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#1
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TS-118A/AP, RF Wattmeter/Dummy load
Hello
I recently went to buy an RF sweep generator and ended up bringing home a TS-118A/AP (Bird) RF wattmeter, as one does! I have some questions:- 1. Given that the RF power sensors for the various bands/power ratings are added external to the meter with only the coax connecting through to the unit,how does it work? I assume the sensors are thermocouple types but there's no separate DC circuit and I can only see a narrow constriction in the sensor with the centre core being a very fine wire. 2. I'm missing the calibration/multiplication factor graph for the MX-1784/U sensor, would anyone have one they'd be prepared to scan and email for me? Any pointers to a full manual on the net would be good also. 3. Although the unit is marked 20-1400MHz at 500W, the MX-1783/U graph shows power levels up to 1200W at 40MHz, I guess the unit is very conservatively rated but does anyone have true figures (not that I intend to work at that sort of power levels). 4. Is it OK to use as a straight dummy load without the sensor, I've tested it at 2m and it seems fine but why the 20MHz lower limit? also it doesn't measure 50 ohms at DC so I guess it can't be a straight resistor so what's the load? I'd appreciate all and any information you can give about the wattmeter, it's not something I'd have planned on buying but it looks like it'll serve all the needs I'd ever have for a high power dummy load/wattmeter other than for the lower HF bands. Thanks in advance John |
#2
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On Sun, 22 Feb 2004 13:35:55 -0000, "owen.home"
wrote: I have two of these units both measure 50 ohms. Also found the manual for it. It will be a while before I could copy it for you. Hello I recently went to buy an RF sweep generator and ended up bringing home a TS-118A/AP (Bird) RF wattmeter, as one does! I have some questions:- 1. Given that the RF power sensors for the various bands/power ratings are added external to the meter with only the coax connecting through to the unit,how does it work? I assume the sensors are thermocouple types but there's no separate DC circuit and I can only see a narrow constriction in the sensor with the centre core being a very fine wire. 2. I'm missing the calibration/multiplication factor graph for the MX-1784/U sensor, would anyone have one they'd be prepared to scan and email for me? Any pointers to a full manual on the net would be good also. The MX-1784 is a tuning shunt used for safety reasons on transmitters with capacitively coupled outputs. 3. Although the unit is marked 20-1400MHz at 500W, the MX-1783/U graph shows power levels up to 1200W at 40MHz, I guess the unit is very conservatively rated but does anyone have true figures (not that I intend to work at that sort of power levels). The manual speced power levels are. Range 20- 1400mhz power 20-100mhz 2-300watts 100-300mhz 2-500watts 300-750mhz 2-125watts 750-1400mhz 2-125 watts 4. Is it OK to use as a straight dummy load without the sensor, I've tested it at 2m and it seems fine but why the 20MHz lower limit? also it doesn't measure 50 ohms at DC so I guess it can't be a straight resistor so what's the load? The lower 20 mhz limit is to prevent damage to the metering circuits. It can be used to DC if you disconnect the metering circuit. I learned the hard way!!!!! It is a straight 50 ohm resistor in the oil. If you measure anything much differnet the resistor is defective. I'd appreciate all and any information you can give about the wattmeter, it's not something I'd have planned on buying but it looks like it'll serve all the needs I'd ever have for a high power dummy load/wattmeter other than for the lower HF bands. Thanks in advance John |
#3
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On Sun, 22 Feb 2004 13:35:55 -0000, "owen.home"
wrote: I have two of these units both measure 50 ohms. Also found the manual for it. It will be a while before I could copy it for you. Hello I recently went to buy an RF sweep generator and ended up bringing home a TS-118A/AP (Bird) RF wattmeter, as one does! I have some questions:- 1. Given that the RF power sensors for the various bands/power ratings are added external to the meter with only the coax connecting through to the unit,how does it work? I assume the sensors are thermocouple types but there's no separate DC circuit and I can only see a narrow constriction in the sensor with the centre core being a very fine wire. 2. I'm missing the calibration/multiplication factor graph for the MX-1784/U sensor, would anyone have one they'd be prepared to scan and email for me? Any pointers to a full manual on the net would be good also. The MX-1784 is a tuning shunt used for safety reasons on transmitters with capacitively coupled outputs. 3. Although the unit is marked 20-1400MHz at 500W, the MX-1783/U graph shows power levels up to 1200W at 40MHz, I guess the unit is very conservatively rated but does anyone have true figures (not that I intend to work at that sort of power levels). The manual speced power levels are. Range 20- 1400mhz power 20-100mhz 2-300watts 100-300mhz 2-500watts 300-750mhz 2-125watts 750-1400mhz 2-125 watts 4. Is it OK to use as a straight dummy load without the sensor, I've tested it at 2m and it seems fine but why the 20MHz lower limit? also it doesn't measure 50 ohms at DC so I guess it can't be a straight resistor so what's the load? The lower 20 mhz limit is to prevent damage to the metering circuits. It can be used to DC if you disconnect the metering circuit. I learned the hard way!!!!! It is a straight 50 ohm resistor in the oil. If you measure anything much differnet the resistor is defective. I'd appreciate all and any information you can give about the wattmeter, it's not something I'd have planned on buying but it looks like it'll serve all the needs I'd ever have for a high power dummy load/wattmeter other than for the lower HF bands. Thanks in advance John |
#4
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Gene
Many thanks for the reply, I understand now - the meter is across the line but isolated at RF with an inductor so that at DC I'm seeing the meter and load in parallel, mine measures fine with the meter disconnected. Thanks for the warning about damaging the meter below 20MHz and the info on the MX-1784/U, I opened it up and can see the inductor to ground. I'd still like to know how the sensors are made up though and I would appreciate a copy of the manual sometime if you get a chance, I'm missing one of the sensors - are they easily available these days? Thanks again John "Gene Tomlinson" wrote in message ... On Sun, 22 Feb 2004 13:35:55 -0000, "owen.home" wrote: I have two of these units both measure 50 ohms. Also found the manual for it. It will be a while before I could copy it for you. Hello I recently went to buy an RF sweep generator and ended up bringing home a TS-118A/AP (Bird) RF wattmeter, as one does! I have some questions:- 1. Given that the RF power sensors for the various bands/power ratings are added external to the meter with only the coax connecting through to the unit,how does it work? I assume the sensors are thermocouple types but there's no separate DC circuit and I can only see a narrow constriction in the sensor with the centre core being a very fine wire. 2. I'm missing the calibration/multiplication factor graph for the MX-1784/U sensor, would anyone have one they'd be prepared to scan and email for me? Any pointers to a full manual on the net would be good also. The MX-1784 is a tuning shunt used for safety reasons on transmitters with capacitively coupled outputs. 3. Although the unit is marked 20-1400MHz at 500W, the MX-1783/U graph shows power levels up to 1200W at 40MHz, I guess the unit is very conservatively rated but does anyone have true figures (not that I intend to work at that sort of power levels). The manual speced power levels are. Range 20- 1400mhz power 20-100mhz 2-300watts 100-300mhz 2-500watts 300-750mhz 2-125watts 750-1400mhz 2-125 watts 4. Is it OK to use as a straight dummy load without the sensor, I've tested it at 2m and it seems fine but why the 20MHz lower limit? also it doesn't measure 50 ohms at DC so I guess it can't be a straight resistor so what's the load? The lower 20 mhz limit is to prevent damage to the metering circuits. It can be used to DC if you disconnect the metering circuit. I learned the hard way!!!!! It is a straight 50 ohm resistor in the oil. If you measure anything much differnet the resistor is defective. I'd appreciate all and any information you can give about the wattmeter, it's not something I'd have planned on buying but it looks like it'll serve all the needs I'd ever have for a high power dummy load/wattmeter other than for the lower HF bands. Thanks in advance John |
#5
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Gene
Many thanks for the reply, I understand now - the meter is across the line but isolated at RF with an inductor so that at DC I'm seeing the meter and load in parallel, mine measures fine with the meter disconnected. Thanks for the warning about damaging the meter below 20MHz and the info on the MX-1784/U, I opened it up and can see the inductor to ground. I'd still like to know how the sensors are made up though and I would appreciate a copy of the manual sometime if you get a chance, I'm missing one of the sensors - are they easily available these days? Thanks again John "Gene Tomlinson" wrote in message ... On Sun, 22 Feb 2004 13:35:55 -0000, "owen.home" wrote: I have two of these units both measure 50 ohms. Also found the manual for it. It will be a while before I could copy it for you. Hello I recently went to buy an RF sweep generator and ended up bringing home a TS-118A/AP (Bird) RF wattmeter, as one does! I have some questions:- 1. Given that the RF power sensors for the various bands/power ratings are added external to the meter with only the coax connecting through to the unit,how does it work? I assume the sensors are thermocouple types but there's no separate DC circuit and I can only see a narrow constriction in the sensor with the centre core being a very fine wire. 2. I'm missing the calibration/multiplication factor graph for the MX-1784/U sensor, would anyone have one they'd be prepared to scan and email for me? Any pointers to a full manual on the net would be good also. The MX-1784 is a tuning shunt used for safety reasons on transmitters with capacitively coupled outputs. 3. Although the unit is marked 20-1400MHz at 500W, the MX-1783/U graph shows power levels up to 1200W at 40MHz, I guess the unit is very conservatively rated but does anyone have true figures (not that I intend to work at that sort of power levels). The manual speced power levels are. Range 20- 1400mhz power 20-100mhz 2-300watts 100-300mhz 2-500watts 300-750mhz 2-125watts 750-1400mhz 2-125 watts 4. Is it OK to use as a straight dummy load without the sensor, I've tested it at 2m and it seems fine but why the 20MHz lower limit? also it doesn't measure 50 ohms at DC so I guess it can't be a straight resistor so what's the load? The lower 20 mhz limit is to prevent damage to the metering circuits. It can be used to DC if you disconnect the metering circuit. I learned the hard way!!!!! It is a straight 50 ohm resistor in the oil. If you measure anything much differnet the resistor is defective. I'd appreciate all and any information you can give about the wattmeter, it's not something I'd have planned on buying but it looks like it'll serve all the needs I'd ever have for a high power dummy load/wattmeter other than for the lower HF bands. Thanks in advance John |
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