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#1
March 8th 04, 07:14 PM
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Radio Shack 220-306 frequency counter -- fried?
I bought one of these last year and it worked OK for RF measurement.
I am now for the first time trying to use it to measure the [digital] frequency at a chip pin. I set it for CMOS/TTL range. It reads 4.9 MHz open circuit and shorted out. Sometimes it reads zero. Nothing changes when I test the chip pin. I get the same result using an oscilloscope probe and solid copper leads. There is supposed to be a 5KHz signal at the pin. I can hear a tone roughly of that frequency (very high) when I put that pin on the input of an amplified speaker. Is my meter fried? Or am I doing something wrong? Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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#2
March 8th 04, 07:39 PM
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On Mon, 08 Mar 2004 18:14:24 GMT, Ken wrote:
I bought one of these last year and it worked OK for RF measurement. I am now for the first time trying to use it to measure the [digital] frequency at a chip pin. I set it for CMOS/TTL range. It reads 4.9 MHz open circuit and shorted out. Sometimes it reads zero. Nothing changes when I test the chip pin. I get the same result using an oscilloscope probe and solid copper leads. There is supposed to be a 5KHz signal at the pin. I can hear a tone roughly of that frequency (very high) when I put that pin on the input of an amplified speaker. Is my meter fried? Or am I doing something wrong? Ken KC2JDY Ken (to reply via email remove "zz" from address) I have an mfj frequency counter -- inexpensive. It works okay on strong signals; about 10 watts & up. Doesn't do worth a darn on QRP signals, 5 watts or less. I'm guessing your chip doesn't put out enough power for the frequency to be detected. You may need a more sensitive lab quality detector. Bob k5qwg |
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#3
March 8th 04, 07:39 PM
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On Mon, 08 Mar 2004 18:14:24 GMT, Ken wrote:
I bought one of these last year and it worked OK for RF measurement. I am now for the first time trying to use it to measure the [digital] frequency at a chip pin. I set it for CMOS/TTL range. It reads 4.9 MHz open circuit and shorted out. Sometimes it reads zero. Nothing changes when I test the chip pin. I get the same result using an oscilloscope probe and solid copper leads. There is supposed to be a 5KHz signal at the pin. I can hear a tone roughly of that frequency (very high) when I put that pin on the input of an amplified speaker. Is my meter fried? Or am I doing something wrong? Ken KC2JDY Ken (to reply via email remove "zz" from address) I have an mfj frequency counter -- inexpensive. It works okay on strong signals; about 10 watts & up. Doesn't do worth a darn on QRP signals, 5 watts or less. I'm guessing your chip doesn't put out enough power for the frequency to be detected. You may need a more sensitive lab quality detector. Bob k5qwg |
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#4
March 8th 04, 10:32 PM
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On Mon, 08 Mar 2004 12:39:08 -0600, Bob Miller
wrote: I have an mfj frequency counter -- inexpensive. It works okay on strong signals; about 10 watts & up. Doesn't do worth a darn on QRP signals, 5 watts or less. I'm guessing your chip doesn't put out enough power for the frequency to be detected. You may need a more sensitive lab quality detector. The TTL input is hard-wired to the source; there is no sniffing. The specs for this meter say 1.5 V max for the TTL signal. I do have an RF voltage probe; maybe it can measure a square wave digital signal that is always positive. Maybe the signal is something like 10 mV and the meter won't read that low. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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#5
March 8th 04, 10:32 PM
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On Mon, 08 Mar 2004 12:39:08 -0600, Bob Miller
wrote: I have an mfj frequency counter -- inexpensive. It works okay on strong signals; about 10 watts & up. Doesn't do worth a darn on QRP signals, 5 watts or less. I'm guessing your chip doesn't put out enough power for the frequency to be detected. You may need a more sensitive lab quality detector. The TTL input is hard-wired to the source; there is no sniffing. The specs for this meter say 1.5 V max for the TTL signal. I do have an RF voltage probe; maybe it can measure a square wave digital signal that is always positive. Maybe the signal is something like 10 mV and the meter won't read that low. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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#6
March 8th 04, 11:28 PM
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If that is the one with the High Impedance setting, try that! The direct
setting may not work right. CL "Ken" wrote in message news  On Mon, 08 Mar 2004 12:39:08 -0600, Bob Miller wrote: I have an mfj frequency counter -- inexpensive. It works okay on strong signals; about 10 watts & up. Doesn't do worth a darn on QRP signals, 5 watts or less. I'm guessing your chip doesn't put out enough power for the frequency to be detected. You may need a more sensitive lab quality detector. The TTL input is hard-wired to the source; there is no sniffing. The specs for this meter say 1.5 V max for the TTL signal. I do have an RF voltage probe; maybe it can measure a square wave digital signal that is always positive. Maybe the signal is something like 10 mV and the meter won't read that low. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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#7
March 8th 04, 11:28 PM
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If that is the one with the High Impedance setting, try that! The direct
setting may not work right. CL "Ken" wrote in message news On Mon, 08 Mar 2004 12:39:08 -0600, Bob Miller wrote: I have an mfj frequency counter -- inexpensive. It works okay on strong signals; about 10 watts & up. Doesn't do worth a darn on QRP signals, 5 watts or less. I'm guessing your chip doesn't put out enough power for the frequency to be detected. You may need a more sensitive lab quality detector. The TTL input is hard-wired to the source; there is no sniffing. The specs for this meter say 1.5 V max for the TTL signal. I do have an RF voltage probe; maybe it can measure a square wave digital signal that is always positive. Maybe the signal is something like 10 mV and the meter won't read that low. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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#8
March 8th 04, 11:55 PM
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On Mon, 8 Mar 2004 17:28:33 -0500, "CL"
wrote: If that is the one with the High Impedance setting, try that! The direct setting may not work right. CL Tried 'em both. No help. Also, I measured the voltage at the subject pin with a Fluke RF voltage probe: 7 millivolts. That is probably 1/100 of what the meter needs on the TTL setting. This is starting to look like an oscilloscope job. To bad I just returned one I had borrowed [for six months]. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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#9
March 8th 04, 11:55 PM
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On Mon, 8 Mar 2004 17:28:33 -0500, "CL"
wrote: If that is the one with the High Impedance setting, try that! The direct setting may not work right. CL Tried 'em both. No help. Also, I measured the voltage at the subject pin with a Fluke RF voltage probe: 7 millivolts. That is probably 1/100 of what the meter needs on the TTL setting. This is starting to look like an oscilloscope job. To bad I just returned one I had borrowed [for six months]. Ken KC2JDY Ken (to reply via email remove "zz" from address) |
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