Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Bob wrote: For a reasonable standard distribution, you probably want one input and many outputs. One in / eight out or one in / 12 out are fairly common. At least the video gizmo we've been dissecting has trouble past one in / 4 out. It has 6 CLC409s, each of which drives 3 BNCs, for 18 outputs. Even if you have all 50 ohm loads and only use 2 outputs per op-amp, that's still 12 outputs. If you cascade them you are at one in to 3 useful outputs. to get to eight you do a lot of jumping from here to there. Each op amp adds it's noise in a cascade. You don't need to cascade anything, because you hardwire the inputs in the configuration you want (1x18, 1x12 + 1x6, or 1x6 + 1x6 + 1x6) (which becomes 1x12, 1x8 + 1x4, or 1x4 + 1x4 + 1x4, assuming again that all of your loads are 50 ohms so you use only two outputs per op-amp). Since most of us have few 50 ohm loads and lots of ~1k ohm loads to feed, the current limit of the CLC409s will not matter as long as we distribute the 50 ohm loads among the op-amps. When I used the Extron, I had it set up to be switchable between 1x18 and 1x12 + 1x6. If you are going to run -185 dbc/Hz phase noise signals, none of these solutions will work. For that stuff you want a totally different approach. The same is true if you are after ADEV at 1x10^-15 at 1 second. Agreed. Also, if you need 120 dB of isolation from output to output or output to input. All of these solutions are for feeding the external reference inputs of various test equipment, radios, etc., not for buffering and isolating signals for serious phase noise or ADEV analysis. All I'm really trying to say here is that the alternative isn't all that tough. You can do it cheap with common parts and not a lot of effort. The time to hack up an existing video box (and do it right) may not be much less than the time to do something much simpler from scratch. One person's not that tough is another person's I don't know how I'd do that. I hacked up a video DA (and did it right, within the limits of re-using the CLC409s) in a couple of hours. I have since built my own DA that has much lower phase noise and ADEV than any source I have or am likely ever to have. By the time you design a PC card and have it made, you are way, way beyond not a lot of effort for lots of people, to say nothing of the metalwork (even if it is just making new front and back plates for an existing Extron box). I can do all of that, and I did, but it appears from the on-list interest in video DAs that a lot of time nuts would rather not be bothered. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
I wrote: All of these solutions are for feeding the external reference inputs of various test equipment, radios, etc., not for buffering and isolating signals for serious phase noise or ADEV analysis. By the time you design a PC card and have it made, you are way, way beyond not a lot of effort for lots of people, to say nothing of the metalwork (even if it is just making new front and back plates for an existing Extron box). I can do all of that, and I did, but it appears from the on-list interest in video DAs that a lot of time nuts would rather not be bothered. I guess what I'm saying is if one is going to the effort to build a DA from scratch, why build something that is just adequate to distribute a reference signal to test equipment and radios? Why not really do it right, and build something that *is* capable of buffering and isolating signals for serious phase noise and ADEV analysis? Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi If you are buying NPO caps that are +/- 20%, get another supplier…. Bob On Aug 9, 2013, at 10:27 PM, briana als...@nc.rr.com wrote: A cap marked 82pf might indeed be 79pf or any value 15-20% either side of the marked value. Depends upon what cap type you use. If you really need 79pf, buy a couple dozen 82 pf caps and select one based upon measurement. Be aware that the measure may be off by 10% too. Regards, Brian On 8/9/2013 8:08 PM, Robert LaJeunesse wrote: Thanks. Might end up more useful than the Pi-network approach I've used a few times before. I appreciate knowing of more tools that can be called upon to help with a design. I just wish the calculators had some way to deal with standard values (like TI's FilterPro). Its frustrating getting a 79pF result and wondering how an 82pF part works. Well, I guess that's what Spice is for... Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 6:41 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] Hi The simplest way to design it is to do a T matching network. Two inductors in the top of the T and one cap to ground. Weather it's a filter or a match, it's the standard three element T lowpass. The logic gate wants to see an inductor at high frequency. The T has an input inductor and that keeps it happy (so would a step up L). Since it's a three element match, you get to pick Z in, Z out, and Q. (with an L network you just would get Z in and Z out). Simply design it for a low Q. Q of three isn't a bad number. Anything up to 5 is practical with rational parts (no tuning). The narrower bandwidth of the higher Q design will increase it's sensitivity to temperature. The lower Q will have a smaller coil / lower impedance above cutoff. If you have 18 to 20 dbm out, you can put a 6 to 8 db pad on it. That will improve the broadband match into the cable. If you want to design it as a filter, everything still works pretty much the same. It's still Zin / Zout and one other number with a three element network. If you want to go to more elements, you can indeed get better filtering at the cost of higher temperature sensitivity. With three elements the harmonics are down 60 db. That's plenty good enough…. LC match calculators (there are many others): http://www.changpuak.ch/electronics/calc_18.php http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html Filter calculator: http://www.calculatoredge.com/electronics/bw%20tee%20low%20pass.htm If you plug the numbers into the calculators you can see what the match does for you in terms of the inductor value. Why not design a flat passband filter? You are only interested in passing 10 MHz. Attenuating other frequencies is not a problem and may be beneficial. The bandwidth is not going to be small enough (with a low Q) to give you trouble. The peaking of the filter gives you a steeper cutoff at harmonic frequencies. It rolls off just like any filter, but it starts from a higher peak. With the T you can do any Zin / Zout ratio provided the Q is high enough. If you want to do low power, set it up as a 100 ohm to 50 ohm or 200 ohm to 50 ohm match. It's a pretty simple solution to the problem that is flexible enough to get the job done. Bob On Aug 9, 2013, at 5:24 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Bob, I need some education. For a low-pass filter I think series L and shunt C. For two inductors that normally means 2-3 capacitors. If you use only one shunt capacitor is the second L in series with it (as a harmonic trap)? Can you point me to a design tool (or equation set) somewhere that shows how to choose values best to match the impedances? thanks, Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 4:57 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi On Aug 10, 2013, at 6:29 AM, Charles Steinmetz csteinm...@yandex.com wrote: I wrote: All of these solutions are for feeding the external reference inputs of various test equipment, radios, etc., not for buffering and isolating signals for serious phase noise or ADEV analysis. By the time you design a PC card and have it made, you are way, way beyond not a lot of effort for lots of people, to say nothing of the metalwork (even if it is just making new front and back plates for an existing Extron box). I can do all of that, and I did, but it appears from the on-list interest in video DAs that a lot of time nuts would rather not be bothered. I guess what I'm saying is if one is going to the effort to build a DA from scratch, why build something that is just adequate to distribute a reference signal to test equipment and radios? Why not really do it right, and build something that *is* capable of buffering and isolating signals for serious phase noise and ADEV analysis? Hi A couple of reasons: 1) You have already gone into or towards the don't know / can't do region with a simple pcb and putting a dozen or so holes in a Hammond box. If you add the complexity of a full blown uber circuit you are much further into that area. If you have lost the entire crowd with an afternoon project, there's little use in talking about a two week project. 2) To do an apples to apples type comparison. The super circuits come up and get compared to the modified DA's. The real comparison circuit is much less complex and pretty easy to design. 3) In general you have one best source for phase noise and another for ADEV. Except in the case of a Cs, and tau's 100 seconds, I've never seen them used as the house standard. The standard gets run to things like counters and signal generators mostly to keep them on frequency. In the case of a Cs, the ones I use have multiple outputs already. 4) Overkill is an issue here. Even if it's TimeNuts, there is a point where good enough is indeed a measurable quantity. A counter only needs a standard that's good to some level, past that it does no better. The same is true of everything I have hooked up to my standard lines. I have a *lot* of standard lines running around the basement …. Bob Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Bob wrote: Ok, each op-amp drives three loads. Each load has a 50 ohm resistor in series with it. Each output could be terminated in 50 ohms. If they all are terminated, the op amp is driving three 100 ohm loads in parallel. The op amp sees 33 1/3 ohm at it's output in that case. That's way below the 100 ohms that the manufacturer seems to be recommending. The circuit is basically the same as the Extron ADA 6 Component that I posted about back in May. I noted: Several units modified as above have been tested and each amplifier drives 3x 50 ohm loads to ~ +13dBm (~ 1 Vrms) with harmonics -65dBc and about 1 dB of headroom. Note that this requires peak currents of ±85 mA from the CLC409s, which are rated for output currents of ±60 mA for maximum reliability (also note that the guaranteed minimum current limit value of the CLC409 is ±50 mA). Thus, for optimum performance, 50 ohm loads should be distributed one or two per amplifier. Note that the reference inputs of many devices is higher than 50 ohms (often ~ 1k ohm), so this may not be an issue in many applications. (see http://www.febo.com/pipermail/time-nuts/attachments/20130522/45ae59f8/attachment-0001.pdf) I do not know for how long a CLC409 will drive 3 parallel 50 ohm back-terminated loads to +13 dBm before failure. My test mule did it continuously for several weeks, but I would not recommend it. Of course, some CLC409s (with current limits closer to the minimum spec) may not drive 3 parallel 50 ohm back-terminated loads to +13 dBm at all. The CLC409 is within its +/- 60 mA maximum reliability spec driving 2 parallel 50 ohm back-terminated loads to +13 dBm (peak current +/- 56 mA), although parts that are right at the 50 mA minimum current limit spec may be starting to current limit. Someone asked how the modified DA performs. In addition to the distortion data above, I posted: Phase noise of -155dBc at 10 MHz was observed on the modified units. Adjacent-output isolation (same CLC409) was 30dB. Non-adjacent-output isolation was 90dB. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi The original design with 3x75 ohm outputs would be driving a 50 ohm load rather than a 33 1/3 ohm load. That would put it in spec for the CLC409 as opposed to just out of spec current limit wise. Bob On Aug 9, 2013, at 2:48 PM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: Ok, each op-amp drives three loads. Each load has a 50 ohm resistor in series with it. Each output could be terminated in 50 ohms. If they all are terminated, the op amp is driving three 100 ohm loads in parallel. The op amp sees 33 1/3 ohm at it's output in that case. That's way below the 100 ohms that the manufacturer seems to be recommending. The circuit is basically the same as the Extron ADA 6 Component that I posted about back in May. I noted: Several units modified as above have been tested and each amplifier drives 3x 50 ohm loads to ~ +13dBm (~ 1 Vrms) with harmonics -65dBc and about 1 dB of headroom. Note that this requires peak currents of ±85 mA from the CLC409s, which are rated for output currents of ±60 mA “for maximum reliability” (also note that the guaranteed minimum current limit value of the CLC409 is ±50 mA). Thus, for optimum performance, 50 ohm loads should be distributed one or two per amplifier. Note that the reference inputs of many devices is higher than 50 ohms (often ~ 1k ohm), so this may not be an issue in many applications. (see http://www.febo.com/pipermail/time-nuts/attachments/20130522/45ae59f8/attachment-0001.pdf) I do not know for how long a CLC409 will drive 3 parallel 50 ohm back-terminated loads to +13 dBm before failure. My test mule did it continuously for several weeks, but I would not recommend it. Of course, some CLC409s (with current limits closer to the minimum spec) may not drive 3 parallel 50 ohm back-terminated loads to +13 dBm at all. The CLC409 is within its +/- 60 mA maximum reliability spec driving 2 parallel 50 ohm back-terminated loads to +13 dBm (peak current +/- 56 mA), although parts that are right at the 50 mA minimum current limit spec may be starting to current limit. Someone asked how the modified DA performs. In addition to the distortion data above, I posted: Phase noise of -155dBc at 10 MHz was observed on the modified units. Adjacent-output isolation (same CLC409) was 30dB. Non-adjacent-output isolation was 90dB. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Bob wrote: The original design with 3x75 ohm outputs would be driving a 50 ohm load rather than a 33 1/3 ohm load. That would put it in spec for the CLC409 as opposed to just out of spec current limit wise. Right. Analog video generally ranges from 0 to +1 V, so as a DC-coupled video amp the peak current into 3x75 ohm loads would be +40/-0 mA. Very comfortably within the capability of a CLC409. A friend recently brought me another commercial video DA, which I'm helping him modify for use as a 1/5/10 MHz DA. It uses EL2099 video drivers, which are specified to provide 440 mA (typical -- 360 mA minimum) of output current. This part should be able to drive 12 or more parallel back-terminated 50 ohm loads to +13 dBm, if desired. (Like the CLC409, the EL2099 is obsolete/NLA.) Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. Bob On Aug 9, 2013, at 4:44 PM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: The original design with 3x75 ohm outputs would be driving a 50 ohm load rather than a 33 1/3 ohm load. That would put it in spec for the CLC409 as opposed to just out of spec current limit wise. Right. Analog video generally ranges from 0 to +1 V, so as a DC-coupled video amp the peak current into 3x75 ohm loads would be +40/-0 mA. Very comfortably within the capability of a CLC409. A friend recently brought me another commercial video DA, which I'm helping him modify for use as a 1/5/10 MHz DA. It uses EL2099 video drivers, which are specified to provide 440 mA (typical -- 360 mA minimum) of output current. This part should be able to drive 12 or more parallel back-terminated 50 ohm loads to +13 dBm, if desired. (Like the CLC409, the EL2099 is obsolete/NLA.) Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Bob, I need some education. For a low-pass filter I think series L and shunt C. For two inductors that normally means 2-3 capacitors. If you use only one shunt capacitor is the second L in series with it (as a harmonic trap)? Can you point me to a design tool (or equation set) somewhere that shows how to choose values best to match the impedances? thanks, Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 4:57 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi The simplest way to design it is to do a T matching network. Two inductors in the top of the T and one cap to ground. Weather it's a filter or a match, it's the standard three element T lowpass. The logic gate wants to see an inductor at high frequency. The T has an input inductor and that keeps it happy (so would a step up L). Since it's a three element match, you get to pick Z in, Z out, and Q. (with an L network you just would get Z in and Z out). Simply design it for a low Q. Q of three isn't a bad number. Anything up to 5 is practical with rational parts (no tuning). The narrower bandwidth of the higher Q design will increase it's sensitivity to temperature. The lower Q will have a smaller coil / lower impedance above cutoff. If you have 18 to 20 dbm out, you can put a 6 to 8 db pad on it. That will improve the broadband match into the cable. If you want to design it as a filter, everything still works pretty much the same. It's still Zin / Zout and one other number with a three element network. If you want to go to more elements, you can indeed get better filtering at the cost of higher temperature sensitivity. With three elements the harmonics are down 60 db. That's plenty good enough…. LC match calculators (there are many others): http://www.changpuak.ch/electronics/calc_18.php http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html Filter calculator: http://www.calculatoredge.com/electronics/bw%20tee%20low%20pass.htm If you plug the numbers into the calculators you can see what the match does for you in terms of the inductor value. Why not design a flat passband filter? You are only interested in passing 10 MHz. Attenuating other frequencies is not a problem and may be beneficial. The bandwidth is not going to be small enough (with a low Q) to give you trouble. The peaking of the filter gives you a steeper cutoff at harmonic frequencies. It rolls off just like any filter, but it starts from a higher peak. With the T you can do any Zin / Zout ratio provided the Q is high enough. If you want to do low power, set it up as a 100 ohm to 50 ohm or 200 ohm to 50 ohm match. It's a pretty simple solution to the problem that is flexible enough to get the job done. Bob On Aug 9, 2013, at 5:24 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Bob, I need some education. For a low-pass filter I think series L and shunt C. For two inductors that normally means 2-3 capacitors. If you use only one shunt capacitor is the second L in series with it (as a harmonic trap)? Can you point me to a design tool (or equation set) somewhere that shows how to choose values best to match the impedances? thanks, Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 4:57 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Bob wrote: I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. The filters add a potential source of close-in phase noise due to the temperature coefficients of the parts. Granted, this may be academic in the case of a simple reference distribution, and you could always do it with harmonic traps instead of BP or LP filters to minimize the problem. Also, I'd rather not generate fast edges in the first place if I don't need them -- they can leak out and be pesky. But these are not religious positions for me. In some cases the digital solution may be preferable. However, I think the large interest in video DAs has more to do with the fact that they are cheap and often need very little modification. When I first wanted to distribute 10 MHz, before I built my own DA, I grabbed an Extron out of the junk pile and modified it in a couple of hours. Indeed, if you can tolerate the mismatch and the overall 2 dB loss, video DAs can often be pressed into service with no modification (not my preferred solution, but it's been done). Digital DAs, OTOH, are more for the person who is rolling his or her own from the ground up. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi For a reasonable standard distribution, you probably want one input and many outputs. One in / eight out or one in / 12 out are fairly common. At least the video gizmo we've been dissecting has trouble past one in / 4 out. If you cascade them you are at one in to 3 useful outputs. to get to eight you do a lot of jumping from here to there. Each op amp adds it's noise in a cascade. Metal work is an issue, and the video boxes do have a case that comes with them. They also have the connectors already mounted to a PCB. A more custom solution would indeed require a bit of fab for a front plate and / or back plate. You would also have to buy connectors to solder to the pcb. With a more custom solution, you could do it right. If 1 in 12 out makes sense, then you do exactly that. If fab is an issue, move all the stuff past one surface. Power wise, a digital DA will run off 1/4 A. A wall wart into a cheap linear regulator on the PCB is the much more rational solution than a built in supply at that level. If you want X out's at 10, Y at 5 and Z outputs at 1 MHz, that's trivially easy once you are running logic. They still make flip flops and divide by 10's. To go nuts, use one of Bert's favorite CPLD's and you can have 10, 5, 1, 0.1 and a couple of others, all off one chip. Design wise, there's not a lot to a DA. A simple double sided PCB will do the job. For the ultra cool approach, go with a 4 layer board and a power plane if you want. It will work just fine either way. The cheap board shops will sell you the board for less than the price of the DA's at auction. That's certainly true of a 2 layer, there are places that will do 4 layer (in modest quantity) for those sort of prices as well. If you are going to run -185 dbc/Hz phase noise signals, none of these solutions will work. For that stuff you want a totally different approach. The same is true if you are after ADEV at 1x10^-15 at 1 second. For any normal piece of test gear, you don't need that sort of thing. Commercial DA's don't do that stuff. The standards normally used (like that Rb ) are nowhere near that level. All I'm really trying to say here is that the alternative isn't all that tough. You can do it cheap with common parts and not a lot of effort. The time to hack up an existing video box (and do it right) may not be much less than the time to do something much simpler from scratch. …. and before it gets asked… yes I've done it, measured it, tested it, use them every day. There have been many millions of those amps (single channel version) built and fielded over the last 20 years. Bob On Aug 9, 2013, at 6:51 PM, Charles Steinmetz csteinm...@yandex.com wrote: Bob wrote: I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. The filters add a potential source of close-in phase noise due to the temperature coefficients of the parts. Granted, this may be academic in the case of a simple reference distribution, and you could always do it with harmonic traps instead of BP or LP filters to minimize the problem. Also, I'd rather not generate fast edges in the first place if I don't need them -- they can leak out and be pesky. But these are not religious positions for me. In some cases the digital solution may be preferable. However, I think the large interest in video DAs has more to do with the fact that they are cheap and often need very little modification. When I first wanted to distribute 10 MHz, before I built my own DA, I grabbed an Extron out of the junk pile and modified it in a couple of hours. Indeed, if you can tolerate the mismatch and the overall 2 dB loss, video DAs can often be pressed into service with no modification (not my preferred solution, but it's been done). Digital DAs, OTOH, are more for the person who is rolling his or her own from the ground up. Best regards, Charles ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Thanks. Might end up more useful than the Pi-network approach I've used a few times before. I appreciate knowing of more tools that can be called upon to help with a design. I just wish the calculators had some way to deal with standard values (like TI's FilterPro). Its frustrating getting a 79pF result and wondering how an 82pF part works. Well, I guess that's what Spice is for... Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 6:41 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] Hi The simplest way to design it is to do a T matching network. Two inductors in the top of the T and one cap to ground. Weather it's a filter or a match, it's the standard three element T lowpass. The logic gate wants to see an inductor at high frequency. The T has an input inductor and that keeps it happy (so would a step up L). Since it's a three element match, you get to pick Z in, Z out, and Q. (with an L network you just would get Z in and Z out). Simply design it for a low Q. Q of three isn't a bad number. Anything up to 5 is practical with rational parts (no tuning). The narrower bandwidth of the higher Q design will increase it's sensitivity to temperature. The lower Q will have a smaller coil / lower impedance above cutoff. If you have 18 to 20 dbm out, you can put a 6 to 8 db pad on it. That will improve the broadband match into the cable. If you want to design it as a filter, everything still works pretty much the same. It's still Zin / Zout and one other number with a three element network. If you want to go to more elements, you can indeed get better filtering at the cost of higher temperature sensitivity. With three elements the harmonics are down 60 db. That's plenty good enough…. LC match calculators (there are many others): http://www.changpuak.ch/electronics/calc_18.php http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html Filter calculator: http://www.calculatoredge.com/electronics/bw%20tee%20low%20pass.htm If you plug the numbers into the calculators you can see what the match does for you in terms of the inductor value. Why not design a flat passband filter? You are only interested in passing 10 MHz. Attenuating other frequencies is not a problem and may be beneficial. The bandwidth is not going to be small enough (with a low Q) to give you trouble. The peaking of the filter gives you a steeper cutoff at harmonic frequencies. It rolls off just like any filter, but it starts from a higher peak. With the T you can do any Zin / Zout ratio provided the Q is high enough. If you want to do low power, set it up as a 100 ohm to 50 ohm or 200 ohm to 50 ohm match. It's a pretty simple solution to the problem that is flexible enough to get the job done. Bob On Aug 9, 2013, at 5:24 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Bob, I need some education. For a low-pass filter I think series L and shunt C. For two inductors that normally means 2-3 capacitors. If you use only one shunt capacitor is the second L in series with it (as a harmonic trap)? Can you point me to a design tool (or equation set) somewhere that shows how to choose values best to match the impedances? thanks, Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 4:57 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
Hi Since you have a handle on the Q (and thus the peaking width) you can come up with a pretty good mental picture of what a value shift will or won't do. For those who can't stand changing out / padding one cap (that's all that you would ever need to do in the is case) LTSpice is indeed your friend. Bob On Aug 9, 2013, at 9:08 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Thanks. Might end up more useful than the Pi-network approach I've used a few times before. I appreciate knowing of more tools that can be called upon to help with a design. I just wish the calculators had some way to deal with standard values (like TI's FilterPro). Its frustrating getting a 79pF result and wondering how an 82pF part works. Well, I guess that's what Spice is for... Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 6:41 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] Hi The simplest way to design it is to do a T matching network. Two inductors in the top of the T and one cap to ground. Weather it's a filter or a match, it's the standard three element T lowpass. The logic gate wants to see an inductor at high frequency. The T has an input inductor and that keeps it happy (so would a step up L). Since it's a three element match, you get to pick Z in, Z out, and Q. (with an L network you just would get Z in and Z out). Simply design it for a low Q. Q of three isn't a bad number. Anything up to 5 is practical with rational parts (no tuning). The narrower bandwidth of the higher Q design will increase it's sensitivity to temperature. The lower Q will have a smaller coil / lower impedance above cutoff. If you have 18 to 20 dbm out, you can put a 6 to 8 db pad on it. That will improve the broadband match into the cable. If you want to design it as a filter, everything still works pretty much the same. It's still Zin / Zout and one other number with a three element network. If you want to go to more elements, you can indeed get better filtering at the cost of higher temperature sensitivity. With three elements the harmonics are down 60 db. That's plenty good enough…. LC match calculators (there are many others): http://www.changpuak.ch/electronics/calc_18.php http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html Filter calculator: http://www.calculatoredge.com/electronics/bw%20tee%20low%20pass.htm If you plug the numbers into the calculators you can see what the match does for you in terms of the inductor value. Why not design a flat passband filter? You are only interested in passing 10 MHz. Attenuating other frequencies is not a problem and may be beneficial. The bandwidth is not going to be small enough (with a low Q) to give you trouble. The peaking of the filter gives you a steeper cutoff at harmonic frequencies. It rolls off just like any filter, but it starts from a higher peak. With the T you can do any Zin / Zout ratio provided the Q is high enough. If you want to do low power, set it up as a 100 ohm to 50 ohm or 200 ohm to 50 ohm match. It's a pretty simple solution to the problem that is flexible enough to get the job done. Bob On Aug 9, 2013, at 5:24 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Bob, I need some education. For a low-pass filter I think series L and shunt C. For two inductors that normally means 2-3 capacitors. If you use only one shunt capacitor is the second L in series with it (as a harmonic trap)? Can you point me to a design tool (or equation set) somewhere that shows how to choose values best to match the impedances? thanks, Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 4:57 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe
Re: [time-nuts] Modified Extron DA [WAS: Rb video]
A cap marked 82pf might indeed be 79pf or any value 15-20% either side of the marked value. Depends upon what cap type you use. If you really need 79pf, buy a couple dozen 82 pf caps and select one based upon measurement. Be aware that the measure may be off by 10% too. Regards, Brian On 8/9/2013 8:08 PM, Robert LaJeunesse wrote: Thanks. Might end up more useful than the Pi-network approach I've used a few times before. I appreciate knowing of more tools that can be called upon to help with a design. I just wish the calculators had some way to deal with standard values (like TI's FilterPro). Its frustrating getting a 79pF result and wondering how an 82pF part works. Well, I guess that's what Spice is for... Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 6:41 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] Hi The simplest way to design it is to do a T matching network. Two inductors in the top of the T and one cap to ground. Weather it's a filter or a match, it's the standard three element T lowpass. The logic gate wants to see an inductor at high frequency. The T has an input inductor and that keeps it happy (so would a step up L). Since it's a three element match, you get to pick Z in, Z out, and Q. (with an L network you just would get Z in and Z out). Simply design it for a low Q. Q of three isn't a bad number. Anything up to 5 is practical with rational parts (no tuning). The narrower bandwidth of the higher Q design will increase it's sensitivity to temperature. The lower Q will have a smaller coil / lower impedance above cutoff. If you have 18 to 20 dbm out, you can put a 6 to 8 db pad on it. That will improve the broadband match into the cable. If you want to design it as a filter, everything still works pretty much the same. It's still Zin / Zout and one other number with a three element network. If you want to go to more elements, you can indeed get better filtering at the cost of higher temperature sensitivity. With three elements the harmonics are down 60 db. That's plenty good enough…. LC match calculators (there are many others): http://www.changpuak.ch/electronics/calc_18.php http://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html Filter calculator: http://www.calculatoredge.com/electronics/bw%20tee%20low%20pass.htm If you plug the numbers into the calculators you can see what the match does for you in terms of the inductor value. Why not design a flat passband filter? You are only interested in passing 10 MHz. Attenuating other frequencies is not a problem and may be beneficial. The bandwidth is not going to be small enough (with a low Q) to give you trouble. The peaking of the filter gives you a steeper cutoff at harmonic frequencies. It rolls off just like any filter, but it starts from a higher peak. With the T you can do any Zin / Zout ratio provided the Q is high enough. If you want to do low power, set it up as a 100 ohm to 50 ohm or 200 ohm to 50 ohm match. It's a pretty simple solution to the problem that is flexible enough to get the job done. Bob On Aug 9, 2013, at 5:24 PM, Robert LaJeunesse rlajeune...@sbcglobal.net wrote: Bob, I need some education. For a low-pass filter I think series L and shunt C. For two inductors that normally means 2-3 capacitors. If you use only one shunt capacitor is the second L in series with it (as a harmonic trap)? Can you point me to a design tool (or equation set) somewhere that shows how to choose values best to match the impedances? thanks, Bob LaJeunesse From: Bob Camp li...@rtty.us To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, August 9, 2013 4:57 PM Subject: Re: [time-nuts] Modified Extron DA [WAS: Rb video] I still think that a distribution amp based on logic ic's is cheaper / simpler / lower power / higher performance. A pair of NC7SZ125's will dump 20 dbm into 50 ohms all day long running at 5.5 volts. Good isolation as well. Do the lowpass filter right and the harmonics are not an issue. Two coils / one cap plus dc blocking does it quite nicely. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. - No virus found in this message. Checked by AVG - www.avg.com Version
