Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Attenuator formula, asymetrical
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 |
#2
|
|||
|
|||
Attenuator formula, asymetrical
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 |
#3
|
|||
|
|||
Attenuator formula, asymetrical
"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 |
#4
|
|||
|
|||
Attenuator formula, asymetrical
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 |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|