ------------          |
>                       |_______________|
>                       |
>                      ===100nF
>                      ===
>                       |
>                      GND
> Can anyone out there tell me how these values are calculated.The frequency of interest
> is 45Mhz

I believe the mixer has a differential input.  The 100nF cap just shorts pin 2 of
the mixer to ground so that the input is single-ended.  You can take that cap
out of the picture.

There are formulas for calculating the values of the rest components, based on the
assumption that the bandwidth of the matching network B < fo/10, where fo = center freq
of the circuit.

|------------------- Rt (>R2)
|          |
|          |
=== C1      |
===         () L
|          ()
R2       ____|          ()
===         ()
=== C2      |
|          |
|          |
------------
|
---
-

1. Calculate:

Qt = fo/B
C = 1/(2*pi*B*Rt)
L = 1/((2*pi*fo)^2*C)
N^2 = Rt/R2

2. Calculate:

Qp = sqrt(Qt^2/N^2 - 1)

3. C1 and C2 are given by:

C2 = Qp/(2*pi*fo*R2)

Cse = C2*(Qp^2+1)/Qp^2

C1 = Cse*C/(Cse - C)

Regards
-T L

```

Article Reference: 2CF239E51B71E72E

### low power transmitter

Date: Tue, 20 Aug 1996 16:19:10 -0700

Original Subject: Re: Q: 2.5(mH?) RFC in 50MHz xtal osc.

```Joshua Andrews wrote:
>
>  Hi all,
> I hope that this schematic can make my question easier to understand.
> This type drawing is something I've never tried.
>  Here's the deal, this should be a VERY low power RF Xmitter for a
> cheap-walkie talkie, fox hunt. My problem is I can't believe that a
> 2.5mH choke is the correct value. If I used a solenoid coil it would
> be HUGE, isn't it more like 2.5uH?
>  Thanks,
>  Joshua
>
>                           ANT.
>                           \I/             2.5(mH?) RFC
>     _______________________|___________________CCCC_______
>   _|_                      |                             |
>   XXXtal-49.860MHz         |________                     |
>  _ |_                      |      _|_  ~90p V-Cap.       |
> |   |_____________________|/      ^|^                    |
> |   |                     |\       |_____________________|
> |   |          2N2222       \e     |             |       |
> |   /                       |      |             |       |
> |   \ R-10K       __________|     _|_        +___|___    /
> |   /            |          |     ^|^.001uF     ===      \
> |   \           _|_         |      |          _______    /  R-47K
> |   |           ^|^ .001uF  /      |          - ===      \
> |   |            |          \470R  |       9V    |       |
> |   |            |          /      |             |       |
> |   |            |          \      |             |       |
> |   |            |          |      |             |       |
> |   |____________|__________|______|_____________|       |
> |________________________________________________________|

Hi all,
I'm sure my first try made everything clear but just in case...
```

Article Reference: EC960653266F3E34

### Lunchbox transmitter

Date: Wed, 10 Jul 96 18:55:50 GMT

Original Subject: Transmitter Question (Involves Transistor Antenna) - lunch.txt [01/01]

```***********************************************************
*
MEMBER NAME: LUNCHBOX                                 *
*
***********************************************************

<%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>
<%>                                                                     <%>
<%>                             Making the                              <%>
<%>                                                                     <%>
<%>                              Lunch Box                              <%>
<%>                              ===== ===                              <%>
<%>                                                                     <%>
<%>              Written, Typed and Created by: Dr. D-Code              <%>
<%>                                                                     <%>
<%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>[%>

Introduction
============

The Lunch Box is a VERY simple transmitter which can be handy for all sorts of
things. It is quite small and can easily be put in a number of places. I have
successfully used it for tapping fones, getting inside info, blackmail and
other such things. The possibilities are endless. I will also include the
about anything. You can also make the transmitter and receiver together in
one box and use it as a walkie talkie.

Materials you will need
=======================

(1) 9 volt battery with battery clip
(1) 25-mfd, 15 volt electrolytic capacitor
(2) .0047 mfd capacitors
(1) .022 mfd capacitor
(1) 51 pf capacitor
(1) 365 pf variable capacitor
(1) Transistor antenna coil
(1) 2N366 transistor
(1) 2N464 transistor
(1) 100k resistor
(1) 5.6k resistor
(1) 10k resistor
(1) 2meg potentiometer with SPST switch
Some good wire, solder, soldering iron, board to put it on, box (optional)

Schematic for The Lunch Box
===========================

This may get a tad confusing but just print it out and pay attention.

[!]
!
51 pf
!
---+----  ------------base   collector
!        )(               2N366       +----+------/\/\/----GND
365 pf     ()              emitter           !
!        )(                 !              !
+--------  ---+----         !              !
!             !    !        !              !
GND            /  .022mfd    !              !
10k\    !        !              !
/   GND       +------------------------emitter
!             !              !             2N464
/           .0047            !          base   collector
2meg  \----+        !              !   +--------+       !
/    !       GND             !   !                !
GND                      !   !                !
+-------------+.0047+--------------------+   !                !
!   +--25mfd-----+
-----------------------------------------+   !            !
microphone                                        +--/\/\/-----+
---------------------------------------------+   100k     !
!
GND---->/<---------------------!+!+!+---------------+
switch                  Battery
from 2meg pot.

=========================

1.  GND means ground
2.  The GND near the switch and the GND by the 2meg potentiometer should be
connected.
3.  Where you see:  )(
()
)( it is the transistor antenna coil with 15 turns of
regular hook-up wire around it.
4.  The middle of the loop on the left side (the left of "()") you should run
a wire down to the "+" which has nothing attached to it. There is a .0047
capacitor on the correct piece of wire.
5.  For the microphone use a magnetic earphone (1k to 2k).
6.  Where you see "[!]" is the antenna. Use about 8 feet of wire to broadcast
approx 300ft. Part 15 of the FCC rules and regulation says you can't
broadcast over 300 feet without a license. (Hahaha). Use more wire for an
antenna for longer distances. (Attach it to the black wire on the fone
line for about a 250 foot antenna!)

Operation of the Lunch Box
==========================

This transmitter will send the signals over the AM radio band. You use the
variable capacitor to adjust what freq. you want to use. Find a good unused
freq. down at the lower end of the scale and you're set. Use the 2 meg pot. to
adjust gain. Just fuck with it until you get what sounds good. The switch on
the 2meg is for turning the Lunch Box on and off. When everything is adjusted,
turn on an AM radio adjust it to where you think the signal is. Have a friend
say some shit thru the Box and tune in to it. That's all there is to it. The
plans for a simple receiver are shown below:

======================

(1) 9 volt battery with battery clip
(1) 365 pf variable capacitor
(1) 51 pf capacitor
(1) 1N38B diode
(1) Transistor antenna coil
(1) 2N366 transistor
(1) SPST toggle switch
(1) 1k to 2k magnetic earphone

======================

[!]
!
51 pf
!
+----+----+
!         !
)       365 pf
(----+    !
)    !    !
+---------+---GND
!
+---*>!----base  collector-----
diode      2N366           earphone
emitter    +-----
!        !
GND       !
-
+
- battery
+
GND------>/<------------+
switch

Closing statement
=================

This two devices can be built for under a total of \$10.00. Not too bad. Using
these devices in illegal ways is your option. If you get caught, I accept NO
responsibility for your actions. This can be a lot of fun if used correctly.
Hook it up to the red wire (I think) on the fone line and it will send the
conversation over the air waves. If you have any problems or are confused,
leave me mail on:Hi-Times=702/832/7469  Warez House=702/827/9273

______________________________________________________________________________

Sysops of other systems may use the file as long as none of it is altered.
______________________________________________________________________________
This has been a High Mountain Hackers Production- (c) 1985 by HMH Industries
______________________________________________________________________________

```

Article Reference: 1EDC44E780AB3341

### mixer analysis

Date: Wed, 13 Mar 1996 21:03:54 -0600

Original Subject: Re: Impedance matching

```Workshop wrote:
>                    To pin 1 of
>                       |  mixer
>                       |
>                 |-----------
>                 |          |
>                 |          |
>                === 47p     |
>                ===         ()
>                 |          ()0.28uH
>   To 50 ohm ____|          ()  To pin 2 of mixer
>    source      ===         ()         |
>                === 220p    |          |
>                 |          |          |
>                 |          |          |
>                 ------------          |
>                       |_______________|
>                       |
>                      ===100nF
>                      ===
>                       |
>                      GND
> Can anyone out there tell me how these values are calculated.The frequency of interest
> is 45Mhz

As long as the loaded Q is reasonable (say at least 10) then the circuit
behaves as a transformer at its resonance. The 100nF to ground is merely
an AC short to ground so that the DC at pin 1 isn't shorted to ground
through the inductor. It does not play a role in the transformer action.

Again, the following is only true at or near resonace. First, the
transformer voltage ratio is approximately

n = ( 47 / (47 + 220) )  ==> 0.176

Thus the impedance ratio is n**2 ==> 0.031.

So, the 1.5K at pin 1 will be transformed down to 1500*0.031 = 46ohms.
That is close enough to 50 ohms for all practical purposes.

Recall that I said earlier that the circuit must be resonant. The
inductor is chosen to resonate the series capacitor network. 47pF in
series with 220pF is 38.7pF. The resonant frequency of 38.7pF and 280nH
is about 49MHz -- close enough again for practical purposes. There is
also usually a few pF of stray capacitance an pin 1 which will lower the
resonance some. Normally it would be included in the calculation.

As a check, the loaded Q is calculated to be about 17 so the initial
assumption of Q>10 holds and the approximations are valid.

That's all there is to it!
```

Article Reference: 3EB614C160C3825E

### simple FM transmitter

Date: 26 Oct 1996 21:54:00 +0100

Original Subject: Re: How to build a radio transmitter

```On 26 Oct 96 (12:15), t96uro@student.hk-r.se wrote:
> Is there any one who knows how build a radio
> transmitter for 70-110 MHz FM?

Yes, me. It's very simple, when you are willing to use a xtal. Modulation can
be done via two BB405B's or similar devices.

VCC
|
|
+-+
| | R1
+-+
|
|        | |
+----------+--------| |------------->>
|          |        | |
XTAL        |
|       |--+        C1
+-------|    T1
|       |--+
+-+         |
| | R2      |
+-+         |
|          |
_|_        _|_
GND        GND

R1 = 470R...2k2 (depending on VCC)
R2 = 1M0
C1 = 4.7pF...68pF
T1 = either BF256A, BF256B or BF245A (other n-channel jfets may be used as
well)

--
Stephan A. Maciej, stephanm@muc.de, "http://www.muc.de/~stephanm/"
```

Article Reference: B6783EC6C873F459

### telephone partyline blocker

Date: 23 Feb 1996 02:59:39 -0500

Original Subject: Re: Telephone blocking circuit?

``` From: jlundgre@delta1.deltanet.com (John Lundgren)

> The way the SCR and zener works is that the first phone that goes
> off-hook gets the full 48 volts DC which makes the 21 V zener conduct
> and fires the SCR for the rest of the time the phone is off hook.
> Any other phone then can't get the 21V to fire the SCR, and they all
> remain open.  Simple and effective.

Some circuits add another zener in series with the SCR allowing an
unprotected line to disconnect the protected lines when it is picked
up, since the voltage will fall below 8.2 volts and turn off the
SCR's. The other diode passes the negative ring voltage.

Anode     Cathode
+ <---+-------------  SCR ---------|<----------+------->
|               Gate      8.5 volt       |
To      |   12 volt      |          zener        |
line     +------|<--------+                       |  To phone
|                                        |
+------|<--------------------------------+

- <---------------------------------------------------->

Bill
```

Article Reference: A005BBC5FC4C020D

Date: Mon, 18 Dec 1995 10:23 EST

Original Subject: Re: Phone Patch

```In Article <4b35uo\$egm@fountain.mindlink.net> "andrew_taylor@mindlink.bc.ca (Andrew Taylor)" says:
> Just wondering if anybody has made a phone Patch (with
> DTMF encode/decoder!)...If you can point me in the right
> direction Id appreciate it!...Im going to be using it
>
> Andrew T.
>
>

This circuit was published in _73_ magazine ~10 years ago.  I've built
lots of them.  Push-to-talk circuit as shown works with most
handhelds, which key their transmitters when a dc path through the
microphone is completed.  Base/mobile rigs use a separate push-to-talk
line.

^  ^
|  |
|  /
T1       |  \ R2 (optional)
C1            |  /         _____
o-----||---)|       |  |       |(     |
)| ______|__.______ |(     \ R1     | PTT
phone   1k )|(8 ohm |    8 ohm)|( 1k  /       ---
line       )|(______._________)|(     \<------o o---o to radio mike input
)|                  |(     /               (use shielded wire.)
o----------)|                  |(_____|_____________o

C1      1 uf 200 volt non-electrolytic.
R1      ~5k screwdriver-adjust pot to set microphone input level.
R2      resistance to equalize speaker and patch levels.
T1, T2  Audio-output transformer: Radio Shack part # 273-1330
(center taps not used).
--

Frank     reid@indiana.edu    W9MKV
```

Article Reference: E0BE023A604EE4BD

### wireless bug

Date: 19 Jul 1996 17:06:49 GMT

Original Subject: Re: Electronic 'bugs', 'recievers', detectors

```   For a simple wireless FM bug you could use this circuit.

/          100k 1/2 W
----------o/   o--------/\/\/\/\/\------+             _______
|                     |   ________       |             \  |  /
-                     |  /        \      |               \|/
---                  C  \/          \     |                | 6" or so
-                      / \   _      \    |                |
---                    |    \| |      | B |                |
|     PNP transistor  |     | |------|---+                |
|                     |   _/|_|      |   |                |
|                      \  \|        /   --- 100 pf        |
_                   E   \/         /    ---               |
>|_) carbon mic           /\________/      |                |
|  or other            |                 |                |
+---------------+-()()()()()()-----------+----------------+
|         _              |
|       ||/|             |
+-------||---------------+
/||

10 -> 365 pf
or fixed

To make L:
|-36t #28 C.T.|
_________________  _
| ||||||||||||||| | |
| ||||||||||||||| | 1/4"
-+------+------+-  -
|      |      |

good luck.

```

page by Fred Stewart, `fstewart@mediaone.net`