|
HP 5245L Counter Oscillator adjust?
I'm trying to download a copy of the manual, but at the rate it's
downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV |
HP 5245L Counter Oscillator adjust?
Scott wrote:
I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net |
HP 5245L Counter Oscillator adjust?
On Apr 26, 11:41*am, "Dave M" wrote:
Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? *I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. *I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. *Check to see if the collector of Q1 is in the ballpark of about -21 volts. *That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. *If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. *That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. *In that case, the oven assembly is bad, and will need to be replaced. *You can attempt ot disassemble the oven and repair the heater, but it's iffy. *One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. *That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. *If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? (and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. Your comparing the HP ref. signal to......what?.... A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. If the oven is working, it will get warm. Simple. Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. Andrew VK3BFA. |
HP 5245L Counter Oscillator adjust?
Andrew VK3BFA wrote:
On Apr 26, 11:41 am, "Dave M" wrote: Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? (and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. Your comparing the HP ref. signal to......what?.... A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. If the oven is working, it will get warm. Simple. Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. Andrew VK3BFA. The 5248L manual is on Agilent's site at http://cp.literature.agilent.com/lit...5248-90001.pdf. I can't say how similar they are to the 5245L, but the DCUs seem to be the same. I used to be a calibration tech many years ago, and while I saw many of both instruments on my bench, I rarely had to repair them; quite reliable. I remember two cases where the counters exhibited the exact problem the OP has; significant oscillator error. Both turned out to be problems with the oven control circuit. I have to disagree with your statement that the OP's error is insignigicant for professional use. That might be true for some hobbiest uses, but for many amateur radio operators and certainly for professional use, it's a very significant error. The original time base spec for the 5245L is 3x10^-9 per day. -- David dgminala at mediacombb dot net |
HP 5245L Counter Oscillator adjust?
On Apr 27, 11:19*pm, "Dave M" wrote:
Andrew VK3BFA wrote: On Apr 26, 11:41 am, "Dave M" wrote: Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. *I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? *(and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. *Your comparing the HP ref. signal to......what?.... A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. If the oven is working, it will get warm. Simple. Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. *You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. Andrew VK3BFA. The 5248L manual is on Agilent's site athttp://cp.literature.agilent.com/litweb/pdf/05248-90001.pdf. I can't say how similar they are to the 5245L, but the DCUs seem to be the same. *I used to be a calibration tech many years ago, and while I saw many of both instruments on my bench, I rarely had to repair them; quite reliable. *I remember two cases where the counters exhibited the exact problem the OP has; significant oscillator error. *Both turned out to be problems with the oven control circuit. I have to disagree with your statement that the OP's error is insignigicant for professional use. *That might be true for some hobbiest uses, but for many amateur radio operators and certainly for professional use, *it's a very significant error. * The original time base spec for the 5245L is 3x10^-9 per day. -- David dgminala at mediacombb dot net David, than you for the link - will try for it, and hopefully it can run overnight here. I stand corrected re accuracy - as I said, I should have dig out the manual, (and, indeed, revise my own theory re where the decimal point goes) a bit better. I was hoping someone like you would stick their head up - helps to talk to someone who has actually worked on them as a job.....thanks mate, appreciated. Andrew VK3BFA. |
HP 5245L Counter Oscillator adjust?
On Apr 27, 11:19*pm, "Dave M" wrote:
Andrew VK3BFA wrote: On Apr 26, 11:41 am, "Dave M" wrote: Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. *I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? *(and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. *Your comparing the HP ref. signal to......what?.... A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. If the oven is working, it will get warm. Simple. Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. *You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. Andrew VK3BFA. The 5248L manual is on Agilent's site athttp://cp.literature.agilent.com/litweb/pdf/05248-90001.pdf. I can't say how similar they are to the 5245L, but the DCUs seem to be the same. *I used to be a calibration tech many years ago, and while I saw many of both instruments on my bench, I rarely had to repair them; quite reliable. *I remember two cases where the counters exhibited the exact problem the OP has; significant oscillator error. *Both turned out to be problems with the oven control circuit. I have to disagree with your statement that the OP's error is insignigicant for professional use. *That might be true for some hobbiest uses, but for many amateur radio operators and certainly for professional use, *it's a very significant error. * The original time base spec for the 5245L is 3x10^-9 per day. -- David dgminala at mediacombb dot net Got it! - thank you. Paid $5 for it as an "under the table" item at a Hamfest. Missing 2 front panel knobs, but will get it working properly before I chase them. Got several plug ins for my 5245L, will investigate if they are compatible.. Still a nice bit of gear.... Andrew VK3BFA. |
HP 5245L Counter Oscillator adjust?
Andrew VK3BFA wrote:
On Apr 26, 11:41 am, "Dave M" wrote: Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? (and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. Your comparing the HP ref. signal to......what?.... Very accurate. It is our Agilent power meter/freq counter (to 26 GHz) and has been cal'd. A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... Yes, I did note the original freq. These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. Well, I'm wanting to measure down to about 10 Hz "accuracy"...in other words I am measuring 189.XXXXX MHz. This is the XTAL freq. for my microwave LO that is multipled by 6 to get to 1136 MHz and that is multiplied by 9 to get to 10224 MHz, for a total multiplication factor of 54. If the oven is working, it will get warm. Simple. Now THAT'S something I need to check. It should be working...the unit is only a bit over 40 years old! ;) Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. None taken. I work on microwave equipment at work all day long and can get a bit worked up about "being on frequency" ;) Thanks for the tips...the manual did finally download, so I'll dig into it soon (the good news is I have two of these, so maybe I'll check the other one and see how close it is. I just bought the second one for its 3-12 GHz mixer). Scott N0EDV Andrew VK3BFA. |
HP 5245L Counter Oscillator adjust?
Dave M wrote:
Andrew VK3BFA wrote: On Apr 26, 11:41 am, "Dave M" wrote: Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? (and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. Your comparing the HP ref. signal to......what?.... A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. If the oven is working, it will get warm. Simple. Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. Andrew VK3BFA. The 5248L manual is on Agilent's site at http://cp.literature.agilent.com/lit...5248-90001.pdf. I can't say how similar they are to the 5245L, but the DCUs seem to be the same. I used to be a calibration tech many years ago, and while I saw many of both instruments on my bench, I rarely had to repair them; quite reliable. I remember two cases where the counters exhibited the exact problem the OP has; significant oscillator error. Both turned out to be problems with the oven control circuit. I have to disagree with your statement that the OP's error is insignigicant for professional use. That might be true for some hobbiest uses, but for many amateur radio operators and certainly for professional use, it's a very significant error. The original time base spec for the 5245L is 3x10^-9 per day. The oven has been mentioned in a few posts. I will try to establish if that is working or if that's where the problem lays. I want to use it to count my 189.XXXXX MHz XTAL freq in my 10 GHz transverter. I need pretty good accuracy since this XTAL is multiplied by a factor of 54 in the LO chain. Thanks for the tip! Scott N0EDV |
HP 5245L Counter Oscillator adjust?
On Apr 27, 8:09*pm, Scott wrote:
Dave M wrote: Andrew VK3BFA wrote: On Apr 26, 11:41 am, "Dave M" wrote: Scott wrote: I'm trying to download a copy of the manual, but at the rate it's downloading, I may have it by Tuesday, April 27th.....2013! Anyhow...does anyone have a copy of how to set the timebase oscillator frequency? I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere...I took off both covers, but any adjustment control is not blatantly obvious.... Scott N0EDV Scott, I've seen the oven temperature control circuit more likely to cause this type of problem. The fact that the oscillator is working eliminates a lot of circuitry. Before you do any more adjusting, do this: Check that the oven temperature control circuit is working. Check to see if the collector of Q1 is in the ballpark of about -21 volts. That point should start out (cold oven) at around -5 volts or so, and go toward -21 volts as the oven warms up. If it stays at the lower voltage, you have a problem with either Q1 or one of the transistors on the oven control assy A25. That same reasoning goes if the voltage at Q1 collector starts out and stays at -35 volts or so. An extreme cause would be that of the oven heater being open. In that case, the oven assembly is bad, and will need to be replaced. You can attempt ot disassemble the oven and repair the heater, but it's iffy. One of the temp sensor components inside the oven might be bad as well. If the oven and the oven control is OK, that means that the oscillator is out of tune. That could be caused by the crystal itself, of one of the capacitors inside the oven. I have an operable oven assembly that we could make a deal on, but since I recently moved from Florida to Alabama and don't have a shop area yet, it's still in storage. If you can wait for a couple of months, I could dig it out for you. You might look on Ebay for an oven; I've seen them offerred there, but not often. -- David dgminala at mediacombb dot net Excuse me for seeming a Patronising Old ******* here, but I feel some basic radio theory is in order here, and to respond to the original question...... Quote. *I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. Response. How accurate is the frequency counter you are using to measure the 10Mhz TXCO? *(and does it have a current calibration certificate?) - unless it is at least an order of magnitude BETTER than the HP, any results will be meaningless. *Your comparing the HP ref. signal to......what?.... A easier way is to zero beat the HP TXCO with WWV. Yes, for the purists, there are problems with this method, (which are NOT relevant here) but if you tune for zerobeat by ear as best you can - by then, the S meter should be pulsating (it can see the beat note, you cant hear it) and then tune. Get really hi-tech, use a GPS locked counter. And I hope you took notes of the original "frequency" and can take it back to this. Its a well aged, ovenized xtal. It will be pretty bloody close, unless someone has been into it before you..... These things were, in their day, laboratory grade instruments. They still are, but have been superseded as technology advanced. You need to learn what the display is telling you, and how much is relevant to what you do. Its unlikely that you will be building something that needs 10-12 accuracy. (A nominal figure, not going to dig the manual out to look) The error you quote is totally insignificant for average amateur (and most professional ) use. If the oven is working, it will get warm. Simple. Plot the frequency change from cold switch on - see how long it takes to stabilise. Do it again, later, when the ambient room temperature has changed. If no shift, its OK. And if it is not working......well, they ARE fascinating instruments, the service manual a joy to read. (Bout the size of the phone book) They even give Boolean equations for it. *You could be entranced by 1960's technology - if you so choose. g Later model ones had a "Oven"light on the front panel - if it was out after warm-up, then it was ok. BTW - anyone got a service manual for a HP5248L counter.......got a gating fault, how similar are they to the 5245L - any HP test gurus out there? In good faith, and hopefully no insult intended or received. Andrew VK3BFA. The 5248L manual is on Agilent's site at http://cp.literature.agilent.com/lit...5248-90001.pdf. I can't say how similar they are to the 5245L, but the DCUs seem to be the same. *I used to be a calibration tech many years ago, and while I saw many of both instruments on my bench, I rarely had to repair them; quite reliable. *I remember two cases where the counters exhibited the exact problem the OP has; significant oscillator error. *Both turned out to be problems with the oven control circuit. I have to disagree with your statement that the OP's error is insignigicant for professional use. *That might be true for some hobbiest uses, but for many amateur radio operators and certainly for professional use, *it's a very significant error. * The original time base spec for the 5245L is 3x10^-9 per day. The oven has been mentioned in a few posts. *I will try to establish if that is working or if that's where the problem lays. *I want to use it to count my 189.XXXXX MHz XTAL freq in my 10 GHz transverter. *I need pretty good accuracy since this XTAL is multiplied by a factor of 54 in the LO chain. *Thanks for the tip! Scott N0EDV QST had an article on GPS frequency standard. Something you might want to check into. I think it was a construction project. Jimmie |
HP 5245L Counter Oscillator adjust?
JIMMIE wrote:
QST had an article on GPS frequency standard. Something you might want to check into. I think it was a construction project. Jimmie Well, it certainly shouldn't be too hard to do. I think the 5245L uses a 1 MHz signal for the external timebase input, so it might just be a matter of dividing the 10 MHz output signal that the GPSDOs that I'm familiar with and supplying it to the external timebase input... |
HP 5245L Counter Oscillator adjust?
In article ,
Scott wrote: I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere. Scott- I have a different HP counter that had a similar problem when I got it. There was a capacitor adjustment in the crystal oven, but it did not have enough range to bring the oscillator to 10.0 MHz. It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I managed to buy the last thermal fuse HP had in stock at the time. Before it arrived, I had fabricated replacements using a thermal fuse from Radio Shack, wired in parallel with a high value resistor which had the correct lead diameter to plug into the wire sockets. Using a rubidium oscillator purchased on E-Bay, I aligned the repaired oscillator fairly accurately using an oscilloscope. After several years, it seems to still be within a fraction of one Hz! It turns out that this is a common problem. I wrote it up and sent it to QST for their Hints & Kinks several years back. Since then, one of the HP designers of the oscillator posted a comment that the thermal fuse wasn't really needed, since the heating element shouldn't cause any damage if left on continuously. Even so, I feel better with the thermal fuse installed! Fred K4DII |
HP 5245L Counter Oscillator adjust?
In article ,
Fred McKenzie wrote: It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I dug out my notes to find out the specifics. My counter is an HP 5334B with Option 1, the high stability oscillator. The oscillator is one of the HP 10811 series. The original thermal fuse, F1, was rated for 108 degrees C. HP revised the part to one rated for 115 degrees C, part number 2110-0617 (10811-80003). The Radio Shack thermal fuse was 270-1322A, rated for 128 degrees C. There is also an NTE Electronics NTE8115, "Thermal Cut-Off", rated for 117 degrees C. Either is larger than the HP part, and is a tight fit. I wrapped them in electrical tape to protect against short circuits. When soldering to the high-value resistors, I clamped the fuse leads in a pair of pliers held with rubber bands. Of course this may not apply to your counter if it doesn't have the crystal oven! Fred K4DII |
HP 5245L Counter Oscillator adjust?
Fred McKenzie wrote:
In article , Scott wrote: I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere. Scott- I have a different HP counter that had a similar problem when I got it. There was a capacitor adjustment in the crystal oven, but it did not have enough range to bring the oscillator to 10.0 MHz. It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I managed to buy the last thermal fuse HP had in stock at the time. Before it arrived, I had fabricated replacements using a thermal fuse from Radio Shack, wired in parallel with a high value resistor which had the correct lead diameter to plug into the wire sockets. Using a rubidium oscillator purchased on E-Bay, I aligned the repaired oscillator fairly accurately using an oscilloscope. After several years, it seems to still be within a fraction of one Hz! It turns out that this is a common problem. I wrote it up and sent it to QST for their Hints & Kinks several years back. Since then, one of the HP designers of the oscillator posted a comment that the thermal fuse wasn't really needed, since the heating element shouldn't cause any damage if left on continuously. Even so, I feel better with the thermal fuse installed! Fred K4DII Thanks Fred! I haven't had time to dig into it yet as I'm out playing on 10 GHz this weekend. Fortunately, I have a second 5245L for comparisons. I did find the capacitor on the oven as you mention, but it did not have enough range as you noted. If the heater is working, does the enclosure get warm? Seems to me that as I was feeling around, it was ice cold on the outside. Maybe we're onto something here! Scott N0EDV |
HP 5245L Counter Oscillator adjust?
Fred McKenzie wrote:
In article , Fred McKenzie wrote: It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I dug out my notes to find out the specifics. My counter is an HP 5334B with Option 1, the high stability oscillator. The oscillator is one of the HP 10811 series. The original thermal fuse, F1, was rated for 108 degrees C. HP revised the part to one rated for 115 degrees C, part number 2110-0617 (10811-80003). The Radio Shack thermal fuse was 270-1322A, rated for 128 degrees C. There is also an NTE Electronics NTE8115, "Thermal Cut-Off", rated for 117 degrees C. Either is larger than the HP part, and is a tight fit. I wrapped them in electrical tape to protect against short circuits. When soldering to the high-value resistors, I clamped the fuse leads in a pair of pliers held with rubber bands. Of course this may not apply to your counter if it doesn't have the crystal oven! Fred K4DII Yes, mine has the oven (and the high stability Oscillator option). I've gotten some good leads on this problem, so when I get a bit more time, I'll rip into it! Thanks again!! Scott N0EDV |
HP 5245L Counter Oscillator adjust?
Fred McKenzie wrote:
In article , Scott wrote: I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere. Scott- I have a different HP counter that had a similar problem when I got it. There was a capacitor adjustment in the crystal oven, but it did not have enough range to bring the oscillator to 10.0 MHz. It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I managed to buy the last thermal fuse HP had in stock at the time. Before it arrived, I had fabricated replacements using a thermal fuse from Radio Shack, wired in parallel with a high value resistor which had the correct lead diameter to plug into the wire sockets. Using a rubidium oscillator purchased on E-Bay, I aligned the repaired oscillator fairly accurately using an oscilloscope. After several years, it seems to still be within a fraction of one Hz! It turns out that this is a common problem. I wrote it up and sent it to QST for their Hints & Kinks several years back. Since then, one of the HP designers of the oscillator posted a comment that the thermal fuse wasn't really needed, since the heating element shouldn't cause any damage if left on continuously. Even so, I feel better with the thermal fuse installed! Fred K4DII Scott I seem to recall that there is a second adjustment inside the plug-in area. I assume you found both of the adjustments. Bill K7NOM |
HP 5245L Counter Oscillator adjust?
Bill Janssen wrote:
Fred McKenzie wrote: In article , Scott wrote: I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere. Scott- I have a different HP counter that had a similar problem when I got it. There was a capacitor adjustment in the crystal oven, but it did not have enough range to bring the oscillator to 10.0 MHz. It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I managed to buy the last thermal fuse HP had in stock at the time. Before it arrived, I had fabricated replacements using a thermal fuse from Radio Shack, wired in parallel with a high value resistor which had the correct lead diameter to plug into the wire sockets. Using a rubidium oscillator purchased on E-Bay, I aligned the repaired oscillator fairly accurately using an oscilloscope. After several years, it seems to still be within a fraction of one Hz! It turns out that this is a common problem. I wrote it up and sent it to QST for their Hints & Kinks several years back. Since then, one of the HP designers of the oscillator posted a comment that the thermal fuse wasn't really needed, since the heating element shouldn't cause any damage if left on continuously. Even so, I feel better with the thermal fuse installed! Fred K4DII Scott I seem to recall that there is a second adjustment inside the plug-in area. I assume you found both of the adjustments. Bill K7NOM I did see a fairly large air variable capacitor sitting next to the oven assembly, but since I didn't know what it was for, I didn't adjust it. I'll go through the manual I downloaded and see if I can get it on frequency. Thanks for the note. Scott N0EDV |
HP 5245L Counter Oscillator adjust?
Scott wrote:
Bill Janssen wrote: Fred McKenzie wrote: In article , Scott wrote: I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere. Scott- I have a different HP counter that had a similar problem when I got it. There was a capacitor adjustment in the crystal oven, but it did not have enough range to bring the oscillator to 10.0 MHz. It turned out that there was an open thermal fuse in the supply line inside the crystal oven. It was a plug-in device about the size of a half watt resistor, maybe smaller. There were two wire-sockets that its leads plugged into. I managed to buy the last thermal fuse HP had in stock at the time. Before it arrived, I had fabricated replacements using a thermal fuse from Radio Shack, wired in parallel with a high value resistor which had the correct lead diameter to plug into the wire sockets. Using a rubidium oscillator purchased on E-Bay, I aligned the repaired oscillator fairly accurately using an oscilloscope. After several years, it seems to still be within a fraction of one Hz! It turns out that this is a common problem. I wrote it up and sent it to QST for their Hints & Kinks several years back. Since then, one of the HP designers of the oscillator posted a comment that the thermal fuse wasn't really needed, since the heating element shouldn't cause any damage if left on continuously. Even so, I feel better with the thermal fuse installed! Fred K4DII Scott I seem to recall that there is a second adjustment inside the plug-in area. I assume you found both of the adjustments. Bill K7NOM I did see a fairly large air variable capacitor sitting next to the oven assembly, but since I didn't know what it was for, I didn't adjust it. I'll go through the manual I downloaded and see if I can get it on frequency. Thanks for the note. Scott N0EDV Scott, Those capacitors inside the plugin bay are medium and fine frequency adjustments. If the coarse frequency adjustment inside the oven won't get it on frequency, then the others certainly won't have enough range to get it right. As I and others have suggested, you really need to verify whether the oven is being heated before you do any more adjusting. Set the coarse tuning back to its starting position and troubleshoot the oven circuitry. I'm convinced that's where you'll find the trouble. Get your voltmeter out and check the oven heater connection. It will tell you a lot. -- David dgminala at mediacombb dot net |
HP 5245L Counter Oscillator adjust?
On May 1, 5:56*pm, Scott wrote:
Fred McKenzie wrote: In article , *Scott wrote: I measure the signal coming out the back of the counter (with another counter) at 10.000066 MHz. *I adjusted the "coarse tune" adjustment on the back of the unit and this is as close as it gets to 10.000000 MHz, so I assume there must be some other adjustment somewhere. Scott- I have a different HP counter that had a similar problem when I got it. There was a capacitor adjustment in the crystal oven, but it did not have enough range to bring the oscillator to 10.0 MHz. It turned out that there was an open thermal fuse in the supply line inside the crystal oven. *It was a plug-in device about the size of a half watt resistor, maybe smaller. *There were two wire-sockets that its leads plugged into. I managed to buy the last thermal fuse HP had in stock at the time. * Before it arrived, I had fabricated replacements using a thermal fuse from Radio Shack, wired in parallel with a high value resistor which had the correct lead diameter to plug into the wire sockets. Using a rubidium oscillator purchased on E-Bay, I aligned the repaired oscillator fairly accurately using an oscilloscope. *After several years, it seems to still be within a fraction of one Hz! It turns out that this is a common problem. *I wrote it up and sent it to QST for their Hints & Kinks several years back. *Since then, one of the HP designers of the oscillator posted a comment that the thermal fuse wasn't really needed, since the heating element shouldn't cause any damage if left on continuously. *Even so, I feel better with the thermal fuse installed! Fred K4DII Thanks Fred! *I haven't had time to dig into it yet as I'm out playing on 10 GHz this weekend. *Fortunately, I have a second 5245L for comparisons. *I did find the capacitor on the oven as you mention, but it did not have enough range as you noted. *If the heater is working, does the enclosure get warm? *Seems to me that as I was feeling around, it was ice cold on the outside. *Maybe we're onto something here! Scott N0EDV Yes, most certainly the oven should be noticeably warm, unless your ambient temperature is already really hot. You can also monitor the current the oven draws (perhaps with some difficulty, depending on how the oven is wired into the circuit). You should see moderately high current when the oven is first turned on, and the current should drop to (very roughly) half as much as the oven reaches operating temperature. I'd expect the oven control loop to be reasonably damped, so the current falls from the startup value to the idling value within just a few seconds and stabilizes without overshoot, or with only minor overshoot. At least that's what I've seen on several models, including the HP10811. These days, you can get some remarkably small and low-power oven oscillators, down to TO-5 transistor can size I believe, and possibly even smaller. The power to run them is low milliwatts. Even temperature-compensated oscillators have gotten remarkably good...I have some 3x5 millimeter ones that are rated half a part per million max deviation over -20C to +55C (and run on about 2.5 milliwatts), and you can get better than that. Cheers, Tom |
HP 5245L Counter Oscillator adjust?
Dave M wrote:
Scott, Those capacitors inside the plugin bay are medium and fine frequency adjustments. If the coarse frequency adjustment inside the oven won't get it on frequency, then the others certainly won't have enough range to get it right. As I and others have suggested, you really need to verify whether the oven is being heated before you do any more adjusting. Set the coarse tuning back to its starting position and troubleshoot the oven circuitry. I'm convinced that's where you'll find the trouble. Get your voltmeter out and check the oven heater connection. It will tell you a lot. Yup...I will delve into the oven circuitry when I get a chance...have a couple other higher priority projects to clean up first... N0EDV |
HP 5245L Counter Oscillator adjust?
K7ITM wrote:
Yes, most certainly the oven should be noticeably warm, unless your ambient temperature is already really hot. You can also monitor the current the oven draws (perhaps with some difficulty, depending on how the oven is wired into the circuit). You should see moderately high current when the oven is first turned on, and the current should drop to (very roughly) half as much as the oven reaches operating temperature. I'd expect the oven control loop to be reasonably damped, so the current falls from the startup value to the idling value within just a few seconds and stabilizes without overshoot, or with only minor overshoot. At least that's what I've seen on several models, including the HP10811. These days, you can get some remarkably small and low-power oven oscillators, down to TO-5 transistor can size I believe, and possibly even smaller. The power to run them is low milliwatts. Even temperature-compensated oscillators have gotten remarkably good...I have some 3x5 millimeter ones that are rated half a part per million max deviation over -20C to +55C (and run on about 2.5 milliwatts), and you can get better than that. Cheers, Tom I don't think it's POSSIBLE to get REALLY HOT here in WI (by some standards, that is...to me, 75 is really hot!) ;) |
| All times are GMT +1. The time now is 01:32 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com