Guys

I'm looking for a formula, or preferably a program, that will let me design
a matching pad that will let me set Z1, z2, and the dB loss. I have the
formulas for the minimum loss pads, but they would require a second
fixed attenuator to set the dB loss to the -20dB I desire. I'm looking to
build some 50 ohm to various higher impedances for use on my signal
generators to match the higher impedances found on boatanchors, etc.

Or, would it just be easier to use a minimum loss pad with a second
symetrical pad to get the desired loss?

Pete

Uncle Peter wrote:

Guys

I'm looking for a formula, or preferably a program, that will let me design
a matching pad that will let me set Z1, z2, and the dB loss. I have the
formulas for the minimum loss pads, but they would require a second
fixed attenuator to set the dB loss to the -20dB I desire. I'm looking to
build some 50 ohm to various higher impedances for use on my signal
generators to match the higher impedances found on boatanchors, etc.

Or, would it just be easier to use a minimum loss pad with a second
symetrical pad to get the desired loss?

Pete


What frequencies and impedance ratios? I like to use RF transformers
with half the attenuation on each side to insure the proper levels and
isolation.

The first ones I wound were on the six hole ferrites for 50 Ohms one
on side, and 75 Ohms on the other. By tapping it at five turns you get a
1.2 -1.0 turn ratio, or, 1.2 * 1.2 * 50 = 70 ohms. Toroids are better
for some ratios and frequencies.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Michael A. Terrell" wrote in message
...
Uncle Peter wrote:

Guys

I'm looking for a formula, or preferably a program, that will let me
design
a matching pad that will let me set Z1, z2, and the dB loss. I have the
formulas for the minimum loss pads, but they would require a second
fixed attenuator to set the dB loss to the -20dB I desire. I'm looking
to
build some 50 ohm to various higher impedances for use on my signal
generators to match the higher impedances found on boatanchors, etc.

Or, would it just be easier to use a minimum loss pad with a second
symetrical pad to get the desired loss?

Pete


What frequencies and impedance ratios? I like to use RF transformers
with half the attenuation on each side to insure the proper levels and
isolation.

The first ones I wound were on the six hole ferrites for 50 Ohms one
on side, and 75 Ohms on the other. By tapping it at five turns you get a
1.2 -1.0 turn ratio, or, 1.2 * 1.2 * 50 = 70 ohms. Toroids are better
for some ratios and frequencies.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

RF transformers would be okay if using the dBm scale, since power is
a constant. For uV measurements they won't work, since the voltage
will be stepped up in the matching. i.e. the uV reading on the
generator will not be the same as the reading on the antenna terminals.
A 20 dB pad gives the same voltage reading (by a factor of ten) permitting
the attenuator scale to be reading without involving winding ratios, etc.
Also,
a 20 dB attenuator virtually assures both devices will be looking into a
close match.

Pete


Someone passed along a link to Reg's website...

http://www.btinternet.com/~g4fgq.regp/padmatch.exe

To design T and Pi attenuators between different source and load
resistances, download program PADMATCH from website below.

Also calculates minimum-loss pads.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

There is a Teledyne program called RF Toolbox that will, among other things
do this for you. E-mail me directly if you can't find it, and I will zip it
up and send it to you.

Pete

" Uncle Peter" wrote in message
news:_SvKf.14739$2c4.2519@dukeread11...

"Michael A. Terrell" wrote in message
...
Uncle Peter wrote:

Guys

I'm looking for a formula, or preferably a program, that will let me
design
a matching pad that will let me set Z1, z2, and the dB loss. I have the
formulas for the minimum loss pads, but they would require a second
fixed attenuator to set the dB loss to the -20dB I desire. I'm looking
to
build some 50 ohm to various higher impedances for use on my signal
generators to match the higher impedances found on boatanchors, etc.

Or, would it just be easier to use a minimum loss pad with a second
symetrical pad to get the desired loss?

Pete


What frequencies and impedance ratios? I like to use RF transformers
with half the attenuation on each side to insure the proper levels and
isolation.

The first ones I wound were on the six hole ferrites for 50 Ohms one
on side, and 75 Ohms on the other. By tapping it at five turns you get a
1.2 -1.0 turn ratio, or, 1.2 * 1.2 * 50 = 70 ohms. Toroids are better
for some ratios and frequencies.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

RF transformers would be okay if using the dBm scale, since power is
a constant. For uV measurements they won't work, since the voltage
will be stepped up in the matching. i.e. the uV reading on the
generator will not be the same as the reading on the antenna terminals.
A 20 dB pad gives the same voltage reading (by a factor of ten) permitting
the attenuator scale to be reading without involving winding ratios, etc.
Also,
a 20 dB attenuator virtually assures both devices will be looking into a
close match.

Pete


Someone passed along a link to Reg's website...

http://www.btinternet.com/~g4fgq.regp/padmatch.exe

I forgot about that one............very good program.

Pete

wrote in message
oups.com...
Download RFSim99 (free: a google search will find it). Install it.
Start it. Pull down "tools." Select "design--attenuator." In the
popup window, select the configuration you want. Enter the desired
source and load impedances and attenuation. Click on "calculate."
Presto. Now go back to the main RFSim99 window and discover the very
many OTHER useful things it can do! There's lots more there than just
simulation.

Cheers,
Tom