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MFJ-269 Antenna/SWR/RF Analyzer
After reading the remarks here and researching the past posts to the
newsgroup on the MFJ-269 I feel I have been missing out on a lot. The best overall description I have found anywhere (including the MFJ web site) is in the current ad in QST. I ordered it Saturday morning and am eagerly awaiting its arrival. John Ferrell, W8CCW On Mon, 7 Nov 2005 07:12:20 -0500, "Bill" wrote: Interesting....if there is something better out there what is it?......been using a 259 since "98" and its done the job for me from beams-wires...co-ax measurement....ans the latest, balancing out the 1/4 wave stubs on a Hygain HighTower, as I added 17 meters to the array!! |
#2
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MFJ-269 Antenna/SWR/RF Analyzer
"John Ferrell" wrote in message ... After reading the remarks here and researching the past posts to the newsgroup on the MFJ-269 I feel I have been missing out on a lot. The best overall description I have found anywhere (including the MFJ web site) is in the current ad in QST. I ordered it Saturday morning and am eagerly awaiting its arrival. John Ferrell, W8CCW I am happy with mine. Only thing I can add is that it eats batteries, and my unit does not like to work below 13 Volts. They do sell a tunable bandpass filter for the lower frequencies. I tried a high pass filter - don't bother, it messes up the phase. Tam/WB2TT |
#3
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MFJ-269 Antenna/SWR/RF Analyzer
Tam/WB2TT wrote:
Only thing I can add is that it eats batteries, ... I run mine off an external rechargable 12v YUASA battery. -- 73, Cecil http://www.qsl.net/w5dxp |
#4
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MFJ-269 Antenna/SWR/RF Analyzer
"Cecil Moore" wrote in message . net... Tam/WB2TT wrote: Only thing I can add is that it eats batteries, ... I run mine off an external rechargable 12v YUASA battery. -- 73, Cecil http://www.qsl.net/w5dxp Never thought of that. I actually have a 12V, 7 AH Yuasa sitting on the file cabinet. I would just have to keep it well charged. Tam |
#5
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MFJ-269 Antenna/SWR/RF Analyzer
Tam/WB2TT wrote:
"Cecil Moore" wrote: Tam/WB2TT wrote: Only thing I can add is that it eats batteries, ... I run mine off an external rechargable 12v YUASA battery. Never thought of that. I actually have a 12V, 7 AH Yuasa sitting on the file cabinet. I would just have to keep it well charged. I use a 2Ah NP2-12 with a molex connector double-sided taped to the underside of the MFJ-259 and charge it with an Astron RS-20M. The battery is smaller than the MFJ and about 3/4" thick. -- 73, Cecil http://www.qsl.net/w5dxp |
#6
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MFJ-269 Antenna/SWR/RF Analyzer
Tam/WB2TT wrote:
I am happy with mine. Only thing I can add is that it eats batteries, and my unit does not like to work below 13 Volts. They do sell a tunable bandpass filter for the lower frequencies. I tried a high pass filter - don't bother, it messes up the phase. If you do want to measure antenna impedance with something like the MFJ and have trouble (as I do) with local broadcasting and other RF, I recommend using a "half wave" filter. This type of filter has reasonable out-of-band attenuation characteristics and doesn't disturb the impedance measurement too much. (Over a limited frequency range it mimics a half wavelength of transmission line.) The impedance disturbance will be the least when the filter is designed to approximately match the measured impedance. It's simply two cascaded pi sections, with each element having the same value of X. For example, a lowpass looks like this: ---.---L---.---L---.--- | | | C 2C C | | | ----.-------.-------.--- For example, a filter with Z0 = 50 ohms (one which mimics a half wavelength of 50 ohm line) has XL = XC = 50. One designed for 7 MHz would have L = 1.14 uH, C = 455 pF. You can wind the coils on small type 2 or 6 powdered iron cores, and use the closest standard value (e.g., 470 pF) for the capacitors. This filter will cause little impedance disturbance at 7 MHz and, for load impedances near 50 ohms, at lower frequencies also. A highpass looks like this: ---.---C---.---C---.--- | | | L L/2 L | | | ----.-------.-------.--- Again, XL = XC = the filter Z0. Make filters according to your particular measurement needs. You can check the amount of disturbance the filter causes by making a known impedance out of a resistor and capacitor or inductor which is about equal to the measured impedance, and measuring it with and without the filter. If you can read German, there's a marvelous book describing how to make a wide variety of measurements with an antenna analyzer, with tricks, tips, and details. It's _HF-Messungen mit einem aktiven Stehwellen-Meßgerät_ by Gerd Janzen, DF6SJ. It's available directly from him at Hochvogelstraße 29, D-87435 Kempten, Germany. Roy Lewallen, W7EL |
#7
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MFJ-269 Antenna/SWR/RF Analyzer
"Roy Lewallen" wrote in message ... Tam/WB2TT wrote: I am happy with mine. Only thing I can add is that it eats batteries, and my unit does not like to work below 13 Volts. They do sell a tunable bandpass filter for the lower frequencies. I tried a high pass filter - don't bother, it messes up the phase. If you do want to measure antenna impedance with something like the MFJ and have trouble (as I do) with local broadcasting and other RF, I recommend using a "half wave" filter. This type of filter has reasonable out-of-band attenuation characteristics and doesn't disturb the impedance measurement too much. (Over a limited frequency range it mimics a half wavelength of transmission line.) The impedance disturbance will be the least when the filter is designed to approximately match the measured impedance. It's simply two cascaded pi sections, with each element having the same value of X. For example, a lowpass looks like this: ---.---L---.---L---.--- | | | C 2C C | | | ----.-------.-------.--- For example, a filter with Z0 = 50 ohms (one which mimics a half wavelength of 50 ohm line) has XL = XC = 50. One designed for 7 MHz would have L = 1.14 uH, C = 455 pF. You can wind the coils on small type 2 or 6 powdered iron cores, and use the closest standard value (e.g., 470 pF) for the capacitors. This filter will cause little impedance disturbance at 7 MHz and, for load impedances near 50 ohms, at lower frequencies also. A highpass looks like this: ---.---C---.---C---.--- | | | L L/2 L | | | ----.-------.-------.--- Again, XL = XC = the filter Z0. Make filters according to your particular measurement needs. You can check the amount of disturbance the filter causes by making a known impedance out of a resistor and capacitor or inductor which is about equal to the measured impedance, and measuring it with and without the filter. If you can read German, there's a marvelous book describing how to make a wide variety of measurements with an antenna analyzer, with tricks, tips, and details. It's _HF-Messungen mit einem aktiven Stehwellen-Meßgerät_ by Gerd Janzen, DF6SJ. It's available directly from him at Hochvogelstraße 29, D-87435 Kempten, Germany. Roy Lewallen, W7EL I will have to try your configuration. I did C - L - C/2 - L -C, with C=1000PF, L=2.2uH. According to SWCad, the gain is flat above 2 MHz, but there is 120 degrees phase shift at 4 MHz, relative to the phase at 100 MHz. Tam/WB2TT |
#8
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MFJ-269 Antenna/SWR/RF Analyzer
Tam/WB2TT wrote:
I will have to try your configuration. I did C - L - C/2 - L -C, with C=1000PF, L=2.2uH. According to SWCad, the gain is flat above 2 MHz, but there is 120 degrees phase shift at 4 MHz, relative to the phase at 100 MHz. The center component should be 2C, or 2000 pF for your experiment, not C/2. The circuit is simply two pi networks in cascade, each having all component reactances equal to the "transmission line" Z0. Each pi section mimics a quarter wave transmission line. Roy Lewallen, W7EL |
#9
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MFJ-269 Antenna/SWR/RF Analyzer
"Roy Lewallen" wrote in message ... Tam/WB2TT wrote: I will have to try your configuration. I did C - L - C/2 - L -C, with C=1000PF, L=2.2uH. According to SWCad, the gain is flat above 2 MHz, but there is 120 degrees phase shift at 4 MHz, relative to the phase at 100 MHz. The center component should be 2C, or 2000 pF for your experiment, not C/2. The circuit is simply two pi networks in cascade, each having all component reactances equal to the "transmission line" Z0. Each pi section mimics a quarter wave transmission line. Roy Lewallen, W7EL Roy, I wasn't too clear, but I have 2 T networks back/back. That makes the center cap C/2. I am going to run SWCad on the Pi configuration later, and see what that does. Tam/WB2TT |
#10
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MFJ-269 Antenna/SWR/RF Analyzer
"Tam/WB2TT" wrote in message ... Meanwhile, I measured the impedance of a Drake 100W dummy load with and without the HPF. All readings without the HPF are within Drake spec. FREQ NO HPF With HPF 4 Mhz 47j2 33j13 7MHz 47j2 55j3 14MHz 47j1 50j7 28MHz 48j2 47j3 50MHz 49j2 54j11 144MHz 53j11 74j36 Everything was connected with UHF adapters, and no coax was used. Ignore the VHF readings,. as the filter was not built that carefully. Capacitors are mica (actual values 1000, 560, 1000), and inductors appear to be 68-2 (2.2uH). If I get a chance later today, I will rewire it into the Pi configuration with the same inductors. Tam/WB2TT |
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