Why A Audio Attenuator:
If you are into ESSB audio, or your
just using some type of outboard audio equipment you may need a
attenuator so that you do not over drive the front end of your
transceiver. This attenuator is used to set down the audio going
into your radio by about 23db. I could have bought one. I
decide to build my. And beside I like the idea of building so of my
own gear and having some of the parts in my junk box it all work
out. I built two of these attenuator but each one was a little
different. The first one I built was a little more involve with more
parts. The two one I built was very simple and only require a few
parts that you may fine in your parts box. I will start with the
simpler one first. Both of these attenuator were design by W2IHY
Julius. These audio attenuator seem to have two name's for them. One
being a Ibox and the other Murf Box.
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a new popup window.
Second Attenuator I Built:
Parts needed for this project.
Resistors R1 2.2k - R2 10k - R3 820 ohm.
2 1/4 phone plug. Or you can use RCA plugs if you like.
1 Audio transformer Stancor TTPC-2 or TTPC-8 telephone coupling
transformer from Allied Electronic
1 Plastic or metal enclosure box. I use a small plastic box from
As you can see from the picture of Fig 1 there is not much to this
unit at all. Very easy to build. Fig 2 is a picture of the
schematic. This was my first attempt using a program to draw this
R2 can be replace with a variable 10k
or 100k resistor if you like. I used a fix resistor in mine and
works great. All resistor are 1/4 watt.
Is The First Audio Attenuator I Built:
This unit is a little more involved and
has more components in it.
Credit for his circuit design is by Julius W2IHY
C4-C6 - .001 uf Mylar
C7 - 100 uf radial electrolytic
C8 - .1 uf monolithic ceramic capacitors
R1,R3.R4 - 1K ohm ¼ watt resistor
R2 - fixed resistor or variable potentiometer
RFC1,RFC2 - put a piece of wire in place of the RF choke
RFC3,RFC4 - 470 uh miniature r.f. Choke
T1 - 1:1 600 ohm Audio Transformer
Other Parts Used :
(1) 1/4 phone plug (2) 8 pin mini din connectors. I
one to accommodate two radios. (1) DPDT switch used to switch
between the two radios. You can used what ever type of connector
that will work best for you.
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Created May 19, 2009