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Title: 75ohm step attenuator usable in a 50ohm environment? Post by: ssbothwell KJ6RSG on February 21, 2013, 11:37:13 PM hi. i have a 75ohm 0-102dB step attenuator i bought at the swapmeet for $5. i was planning to swap out the resistors to make it a 50ohm device but i am wondering if it is necessary. when used in a 50ohm environment the attenuation seems to be only marginally off from 50ohm pi pads. i was mainly planning to use it in an IMD measurement setup, if that matters.
also, i've attached a photo i found online of the attenuator in question. anyone have any idea what its power rating might be? Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: Pete, WA2CWA on February 21, 2013, 11:42:00 PM Who is the manufacturer?
Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: ssbothwell KJ6RSG on February 22, 2013, 12:07:55 AM Telonic Model TG-975
Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: Pete, WA2CWA on February 22, 2013, 12:14:59 AM Specs:
http://www.ctg123.com/rapid-quote-system/request/?p=TG975 Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: KK4YY on February 22, 2013, 04:48:46 AM If it were mine I'd stick a label on it that reads "50 ohms" and use it. If you wanted to, you could build two 50 to 75 ohm minimum loss pads to use at each end if you can tolerate the additional losses. Then it will perform to spec. http://www.maximintegrated.com/app-notes/index.mvp/id/972
For $5 you practically stole the thing! Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: MikeKE0ZUinkcmo on February 22, 2013, 07:01:25 AM If you just want an attenuator, and don't care what the actual voltage levels are at the output, just use it as is, but I'd do as you originally planned and make it a 50 Ohm unit.
Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: KM1H on February 23, 2013, 05:09:51 PM In the dark ages of the mid 80's when I was well along in converting to 75 Ohms (CATV came to town and a case of beer donated weekly yielded many treasures) I built an attenuator out of an ARRL HB article and tweaked it using the 75 Ohm network analyzer at work for VHF and still use it but it is a bit clunky.
If you wish to swap I can likely dig up an extra commercial 50 Ohm version that looks similar to yours. Might be KAY, HP or something else. Carl Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: ssbothwell KJ6RSG on February 23, 2013, 06:00:43 PM holy cow, a telonic 975B is on ebay for $90 right now. is this thing actually worth some money?
to get a complete set of new resistors to convert it to 50ohm i would end up spending ~$10 + shipping (for 1/2W metal film resistors, maybe i could go cheaper with carbon). i would hate to spend money to convert this thing if it in fact is actually desirable to someone as is. carl, if you have a 50ohm model with bnc connectors then i would probably be willing to do that trade. especially if you have an HP brand one. most of my workbench is HP and i trust their products. ;D Title: Re: 75ohm step attenuator usable in a 50ohm environment? Post by: KM1H on February 27, 2013, 09:19:26 PM Keep an eye on your PM's; I'll be looking for it. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Carl |