Re: [time-nuts] DDS on AD9852
I'm new to this list, so please forgive me if I am missing some older information not in your post. I also believe you are overdriving the amplifier, but the oscilloscope display scaling is confusing us. Several things stand out at me from your message: * The AD9858 has a current-mode D/A output. So I assume you must have some transformer or amplifier on a development board between the AD9858 output pin and the signal you show in the 2.jpg image. * The Rigol oscilloscope image 2.jpg shows a 6.6 Vp-p signal (6.6 divisions p-p at 1 V/div). * The other signal 1.jpg or the apparently identical signal 3.jpg show a 33 Vp-p signal (6.6 divisions p-p at 5 V/div). This is far too high a voltage to be realistically present at the output of that little Ten-Tec amplifier. * My guess is that you somehow have the scope fooled into thinking it has a X10 probe attached, but have a X1 connection. So I'm guessing that 2.jpg is actually showing 660 mVp-p, and 1.jpg is actually showing 3.3 Vp-p. * I can't find any detailed specs for the Ten-Tec model 1001 amplifier (such as the schematic or which amplifier MMIC or transistor it uses), but it appears to be rated for about 18 dB gain. That's a voltage gain of around 8. * With an input of 660 mVp-p, the Ten-Tec amplifier output swing would be (0.66)(8) = 5.3 Vp-p (if the amplifier could swing that far). But the amplifier is probably strongly overloaded, since it's designed for small signals (such as a receiver preamplifier). * So I think your 1.jpg waveform is showing the output of an *overdriven amplifier*. But without knowing the oscilloscope probing details (was the oscilloscope connected using a matched 50 ohm cable with proper termination at the scope end), oscilloscope vertical scaling, and schematic of the model 1001 amplifier (including it's power supply voltage) it's not possible to be certain. * If you inserted a 6 dB attenuator (voltage ratio of 2X) at the input of the amplifier, I would guess that the amplifier output would appear reasonably close to a sinewave, although the amplifier might still be in compression and generating significant harmonics. The amplifier must be terminated in 50 ohms for it to work properly. -- Bill Byrom N5BB On Sat, Jan 17, 2015, at 01:51 AM, Tom Miller wrote: - Original Message - From: d0ct0r t...@patoka.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, January 17, 2015 12:02 AM Subject: [time-nuts] DDS on AD9852 Hello, I would like to ask some advise about the signal distortion I get from my DDS project. The T-Bolt GPSDO is in use as a REF signal source (10Mhz) for AD9858 DDS. This chip has two COS analog outputs which opposite to each other. I am using 20x reference multiplier in my project. And I am using Low Pass filter and RF amplifier connected to ONE of the COS output. The other output has no filter or op-amp on it. Attached is four files with OSC screen shots, where the signal which goes through the filter and amplifier somehow distorted. In contrary, the signal from another output (without filter and op-amp) has near perfect curve. I am using the same cable for connection to Oscilloscope.. And I set 5 Mhz output on DDS as an example. In this my project I am using Ten-Tec broadband pre-amp. The filter is standard Chebyshev Low Pass filter made by MINI-CIRCUITS. Model PLP-90 (81 Mhz). Here is the link to Ten-Tec http://www.tentec.com/products/Universal-Low%252dNoise-Broadband-DC-to-1-GHz-RF-Preamp-%252d-Model-1001.html Is it normal to have that kind of distortions for the signal, or something wrong with design ? -- WBW, V.P. You are overdriving the amplifier. What is the part number of Q1? It looks like a MAR-xx something. The Tentek page does not have any good technical details on the amp that I could find. What info do you have? Regards _ 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] DDS on AD9852
The DDS puts out perhaps a volt far to large for a preamp device. I suspect like everyone else you are clipping. Just take a 2n3904 use it as a common collector/buffer and bias the emitter for a clean cycle and see what level you get. Regrads Paul WB8TSL On Sat, Jan 17, 2015 at 2:51 AM, Tom Miller tmiller11...@verizon.net wrote: - Original Message - From: d0ct0r t...@patoka.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, January 17, 2015 12:02 AM Subject: [time-nuts] DDS on AD9852 Hello, I would like to ask some advise about the signal distortion I get from my DDS project. The T-Bolt GPSDO is in use as a REF signal source (10Mhz) for AD9858 DDS. This chip has two COS analog outputs which opposite to each other. I am using 20x reference multiplier in my project. And I am using Low Pass filter and RF amplifier connected to ONE of the COS output. The other output has no filter or op-amp on it. Attached is four files with OSC screen shots, where the signal which goes through the filter and amplifier somehow distorted. In contrary, the signal from another output (without filter and op-amp) has near perfect curve. I am using the same cable for connection to Oscilloscope.. And I set 5 Mhz output on DDS as an example. In this my project I am using Ten-Tec broadband pre-amp. The filter is standard Chebyshev Low Pass filter made by MINI-CIRCUITS. Model PLP-90 (81 Mhz). Here is the link to Ten-Tec http://www.tentec.com/products/Universal-Low%252dNoise-Broadband-DC-to-1- GHz-RF-Preamp-%252d-Model-1001.html Is it normal to have that kind of distortions for the signal, or something wrong with design ? -- WBW, V.P. You are overdriving the amplifier. What is the part number of Q1? It looks like a MAR-xx something. The Tentek page does not have any good technical details on the amp that I could find. What info do you have? Regards ___ 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] DDS on AD9852
Hello, That Q1 is MAV1-0104 made by Mini-Circuits. This part is exact replacement for the MSA-0104, which was in TenTec kits early. The schematic of that pre-amp is pretty simple: +12 V | [ ] (470 Ohm) | L1 (100uH) | 50ohm input ---||-- Q1 -||-50 Ohm output 0.01 0.01 You are overdriving the amplifier. What is the part number of Q1? It looks like a MAR-xx something. The Tentek page does not have any good technical details on the amp that I could find. What info do you have? Regards -- WBW, V.P. ___ 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] DDS on AD9852
Hi The amp you are using has about 18.5 db of gain. It’s a typical self biased transistor style amp. From the part number, it’s got a ~ 1.5 dbm output limit at 1 db compression. That gives you a max input level of -17 dbm when the amp is in compression. If you want reasonable noise performance, you would stay 10 db below those numbers. That would put you in the -29 dbm range. -20 dbm is 31 mv peak to peak. That’s way below the levels you have running around on your scope displays. Because these amps are fairly simple in construction, when you drive them with large signals, you upset the bias. That changes the operation point. It can easily lead to all sorts of odd distortion. Before it does that it often leads to increased noise. Typically when you are after a quiet 7 to 10 dbm output (as in low phase noise and low harmonics) you go for at least a 16 dbm (1 db compression) amp and possibly one at 20 dbm. There are exceptions to this, but most of the simple little amps work this way. Bob On Jan 17, 2015, at 12:02 AM, d0ct0r t...@patoka.org wrote: Hello, I would like to ask some advise about the signal distortion I get from my DDS project. The T-Bolt GPSDO is in use as a REF signal source (10Mhz) for AD9858 DDS. This chip has two COS analog outputs which opposite to each other. I am using 20x reference multiplier in my project. And I am using Low Pass filter and RF amplifier connected to ONE of the COS output. The other output has no filter or op-amp on it. Attached is four files with OSC screen shots, where the signal which goes through the filter and amplifier somehow distorted. In contrary, the signal from another output (without filter and op-amp) has near perfect curve. I am using the same cable for connection to Oscilloscope.. And I set 5 Mhz output on DDS as an example. In this my project I am using Ten-Tec broadband pre-amp. The filter is standard Chebyshev Low Pass filter made by MINI-CIRCUITS. Model PLP-90 (81 Mhz). Here is the link to Ten-Tec http://www.tentec.com/products/Universal-Low%252dNoise-Broadband-DC-to-1-GHz-RF-Preamp-%252d-Model-1001.html Is it normal to have that kind of distortions for the signal, or something wrong with design ? -- WBW, V.P.4.jpg1.jpg2.jpg3.jpg___ 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] DDS on AD9852
Hi, I am not clear about the little sawtooth riding on the signal, but it looks like you are running out of headroom on the Ten-Tec preamp. The Ten-Tec preamp would not be my first choice for the job. One of the Minicircuits MMIC's would probably be a better choice depending upon your frequency range requirements. BillWB6BNQ d0ct0r wrote: Hello, I would like to ask some advise about the signal distortion I get from my DDS project. The T-Bolt GPSDO is in use as a REF signal source (10Mhz) for AD9858 DDS. This chip has two COS analog outputs which opposite to each other. I am using 20x reference multiplier in my project. And I am using Low Pass filter and RF amplifier connected to ONE of the COS output. The other output has no filter or op-amp on it. Attached is four files with OSC screen shots, where the signal which goes through the filter and amplifier somehow distorted. In contrary, the signal from another output (without filter and op-amp) has near perfect curve. I am using the same cable for connection to Oscilloscope.. And I set 5 Mhz output on DDS as an example. In this my project I am using Ten-Tec broadband pre-amp. The filter is standard Chebyshev Low Pass filter made by MINI-CIRCUITS. Model PLP-90 (81 Mhz). Here is the link to Ten-Tec http://www.tentec.com/products/Universal-Low%252dNoise-Broadband-DC-to-1-GHz-RF-Preamp-%252d-Model-1001.html Is it normal to have that kind of distortions for the signal, or something wrong with design ? ___ 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] DDS on AD9852
- Original Message - From: d0ct0r t...@patoka.org To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, January 17, 2015 12:02 AM Subject: [time-nuts] DDS on AD9852 Hello, I would like to ask some advise about the signal distortion I get from my DDS project. The T-Bolt GPSDO is in use as a REF signal source (10Mhz) for AD9858 DDS. This chip has two COS analog outputs which opposite to each other. I am using 20x reference multiplier in my project. And I am using Low Pass filter and RF amplifier connected to ONE of the COS output. The other output has no filter or op-amp on it. Attached is four files with OSC screen shots, where the signal which goes through the filter and amplifier somehow distorted. In contrary, the signal from another output (without filter and op-amp) has near perfect curve. I am using the same cable for connection to Oscilloscope.. And I set 5 Mhz output on DDS as an example. In this my project I am using Ten-Tec broadband pre-amp. The filter is standard Chebyshev Low Pass filter made by MINI-CIRCUITS. Model PLP-90 (81 Mhz). Here is the link to Ten-Tec http://www.tentec.com/products/Universal-Low%252dNoise-Broadband-DC-to-1-GHz-RF-Preamp-%252d-Model-1001.html Is it normal to have that kind of distortions for the signal, or something wrong with design ? -- WBW, V.P. You are overdriving the amplifier. What is the part number of Q1? It looks like a MAR-xx something. The Tentek page does not have any good technical details on the amp that I could find. What info do you have? Regards ___ 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.
