|
On Sun, 02 May 2004 09:04:33 -0500, John Fields
wrote: On Sun, 02 May 2004 14:09:44 +0100, Paul Burridge wrote: On Sat, 1 May 2004 15:30:18 -0400, "Ralph Mowery" wrote: The generators are more of a voltage source. They will deliver their rated output when loaded to the proper impedance. Load it with 50 ohms and see if it gives the rated output. If not try 70 ohms, or another value. One of the reasons for using a 6 db pad is that it helps isolate the impedance of the generator and receiver. My main sig gen states "output EMF using 6dB pad" next to the socket. WTF is a "6dB pad"? --- A 6dB attenuator. --- Also, less commonly, a device used to match the impedance of a generator to the impedance of a transmission line or a load, or the impedance of a transmission line to the impedance of a load. The impedance of the generator, line, and/or load are assumed to be purely resistive, and there is always loss associated with the transformation. Devices which exhibit the least loss are called "minimum loss pads", and http://www.maxim-ic.com/appnotes.cfm/appnote_number/972 gives a good description of the process involved in designing one. The reference given to Bruno Weinschel and the ITT handbook (as we old-timers call it) is particularly good, and if you're interested in RF (or just about anything else...) and you can buy a copy of it you should. BTW, since a pad is usually rated in terms of the power it's supposed to lose between its input and its output, the reference to "output EMF" on your generator may be what it supposed to be with a 3dB pad on its output. Easy way to find out would be to build a 3dB and a 6dB pad to find out. For a 50 ohm tee pad, here are the resistor values you'll need for -3dB: 0dBIN--[8.55]-+-[8.55]---3dBOUT | [141.93] | GND-----------+-----------GND and for -6dB: 0dBIN--[16.61]-+-[16.61]---3dBOUT | [66.93] | GND------------+-----------GND The input goes directly to your generator, (assuming its output impedance is 50+j0 ohms) a 50 ohm resistor gets connected across the output of the pad, and you'll measure the voltage across the 50 ohm resistor. Use non-inductive resistors (carbon comp if you can get them) and keep the leads short. That is, ********KEEP THE LEADS SHORT*********. -- John Fields |
The model number ain't gonna mean a lot to anyone as this is a very
old piece of kit (1950s) that I keep mainly out of a sense of reverence for the past. :-) It's an old ex-RAF AVO. I have posted a picture of the socket to a.b.s.e under this same thread title... BTW, there's a 5p coin shown for scale, but since that won't mean much to anyone outside Britain, the outer of the socket is approx. 1" in diameter (which won't mean much to anyone in europe but it serves them right for adopting the metric system.:-)) ====================== Since Britain is part of Europe you probably mean 'anyone in continental europe' Just for your info ,the metric system was introduced /imposed by Napoleon (eg more than 200 years ago) For once he did the right thing ;) . Frank GM0CSZ / KN6WH |
The model number ain't gonna mean a lot to anyone as this is a very
old piece of kit (1950s) that I keep mainly out of a sense of reverence for the past. :-) It's an old ex-RAF AVO. I have posted a picture of the socket to a.b.s.e under this same thread title... BTW, there's a 5p coin shown for scale, but since that won't mean much to anyone outside Britain, the outer of the socket is approx. 1" in diameter (which won't mean much to anyone in europe but it serves them right for adopting the metric system.:-)) ====================== Since Britain is part of Europe you probably mean 'anyone in continental europe' Just for your info ,the metric system was introduced /imposed by Napoleon (eg more than 200 years ago) For once he did the right thing ;) . Frank GM0CSZ / KN6WH |
Paul Burridge wrote in message ... Hi, I have a spare RF signal generator that has an unmarked output from a type of socket I've never seen before. What's the simplest way of establishing its output impedance? I've had a few ideas but no doubt someone out there will know of something better, since I always seem to end up making unnecessary work for myself. Any suggestions? p. -- The BBC: licenced at public expense to spread lies. Those ex-military AVO's were really nice g.p. signal generators though could never afford one. Seem to remember they were 50ohms out. The o/p socket and plug were standard 50's military chic and still available. regards john |
Paul Burridge wrote in message ... Hi, I have a spare RF signal generator that has an unmarked output from a type of socket I've never seen before. What's the simplest way of establishing its output impedance? I've had a few ideas but no doubt someone out there will know of something better, since I always seem to end up making unnecessary work for myself. Any suggestions? p. -- The BBC: licenced at public expense to spread lies. Those ex-military AVO's were really nice g.p. signal generators though could never afford one. Seem to remember they were 50ohms out. The o/p socket and plug were standard 50's military chic and still available. regards john |
On Sun, 02 May 2004 14:08:38 +0100, Paul Burridge
wrote: On Sun, 02 May 2004 02:43:18 GMT, (John Crighton) wrote: Hello Paul, what is the brand name and model number of your RF signal generator. Can you descibe the socket to us. Thanks John (and others). The model number ain't gonna mean a lot to anyone as this is a very old piece of kit (1950s) that I keep mainly out of a sense of reverence for the past. :-) It's an old ex-RAF AVO. I have posted a picture of the socket to a.b.s.e under this same thread title... BTW, there's a 5p coin shown for scale, but since that won't mean much to anyone outside Britain, the outer of the socket is approx. 1" in diameter (which won't mean much to anyone in europe but it serves them right for adopting the metric system.:-)) -- The BBC: licenced at public expense to spread lies. Go on, tell us the model number, there are a lot of us still interested in boat anchor style test equipment. Is this unit similar to your sig gen http://www.thevalvepage.com/testeq/avo/sg3/sg3.htm http://www.thevalvepage.com/testeq/testeq.htm Unfotunately the connector has been removed and a BNC type fitted. I am guessing that you want to keep the original connector on the sig gen and find a matching connector to make a short test lead. Old Style connector to BNC. My news group service doesn't allow me to see the group a.b.s.e Pity. So I can not see the picture you posted. So, what are the results of connecting your ohm meter to the RF out put connector (with the unit switched off) and measuring the resistance on all attenuator positions. On one of the lower frequency ranges when you connect up your cro via a "T" piece to the sig gen with say a 75 ohm load. Does the output level jump up to double when the load is removed? Repeat the experiment with a 50 ohm load. If the voltage doubles from loaded to no load, you will be laughing. But I don't think you will be that lucky. I am guessing it will be closer to 75 ohm output impedance. Try different value loads and let us know how you got on. Cheerio, John Crighton Sydney |
On Sun, 02 May 2004 14:08:38 +0100, Paul Burridge
wrote: On Sun, 02 May 2004 02:43:18 GMT, (John Crighton) wrote: Hello Paul, what is the brand name and model number of your RF signal generator. Can you descibe the socket to us. Thanks John (and others). The model number ain't gonna mean a lot to anyone as this is a very old piece of kit (1950s) that I keep mainly out of a sense of reverence for the past. :-) It's an old ex-RAF AVO. I have posted a picture of the socket to a.b.s.e under this same thread title... BTW, there's a 5p coin shown for scale, but since that won't mean much to anyone outside Britain, the outer of the socket is approx. 1" in diameter (which won't mean much to anyone in europe but it serves them right for adopting the metric system.:-)) -- The BBC: licenced at public expense to spread lies. Go on, tell us the model number, there are a lot of us still interested in boat anchor style test equipment. Is this unit similar to your sig gen http://www.thevalvepage.com/testeq/avo/sg3/sg3.htm http://www.thevalvepage.com/testeq/testeq.htm Unfotunately the connector has been removed and a BNC type fitted. I am guessing that you want to keep the original connector on the sig gen and find a matching connector to make a short test lead. Old Style connector to BNC. My news group service doesn't allow me to see the group a.b.s.e Pity. So I can not see the picture you posted. So, what are the results of connecting your ohm meter to the RF out put connector (with the unit switched off) and measuring the resistance on all attenuator positions. On one of the lower frequency ranges when you connect up your cro via a "T" piece to the sig gen with say a 75 ohm load. Does the output level jump up to double when the load is removed? Repeat the experiment with a 50 ohm load. If the voltage doubles from loaded to no load, you will be laughing. But I don't think you will be that lucky. I am guessing it will be closer to 75 ohm output impedance. Try different value loads and let us know how you got on. Cheerio, John Crighton Sydney |
On Sun, 02 May 2004 11:35:08 -0500, John Fields wrote:
On Sun, 02 May 2004 09:04:33 -0500, John Fields wrote: snip John helping Paul with terminology http://www.maxim-ic.com/appnotes.cfm/appnote_number/972 Once in a while, I can post a helpful link (I've got plenty of tech info links, but most don't usually apply to the topic at hand whatever that may be) , but some of you guys, like Spehro, You, etc., ... it's like you can pull horshoe out of yer asses :) You must do more digging than I do. I got a kick out of this link because I have the opposite situation. I don't need an MLP becuse I have an SLM tha *is* 75 ohfriggin'megas :) and the link dealt with ... you know. snip John still helping but going the extra furlong or so Use non-inductive resistors (carbon comp if you can get them) and keep the leads short. That is, ********KEEP THE LEADS SHORT*********. ^^^^^^^^^^ advice that should be unsnipped. Er, snip the leads, though. -- Best Regards, Mike |
On Sun, 02 May 2004 11:35:08 -0500, John Fields wrote:
On Sun, 02 May 2004 09:04:33 -0500, John Fields wrote: snip John helping Paul with terminology http://www.maxim-ic.com/appnotes.cfm/appnote_number/972 Once in a while, I can post a helpful link (I've got plenty of tech info links, but most don't usually apply to the topic at hand whatever that may be) , but some of you guys, like Spehro, You, etc., ... it's like you can pull horshoe out of yer asses :) You must do more digging than I do. I got a kick out of this link because I have the opposite situation. I don't need an MLP becuse I have an SLM tha *is* 75 ohfriggin'megas :) and the link dealt with ... you know. snip John still helping but going the extra furlong or so Use non-inductive resistors (carbon comp if you can get them) and keep the leads short. That is, ********KEEP THE LEADS SHORT*********. ^^^^^^^^^^ advice that should be unsnipped. Er, snip the leads, though. -- Best Regards, Mike |
| All times are GMT +1. The time now is 04:52 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com