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SWR and resonance measurements without an MFJ269 or equiv.
Some friends and I have been looking into making antennas for 70 cm.
and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? What kind of "SWR meter" are you talking about? The '8640 may or may not have enough power to be suitable. |
SWR and resonance measurements without an MFJ269 or equiv.
On 18 Dec 2006 10:39:54 -0800, Wes wrote in .com:
Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? What kind of "SWR meter" are you talking about? The '8640 may or may not have enough power to be suitable. A fairly el-cheapo no-name, but appearently good-enough on 2m and from 420 to 450 MHz. I haven't fiddled with it to see how much drive power is required. I suppose I can get a couple of RF amplitude measuring chips and make the critter active instead of passive, if necessary. The 8640, IIRC, is good for +20 dBm (3V) into 50 Ohms, or a lusty 180 mW flat-out, but the finals on the 8640 are unobtainium and so I'm minded to stay well below that -- and even lower outside the ham bands. -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
In article ,
"Mike Andrews" wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? Mike- You have to try it to find out. One problem is that your SWR meter's diode output is non-linear for very low voltages, resulting in SWR being higher than indicated for low values of SWR. You may be able to get around this with a hand-calibrated dial on the meter, or a calibration correction chart. Fred K4DII |
SWR and resonance measurements without an MFJ269 or equiv.
Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
In article ,
Fred McKenzie wrote: In article , "Mike Andrews" wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? Mike- You have to try it to find out. One problem is that your SWR meter's diode output is non-linear for very low voltages, resulting in SWR being higher than indicated for low values of SWR. You may be able to get around this with a hand-calibrated dial on the meter, or a calibration correction chart. Fred K4DII Analog devices makes RF-log amp/detector chips which are good to microwave frequencies (basically RF in, 10mv per dBm out, from -80dBm to 0dBm). Replace the SWR meter's detector with one of these. -- /* AB1GO */ /* Joseph H. Allen */ int a[1817];main(z,p,q,r){for(p=80;q+p-80;p-=2*a[p])for(z=9;z--;)q=3&(r=time(0) +r*57)/7,q=q?q-1?q-2?1-p%79?-1:0:p%79-77?1:0:p1659?79:0:p158?-79:0,q?!a[p+q*2 ]?a[p+=a[p+=q]=q]=q:0:0;for(;q++-1817;)printf(q%79?"%c":"%c\n"," #"[!a[q-1]]);} |
SWR and resonance measurements without an MFJ269 or equiv.
Joseph H Allen wrote: Analog devices makes RF-log amp/detector chips which are good to microwave frequencies (basically RF in, 10mv per dBm out, from -80dBm to 0dBm). Replace the SWR meter's detector with one of these. -- Andy writes: I built one of those up -- the version that goes to 500 Mhz -- and I use it with a Mini-Ckts Fwd/Ref bridge and a Measurements 202, which only puts out around 0 dbm. It works like a charm. I use the 202 to get reference measurements and use that system to tune antennae and transmission lines. It's a very very sensitive RF power meter and, while the absolute accuracy may not be the best, it's very good for using low power signal sources and taking relative measurement. Andy W4OAH |
SWR and resonance measurements without an MFJ269 or equiv.
On Mon, 18 Dec 2006 15:08:17 +0000 (UTC), "Mike Andrews"
wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? You can achieve a lot on 70cm with an HT and a simple field strength meter. Think matching stubs & shorting bars... John Ferrell W8CCW |
SWR and resonance measurements without an MFJ269 or equiv.
On Mon, 18 Dec 2006, Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, You did not say what an 8640B is. Signal generator? Transmitter? Power out? Main thing is to get the "forward" power to read something on the meter (preferably full scale, but even if you get half or quarter scale, then you are able to get a rough idea of usabiltiy of the meter). Then see what it shows on the "reflected" scale. Figure ver roughly if the reflected power is half the forward (regardless of the actual location on the meter scale), then you have about 3:1 SWR. Turn the meter around to get an idea if the diodes (and associated circuitry) are well matched for forward and reflected. I have used a number of el-cheapo CB SWR meters even up on two meters and they work surprisingly well, even more sensitive than ham SWR meters for VHF-UHF, and not that far off of what the ham SWR meters report, and so are good for handie-talkie measurements. So, yes, you should get useful ball park figures. running the signal through the SWR meter to the antenna? Or am I way off in left field? -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
On Tue, 19 Dec 2006 09:58:41 -0500, Straydog wrote in m:
On Mon, 18 Dec 2006, Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, You did not say what an 8640B is. Signal generator? Transmitter? Power out? Lab-grade RF signal generator, official range from 500 KHz to 1.024 MHz. In practice it's good from 455 KHz up to about 1.2 GHz. Includes FM, AM, and pulse modulation, with either internal modulation at variable frequencies and amplitude (AM) or deviation (FM) or external modulation. Has a very nice 6 1/2 digit counter good up to 1.2 GHz. Output range is from -130 dBm (100 nanoVolts) to +20 dBm (3 Volts) into 50 Ohms. It's a _very_ nice piece of gear indeed. You can see a picture of mine (and other stuff on the workbench) at http://mikea.ath.cx/testgear/index.html. Main thing is to get the "forward" power to read something on the meter (preferably full scale, but even if you get half or quarter scale, then you are able to get a rough idea of usabiltiy of the meter). Then see what it shows on the "reflected" scale. Figure ver roughly if the reflected power is half the forward (regardless of the actual location on the meter scale), then you have about 3:1 SWR. Turn the meter around to get an idea if the diodes (and associated circuitry) are well matched for forward and reflected. I have used a number of el-cheapo CB SWR meters even up on two meters and they work surprisingly well, even more sensitive than ham SWR meters for VHF-UHF, and not that far off of what the ham SWR meters report, and so are good for handie-talkie measurements. So, yes, you should get useful ball park figures. That's good to hear. I got to thinking about what an MFJ-259 or -269 does, and decided that I only needed a sensitive-enough SWR meter that would give reasonably accurate readings from 100 MHz to 1.2 GHz, since I already had the signal source. Of course, the HP 8640B weighs about 40 pounds, and is a good deal less portable than the MFJ products, but if I can get this working, I'll be able to do things it won't. running the signal through the SWR meter to the antenna? Or am I way off in left field? Looks like I'm well inside the ballpark and that I have some design and construction to do. This should be fun. Thanks! -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
I don't think using your 8640B as a signal source to read on a wattmeter
is going to cut it. +20 dBm is only 100 mW. Unless you have a wattmeter that has a 100 mW or so range, you aren't going to get much needle deflection. The lowest range on my Telewave wattmeter is 5 Watts. Scott N0EDV Mike Andrews wrote: On Tue, 19 Dec 2006 09:58:41 -0500, Straydog wrote in m: On Mon, 18 Dec 2006, Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, You did not say what an 8640B is. Signal generator? Transmitter? Power out? Lab-grade RF signal generator, official range from 500 KHz to 1.024 MHz. In practice it's good from 455 KHz up to about 1.2 GHz. Includes FM, AM, and pulse modulation, with either internal modulation at variable frequencies and amplitude (AM) or deviation (FM) or external modulation. Has a very nice 6 1/2 digit counter good up to 1.2 GHz. Output range is from -130 dBm (100 nanoVolts) to +20 dBm (3 Volts) into 50 Ohms. It's a _very_ nice piece of gear indeed. You can see a picture of mine (and other stuff on the workbench) at http://mikea.ath.cx/testgear/index.html. Main thing is to get the "forward" power to read something on the meter (preferably full scale, but even if you get half or quarter scale, then you are able to get a rough idea of usabiltiy of the meter). Then see what it shows on the "reflected" scale. Figure ver roughly if the reflected power is half the forward (regardless of the actual location on the meter scale), then you have about 3:1 SWR. Turn the meter around to get an idea if the diodes (and associated circuitry) are well matched for forward and reflected. I have used a number of el-cheapo CB SWR meters even up on two meters and they work surprisingly well, even more sensitive than ham SWR meters for VHF-UHF, and not that far off of what the ham SWR meters report, and so are good for handie-talkie measurements. So, yes, you should get useful ball park figures. That's good to hear. I got to thinking about what an MFJ-259 or -269 does, and decided that I only needed a sensitive-enough SWR meter that would give reasonably accurate readings from 100 MHz to 1.2 GHz, since I already had the signal source. Of course, the HP 8640B weighs about 40 pounds, and is a good deal less portable than the MFJ products, but if I can get this working, I'll be able to do things it won't. running the signal through the SWR meter to the antenna? Or am I way off in left field? Looks like I'm well inside the ballpark and that I have some design and construction to do. This should be fun. Thanks! |
SWR and resonance measurements without an MFJ269 or equiv.
On Tue, 19 Dec 2006 18:36:43 +0000, Scott wrote in :
I don't think using your 8640B as a signal source to read on a wattmeter is going to cut it. +20 dBm is only 100 mW. Unless you have a wattmeter that has a 100 mW or so range, you aren't going to get much needle deflection. The lowest range on my Telewave wattmeter is 5 Watts. Agreed. I'm looking at some RF log-amp chips from various places and some RF sensor chips I saw in a construction article I can't locate right now, so that I can get something useful with signal levels in the Part-15 range. I don't know what I'll wind up with, but it'll be interesting. I'll share when it's soup. -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
In article ,
"Mike Andrews" wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? Mike- I think you are on the right track with the RF log-amps. Another idea - I understand the MFJ-259 has a standard SWR configuration with a built-in signal source that uses an ALC to keep forward power at the equivalent of full scale. Why not replace the 259 signal source with the HP 8640B? Fred K4DII |
SWR and resonance measurements without an MFJ269 or equiv.
On Tue, 19 Dec 2006 15:04:58 -0500, Fred McKenzie wrote in :
In article , "Mike Andrews" wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, running the signal through the SWR meter to the antenna? Or am I way off in left field? Mike- I think you are on the right track with the RF log-amps. Another idea - I understand the MFJ-259 has a standard SWR configuration with a built-in signal source that uses an ALC to keep forward power at the equivalent of full scale. Why not replace the 259 signal source with the HP 8640B? I hadn't thought of that. I suppose I could put a jack on the 259's case, and a switch to select the 8640B, which has _marvelous_ ALC all its own. The switch, and some RG-174, ought to be good enough for what I'll be asking them to do. But that changes the question to "Is the 259's SWR sensor good enough above 175 MHz, and especially around 33 cm to 25 cm, to give real-world answers?" I'll never know if I don't try. I may have to buy a factory UHF-and-above antenna analyzer to validate my answers, of course. I'm sure W5DNA will understand why we're eating potato soup for two or three months. Thanks! -- Mike Andrews, W5EGO Tired old sysadmin |
SWR and resonance measurements without an MFJ269 or equiv.
I'd start by measuring a standard or two. You can get pretty decent
termination resistors on eBay for a modest cost. If your system measures close to 1:1 when terminated with one of those, you're off to a good start. Next I'd make up a 50 ohm microstrip line terminated with a 50 ohm chip resistor. If that reads close to what the 50 ohm termination did, then I'd measure the SWR with some different load values, say 25 and 100 ohms. These of course could be made from two 50 ohm chip resistors. You could get more elaborate with the calibration by introducing reactive loads, but just the three data points should be enough to give you some confidence in your SWR measurements, at least near 1:1 where your primary interest is. Roy Lewallen, W7EL |
SWR and resonance measurements without an MFJ269 or equiv.
Just one comment, about halfway down.... On Tue, 19 Dec 2006, Mike Andrews wrote: On Tue, 19 Dec 2006 09:58:41 -0500, Straydog wrote in m: On Mon, 18 Dec 2006, Mike Andrews wrote: Some friends and I have been looking into making antennas for 70 cm. and higher frequencies, but we don't have an MFJ-269; my MFJ-259 tops out at 175 MHz. I _do_, however, have an SWR meter that supposedly works up to 500 MHz( and maybe higher), and an HP 8640B that is good to about 1.2 GHz. If the SWR meter is sensitive enough, could I get at least ballpark SWR values using the 8640B as a source, You did not say what an 8640B is. Signal generator? Transmitter? Power out? Lab-grade RF signal generator, official range from 500 KHz to 1.024 MHz. In practice it's good from 455 KHz up to about 1.2 GHz. Includes FM, AM, and pulse modulation, with either internal modulation at variable frequencies and amplitude (AM) or deviation (FM) or external modulation. Has a very nice 6 1/2 digit counter good up to 1.2 GHz. Output range is from -130 dBm (100 nanoVolts) to +20 dBm (3 Volts) into 50 Ohms. 3 volts into 50 ohms isn't much power. ~3/50 of an amp, means about 180 milliwatts. The most sensitive calibrated SWR meters will read zero to 5 watts full scale, so 180 milliwatts might move your needle for forward power about 5-10 degrees of arc away from the leftmost peg towards the rightmost peg on the dial. That doesn't give you much indication of reflected power since a 3:1 ratio would then mean movement of the needle about 2.5 to 5 degrees of arc, respectively. The elcheapo CB SWR meters _might_ be more sensitive since more power _should_ transfer to the measuring bars because 2 meters is some 5 times higher in frequency and the CB SWR meters are meant to operate at max 3-4 watts of RF output from the CB rigs. But, you'll have to try it. ===== no change to below, included for reference and context ===== It's a _very_ nice piece of gear indeed. You can see a picture of mine (and other stuff on the workbench) at http://mikea.ath.cx/testgear/index.html. Main thing is to get the "forward" power to read something on the meter (preferably full scale, but even if you get half or quarter scale, then you are able to get a rough idea of usabiltiy of the meter). Then see what it shows on the "reflected" scale. Figure ver roughly if the reflected power is half the forward (regardless of the actual location on the meter scale), then you have about 3:1 SWR. Turn the meter around to get an idea if the diodes (and associated circuitry) are well matched for forward and reflected. I have used a number of el-cheapo CB SWR meters even up on two meters and they work surprisingly well, even more sensitive than ham SWR meters for VHF-UHF, and not that far off of what the ham SWR meters report, and so are good for handie-talkie measurements. So, yes, you should get useful ball park figures. That's good to hear. I got to thinking about what an MFJ-259 or -269 does, and decided that I only needed a sensitive-enough SWR meter that would give reasonably accurate readings from 100 MHz to 1.2 GHz, since I already had the signal source. Of course, the HP 8640B weighs about 40 pounds, and is a good deal less portable than the MFJ products, but if I can get this working, I'll be able to do things it won't. running the signal through the SWR meter to the antenna? Or am I way off in left field? Looks like I'm well inside the ballpark and that I have some design and construction to do. This should be fun. Thanks! -- Mike Andrews, W5EGO Tired old sysadmin |
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