Re: [Flexradio] blown SDR-1000 final opamp
Ahti, Dudley: I'm using a Delta 44. That's interesting, I had been thinking the amp failed due to output issues as I've rarely seen opamps fail due input drive problems. I hadn't checked the circuit but in most designs the would have been limited at some earlier stage. Ahti, how did you set up the diodes? Back to back from the high side of the input transformer to ground, or across the differential inputs or? While this is an easy fix to implement and does make the circuit more robust as I asked I doubt it will fix the issue. I will give it a try though. In both cases where the chip failed the drive setting was less than 10 and the rig was in tune mode for a few seconds. In addition, for the almost half year I've had this working the rig was terminated in a 50 ohm resistor in the linear. In both cases where it failed the radio was working into some other load. If it's extreme swr sensitivity or possibly parasitics I can guess at the causes but I do not know what the logical troubleshooting procedure would be. -Pete -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 11:54 PM To: Dudley Hurry [EMAIL PROTECTED] Cc: Pete Ferrand [EMAIL PROTECTED], flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Dudley and Pete, The absolute maximum differential input voltage for OPA2674 is +/-1.2V. For that reason I used clamping diodes for protection in one instrumentation application of SDR-1000 when I was not sure the operators remember to keep the sound card output at reasonable level. Be careful though not to distort the signal. 73, Ahti OH2RZ On 10/12/2008, Dudley Hurry [EMAIL PROTECTED] wrote: Pete, You did not mention what sound card you are using, but if the sound card output is too high you can easily overdrive the low level driver, particularly the PreSonus can drive more than 4 volts peak to peak.. 73, Dudley WA5QPZ Pete Ferrand wrote: Ahti: Thank you for taking the time to reply. My radio has the OPA2674 and that is what it had originally. The issue is not one of a short circuit, but most probably one of dealing with a high impedance load which would send the voltage up beyond what the part can handle. At least that's what I'm guessing; I'm not sure of the correct troubleshooting procedure for this kind of fault. My hope was that someone has figured out how to make the circuit more robust but since yours was the only reply and there's no mention of it in the archives I suppose that hasn't happened. 73, -Pete WB2QLL Somers, WI -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 4:54 AM To: Pete Ferrand [EMAIL PROTECTED] Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Pete, The very old SDR-1000 units have OPA2677 as the final amplifier and cannot stand short circuit. The newer radios use OPA2674 that has internal short circuit protection. Anyhow, ask Flex people directly, they know better the difficulties with some of the first production units. 73, Ahti OH2RZ On 09/12/2008, Pete Ferrand [EMAIL PROTECTED] wrote: Some months ago I blew the final opamp in my 1W SDR-1000 whilst matching it to a linear. Wasn't happy about that but since I accidentally hooked up the attenuator resistors wrong I wasn't too surprised since the rig saw a very high impedance. Worked fine ever since. Unfortunately I'm less happy about blowing the amp this morning, about a half year after that first incident, whilst trying it on six meters for the first time. Without the linear which doesn't cover six. Just wanted to see if I could work a couple locals. As far as the MFJ-269 showed there was a perfect match into the ATU but when I increased the power beyond about a tenth of a watt output the opamp popped again. Besides the time and money aspect, the circuit board clearly can't take a lot of parts replacements. Has anyone figured out how better to protect this part? Or some better solution. This is a four stack including the rfe board, older version with nylon spacers. Thanks. -Pete WB2QLL Somers, WI ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz
Re: [Flexradio] blown SDR-1000 final opamp
I have accidentially made all sorts of mismatching the output from my OPA2674 and never have blown it. Running audio with Ozy/Janus and more than 1W rf-output. Maybe the reason is that you have overdriven the audio input. Gerd, DJ8AY -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Pete Ferrand Sent: Wednesday, December 10, 2008 4:16 AM To: Ahti Aintila Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Ahti: Thank you for taking the time to reply. My radio has the OPA2674 and that is what it had originally. The issue is not one of a short circuit, but most probably one of dealing with a high impedance load which would send the voltage up beyond what the part can handle. At least that's what I'm guessing; I'm not sure of the correct troubleshooting procedure for this kind of fault. My hope was that someone has figured out how to make the circuit more robust but since yours was the only reply and there's no mention of it in the archives I suppose that hasn't happened. 73, -Pete WB2QLL Somers, WI -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 4:54 AM To: Pete Ferrand [EMAIL PROTECTED] Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Pete, The very old SDR-1000 units have OPA2677 as the final amplifier and cannot stand short circuit. The newer radios use OPA2674 that has internal short circuit protection. Anyhow, ask Flex people directly, they know better the difficulties with some of the first production units. 73, Ahti OH2RZ On 09/12/2008, Pete Ferrand [EMAIL PROTECTED] wrote: Some months ago I blew the final opamp in my 1W SDR-1000 whilst matching it to a linear. Wasn't happy about that but since I accidentally hooked up the attenuator resistors wrong I wasn't too surprised since the rig saw a very high impedance. Worked fine ever since. Unfortunately I'm less happy about blowing the amp this morning, about a half year after that first incident, whilst trying it on six meters for the first time. Without the linear which doesn't cover six. Just wanted to see if I could work a couple locals. As far as the MFJ-269 showed there was a perfect match into the ATU but when I increased the power beyond about a tenth of a watt output the opamp popped again. Besides the time and money aspect, the circuit board clearly can't take a lot of parts replacements. Has anyone figured out how better to protect this part? Or some better solution. This is a four stack including the rfe board, older version with nylon spacers. Thanks. -Pete WB2QLL Somers, WI ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
Re: [Flexradio] blown SDR-1000 final opamp
Pete, Dudley, I used protection circuit outside the SDR-1000 in the both audio cables. It was with a 100 ohm current limiting resistor and two opposite parallel connected strings of 3 silicon diodes (1N4148). Nominally this limits the input voltage to 2.1Vpp. In my case also the unit from the first production run showed parasitic oscillations that were cured by grinding off some copper foil around the input/output pads to reduce the ground capacitance. Additional 3 units from the later production runs are completely stabile. Ahti On 10/12/2008, Pete Ferrand [EMAIL PROTECTED] wrote: Ahti, Dudley: I'm using a Delta 44. That's interesting, I had been thinking the amp failed due to output issues as I've rarely seen opamps fail due input drive problems. I hadn't checked the circuit but in most designs the would have been limited at some earlier stage. Ahti, how did you set up the diodes? Back to back from the high side of the input transformer to ground, or across the differential inputs or? While this is an easy fix to implement and does make the circuit more robust as I asked I doubt it will fix the issue. I will give it a try though. In both cases where the chip failed the drive setting was less than 10 and the rig was in tune mode for a few seconds. In addition, for the almost half year I've had this working the rig was terminated in a 50 ohm resistor in the linear. In both cases where it failed the radio was working into some other load. If it's extreme swr sensitivity or possibly parasitics I can guess at the causes but I do not know what the logical troubleshooting procedure would be. -Pete -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 11:54 PM To: Dudley Hurry [EMAIL PROTECTED] Cc: Pete Ferrand [EMAIL PROTECTED], flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Dudley and Pete, The absolute maximum differential input voltage for OPA2674 is +/-1.2V. For that reason I used clamping diodes for protection in one instrumentation application of SDR-1000 when I was not sure the operators remember to keep the sound card output at reasonable level. Be careful though not to distort the signal. 73, Ahti OH2RZ On 10/12/2008, Dudley Hurry [EMAIL PROTECTED] wrote: Pete, You did not mention what sound card you are using, but if the sound card output is too high you can easily overdrive the low level driver, particularly the PreSonus can drive more than 4 volts peak to peak.. 73, Dudley WA5QPZ Pete Ferrand wrote: Ahti: Thank you for taking the time to reply. My radio has the OPA2674 and that is what it had originally. The issue is not one of a short circuit, but most probably one of dealing with a high impedance load which would send the voltage up beyond what the part can handle. At least that's what I'm guessing; I'm not sure of the correct troubleshooting procedure for this kind of fault. My hope was that someone has figured out how to make the circuit more robust but since yours was the only reply and there's no mention of it in the archives I suppose that hasn't happened. 73, -Pete WB2QLL Somers, WI -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 4:54 AM To: Pete Ferrand [EMAIL PROTECTED] Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Pete, The very old SDR-1000 units have OPA2677 as the final amplifier and cannot stand short circuit. The newer radios use OPA2674 that has internal short circuit protection. Anyhow, ask Flex people directly, they know better the difficulties with some of the first production units. 73, Ahti OH2RZ On 09/12/2008, Pete Ferrand [EMAIL PROTECTED] wrote: Some months ago I blew the final opamp in my 1W SDR-1000 whilst matching it to a linear. Wasn't happy about that but since I accidentally hooked up the attenuator resistors wrong I wasn't too surprised since the rig saw a very high impedance. Worked fine ever since. Unfortunately I'm less happy about blowing the amp this morning, about a half year after that first incident, whilst trying it on six meters for the first time. Without the linear which doesn't cover six. Just wanted to see if I could work a couple locals. As far as the MFJ-269 showed there was a perfect match into the ATU but when I increased the power beyond about a tenth of a watt output the opamp popped again. Besides the time and money aspect, the circuit board clearly can't take a lot of parts replacements. Has anyone figured out how better to protect this part? Or some better solution. This is a four stack including the rfe board, older version with nylon spacers. Thanks. -Pete WB2QLL Somers, WI ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives:
Re: [Flexradio] blown SDR-1000 final opamp
Hi Ahti, thanks for the information. I will have a look on my pcb-layout with respect to these guidelines. 73, Gerd DJ8AY -Original Message- From: Ahti Aintila [mailto:[EMAIL PROTECTED] Sent: Wednesday, December 10, 2008 12:38 PM To: [EMAIL PROTECTED] Cc: Pete Ferrand; flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Gerd, I completely agree with you. Nevertheless, the following excerpt from the data sheet may help understanding the instability problems: DRIVING CAPACITIVE LOADS One of the most demanding and yet very common load conditions for an op amp is capacitive loading. Often, the capacitive load is the input of an analog-to-digital (A/D) converterçincluding additional external capacitance that may be recommended to improve the A/D converter linearity. A high-speed, high open-loop gain amplifier like the OPA2674 can be very susceptible to decreased stability and closed-loop response peaking when a capacitive load is placed directly on the output pin. When the amplifier open-loop output resistance is considered, this capacitive load introduces an additional pole in the signal path that can decrease the phase margin. Several external solutions to this problem have been suggested. When the primary considerations are frequency response flatness, pulse response fidelity, and/or distortion, the simplest and most effective solution is to isolate the capacitive load from the feedback loop by inserting a series isolation resistor between the amplifier output and the capacitive load. This does not eliminate the pole from the loop response, but rather shifts it and adds a zero at a higher frequency. The additional zero acts to cancel the phase lag from the capacitive load pole, thus increasing the phase margin and improving stability. The Typical Characteristics show the Recommended RS vs Capacitive Load and the resulting frequency response at the load. Parasitic capacitive loads greater than 2pF can begin to degrade the performance of the OPA2674. Long PC board traces, unmatched cables, and connections to multiple devices can easily cause this value to be exceeded. Always consider this effect carefully, and add the recommended series resistor as close as possible to the OPA2674 output pin (see the Board Layout Guidelines section). BOARD LAYOUT GUIDELINES Achieving optimum performance with a high-frequency amplifier like the OPA2674 requires careful attention to board layout parasitic and external component types. Recommendations that optimize performance include: a) Minimize parasitic capacitance to any AC ground for all of the signal I/O pins. Parasitic capacitance on the output and inverting input pins can cause instability; on the noninverting input, it can react with the source impedance to cause unintentional band limiting. To reduce unwanted capacitance, a window around the signal I/O pins should be opened in all of the ground and power planes around those pins. Otherwise, ground and power planes should be unbroken elsewhere on the board. 73, Ahti OH2RZ On 10/12/2008, Gerd Loch [EMAIL PROTECTED] wrote: I have accidentially made all sorts of mismatching the output from my OPA2674 and never have blown it. Running audio with Ozy/Janus and more than 1W rf-output. Maybe the reason is that you have overdriven the audio input. Gerd, DJ8AY -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Pete Ferrand Sent: Wednesday, December 10, 2008 4:16 AM To: Ahti Aintila Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Ahti: Thank you for taking the time to reply. My radio has the OPA2674 and that is what it had originally. The issue is not one of a short circuit, but most probably one of dealing with a high impedance load which would send the voltage up beyond what the part can handle. At least that's what I'm guessing; I'm not sure of the correct troubleshooting procedure for this kind of fault. My hope was that someone has figured out how to make the circuit more robust but since yours was the only reply and there's no mention of it in the archives I suppose that hasn't happened. 73, -Pete WB2QLL Somers, WI -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 4:54 AM To: Pete Ferrand [EMAIL PROTECTED] Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Pete, The very old SDR-1000 units have OPA2677 as the final amplifier and cannot stand short circuit. The newer radios use OPA2674 that has internal short circuit protection. Anyhow, ask Flex people directly, they know better the difficulties with some of the first production units. 73, Ahti OH2RZ On 09/12/2008, Pete Ferrand [EMAIL PROTECTED] wrote: Some months ago I blew the final opamp in my 1W SDR-1000 whilst matching it to a linear. Wasn't happy about that but since I accidentally hooked up the attenuator resistors wrong I
Re: [Flexradio] blown SDR-1000 final opamp
Gerd, I completely agree with you. Nevertheless, the following excerpt from the data sheet may help understanding the instability problems: DRIVING CAPACITIVE LOADS One of the most demanding and yet very common load conditions for an op amp is capacitive loading. Often, the capacitive load is the input of an analog-to-digital (A/D) converterçincluding additional external capacitance that may be recommended to improve the A/D converter linearity. A high-speed, high open-loop gain amplifier like the OPA2674 can be very susceptible to decreased stability and closed-loop response peaking when a capacitive load is placed directly on the output pin. When the amplifier open-loop output resistance is considered, this capacitive load introduces an additional pole in the signal path that can decrease the phase margin. Several external solutions to this problem have been suggested. When the primary considerations are frequency response flatness, pulse response fidelity, and/or distortion, the simplest and most effective solution is to isolate the capacitive load from the feedback loop by inserting a series isolation resistor between the amplifier output and the capacitive load. This does not eliminate the pole from the loop response, but rather shifts it and adds a zero at a higher frequency. The additional zero acts to cancel the phase lag from the capacitive load pole, thus increasing the phase margin and improving stability. The Typical Characteristics show the Recommended RS vs Capacitive Load and the resulting frequency response at the load. Parasitic capacitive loads greater than 2pF can begin to degrade the performance of the OPA2674. Long PC board traces, unmatched cables, and connections to multiple devices can easily cause this value to be exceeded. Always consider this effect carefully, and add the recommended series resistor as close as possible to the OPA2674 output pin (see the Board Layout Guidelines section). BOARD LAYOUT GUIDELINES Achieving optimum performance with a high-frequency amplifier like the OPA2674 requires careful attention to board layout parasitic and external component types. Recommendations that optimize performance include: a) Minimize parasitic capacitance to any AC ground for all of the signal I/O pins. Parasitic capacitance on the output and inverting input pins can cause instability; on the noninverting input, it can react with the source impedance to cause unintentional band limiting. To reduce unwanted capacitance, a window around the signal I/O pins should be opened in all of the ground and power planes around those pins. Otherwise, ground and power planes should be unbroken elsewhere on the board. 73, Ahti OH2RZ On 10/12/2008, Gerd Loch [EMAIL PROTECTED] wrote: I have accidentially made all sorts of mismatching the output from my OPA2674 and never have blown it. Running audio with Ozy/Janus and more than 1W rf-output. Maybe the reason is that you have overdriven the audio input. Gerd, DJ8AY -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Pete Ferrand Sent: Wednesday, December 10, 2008 4:16 AM To: Ahti Aintila Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Ahti: Thank you for taking the time to reply. My radio has the OPA2674 and that is what it had originally. The issue is not one of a short circuit, but most probably one of dealing with a high impedance load which would send the voltage up beyond what the part can handle. At least that's what I'm guessing; I'm not sure of the correct troubleshooting procedure for this kind of fault. My hope was that someone has figured out how to make the circuit more robust but since yours was the only reply and there's no mention of it in the archives I suppose that hasn't happened. 73, -Pete WB2QLL Somers, WI -Original Message- From: Ahti Aintila [EMAIL PROTECTED] Sent: Dec 9, 2008 4:54 AM To: Pete Ferrand [EMAIL PROTECTED] Cc: flexradio@flex-radio.biz Subject: Re: [Flexradio] blown SDR-1000 final opamp Pete, The very old SDR-1000 units have OPA2677 as the final amplifier and cannot stand short circuit. The newer radios use OPA2674 that has internal short circuit protection. Anyhow, ask Flex people directly, they know better the difficulties with some of the first production units. 73, Ahti OH2RZ On 09/12/2008, Pete Ferrand [EMAIL PROTECTED] wrote: Some months ago I blew the final opamp in my 1W SDR-1000 whilst matching it to a linear. Wasn't happy about that but since I accidentally hooked up the attenuator resistors wrong I wasn't too surprised since the rig saw a very high impedance. Worked fine ever since. Unfortunately I'm less happy about blowing the amp this morning, about a half year after that first incident, whilst trying it on six meters for the first time. Without the linear which doesn't cover six. Just wanted to see if I could work a couple locals. As far as the MFJ-269
[Flexradio] Sensitivity
Hello fellow Flexers. This was posted on the IC7700 Yahoo group the other day. Some comments would be interesting. Thank you. 73... Jon W1MNK Wow, that surprises me.. I thought the IC-7700 would have better noise floor figures when signal sensitivy is equal with the Pro 3. When you're into the -140 dBm MDS range, I would expect some sampling variance from rig-to-rig. The ARRL lab engineers are testing one unit, not a large sample. So, on any given day, they may end up with a unit that measures slightly better or worse than another production unit. Now compare MDS in the QST Product Reviews at 14 50 MHz across a range of transceivers from competing manufacturers. Generally, the Icom rigs are far and away more sensitive than their competition. For example, look at the MDS for the new SDR product like the Flex-5000A. ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
Re: [Flexradio] Sensitivity
Sensitivity is nice, but you hit a limit of *usable* sensitivity in the HF bands due to atmospheric noise. At least that's _my_ take on it Jim KQ6EA --- On Wed, 12/10/08, Jon Maguire [EMAIL PROTECTED] wrote: From: Jon Maguire [EMAIL PROTECTED] Subject: [Flexradio] Sensitivity To: FlexRadio Reflector FlexRadio@flex-radio.biz Date: Wednesday, December 10, 2008, 9:20 AM Hello fellow Flexers. This was posted on the IC7700 Yahoo group the other day. Some comments would be interesting. Thank you. 73... Jon W1MNK Wow, that surprises me.. I thought the IC-7700 would have better noise floor figures when signal sensitivy is equal with the Pro 3. When you're into the -140 dBm MDS range, I would expect some sampling variance from rig-to-rig. The ARRL lab engineers are testing one unit, not a large sample. So, on any given day, they may end up with a unit that measures slightly better or worse than another production unit. Now compare MDS in the QST Product Reviews at 14 50 MHz across a range of transceivers from competing manufacturers. Generally, the Icom rigs are far and away more sensitive than their competition. For example, look at the MDS for the new SDR product like the Flex-5000A. ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
Re: [Flexradio] Sensitivity
When I make measurements on my homebrew receivers in the -136 dBm range (using an HP8640B), I definitely notice a time of day sensitivity variation. I have chalk this up to external atmospheric noise (20m/30m) bleeding through the coax. I understand coax shielding is only good for ~30 db of attenuation. I just say this to affirm that making sensitivity measurements on very sensitive receivers with out a shielded cage can be a bit difficult. - Dan, N7VE -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lux, James P Sent: Wednesday, December 10, 2008 11:26 AM To: Jon Maguire; FlexRadio Reflector Subject: Re: [Flexradio] Sensitivity Sensitivity measurements are a canard, anyway, at least for HF. Atmospheric noise is going to dominate receiver noise for the most part. What you REALLY want to know is the instantaneous dynamic range (how big a signal next to my signal can I tolerate). Not only that, but making quality measurements at -140dBm or -150dBm is non-trivial. (we do this at work for space radios) How do you know that you're not getting wideband hash from the computer in the next room leaking into your test set? What's the precision of your attenuator that's giving you your test signal? You might have a precision 0dBm source, and the signal generator has 10dB steps, but I'll bet that the 140dB step has a pretty big uncertainty. (just from packaging issues) (Agilent E8663B which goes down to -135dBm, only has level accuracies to -80dBm, where it's +/-0.8dB) (Agilent E4418B power meter with the 8481D head (which goes down to -70dBm) is good to 1-2%) -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jon Maguire Sent: Wednesday, December 10, 2008 9:21 AM To: FlexRadio Reflector Subject: [Flexradio] Sensitivity Hello fellow Flexers. This was posted on the IC7700 Yahoo group the other day. Some comments would be interesting. Thank you. 73... Jon W1MNK Wow, that surprises me.. I thought the IC-7700 would have better noise floor figures when signal sensitivy is equal with the Pro 3. When you're into the -140 dBm MDS range, I would expect some sampling variance from rig-to-rig. The ARRL lab engineers are testing one unit, not a large sample. So, on any given day, they may end up with a unit that measures slightly better or worse than another production unit. Now compare MDS in the QST Product Reviews at 14 50 MHz across a range of transceivers from competing manufacturers. Generally, the Icom rigs are far and away more sensitive than their competition. For example, look at the MDS for the new SDR product like the Flex-5000A. ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
Re: [Flexradio] Sensitivity
How long is the cable between the 8640 and the radio? Do you have a cap on the counter output on the back of the 8640? I often see a 1 dB variation between measurements made with a 30 minute warm-up and an 8 hour warm-up. The change can go either way. I usually double check the noise floor against two 8662As and one 8642A. One certainly is into measurement uncertainty at -135 dBm and below. Does it really matter? As others have said, external noise predominates on 20 and below, and likely even on 15 meters. On 6 meters the preamp is inadequate on the K3 and the Omni-VII, and I assume the Flex. I don't believe preamp 2 on my Pro III has rendered any signals on 6 meters better than preamp 1. I see a 10 dB increase in broadband noise when pointing the 6 meter yagi towards a 278 tower wind farm 20 miles away. Elecraft has a nice 6 meter preamp, but I have not seen it. Lets hope we get some sun spots one of these days so we can start worrying about very weak signals on 10 or 12 meters. Before that I need to get a 10 meter yagi in the air! 73, Rob NC0B Tayloe Dan-P26412 [EMAIL PROTECTED] 12/10/2008 3:26 PM When I make measurements on my homebrew receivers in the -136 dBm range (using an HP8640B), I definitely notice a time of day sensitivity variation. I have chalk this up to external atmospheric noise (20m/30m) bleeding through the coax. I understand coax shielding is only good for ~30 db of attenuation. I just say this to affirm that making sensitivity measurements on very sensitive receivers with out a shielded cage can be a bit difficult. - Dan, N7VE -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Lux, James P Sent: Wednesday, December 10, 2008 11:26 AM To: Jon Maguire; FlexRadio Reflector Subject: Re: [Flexradio] Sensitivity Sensitivity measurements are a canard, anyway, at least for HF. Atmospheric noise is going to dominate receiver noise for the most part. What you REALLY want to know is the instantaneous dynamic range (how big a signal next to my signal can I tolerate). Not only that, but making quality measurements at -140dBm or -150dBm is non-trivial. (we do this at work for space radios) How do you know that you're not getting wideband hash from the computer in the next room leaking into your test set? What's the precision of your attenuator that's giving you your test signal? You might have a precision 0dBm source, and the signal generator has 10dB steps, but I'll bet that the 140dB step has a pretty big uncertainty. (just from packaging issues) (Agilent E8663B which goes down to -135dBm, only has level accuracies to -80dBm, where it's +/-0.8dB) (Agilent E4418B power meter with the 8481D head (which goes down to -70dBm) is good to 1-2%) -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Jon Maguire Sent: Wednesday, December 10, 2008 9:21 AM To: FlexRadio Reflector Subject: [Flexradio] Sensitivity Hello fellow Flexers. This was posted on the IC7700 Yahoo group the other day. Some comments would be interesting. Thank you. 73... Jon W1MNK Wow, that surprises me.. I thought the IC-7700 would have better noise floor figures when signal sensitivy is equal with the Pro 3. When you're into the -140 dBm MDS range, I would expect some sampling variance from rig-to-rig. The ARRL lab engineers are testing one unit, not a large sample. So, on any given day, they may end up with a unit that measures slightly better or worse than another production unit. Now compare MDS in the QST Product Reviews at 14 50 MHz across a range of transceivers from competing manufacturers. Generally, the Icom rigs are far and away more sensitive than their competition. For example, look at the MDS for the new SDR product like the Flex-5000A. ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ -- If this email is spam, report it here: http://www.onlymyemail.com/view/?action=reportSpamId=ODExMjI6ODEwMTk2ODY0OnJvYkBuYzBiLmNvbQ%3D%3D
Re: [Flexradio] Sensitivity
-Original Message- From: Tayloe Dan-P26412 [mailto:[EMAIL PROTECTED] Sent: Wednesday, December 10, 2008 2:26 PM To: Lux, James P; Jon Maguire; FlexRadio Reflector Subject: RE: [Flexradio] Sensitivity When I make measurements on my homebrew receivers in the -136 dBm range (using an HP8640B), I definitely notice a time of day sensitivity variation. I have chalk this up to external atmospheric noise (20m/30m) bleeding through the coax. I understand coax shielding is only good for ~30 db of attenuation. I just say this to affirm that making sensitivity measurements on very sensitive receivers with out a shielded cage can be a bit difficult. - Dan, N7VE Double shielded coax helps, as does careful attention to connectors, etc. A bigger problem is leakage from inside the generator to inside the radio, particularly for most consumer equipment (e.g. your run of the mill ham rig). I'd be surprised if the outside the case to inside the case isolation on, say, my IC7000, is better than 50-60dB. It's good enough that it meets radiated spurious emissions (so the LO leakage isn't TOO big..) We won't even talk about the shielding on my SDR1000 3 board stack at home... (there is none).. It radiates the DDS quite nicely. Actually, when doing some research here at work with an array of SDR1Ks, I used the leakage back out the antenna port in Rx mode and received by another SDR1K to measure relative frequency offsets. I don't recall if the ARRL lab or Rob Sherwood measured conducted or radiated emissions on the SDR1K (in a box) or the F5K. For example, the Agilent E8663B is only specified to meet IEC 61326/CISPR 11, Group 1, Class A. (oddly, that spec only covers above 30MHz.. But no matter, it's 40dB(uV/m) for 30 to 230 MHz. Compare that to a receiver sensitivity of a few microvolts, and your leaky coax doesn't have to be very long to pick that up.) James Lux, P.E. Task Manager, SOMD Software Defined Radios Flight Communications Systems Section Jet Propulsion Laboratory 4800 Oak Grove Drive, Mail Stop 161-213 Pasadena, CA, 91109 +1(818)354-2075 phone +1(818)393-6875 fax ___ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
