Re: [time-nuts] FRS-C TTL / sine outboard filter question
Hi Leigh, I can't comment on the crystal filter option., but I've found that the packaged filters and filter/balun modules from old 10Mb/s Ethernet cards work well. See this excellent little page by Dave G4HUP http://g4hup.com/DA/Filters%20Transformers%20and%20DC%20Converters.pdf Robert G8RPI. --- On Wed, 23/6/10, Leigh L. Klotz, Jr WA5ZNU le...@wa5znu.org wrote: From: Leigh L. Klotz, Jr WA5ZNU le...@wa5znu.org Subject: [time-nuts] FRS-C TTL / sine outboard filter question To: time nuts time-nuts@febo.com Date: Wednesday, 23 June, 2010, 5:54 At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. ___ 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] FRS-C TTL / sine outboard filter question
On a military satcom program in the mid 80's that I worked on, we used a 10 MHz crystal filter with about a 100 Hz BW to reduce phase noise of our Rb source. Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ 07731 732-886-5960 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Leigh L. Klotz, Jr WA5ZNU Sent: Wednesday, June 23, 2010 12:54 AM To: time nuts Subject: [time-nuts] FRS-C TTL / sine outboard filter question At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. ___ 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] FRS-C TTL / sine outboard filter question
If your concern is to clean up the harmonics, a crystal ladder filter is probably not the best choice, a low pass filter would be easier to design, would probably require no adjustment and be cheaper in parts with less effect on the fundamental signal you are interested in. If your concern is cleanliness and close-in phase noise (as Mike referred to), then a narrow crystal filter would indeed be a better choice. Keep in mind that ladder filters have an assymetric frequency response. That may or may not help you. On the other end, if you are going to drive any kind of digital circuitry, a square wave (even distorted) is probably better than a sine wave. Didier Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Leigh L. Klotz, Jr WA5ZNU le...@wa5znu.org Sender: time-nuts-boun...@febo.com Date: Tue, 22 Jun 2010 21:54:01 To: time nutstime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] FRS-C TTL / sine outboard filter question At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. ___ 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] FRS-C TTL / sine outboard filter question
At 12:54 AM 6/23/2010, Leigh L. Klotz, Jr WA5ZNU wrote... At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Connector board? No such beast described in the manual. Do you mean the A3 power supply board, which has the i/o connector on it? Active board? Ditto. Do you mean the A4 oscillator board, which has a 20 MHz VCXO on it? There's no 15 MHz anywhere in an FRS-C. Here's a manual: http://www.to-way.com/tf/frs.pdf Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. It sounds like you made the changes to the A4 oscillator board, but not the ones to the A3 power supply board (several inductors, resistors and caps). I found that using a 1 uF for C16, instead of the documented 0.1 uF, gives a better signal. See the top of page A-15 in the manual. ___ 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] FRS-C TTL / sine outboard filter question
In a message dated 23/06/2010 14:12:00 GMT Daylight Time, mi...@flatsurface.com writes: At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Connector board? No such beast described in the manual. Do you mean the A3 power supply board, which has the i/o connector on it? Active board? Ditto. Do you mean the A4 oscillator board, which has a 20 MHz VCXO on it? There's no 15 MHz anywhere in an FRS-C. -- The connector board and missing 15MHz board are external parts from the Lucent unit that originally contained them, not internal to the FRS module. The 15MHz board, active in that it contains electronics circuitry, isn't of much use to most folks anyway but the connector board carries the special D type connector with coax insert that interfaces to the FRS so that's extremely useful. regards Nigel GM8PZR ___ 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] FRS-C TTL / sine outboard filter question
... Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. It sounds like you made the changes to the A4 oscillator board, but not the ones to the A3 power supply board (several inductors, resistors and caps). I found that using a 1 uF for C16, instead of the documented 0.1 uF, gives a better signal. See the top of page A-15 in the manual. Exactly that's probably the culprit. If you need a sine wave output but don't want to change anything inside, just add a lowpass filter. A 5th order LPF (three inductors/ 2 caps or vice versa) should give you a clean sine wave output. Just add a coupling cap to remove the DC component. Adrian ___ 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] FRS-C TTL / sine outboard filter question
Mike S wrote: It sounds like you made the changes to the A4 oscillator board, but not the ones to the A3 power supply board (several inductors, resistors and caps). I found that using a 1 uF for C16, instead of the documented 0.1 uF, gives a better signal. See the top of page A-15 in the manual. Thank you. This is just what I needed to hear. I had clearly overlooked that page. I've made an attempt at reading page A-15 for the 10 MHz sine option, and consulted the schematic and parts list on the succeeding pages. I still don't have legible values for L1, L2, and R16. If you have these values we can document the rest of this process in one place. 10 MHz sine TTL L1 ?.? uH L1 OMIT L2 1? uH Replace with R23 130 OHM 1 WATT R16 ?10 OHM NOM100 OHM NOM R17 1.0K 274 OHM NOM 1/4W R18 1.0K OMIT C8 47pF NOM JUMPER C9 6800pf NOM 0.47 uF NOM C16 0.1uF [1uF: see above] JUMPER C17 240pF NOM NP0 OMIT INSTALL JUMPER A-0 Leigh. ___ 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] FRS-C TTL / sine outboard filter question
... [snip] If you need a sine wave output but don't want to change anything inside, just add a lowpass filter. A 5th order LPF (three inductors/ 2 caps or vice versa) should give you a clean sine wave output. Just add a coupling cap to remove the DC component. Adrian _ Thank you, Adrian. I'll pursue both options, internal fixes and external filter. A multi-pole LPF is easily understood, and I don't believe I care about passband ripple, though I wonder a little about the effect of the coupling on phase changes (i.e., does this have any unfortunate effect on adev?). I still don't know if a crystal ladder filter will suppress the harmonics, but I did get the answers that make me not need to ask anymore (1. fix the internal filter, 2. use the high Q xtal filter for optional removal of close-in noise) Given time I would do all of these things, but I may not get to them all! Leigh. ___ 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] FRS-C TTL / sine outboard filter question
At 04:19 PM 6/23/2010, Leigh L. Klotz, Jr. WA5ZNU wrote... If you have these values we can document the rest of this process in one place. 10 MHz sine TTL L1 ?.? uH L1 OMIT L2 1? uH Replace with R23 130 OHM 1 WATT R16 ?10 OHM NOM100 OHM NOM R17 1.0K 274 OHM NOM 1/4W R18 1.0K OMIT C8 47pF NOM JUMPER C9 6800pf NOM 0.47 uF NOM C16 0.1uF [1uF: see above] JUMPER C17 240pF NOM NP0 OMIT INSTALL JUMPER A-0 Here are the values I used. L1 6.8 uH L2 15 uH R16 910 Ohm nom R17 1.0K nom R18 1.0K C8 47 pF nom C9 6800 pF nom C16 0.1 uF (but 1.0 uF provides much cleaner signal) C17 240 pF NPO nom ___ 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] FRS-C TTL / sine outboard filter question
Leigh, A narrow filter around 10MHz is likely to show phase ripple in its passband, and that will most certainly vary over temperature, not a good thing for ADEV, that's why a LPF is preferred. Also, most crystal filters may not be happy with the output level of a typical OCXO, so you would have to attenuate the signal before the filter and amplify it after, an unnecessary complexity that will not help ADEV. Crystal filters are not usually used for harmonic suppression because away from the resonance, crystals are good capacitors, so you will probably not find much data, and if you find data, it will probably suck :) In most applications, they are preceded and followed by L-C filters to normalize the out-of-band response. Didier Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: Leigh L. Klotz, Jr. WA5ZNU le...@wa5znu.org Sender: time-nuts-boun...@febo.com Date: Wed, 23 Jun 2010 13:44:37 To: Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] FRS-C TTL / sine outboard filter question ... [snip] If you need a sine wave output but don't want to change anything inside, just add a lowpass filter. A 5th order LPF (three inductors/ 2 caps or vice versa) should give you a clean sine wave output. Just add a coupling cap to remove the DC component. Adrian _ Thank you, Adrian. I'll pursue both options, internal fixes and external filter. A multi-pole LPF is easily understood, and I don't believe I care about passband ripple, though I wonder a little about the effect of the coupling on phase changes (i.e., does this have any unfortunate effect on adev?). I still don't know if a crystal ladder filter will suppress the harmonics, but I did get the answers that make me not need to ask anymore (1. fix the internal filter, 2. use the high Q xtal filter for optional removal of close-in noise) Given time I would do all of these things, but I may not get to them all! Leigh. ___ 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] FRS-C TTL / sine outboard filter question
Thank you, Didier. That pretty much sums it up. I was aware of the signal level issue but didn't consider that passband ripple would be temperature sensitive. It's fun learning to think in the long time domain. In the meantime I've found a 10 mbit ethernet ISA card in my office and will follow Robert G8RPI's suggestion to use G4HUP's document to obtain a ready-made 10 MHz filter from it. Plus as a bonus the box had a BNC T connector in it. Leigh/WA5ZNU ___ 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] FRS-C TTL / sine outboard filter question
I do not understand why the passband ripple would be of any consequence in the big (or small as we typically talk about) picture. During any measurement interval, it will be a constant, for all practical purposes, including ours. A measurement at a different time, at a different temperature that may adversely affect where the ripple is, it will certainly create a slightly different amplitude and phase delay, however, again, a constant through the measurement process, not affecting the result. When we were designing the system I mentioned previously, both Dave and Fred of NIST were in assistance, as well as the staff of the relevant departments of MIT's LL, and no one saw any issues. Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ 07731 732-886-5960 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Leigh L. Klotz, Jr. WA5ZNU Sent: Wednesday, June 23, 2010 6:15 PM To: did...@cox.net; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] FRS-C TTL / sine outboard filter question Thank you, Didier. That pretty much sums it up. I was aware of the signal level issue but didn't consider that passband ripple would be temperature sensitive. It's fun learning to think in the long time domain. In the meantime I've found a 10 mbit ethernet ISA card in my office and will follow Robert G8RPI's suggestion to use G4HUP's document to obtain a ready-made 10 MHz filter from it. Plus as a bonus the box had a BNC T connector in it. Leigh/WA5ZNU ___ 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] FRS-C TTL / sine outboard filter question
Mike, I agree with you that for SatCom application, long term stability is not as much of a concern, phase noise typically is the main issue. But I suspect that for a time nuts looking at stability over periods of hours or days, temperature effects cannot be ignored. Passband ripple usually goes with group delay ripple, and that delay will change with temperature. For instance, on the Tek 494P I have, the 30Hz crystal filter is thermostatically regulated. When the instrument is cold, there is no signal at all... Didier --Original Message-- From: Mike Feher To: Time-Nuts To: Didier Juges via Cox Subject: RE: [time-nuts] FRS-C TTL / sine outboard filter question Sent: Jun 23, 2010 8:41 PM I do not understand why the passband ripple would be of any consequence in the big (or small as we typically talk about) picture. During any measurement interval, it will be a constant, for all practical purposes, including ours. A measurement at a different time, at a different temperature that may adversely affect where the ripple is, it will certainly create a slightly different amplitude and phase delay, however, again, a constant through the measurement process, not affecting the result. When we were designing the system I mentioned previously, both Dave and Fred of NIST were in assistance, as well as the staff of the relevant departments of MIT's LL, and no one saw any issues. Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ 07731 732-886-5960 -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Leigh L. Klotz, Jr. WA5ZNU Sent: Wednesday, June 23, 2010 6:15 PM To: did...@cox.net; Discussion of precise time and frequency measurement Subject: Re: [time-nuts] FRS-C TTL / sine outboard filter question Thank you, Didier. That pretty much sums it up. I was aware of the signal level issue but didn't consider that passband ripple would be temperature sensitive. It's fun learning to think in the long time domain. In the meantime I've found a 10 mbit ethernet ISA card in my office and will follow Robert G8RPI's suggestion to use G4HUP's document to obtain a ready-made 10 MHz filter from it. Plus as a bonus the box had a BNC T connector in it. Leigh/WA5ZNU ___ 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. Sent from my BlackBerry Wireless thingy while I do other things... ___ 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] FRS-C TTL / sine outboard filter question
At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. ___ 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] FRS-C TTL / sine outboard filter question
Leigh, I have the same FRS-C TTL unit. I do not have a manual. Would you be so kind as to send the conversation info to me? Thanks, Dave W6TE - Original Message - From: Leigh L. Klotz, Jr WA5ZNUmailto:le...@wa5znu.org To: time nutsmailto:time-nuts@febo.com Sent: Tuesday, June 22, 2010 9:54 PM Subject: [time-nuts] FRS-C TTL / sine outboard filter question At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. ___ time-nuts mailing list -- time-nuts@febo.commailto:time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nutshttps://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] FRS-C TTL / sine outboard filter question
What load do you have it running into? It maybe that you need to load it into 50 ohms. Steve On 23 June 2010 16:54, Leigh L. Klotz, Jr WA5ZNU le...@wa5znu.org wrote: At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked TTL internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it. Mine is marked TTL internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground. The output now doesn't have the tremendous overshoot it used to have, but it's also not very sinusoidal. That's not surprising given the simplicity of the on-board filter. Instead of a multi-stage LC filter, I wondered about a crystal ladder filter: since the output frequency is fixed, the high Q and low cost of the crystal filter might be an advantage, but I wasn't sure about how effective xtal ladder filters are at suppressing harmonics, as each individual crystals would have odd overtone responses, so it might not be a good plan. Does anyone have practical experience with a filter topology for cleaning up the output of the FRS-C at 10 MHz? Leigh. P.S. Just so that I can be topical, note that the FRS-C has a C-field adjustment 0-5V input, so I could use it as the reference oscillator for a TPLL. ___ 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. -- Steve Rooke - ZL3TUV G8KVD The only reason for time is so that everything doesn't happen at once. - Einstein ___ 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.
