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Field Strength
Hi all,
I wanted to build an RF relative field strength meter, so set about searching on the Web for any existing designs. Those I turned up weren't particularly impressive, so I decided to start from scratch and design my own. I've just completed that this afternoon. I've allowed for 0.25mV input to give rise to FSD on the microammeter. Question being, however, is that going to be sensitive enough? Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? I guess I should have posed this question *before* designing it, but who among us can honestly say they haven't designed something without knowing what the spec is? :-) Anyway, ballpark figures gentlemen, please. p. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
I wanted to build an RF relative field strength meter, I've allowed for 0.25mV
input to give rise to FSD on the microammeter. Question being, however, is that going to be sensitive enough? Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? Figuring the field strenth of a .5 W xmtr at 6 feet is difficult. Depends on the antennas on the xmtr and the FSM and their polarization. Also, depends on the sensisitivty of your FSM (field strength doesn't depend on sensisitivty but your reading will). Since this is a *relative FSM* I would get something working, use that as a reference, and go from there. 73 Gary N4AST |
I wanted to build an RF relative field strength meter, I've allowed for 0.25mV
input to give rise to FSD on the microammeter. Question being, however, is that going to be sensitive enough? Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? Figuring the field strenth of a .5 W xmtr at 6 feet is difficult. Depends on the antennas on the xmtr and the FSM and their polarization. Also, depends on the sensisitivty of your FSM (field strength doesn't depend on sensisitivty but your reading will). Since this is a *relative FSM* I would get something working, use that as a reference, and go from there. 73 Gary N4AST |
Paul Burridge wrote:
Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? I'll SWAG & hope I'll be corrected if I tell ya wrong. Assuming a 1/2 wave antenna on the xmit & rcv, take the volts/meter you're applying on the antenna, divide by 4 PI / (distance)^2, with distance being in wavelengths. Then there is the famous propogation equations which involves 32, recieve and transmit antenna gains, and the log of the distance and frequency. You can then go from power to voltage according to the antenna Z. I'll look up the equation for you if you don't get a better answer. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
Paul Burridge wrote:
Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? I'll SWAG & hope I'll be corrected if I tell ya wrong. Assuming a 1/2 wave antenna on the xmit & rcv, take the volts/meter you're applying on the antenna, divide by 4 PI / (distance)^2, with distance being in wavelengths. Then there is the famous propogation equations which involves 32, recieve and transmit antenna gains, and the log of the distance and frequency. You can then go from power to voltage according to the antenna Z. I'll look up the equation for you if you don't get a better answer. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
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Scott Stephens wrote:
Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** Your web site is very hard to read with the dark blue background and black text. A lot of people have vision problems, and can not read this color combination. -- 13 days! Michael A. Terrell Central Florida |
Scott Stephens wrote:
Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** Your web site is very hard to read with the dark blue background and black text. A lot of people have vision problems, and can not read this color combination. -- 13 days! Michael A. Terrell Central Florida |
What you are descrbing is a "signal sniffer", not a signal strength meter.
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What you are descrbing is a "signal sniffer", not a signal strength meter.
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On Fri, 12 Dec 2003 16:41:06 +0000, Paul Burridge
wrote: Hi all, I wanted to build an RF relative field strength meter, so set about searching on the Web for any existing designs. Those I turned up weren't particularly impressive, so I decided to start from scratch and design my own. I've just completed that this afternoon. I've allowed for 0.25mV input to give rise to FSD on the microammeter. Question being, however, is that going to be sensitive enough? Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? I guess I should have posed this question *before* designing it, but who among us can honestly say they haven't designed something without knowing what the spec is? :-) Anyway, ballpark figures gentlemen, please. p. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill Hello Paul, have a look here, http://www.alphalink.com.au/~parkerp/noapr97.htm Here is a crystal set circuit. http://circuitos.tripod.cl/schem/r85.gif Convert it to a field strength meter by Replacing the headphones with a large sensitive meter, something big enough that you can still see the pointer, when viewed from across the room. Bigger the better. Use a germanium diode. Use a metal box. Use a short telescopic aerial. Coil and variable capacitor to cover, 40Mhz,. 35Mhz and 27Mhz, I am guessing those are the frequencies of interest, use a switch if necessary to add/remove some turns or add/remove a capacitor. I know you have a grid dip oscillator so fiddling the coil and capacitor values to get the frequency ranges will be a snack for you. Using your field strength meter only six feet away is too close. Keep it as far away as possible from your radio control transmitter but still being able to see it, that is the reason for the big meter movement. I am thinking of big cheap plastic 6 inch square types. Anything will do so long as you can see it from across the room and the movement is microamps full scale and not milliamps. I am sure I have explained this to you yonks ago, well, if I have, never mind. maybe you forgot :-) Set up your known good commercial radio control set at one end of the room, and field strength meter at the other side of the room. Note the meter reading. Now compare readings with your experimental transmitter. Is it more or less? Make adjustments to your experimental transmitter. This is the fun part. I found that sitting my field strength meter (even though it had rubber feet) on my wife's metal serving tray reduced hand capacitance and made it nicer to adjust. So experiment with and without a sheet metal base. Maybe the first circuit without a parallel tuned circuit would be less fuss to use. Maybe you can knock up both types and tell us which was better. Heh heh heh.... Regards, John Crighton Sydney |
On Fri, 12 Dec 2003 16:41:06 +0000, Paul Burridge
wrote: Hi all, I wanted to build an RF relative field strength meter, so set about searching on the Web for any existing designs. Those I turned up weren't particularly impressive, so I decided to start from scratch and design my own. I've just completed that this afternoon. I've allowed for 0.25mV input to give rise to FSD on the microammeter. Question being, however, is that going to be sensitive enough? Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? I guess I should have posed this question *before* designing it, but who among us can honestly say they haven't designed something without knowing what the spec is? :-) Anyway, ballpark figures gentlemen, please. p. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill Hello Paul, have a look here, http://www.alphalink.com.au/~parkerp/noapr97.htm Here is a crystal set circuit. http://circuitos.tripod.cl/schem/r85.gif Convert it to a field strength meter by Replacing the headphones with a large sensitive meter, something big enough that you can still see the pointer, when viewed from across the room. Bigger the better. Use a germanium diode. Use a metal box. Use a short telescopic aerial. Coil and variable capacitor to cover, 40Mhz,. 35Mhz and 27Mhz, I am guessing those are the frequencies of interest, use a switch if necessary to add/remove some turns or add/remove a capacitor. I know you have a grid dip oscillator so fiddling the coil and capacitor values to get the frequency ranges will be a snack for you. Using your field strength meter only six feet away is too close. Keep it as far away as possible from your radio control transmitter but still being able to see it, that is the reason for the big meter movement. I am thinking of big cheap plastic 6 inch square types. Anything will do so long as you can see it from across the room and the movement is microamps full scale and not milliamps. I am sure I have explained this to you yonks ago, well, if I have, never mind. maybe you forgot :-) Set up your known good commercial radio control set at one end of the room, and field strength meter at the other side of the room. Note the meter reading. Now compare readings with your experimental transmitter. Is it more or less? Make adjustments to your experimental transmitter. This is the fun part. I found that sitting my field strength meter (even though it had rubber feet) on my wife's metal serving tray reduced hand capacitance and made it nicer to adjust. So experiment with and without a sheet metal base. Maybe the first circuit without a parallel tuned circuit would be less fuss to use. Maybe you can knock up both types and tell us which was better. Heh heh heh.... Regards, John Crighton Sydney |
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On Sat, 13 Dec 2003 11:58:39 GMT, (John Crighton)
wrote: Hello Paul, have a look here, http://www.alphalink.com.au/~parkerp/noapr97.htm Hi John, Always nice to have your input. I did actually come across the circuit you point to above during my search of the Web, but rejected it as probably not being sensitive enough. I thought I could maybe do a little better by having a stab at it myself - with the assistance of LTSpice of course! Many thanks to the other respondents to this thread, but no one seems to have been able to SWAG the actual likely signal level in mV or uV. So I thought what the hell and built my original design from yesterday. I've just finished it and am surprised and pleased to report that it worked fine first time! The sensitivity is a little on the low side, but *remarkably* close to what I'd set out to achieve. With a 100mW transmitter some 4 feet away, I can tune for 40Mhz and tweak the sensitivity and get a peak at S9 on the CB radio type signal meter I'm using for this purpose. That would have done me just fine had you not suggested making the measurements from some greater distance! So I either live with it as it is and use is at say 6 feet away or stick in an extra voltage amplification stage for 'far field' testing (do I *really* need this for my purposes?) Incidentally, you were dead right about the tea-tray idea. It turns out the grounded areas of the PCB really need to be earthed to a decent, proper ground/earth rod via the mains supply. It makes a *huge* difference to the sensitivity and drastically reduces the annoying effects of hand capacitance when tuning and tweaking. I'll post the schematic I arrived at later under another thread and maybe someone can suggest a few mods that might up the sens. without a complete redesign. Is it really that important to make the measurements from 10 feet or more away? -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Fri, 12 Dec 2003 16:41:06 +0000, Paul Burridge
wrote: Hi all, I wanted to build an RF relative field strength meter, so set about searching on the Web for any existing designs. Those I turned up weren't particularly impressive, so I decided to start from scratch and design my own. PA0SE made a good one for 136kHz and higher, believe you'll find it described on http://www.qsl.net/on7yd/ and many other places 73 Jan-Martin, LA8AK http://home.online.no/~la8ak/c.htm -- remove ,xnd to reply (Spam precaution!) |
On Fri, 12 Dec 2003 16:41:06 +0000, Paul Burridge
wrote: Hi all, I wanted to build an RF relative field strength meter, so set about searching on the Web for any existing designs. Those I turned up weren't particularly impressive, so I decided to start from scratch and design my own. PA0SE made a good one for 136kHz and higher, believe you'll find it described on http://www.qsl.net/on7yd/ and many other places 73 Jan-Martin, LA8AK http://home.online.no/~la8ak/c.htm -- remove ,xnd to reply (Spam precaution!) |
On Sat, 13 Dec 2003 20:50:47 +0000,
said... On Sat, 13 Dec 2003 11:58:39 GMT, (John Crighton) wrote: Hello Paul, have a look here, http://www.alphalink.com.au/~parkerp/noapr97.htm Hi John, Always nice to have your input. I did actually come across the circuit you point to above during my search of the Web, but rejected it as probably not being sensitive enough. I thought I could maybe do a little better by having a stab at it myself - with the assistance of LTSpice of course! Many thanks to the other respondents to this thread, but no one seems to have been able to SWAG the actual likely signal level in mV or uV. Because you didn't provide enough info, dude. That much could've been inferred from the eqs I gave you. And you asked for "field strength" in the wrong units. it's V/m or mV/m or uV/m. Hell I'd give it to you in kV/m if you wanted. You'll never know what it is if you can't determine the voltage present at the meter antenna's terminals and it should be a dipole. So I thought what the hell and built my original design from yesterday. I've just finished it and am surprised and pleased to report that it worked fine first time! The sensitivity is a little on the low side, but *remarkably* close to what I'd set out to achieve. With a 100mW transmitter some 4 feet away, I can tune for 40Mhz and clues. so you're still on that project. tweak the sensitivity and get a peak at S9 on the CB radio type signal meter I'm using for this purpose. :) ! Adjust the meter to get the answer you want. Ok. That would have done me just fine had you not suggested making the measurements from some greater distance! So I either live with it as it is and use is at say 6 feet away or stick in an extra voltage amplification stage for 'far field' testing (do I *really* need this for my purposes?) lessee 40MHz is 7.5m lambda so the far field starts at around 3.75 meter per the eq I gave you for that. I think that 1st eq I gave was for a vertical and it's ****ing with me. I'll use a distance of 6m. since you seem to want to know power try the path loss eq 32.45 + 20log(f) + 20log(d) = 20db f in MHz, d in km 10log(Pr/Pt) = -20dB but EIRP = Pt.G G is antenna gain and you didn't give that info. so I'll use G = 1 Pr = 1mW Pr.G = E^2/Z voltage at input to Rx G is Rx antenna gain, I'll use 1 E = 224 mV rms Let me know if I f'd up anything. Lots of distractions and I'm trying to hurry and do other work. Mike Buy 'em books, send 'em to school, and all they want to do is eat the teachers ;) Incidentally, you were dead right about the tea-tray idea. It turns out the grounded areas of the PCB really need to be earthed to a decent, proper ground/earth rod via the mains supply. It makes a *huge* difference to the sensitivity and drastically reduces the annoying effects of hand capacitance when tuning and tweaking. I'll post the schematic I arrived at later under another thread and maybe someone can suggest a few mods that might up the sens. without a complete redesign. Is it really that important to make the measurements from 10 feet or more away? |
On Sat, 13 Dec 2003 20:50:47 +0000,
said... On Sat, 13 Dec 2003 11:58:39 GMT, (John Crighton) wrote: Hello Paul, have a look here, http://www.alphalink.com.au/~parkerp/noapr97.htm Hi John, Always nice to have your input. I did actually come across the circuit you point to above during my search of the Web, but rejected it as probably not being sensitive enough. I thought I could maybe do a little better by having a stab at it myself - with the assistance of LTSpice of course! Many thanks to the other respondents to this thread, but no one seems to have been able to SWAG the actual likely signal level in mV or uV. Because you didn't provide enough info, dude. That much could've been inferred from the eqs I gave you. And you asked for "field strength" in the wrong units. it's V/m or mV/m or uV/m. Hell I'd give it to you in kV/m if you wanted. You'll never know what it is if you can't determine the voltage present at the meter antenna's terminals and it should be a dipole. So I thought what the hell and built my original design from yesterday. I've just finished it and am surprised and pleased to report that it worked fine first time! The sensitivity is a little on the low side, but *remarkably* close to what I'd set out to achieve. With a 100mW transmitter some 4 feet away, I can tune for 40Mhz and clues. so you're still on that project. tweak the sensitivity and get a peak at S9 on the CB radio type signal meter I'm using for this purpose. :) ! Adjust the meter to get the answer you want. Ok. That would have done me just fine had you not suggested making the measurements from some greater distance! So I either live with it as it is and use is at say 6 feet away or stick in an extra voltage amplification stage for 'far field' testing (do I *really* need this for my purposes?) lessee 40MHz is 7.5m lambda so the far field starts at around 3.75 meter per the eq I gave you for that. I think that 1st eq I gave was for a vertical and it's ****ing with me. I'll use a distance of 6m. since you seem to want to know power try the path loss eq 32.45 + 20log(f) + 20log(d) = 20db f in MHz, d in km 10log(Pr/Pt) = -20dB but EIRP = Pt.G G is antenna gain and you didn't give that info. so I'll use G = 1 Pr = 1mW Pr.G = E^2/Z voltage at input to Rx G is Rx antenna gain, I'll use 1 E = 224 mV rms Let me know if I f'd up anything. Lots of distractions and I'm trying to hurry and do other work. Mike Buy 'em books, send 'em to school, and all they want to do is eat the teachers ;) Incidentally, you were dead right about the tea-tray idea. It turns out the grounded areas of the PCB really need to be earthed to a decent, proper ground/earth rod via the mains supply. It makes a *huge* difference to the sensitivity and drastically reduces the annoying effects of hand capacitance when tuning and tweaking. I'll post the schematic I arrived at later under another thread and maybe someone can suggest a few mods that might up the sens. without a complete redesign. Is it really that important to make the measurements from 10 feet or more away? |
In (rec.radio.amateur.homebrew), Michael A. Terrell wrote:
Scott Stephens wrote: Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** Your web site is very hard to read with the dark blue background and black text. A lot of people have vision problems, and can not read this color combination. On my system (FreeBSD) with the Mozilla FireBird browser, the text and images are in light-colored windows inside the dark background, and it's not at all difficult to read. The Netscape 4.6 browser on the same system _does_ put the black text directly on the dark-blue background, and it is decidedly unpleasant. A newer browser might be nice, but it also would be good if web page designers built pages with older code in mind. It _definitely_ has some cool stuff. Thanks, Scott! -- Comparing Knuth with O'Reilly books is like comparing Unix with Windows. -- Abigail, in the Monastery |
In (rec.radio.amateur.homebrew), Michael A. Terrell wrote:
Scott Stephens wrote: Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** Your web site is very hard to read with the dark blue background and black text. A lot of people have vision problems, and can not read this color combination. On my system (FreeBSD) with the Mozilla FireBird browser, the text and images are in light-colored windows inside the dark background, and it's not at all difficult to read. The Netscape 4.6 browser on the same system _does_ put the black text directly on the dark-blue background, and it is decidedly unpleasant. A newer browser might be nice, but it also would be good if web page designers built pages with older code in mind. It _definitely_ has some cool stuff. Thanks, Scott! -- Comparing Knuth with O'Reilly books is like comparing Unix with Windows. -- Abigail, in the Monastery |
It's too bad it isn't that simple.
A 1V/m field doesn't result in one volt at the feedpoint of a perfectly matched one meter dipole or monopole, and the value it does induce depends on the quality of the impedance match as well as the fraction of a wavelength the one meter antenna length represents. And, if one volt does appear at the feedpoint, it's very unlikely that a simple circuit will measure it as one volt. Probably best to stick with your $1.5 kilobuck meter if you really want to measure field strength. Roy Lewallen, W7EL Active8 wrote: On 13 Dec 2003 03:50:41 -0800, said... What you are descrbing is a "signal sniffer", not a signal strength meter. Who are you replying to? Paul did not say Signal Stength Meter, but the guy you replied to kinda hints at it when he mentions power level. I would have to say that my 1GHz Signal Level Meter, which cost $1500 would be the better than a relative field strength meter, but if he measures say, 1V with his Tx off and 2V with it on, then that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m. Mike |
It's too bad it isn't that simple.
A 1V/m field doesn't result in one volt at the feedpoint of a perfectly matched one meter dipole or monopole, and the value it does induce depends on the quality of the impedance match as well as the fraction of a wavelength the one meter antenna length represents. And, if one volt does appear at the feedpoint, it's very unlikely that a simple circuit will measure it as one volt. Probably best to stick with your $1.5 kilobuck meter if you really want to measure field strength. Roy Lewallen, W7EL Active8 wrote: On 13 Dec 2003 03:50:41 -0800, said... What you are descrbing is a "signal sniffer", not a signal strength meter. Who are you replying to? Paul did not say Signal Stength Meter, but the guy you replied to kinda hints at it when he mentions power level. I would have to say that my 1GHz Signal Level Meter, which cost $1500 would be the better than a relative field strength meter, but if he measures say, 1V with his Tx off and 2V with it on, then that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m. Mike |
On Sat, 13 Dec 2003 17:39:27 -0800, said...
It's too bad it isn't that simple. A 1V/m field doesn't result in one volt at the feedpoint of a perfectly matched one meter dipole or monopole, and the value it does induce depends on the quality of the impedance match you mean antenna to free space, right? as well as the fraction of a wavelength the one meter antenna length represents. amplify, very please. por favor. Refresh my ram. | E(uV/m) | V (dBmV) = 20log | --------- / 1000 | | 0.021f(MHz) | plus correction for distance (regulations for limits are for specific measuring distances), etc. I'll mull the above eq over. Gotta figure out where the .021 came from, but not now. My eyes are getting fatigued from this 'puter. And, if one volt does appear at the feedpoint, it's very unlikely that a simple circuit will measure it as one volt. It would have to be calibrated to compensate for the circuit. Maybe that's why it's called a "relative" field strength meter. Relative to another signal or no signal ;) Probably best to stick with your $1.5 kilobuck meter if you really want to measure field strength. I don't. He does :) At least not tonight. But my SLM *will* measure field strenth using a cheap ass dipole cut to the frequency of interest with or without an external preamp and do it to the satisfaction of the FCC, assuming it's calibrated. I even have a near-field probe, not so cheap. It beats guess work. I wouldn't expect his sniffer to be real accurate but he did ask for guesstimates. Started off as "around 4 feet" for a half watter now we're at 100mW - prob his reference Tx. BRs, Mike Roy Lewallen, W7EL Active8 wrote: On 13 Dec 2003 03:50:41 -0800, said... What you are descrbing is a "signal sniffer", not a signal strength meter. Who are you replying to? Paul did not say Signal Stength Meter, but the guy you replied to kinda hints at it when he mentions power level. I would have to say that my 1GHz Signal Level Meter, which cost $1500 would be the better than a relative field strength meter, but if he measures say, 1V with his Tx off and 2V with it on, then that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m. Mike |
On Sat, 13 Dec 2003 17:39:27 -0800, said...
It's too bad it isn't that simple. A 1V/m field doesn't result in one volt at the feedpoint of a perfectly matched one meter dipole or monopole, and the value it does induce depends on the quality of the impedance match you mean antenna to free space, right? as well as the fraction of a wavelength the one meter antenna length represents. amplify, very please. por favor. Refresh my ram. | E(uV/m) | V (dBmV) = 20log | --------- / 1000 | | 0.021f(MHz) | plus correction for distance (regulations for limits are for specific measuring distances), etc. I'll mull the above eq over. Gotta figure out where the .021 came from, but not now. My eyes are getting fatigued from this 'puter. And, if one volt does appear at the feedpoint, it's very unlikely that a simple circuit will measure it as one volt. It would have to be calibrated to compensate for the circuit. Maybe that's why it's called a "relative" field strength meter. Relative to another signal or no signal ;) Probably best to stick with your $1.5 kilobuck meter if you really want to measure field strength. I don't. He does :) At least not tonight. But my SLM *will* measure field strenth using a cheap ass dipole cut to the frequency of interest with or without an external preamp and do it to the satisfaction of the FCC, assuming it's calibrated. I even have a near-field probe, not so cheap. It beats guess work. I wouldn't expect his sniffer to be real accurate but he did ask for guesstimates. Started off as "around 4 feet" for a half watter now we're at 100mW - prob his reference Tx. BRs, Mike Roy Lewallen, W7EL Active8 wrote: On 13 Dec 2003 03:50:41 -0800, said... What you are descrbing is a "signal sniffer", not a signal strength meter. Who are you replying to? Paul did not say Signal Stength Meter, but the guy you replied to kinda hints at it when he mentions power level. I would have to say that my 1GHz Signal Level Meter, which cost $1500 would be the better than a relative field strength meter, but if he measures say, 1V with his Tx off and 2V with it on, then that's 1V and if his Rx antenna is a 1m dipole, that's 1V/m. Mike |
Mike Andrews wrote:
On my system (FreeBSD) with the Mozilla FireBird browser, the text and images are in light-colored windows inside the dark background, and it's not at all difficult to read. The Netscape 4.6 browser on the same system _does_ put the black text directly on the dark-blue background, and it is decidedly unpleasant. A newer browser might be nice, but it also would be good if web page designers built pages with older code in mind. It _definitely_ has some cool stuff. Thanks, Scott! -- Comparing Knuth with O'Reilly books is like comparing Unix with Windows. -- Abigail, in the Monastery I have several other browsers, but I prefer using Netscape 4.79. Some websites are a royal pain. I recently ran into an electronics distributor who put their entire website in "Flash". There is no way I will wait five minutes or more per page to download and run stupid animation when I am looking for parts. I have seen a bunch of sites with a white background and a very pale yellow text. My website isn't perfect, but I but a lot of work into making it easy to use and I asked for, and used, feedback from members of a couple newsgroups. You can see it at: http://home.earthlink.net/~mike.terrell/ I still have a lot of work to do to the site, but a website is never really finished, is it? -- 11 days! Michael A. Terrell Central Florida |
Mike Andrews wrote:
On my system (FreeBSD) with the Mozilla FireBird browser, the text and images are in light-colored windows inside the dark background, and it's not at all difficult to read. The Netscape 4.6 browser on the same system _does_ put the black text directly on the dark-blue background, and it is decidedly unpleasant. A newer browser might be nice, but it also would be good if web page designers built pages with older code in mind. It _definitely_ has some cool stuff. Thanks, Scott! -- Comparing Knuth with O'Reilly books is like comparing Unix with Windows. -- Abigail, in the Monastery I have several other browsers, but I prefer using Netscape 4.79. Some websites are a royal pain. I recently ran into an electronics distributor who put their entire website in "Flash". There is no way I will wait five minutes or more per page to download and run stupid animation when I am looking for parts. I have seen a bunch of sites with a white background and a very pale yellow text. My website isn't perfect, but I but a lot of work into making it easy to use and I asked for, and used, feedback from members of a couple newsgroups. You can see it at: http://home.earthlink.net/~mike.terrell/ I still have a lot of work to do to the site, but a website is never really finished, is it? -- 11 days! Michael A. Terrell Central Florida |
On Sat, 13 Dec 2003 23:59:21 GMT, Active8
,invalid wrote: clues. so you're still on that project. Well, it's *related* to "that" project, yes. tweak the sensitivity and get a peak at S9 on the CB radio type signal meter I'm using for this purpose. :) ! Adjust the meter to get the answer you want. Ok. Yes! I'm only interested in *relative* field strength. That's why I asked for a "ballpark figure" to be plucked from the air. I think you may be thinking of some fancy type of instrument like some guy mentioned he had that cost 1500 bux. These ham-type jobs I'm interested in cost just pennies to make as they don't need any absolute standard of accuracy; only a relative indication. You tweak the meter's sensitivity control to show antenna A of the TX giving rise to say S5 on the meter. You then change to antenna B and see if the reading is any higher or lower. It's really as simple as that. I'll use a distance of 6m. Noted, thanks. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Sat, 13 Dec 2003 23:59:21 GMT, Active8
,invalid wrote: clues. so you're still on that project. Well, it's *related* to "that" project, yes. tweak the sensitivity and get a peak at S9 on the CB radio type signal meter I'm using for this purpose. :) ! Adjust the meter to get the answer you want. Ok. Yes! I'm only interested in *relative* field strength. That's why I asked for a "ballpark figure" to be plucked from the air. I think you may be thinking of some fancy type of instrument like some guy mentioned he had that cost 1500 bux. These ham-type jobs I'm interested in cost just pennies to make as they don't need any absolute standard of accuracy; only a relative indication. You tweak the meter's sensitivity control to show antenna A of the TX giving rise to say S5 on the meter. You then change to antenna B and see if the reading is any higher or lower. It's really as simple as that. I'll use a distance of 6m. Noted, thanks. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
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On Sun, 14 Dec 2003 13:59:38 GMT, Active8
,invalid wrote: Yup. gave you the eqs to figure out your ballpark figure. I figured a ballpark figure might work if you gould figure out how much voltage appeared at your RFSM antenna. had I known you had a reference transmitter i might have suggested checking your RFSM reading at one location with the ref and another closer location with the test Tx, identical readings indicating sucess or close to it. I'll use a distance of 6m. Noted, thanks. Just curious, but would carrying out comparative measurements at say only 6 to 10 feet give rise to invalid readings?? -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 14 Dec 2003 13:59:38 GMT, Active8
,invalid wrote: Yup. gave you the eqs to figure out your ballpark figure. I figured a ballpark figure might work if you gould figure out how much voltage appeared at your RFSM antenna. had I known you had a reference transmitter i might have suggested checking your RFSM reading at one location with the ref and another closer location with the test Tx, identical readings indicating sucess or close to it. I'll use a distance of 6m. Noted, thanks. Just curious, but would carrying out comparative measurements at say only 6 to 10 feet give rise to invalid readings?? -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
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On Sun, 14 Dec 2003 16:47:09 GMT, Active8
,invalid wrote: I remember the 40MHz part, but I'm not sure what yer up to. Just curious You once referred to me as the "battlebots guy" - although I post on many other aspects of electronic design as well, so that's not entirely accurate. I trust this jogs your memory. :-) -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
On Sun, 14 Dec 2003 16:47:09 GMT, Active8
,invalid wrote: I remember the 40MHz part, but I'm not sure what yer up to. Just curious You once referred to me as the "battlebots guy" - although I post on many other aspects of electronic design as well, so that's not entirely accurate. I trust this jogs your memory. :-) -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
Paul Burridge wrote: Hi all, I wanted to build an RF relative field strength meter, so set about searching on the Web for any existing designs. Those I turned up weren't particularly impressive, so I decided to start from scratch and design my own. I've just completed that this afternoon. I've allowed for 0.25mV input to give rise to FSD on the microammeter. Question being, however, is that going to be sensitive enough? Yes. If it's not, either move closer, or add an op amp with a gain control after the diode(s) & cap. Mine uses 2 gain controls - 1 on the input to the op amp, and one that sets the gain of the op amp. A further improvement is the use of a cheap DPM - no parallax and a wider "full scale" range with no loss of sensitivity. The downside of the cheap DPM was the need for 2 9 volt batteries. (I have since built a small DC-DC converter that occupies the volume of a single 9V battery. That may allow using a single rechargeable 9V to power the converter - but I haven't tried it yet to be sure that the converter doesn't produce noise that would be detected by the instrument. The converter does produce dual 9V fully isolated outputs at at least 10 ma per output, way more than the instrument needs.) Does anyone have any idea what the field strength in microvolts or millivolts is from a half Watt transmitter at about 6 feet away? I guess I should have posed this question *before* designing it, but who among us can honestly say they haven't designed something without knowing what the spec is? :-) Anyway, ballpark figures gentlemen, please. p. -- "I expect history will be kind to me, since I intend to write it." - Winston Churchill |
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