Re: [Repeater-Builder] Sinclair C-Series cable lengths
Jeff, Speaking of the RLB, did you ever get one of the newer RLB's from Amtronix? I still interested in someone measuring the parameters of that unit against one of the more expensive RLB's, such as the Eagle brand. If the measurements are fairly close to each other, then the Amtronix RLB would be a good unit to have, especially for the price that he's asking. Also, your post below was really good information to have. Thanks! 73, Don, KD9PT - Original Message - From: Jeff DePolo To: Repeater-Builder@yahoogroups.com Sent: Tuesday, April 20, 2010 5:46 PM Subject: RE: [Repeater-Builder] Sinclair C-Series cable lengths I adjusted the loop positions, trying to maintain symmetry of the curve, aiming for 1 db on the analyzer. I didn't adjust the loops while looking at the RL. How would I translate RL into IL? You can't directly translate from RL to IL or vice-versa. Here's how to tune a pass cavity: 1. Ballpark the insertion loss using the stickers on the loops and/or by measuring the insertion loss at whatever frequency the cavity is presently tuned to. 2. Rough-tune the cavity to something near your desired frequency. Don't bother being too critical here - the resonant frequency is going to wander a bit as you adjust the loops in the following steps. 3. Terminate one cavity port with a high-quality 50 ohm load (high quality: = 30 dB return loss). Connect your RLB to your SA/TG, with the DUT port connected to the other port on the cavity. You *must* use a cable between the DUT port and the cavity that is known to have excellent return loss! The cables between the SA/TG and RLB should be good quality, but are nowhere near as critical as the cable between the RLB and the device under test. 4. While measuring the return loss, make minor adjustments to one of the loops to maximize the return loss. Again, ignore the frequency of the return loss dip, it's going to vary slightly as you adjust the loop, just go for maximum return loss at whatever frequency the dip happens to fall at. Keep the screws snugged down well on the loop assembly; if it's not sitting tight and flush in the top of the cavity the tuning will change when you go to tighten the screws later. There's a little chicken-and-egg here; you have to loosen the screws to adjust the loop, but when you tighten them it's going to change it a bit, so you have to emperically find the sweet spot. With most cavities, you should have no problem getting well in excess of 20 dB return loss - shoot for 30 dB if you can, even though at that point uncertainty due to the test equipment's limitations will be dominating the measurement accuracy. 5. Reverse the connections you set up in #2 above. Check to make sure the return loss is still high looking into the other port (it should be). 6. NOW, adjust the resonant frequency using the rod to put the return loss maxima it where you want it (i.e. at your pass frequency). Assuming the cavity was rough-tuned in step #2 above, the return loss should not change as you fine-tune the resonant frequency. 7. THEN, check the insertion loss through the cavity using the SA/TG. It should be fairly close to what you set it to in #1 above; if it's more/less than what you'd like, adjust ONE loop for more/less insertion loss, and then repeat again from step #3. DO NOT adjust the resonant frequency via the tuning rod during this step!!! Unless the cavity was poorly designed, tuned, or handled, the return loss maximum should align very closely with the insertion loss minimum. Once you've properly tuned the cavities individually, then cable them together and re-check return loss and insertion loss. Report back how it goes and what numbers you come up with. --- Jeff WN3A
RE: [Repeater-Builder] Sinclair C-Series cable lengths
Yep, I did get one. I did some preliminary testing and it compares favorably to the Eagle in most regards. Rick is contemplating making some additional refinements, some of which are based on my testing, so I'm waiting to hear back from him. If he decides to make changes, I'll wait until he sends me the final version for complete testing. --- Jeff -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Don Kupferschmidt Sent: Wednesday, April 21, 2010 12:26 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Sinclair C-Series cable lengths Jeff, Speaking of the RLB, did you ever get one of the newer RLB's from Amtronix? I still interested in someone measuring the parameters of that unit against one of the more expensive RLB's, such as the Eagle brand. If the measurements are fairly close to each other, then the Amtronix RLB would be a good unit to have, especially for the price that he's asking. Also, your post below was really good information to have. Thanks! 73, Don, KD9PT - Original Message - From: Jeff DePolo mailto:j...@broadsci.com To: Repeater-Builder@yahoogroups.com mailto:Repeater-Builder@yahoogroups.com Sent: Tuesday, April 20, 2010 5:46 PM Subject: RE: [Repeater-Builder] Sinclair C-Series cable lengths I adjusted the loop positions, trying to maintain symmetry of the curve, aiming for 1 db on the analyzer. I didn't adjust the loops while looking at the RL. How would I translate RL into IL? You can't directly translate from RL to IL or vice-versa. Here's how to tune a pass cavity: 1. Ballpark the insertion loss using the stickers on the loops and/or by measuring the insertion loss at whatever frequency the cavity is presently tuned to. 2. Rough-tune the cavity to something near your desired frequency. Don't bother being too critical here - the resonant frequency is going to wander a bit as you adjust the loops in the following steps. 3. Terminate one cavity port with a high-quality 50 ohm load (high quality: = 30 dB return loss). Connect your RLB to your SA/TG, with the DUT port connected to the other port on the cavity. You *must* use a cable between the DUT port and the cavity that is known to have excellent return loss! The cables between the SA/TG and RLB should be good quality, but are nowhere near as critical as the cable between the RLB and the device under test. 4. While measuring the return loss, make minor adjustments to one of the loops to maximize the return loss. Again, ignore the frequency of the return loss dip, it's going to vary slightly as you adjust the loop, just go for maximum return loss at whatever frequency the dip happens to fall at. Keep the screws snugged down well on the loop assembly; if it's not sitting tight and flush in the top of the cavity the tuning will change when you go to tighten the screws later. There's a little chicken-and-egg here; you have to loosen the screws to adjust the loop, but when you tighten them it's going to change it a bit, so you have to emperically find the sweet spot. With most cavities, you should have no problem getting well in excess of 20 dB return loss - shoot for 30 dB if you can, even though at that point uncertainty due to the test equipment's limitations will be dominating the measurement accuracy. 5. Reverse the connections you set up in #2 above. Check to make sure the return loss is still high looking into the other port (it should be). 6. NOW, adjust the resonant frequency using the rod to put the return loss maxima it where you want it (i.e. at your pass frequency). Assuming the cavity was rough-tuned in step #2 above, the return loss should not change as you fine-tune the resonant frequency. 7. THEN, check the insertion loss through the cavity using the SA/TG. It should be fairly close to what you set it to in #1 above; if it's more/less than what you'd like, adjust ONE loop for more/less insertion loss, and then repeat again from step #3. DO NOT adjust the resonant frequency via the tuning rod during this step!!! Unless the cavity was poorly designed, tuned, or handled, the return loss maximum should align very closely with the insertion loss minimum. Once you've properly tuned the cavities individually, then cable them together and re-check return loss and insertion loss. Report back how
RE: [Repeater-Builder] Sinclair C-Series cable lengths
I have 2 C-Series bandpass cavities, with individual I.L. set at 1.0 db each. When I couple them together and measure, I get a total I.L. of 2.9 db. I should see something like 2.1 or 2.2. I have measured the coupling cable and see .1 db, so the cable is good. Anyone have an idea why the loss is so high when coupled? Most likely they aren't tuned correctly for maximum return loss, and when you cascade them, the resonant frequency is no longer where you thought it was (i.e. a detuning effect). Have you measured the return loss of the cavities individually? --- Jeff WN3A
Re: [Repeater-Builder] Sinclair C-Series cable lengths
The cavities were initially tuned individually and the loop positions set for 1 db IL. They were then coupled together using a 18.5 cable and the rods touched up to re-establish resonance. The measured IL is now 2.9. The loop positions were not changed after coupling. When using the RL bridge I do not see one clear notch, but rather a notch that has a bump; kinda looks like 2 notches. This is what I always see even when cavities are factory tuned, so I'm confident that the tuning is OK. On Tue, Apr 20, 2010 at 9:26 AM, Jeff DePolo j...@broadsci.com wrote: I have 2 C-Series bandpass cavities, with individual I.L. set at 1.0 db each. When I couple them together and measure, I get a total I.L. of 2.9 db. I should see something like 2.1 or 2.2. I have measured the coupling cable and see .1 db, so the cable is good. Anyone have an idea why the loss is so high when coupled? Most likely they aren't tuned correctly for maximum return loss, and when you cascade them, the resonant frequency is no longer where you thought it was (i.e. a detuning effect). Have you measured the return loss of the cavities individually? --- Jeff WN3A
RE: [Repeater-Builder] Sinclair C-Series cable lengths
The cavities were initially tuned individually and the loop positions set for 1 db IL. They were then coupled together using a 18.5 cable and the rods touched up to re-establish resonance. If the cavities had good return loss individually, there shouldn't be a need to touch up the tuning when they are cascaded. That's what I was saying originally with my detuning comment. The loop positions were not changed after coupling. But were the loops adjusted to maximize return loss at the desired inseretion loss setting? That's the key point. Or did you just dial in 1 dB of insertion loss and call it good? When using the RL bridge I do not see one clear notch, but rather a notch that has a bump; kinda looks like 2 notches. Again, this may be indicitive of them not being tuned correctly. This is what I always see even when cavities are factory tuned ??? There's no acceptable generalization when it comes to how cavity filters behave when cascaded. Two cavities used as a window filter with an extended passband will look different for both transmission and reflection than would two cavities tuned (and cabled) to pass a single frequency. I'm confident that the tuning is OK. I wouldn't be so sure, as it seems likely that's the problem. --- Jeff
Re: [Repeater-Builder] Sinclair C-Series cable lengths
Looks to me like there is an incorrect interconnect cable length. If you are intending to tune both to the same frequency, you should see a single response, not two. Chuck WB2EDV - Original Message - From: Larry Horlick To: Repeater-Builder@yahoogroups.com Sent: Tuesday, April 20, 2010 12:38 PM Subject: Re: [Repeater-Builder] Sinclair C-Series cable lengths The cavities were initially tuned individually and the loop positions set for 1 db IL. They were then coupled together using a 18.5 cable and the rods touched up to re-establish resonance. The measured IL is now 2.9. The loop positions were not changed after coupling. When using the RL bridge I do not see one clear notch, but rather a notch that has a bump; kinda looks like 2 notches. This is what I always see even when cavities are factory tuned, so I'm confident that the tuning is OK. On Tue, Apr 20, 2010 at 9:26 AM, Jeff DePolo j...@broadsci.com wrote: I have 2 C-Series bandpass cavities, with individual I.L. set at 1.0 db each. When I couple them together and measure, I get a total I.L. of 2.9 db. I should see something like 2.1 or 2.2. I have measured the coupling cable and see .1 db, so the cable is good. Anyone have an idea why the loss is so high when coupled? Most likely they aren't tuned correctly for maximum return loss, and when you cascade them, the resonant frequency is no longer where you thought it was (i.e. a detuning effect). Have you measured the return loss of the cavities individually? --- Jeff WN3A -- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.801 / Virus Database: 271.1.1/2822 - Release Date: 04/20/10 02:31:00
Re: [Repeater-Builder] Sinclair C-Series cable lengths
But were the loops adjusted to maximize return loss at the desired inseretion loss setting? That's the key point. Or did you just dial in 1 dB of insertion loss and call it good? Not sure what u mean??
RE: [Repeater-Builder] Sinclair C-Series cable lengths
What process did you go through when setting the insertion loss to the 1 dB you were targetting? Did you optimize the coupling angle of the loops for maximum return loss at (or near) the desired 1 dB of insertion loss? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Larry Horlick Sent: Tuesday, April 20, 2010 5:54 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Sinclair C-Series cable lengths But were the loops adjusted to maximize return loss at the desired inseretion loss setting? That's the key point. Or did you just dial in 1 dB of insertion loss and call it good? Not sure what u mean?? No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.801 / Virus Database: 271.1.1/2792 - Release Date: 04/20/10 02:31:00
Re: [Repeater-Builder] Sinclair C-Series cable lengths
I adjusted the loop positions, trying to maintain symmetry of the curve, aiming for 1 db on the analyzer. I didn't adjust the loops while looking at the RL. How would I translate RL into IL? On Tue, Apr 20, 2010 at 6:02 PM, Jeff DePolo j...@broadsci.com wrote: What process did you go through when setting the insertion loss to the 1 dB you were targetting? Did you optimize the coupling angle of the loops for maximum return loss at (or near) the desired 1 dB of insertion loss? --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.comRepeater-Builder%40yahoogroups.com [mailto:Repeater-Builder@yahoogroups.comRepeater-Builder%40yahoogroups.com] On Behalf Of Larry Horlick Sent: Tuesday, April 20, 2010 5:54 PM To: Repeater-Builder@yahoogroups.comRepeater-Builder%40yahoogroups.com Subject: Re: [Repeater-Builder] Sinclair C-Series cable lengths But were the loops adjusted to maximize return loss at the desired inseretion loss setting? That's the key point. Or did you just dial in 1 dB of insertion loss and call it good? Not sure what u mean?? No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.801 / Virus Database: 271.1.1/2792 - Release Date: 04/20/10 02:31:00
RE: [Repeater-Builder] Sinclair C-Series cable lengths
I adjusted the loop positions, trying to maintain symmetry of the curve, aiming for 1 db on the analyzer. I didn't adjust the loops while looking at the RL. How would I translate RL into IL? You can't directly translate from RL to IL or vice-versa. Here's how to tune a pass cavity: 1. Ballpark the insertion loss using the stickers on the loops and/or by measuring the insertion loss at whatever frequency the cavity is presently tuned to. 2. Rough-tune the cavity to something near your desired frequency. Don't bother being too critical here - the resonant frequency is going to wander a bit as you adjust the loops in the following steps. 3. Terminate one cavity port with a high-quality 50 ohm load (high quality: = 30 dB return loss). Connect your RLB to your SA/TG, with the DUT port connected to the other port on the cavity. You *must* use a cable between the DUT port and the cavity that is known to have excellent return loss! The cables between the SA/TG and RLB should be good quality, but are nowhere near as critical as the cable between the RLB and the device under test. 4. While measuring the return loss, make minor adjustments to one of the loops to maximize the return loss. Again, ignore the frequency of the return loss dip, it's going to vary slightly as you adjust the loop, just go for maximum return loss at whatever frequency the dip happens to fall at. Keep the screws snugged down well on the loop assembly; if it's not sitting tight and flush in the top of the cavity the tuning will change when you go to tighten the screws later. There's a little chicken-and-egg here; you have to loosen the screws to adjust the loop, but when you tighten them it's going to change it a bit, so you have to emperically find the sweet spot. With most cavities, you should have no problem getting well in excess of 20 dB return loss - shoot for 30 dB if you can, even though at that point uncertainty due to the test equipment's limitations will be dominating the measurement accuracy. 5. Reverse the connections you set up in #2 above. Check to make sure the return loss is still high looking into the other port (it should be). 6. NOW, adjust the resonant frequency using the rod to put the return loss maxima it where you want it (i.e. at your pass frequency). Assuming the cavity was rough-tuned in step #2 above, the return loss should not change as you fine-tune the resonant frequency. 7. THEN, check the insertion loss through the cavity using the SA/TG. It should be fairly close to what you set it to in #1 above; if it's more/less than what you'd like, adjust ONE loop for more/less insertion loss, and then repeat again from step #3. DO NOT adjust the resonant frequency via the tuning rod during this step!!! Unless the cavity was poorly designed, tuned, or handled, the return loss maximum should align very closely with the insertion loss minimum. Once you've properly tuned the cavities individually, then cable them together and re-check return loss and insertion loss. Report back how it goes and what numbers you come up with. --- Jeff WN3A
Re: [Repeater-Builder] Sinclair C-Series cable lengths
Jeff, Thanks for the detailed instructions. I understand everything, but I'm confused about one detail. Using this method will produce the largest RL and consequently the lowest IL. But I don't want the lowest IL; I want a specific value, i.e. 1 db per cavity. How do I use RLB to set a specific IL? On Tue, Apr 20, 2010 at 6:46 PM, Jeff DePolo j...@broadsci.com wrote: I adjusted the loop positions, trying to maintain symmetry of the curve, aiming for 1 db on the analyzer. I didn't adjust the loops while looking at the RL. How would I translate RL into IL? You can't directly translate from RL to IL or vice-versa. Here's how to tune a pass cavity: 1. Ballpark the insertion loss using the stickers on the loops and/or by measuring the insertion loss at whatever frequency the cavity is presently tuned to. 2. Rough-tune the cavity to something near your desired frequency. Don't bother being too critical here - the resonant frequency is going to wander a bit as you adjust the loops in the following steps. 3. Terminate one cavity port with a high-quality 50 ohm load (high quality: = 30 dB return loss). Connect your RLB to your SA/TG, with the DUT port connected to the other port on the cavity. You *must* use a cable between the DUT port and the cavity that is known to have excellent return loss! The cables between the SA/TG and RLB should be good quality, but are nowhere near as critical as the cable between the RLB and the device under test. 4. While measuring the return loss, make minor adjustments to one of the loops to maximize the return loss. Again, ignore the frequency of the return loss dip, it's going to vary slightly as you adjust the loop, just go for maximum return loss at whatever frequency the dip happens to fall at. Keep the screws snugged down well on the loop assembly; if it's not sitting tight and flush in the top of the cavity the tuning will change when you go to tighten the screws later. There's a little chicken-and-egg here; you have to loosen the screws to adjust the loop, but when you tighten them it's going to change it a bit, so you have to emperically find the sweet spot. With most cavities, you should have no problem getting well in excess of 20 dB return loss - shoot for 30 dB if you can, even though at that point uncertainty due to the test equipment's limitations will be dominating the measurement accuracy. 5. Reverse the connections you set up in #2 above. Check to make sure the return loss is still high looking into the other port (it should be). 6. NOW, adjust the resonant frequency using the rod to put the return loss maxima it where you want it (i.e. at your pass frequency). Assuming the cavity was rough-tuned in step #2 above, the return loss should not change as you fine-tune the resonant frequency. 7. THEN, check the insertion loss through the cavity using the SA/TG. It should be fairly close to what you set it to in #1 above; if it's more/less than what you'd like, adjust ONE loop for more/less insertion loss, and then repeat again from step #3. DO NOT adjust the resonant frequency via the tuning rod during this step!!! Unless the cavity was poorly designed, tuned, or handled, the return loss maximum should align very closely with the insertion loss minimum. Once you've properly tuned the cavities individually, then cable them together and re-check return loss and insertion loss. Report back how it goes and what numbers you come up with. --- Jeff WN3A
RE: [Repeater-Builder] Sinclair C-Series cable lengths
Thanks for the detailed instructions. I understand everything, but I'm confused about one detail. Using this method will produce the largest RL and consequently the lowest IL. Well, sort of. You want the most return loss AT THE DESIRED INSERTION LOSS. Maximizing return doesn't mean you have the minimum insertion loss. A 20 dB pad might have great return loss, but obviously it also has 20 dB of insertion loss! But I don't want the lowest IL; I want a specific value, i.e. 1 db per cavity. Right, and that's what you set in #1 in my instructions/notes. You rough in the insertion loss setting initially, but the actual tuning of the cavity is done based on return loss. In step 7 you measure the final insertion loss after you're done tuning. If it's too high or too low, you increase/decrease the coupling respectively and re-tune from scratch. If my instuction on changing the coupling again in step #7 and then re-tuning from scratch confused you, I apologize, I probably should have been more clear. If you change the coupling of one loop to increase/decrease the insertion loss, then you should be adjusting the OTHER loop in the next round of tuning. Obviously if you adjust one loop and then go back through the same procedure with the test equipment connected to that same loop you just adjusted, you're just going to end back up where you started. So, just so we're clear, if you're going to connect the RLB to port A, you would want to increase/decrease the insertion loss by adjusting the port B loop in step 7 before re-tuning starting at step 3. How do I use RLB to set a specific IL? You don't. An RLB measures return loss (obviously). The SA/TG alone is used to measure the insertion loss. --- Jeff WN3A 1. Ballpark the insertion loss using the stickers on the loops and/or by measuring the insertion loss at whatever frequency the cavity is presently tuned to. 2. Rough-tune the cavity to something near your desired frequency. Don't bother being too critical here - the resonant frequency is going to wander a bit as you adjust the loops in the following steps. 3. Terminate one cavity port with a high-quality 50 ohm load (high quality: = 30 dB return loss). Connect your RLB to your SA/TG, with the DUT port connected to the other port on the cavity. You *must* use a cable between the DUT port and the cavity that is known to have excellent return loss! The cables between the SA/TG and RLB should be good quality, but are nowhere near as critical as the cable between the RLB and the device under test. 4. While measuring the return loss, make minor adjustments to one of the loops to maximize the return loss. Again, ignore the frequency of the return loss dip, it's going to vary slightly as you adjust the loop, just go for maximum return loss at whatever frequency the dip happens to fall at. Keep the screws snugged down well on the loop assembly; if it's not sitting tight and flush in the top of the cavity the tuning will change when you go to tighten the screws later. There's a little chicken-and-egg here; you have to loosen the screws to adjust the loop, but when you tighten them it's going to change it a bit, so you have to emperically find the sweet spot. With most cavities, you should have no problem getting well in excess of 20 dB return loss - shoot for 30 dB if you can, even though at that point uncertainty due to the test equipment's limitations will be dominating the measurement accuracy. 5. Reverse the connections you set up in #2 above. Check to make sure the return loss is still high looking into the other port (it should be). 6. NOW, adjust the resonant frequency using the rod to put the return loss maxima it where you want it (i.e. at your pass frequency). Assuming the cavity was rough-tuned in step #2 above, the return loss should not change as you fine-tune the resonant frequency. 7. THEN, check the insertion loss through the cavity using the SA/TG. It should be fairly close to what you set it to in #1 above; if it's more/less than what you'd like, adjust ONE loop for more/less insertion loss, and then repeat again from step #3. DO NOT adjust the resonant frequency via the tuning rod during this step!!! Unless the cavity was poorly designed, tuned, or handled, the return loss maximum should align very closely with the insertion loss minimum. Once you've properly tuned the cavities individually, then cable them together and re-check return loss and insertion loss. Report back how it goes and what numbers you come up with.
Re: [Repeater-Builder] Sinclair C-Series cable lengths
Jeff, But for the purpose of this exercise, setting the loops, the position of max RL has to be the position of min. IL? No? Is my thinking completely flawed here? I've never used an RLB to set the loops; I've always used an SA/TG. I also have several different tutorials on cavity tuning, but none even touch on the IL adjustment. lh On Tue, Apr 20, 2010 at 7:52 PM, Jeff DePolo j...@broadsci.com wrote: Thanks for the detailed instructions. I understand everything, but I'm confused about one detail. Using this method will produce the largest RL and consequently the lowest IL. Well, sort of. You want the most return loss AT THE DESIRED INSERTION LOSS. Maximizing return doesn't mean you have the minimum insertion loss. A 20 dB pad might have great return loss, but obviously it also has 20 dB of insertion loss! But I don't want the lowest IL; I want a specific value, i.e. 1 db per cavity. Right, and that's what you set in #1 in my instructions/notes. You rough in the insertion loss setting initially, but the actual tuning of the cavity is done based on return loss. In step 7 you measure the final insertion loss after you're done tuning. If it's too high or too low, you increase/decrease the coupling respectively and re-tune from scratch. If my instuction on changing the coupling again in step #7 and then re-tuning from scratch confused you, I apologize, I probably should have been more clear. If you change the coupling of one loop to increase/decrease the insertion loss, then you should be adjusting the OTHER loop in the next round of tuning. Obviously if you adjust one loop and then go back through the same procedure with the test equipment connected to that same loop you just adjusted, you're just going to end back up where you started. So, just so we're clear, if you're going to connect the RLB to port A, you would want to increase/decrease the insertion loss by adjusting the port B loop in step 7 before re-tuning starting at step 3. How do I use RLB to set a specific IL? You don't. An RLB measures return loss (obviously). The SA/TG alone is used to measure the insertion loss. --- Jeff WN3A 1. Ballpark the insertion loss using the stickers on the loops and/or by measuring the insertion loss at whatever frequency the cavity is presently tuned to. 2. Rough-tune the cavity to something near your desired frequency. Don't bother being too critical here - the resonant frequency is going to wander a bit as you adjust the loops in the following steps. 3. Terminate one cavity port with a high-quality 50 ohm load (high quality: = 30 dB return loss). Connect your RLB to your SA/TG, with the DUT port connected to the other port on the cavity. You *must* use a cable between the DUT port and the cavity that is known to have excellent return loss! The cables between the SA/TG and RLB should be good quality, but are nowhere near as critical as the cable between the RLB and the device under test. 4. While measuring the return loss, make minor adjustments to one of the loops to maximize the return loss. Again, ignore the frequency of the return loss dip, it's going to vary slightly as you adjust the loop, just go for maximum return loss at whatever frequency the dip happens to fall at. Keep the screws snugged down well on the loop assembly; if it's not sitting tight and flush in the top of the cavity the tuning will change when you go to tighten the screws later. There's a little chicken-and-egg here; you have to loosen the screws to adjust the loop, but when you tighten them it's going to change it a bit, so you have to emperically find the sweet spot. With most cavities, you should have no problem getting well in excess of 20 dB return loss - shoot for 30 dB if you can, even though at that point uncertainty due to the test equipment's limitations will be dominating the measurement accuracy. 5. Reverse the connections you set up in #2 above. Check to make sure the return loss is still high looking into the other port (it should be). 6. NOW, adjust the resonant frequency using the rod to put the return loss maxima it where you want it (i.e. at your pass frequency). Assuming the cavity was rough-tuned in step #2 above, the return loss should not change as you fine-tune the resonant frequency. 7. THEN, check the insertion loss through the cavity using the SA/TG. It should be fairly close to what you set it to in #1 above; if it's more/less than what you'd like, adjust ONE loop for more/less insertion loss, and then repeat again from step #3. DO NOT adjust the resonant frequency via the tuning rod during this step!!! Unless the cavity was poorly designed, tuned, or handled, the return loss maximum should align very closely with the insertion loss minimum. Once you've properly tuned the cavities individually,
RE: [Repeater-Builder] Sinclair C-Series cable lengths
Jeff, But for the purpose of this exercise, setting the loops, the position of max RL has to be the position of min. IL? No? That's what I said in #7. After you've tuned the cavity to resonance based on RL, you check the IL. The frequency of the RL maxima (dip) should coincide with the insertion loss minima (peak) if everything is done right. I've never used an RLB to set the loops; I've always used an SA/TG. Like I said, you have to use the SA/TG to view the transmission response in order to quantify how much insertion loss you have, and that's why I suggested you rough in the insertion loss initially, and, if necessary, do a second round of tuning if you find, after all's said and done, that the final measured insertion loss is too far off your original target. To say it another way, you coarse-tune the loops targeting your desired insertion loss, then you fine-tune looking at return loss. Note that everything I'm telling you is how to tune up a single cavity. Once you have the two tuned up independently, go ahead and connect them together and report back the results. I also have several different tutorials on cavity tuning, but none even touch on the IL adjustment. I think a lot of manufacturers assume that the field tech has no way of measuring return loss (either with a SNA, VNA, or SA/TG+RLB). So, they put those little stickers near the loops with index marks that indicate (sometimes vaguely) where the loops need to be set to achieve the desired insertion loss, and they assume that the return loss will come out close enough for field work. --- Jeff WN3A
Re: [Repeater-Builder] Sinclair C-Series cable lengths
At 4/19/2010 10:24, you wrote: I have 2 C-Series bandpass cavities, with individual I.L. set at 1.0 db each. When I couple them together and measure, I get a total I.L. of 2.9 db. I should see something like 2.1 or 2.2. I have measured the coupling cable and see .1 db, so the cable is good. Anyone have an idea why the loss is so high when coupled? Did you actually measure the individual loss of each can, or are you just going by the indicators on the loops? Try changing the length of cable between the cans. I think an electrical 1/4 wave multiple (1/4, 3/4, 5/4, etc.) is what you want. Bob NO6B
Re: [Repeater-Builder] Sinclair C-Series cable lengths
These are measured values using a Service Monitor. I have two charts that show the cable lengths, but the values are not the same. They differ by 1 for the same frequency. Would that produce the effect I'm seeing? On Mon, Apr 19, 2010 at 8:16 PM, n...@no6b.com wrote: At 4/19/2010 10:24, you wrote: I have 2 C-Series bandpass cavities, with individual I.L. set at 1.0 db each. When I couple them together and measure, I get a total I.L. of 2.9 db. I should see something like 2.1 or 2.2. I have measured the coupling cable and see .1 db, so the cable is good. Anyone have an idea why the loss is so high when coupled? Did you actually measure the individual loss of each can, or are you just going by the indicators on the loops? Try changing the length of cable between the cans. I think an electrical 1/4 wave multiple (1/4, 3/4, 5/4, etc.) is what you want. Bob NO6B
Re: [Repeater-Builder] Sinclair C-Series cable lengths
At 4/19/2010 17:24, you wrote: These are measured values using a Service Monitor. I have two charts that show the cable lengths, but the values are not the same. They differ by 1 for the same frequency. Would that produce the effect I'm seeing? Depends on what frequency band we're talking about. 1 is not enough @ 2 meters to make a significant change. Try changing the length by about a foot for 2 meters, or 4 @ 440. Bob NO6B
Re: [Repeater-Builder] Sinclair C-Series cable lengths
The freq in question is 166 mHz. One chart gives me 19 and the other 18. I didn't think 1 at this freq would make much difference. I'm also not clear if the length is after the connectors are installed or the cut cable before installing the connectors. Which do you think it is? On Mon, Apr 19, 2010 at 8:42 PM, n...@no6b.com wrote: At 4/19/2010 17:24, you wrote: These are measured values using a Service Monitor. I have two charts that show the cable lengths, but the values are not the same. They differ by 1 for the same frequency. Would that produce the effect I'm seeing? Depends on what frequency band we're talking about. 1 is not enough @ 2 meters to make a significant change. Try changing the length by about a foot for 2 meters, or 4 @ 440. Bob NO6B
Re: [Repeater-Builder] Sinclair C-Series cable lengths
The units I have seen appear to have a 1/2 wavelength of cable. The loops are typically 1/8 wavelength equivalent and with 2 loops and the cable will equal 3/4 wavelength. I have also seen some of the old (rounded top) Sinclair cans with side connectors joined together with only a double female adaptor which would be equal to 1/4 wavelength connection. The cable length is not super critical. Burt VE2BMQ n...@no6b.com wrote: At 4/19/2010 10:24, you wrote: I have 2 C-Series bandpass cavities, with individual I.L. set at 1.0 db each. When I couple them together and measure, I get a total I.L. of 2.9 db. I should see something like 2.1 or 2.2. I have measured the coupling cable and see .1 db, so the cable is good. Anyone have an idea why the loss is so high when coupled? Did you actually measure the individual loss of each can, or are you just going by the indicators on the loops? Try changing the length of cable between the cans. I think an electrical 1/4 wave multiple (1/4, 3/4, 5/4, etc.) is what you want. Bob NO6B Yahoo! Groups Links
