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Re: Tracing receive signal for low signal
If your goal is to repair your radio, I would short circuit your signal tracing a moment and try to decide what else might be wrong. Does the display work correctly? Do you hear any signals on your antenna. Does the same antenna pick up signals well with your other radio.
I would look at the connectors. Particularly the 8 pin audio connector. at the front of the board. I have had connection issues with it. Can you flick that harness while listening and introduce microphony. Before I got my last radio working I had to remove the wire from each port on the connector and tighten them up. The V4 board does not have a strong audio. If your goal is to learn how to use your signal tracer it might pay to start on something that is working. 73 Dave k0mbt |
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My first Homebrewed radio: The DC40
Hello everyone, I documented the entire process with as much detail as I could, and I hope you'll check out the series. It took nearly as long to write as it did to build the radio :p? |
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Re: Tracing receive signal for low signal
¿ªÔÆÌåÓýSame stage gains mentioned in dB found here on the homebrew UBITX receiver where I measured each 50 ohm block separately with a 50 ohm termination, except that I¡¯m using a 45 MHz LC filter with 3-4 dB loss. ?But not having built anything until a couple years ago I¡¯m very sympathetic to trying to measure each stage correctly until you get good at using whatever tools you have, and how hard it is to measure the sub¡ª80 dBm levels. ?Having a standard like the old 3 band Elecraft 1 and 50 microvolt standard is a big time saver for deciding whether or ?not the system is good/not good. You¡¯re getting a lot of good advice if you can do those measurements. Good luck. Scott Ka9p Make something good happen! On Dec 22, 2018, at 11:01 PM, jim via Groups.Io <ab7vf@...> wrote:
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Re: Tracing receive signal for low signal
Similar to Jim's measurements These are approximate since I don't have equipment that can measure to microvolts - I estimated based on my max volts into my attenuator and calculating the lower voltages. I was limited couldn't get to .1 vp-p in cases since my signal generator only goes to 3.5v I was putting through a -40 db attenuator Oscilloscope at volume high Signal generator at: at Antenna 2000+ uV to get to .1 v p-p at TP 17 8000 uV only produced 12mv p-p at TP 16 8000 uV only produced 12mv p-p at TP 14 8000 uV only produced 20mv p-p at TP 13 8000uV only produced 15mv p-p So definitely seems like something is weird the best signal happens inputting at the antenna rather than anywhere else. |
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Re: Tracing receive signal for low signal
jim
Frankly, I would not mind seeing other measurements ...at least to form SOME sort of baseline ...As I said ...Quick and dirty
Don't like 'em ..delete 'em ....Measure your own and share There has been a whole LOT of theory/smoke and mirrors/hand-waving and just plain (imho) bs bandied about ....But DO provide some sort of REFERENCE ...Top o' audio pot was easy-peasy and very low bandwidth Jim
On Saturday, December 22, 2018, 6:17:58 PM PST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Assuming your signal generator can correctly inject the levels shown in the chart, you should get rational results here regardless of the different frequencies. Namely,? ? Perhaps 1 or 2 dB loss through the LPF at L1,2,3,4 ? 6dB through the mixers ? Maybe 3 or 4 dB through the two crystal filters ? And around 10 or 12 dB through the 45mhz amp, 16dB through the 12mhz amp. I do like the way you went about the measurements though, looking only at the audio with the scope means just about any scope could be used there. Or perhaps a diode peak detector and a dc voltmeter. The signal generator could be an si5351 driving a step attenuator. Jerry On Sat, Dec 22, 2018 at 05:51 PM, jim wrote: different frequencies .... |
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Re: Tracing receive signal for low signal
? Perhaps 1 or 2 dB loss through the LPF at L1,2,3,4
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? 6dB loss through the mixers ? Maybe 3 or 4 dB loss through the two crystal filters ? And around 10 or 12 dB gain through the 45mhz amp, 16dB through the 12mhz amp. On Sat, Dec 22, 2018 at 06:17 PM, Jerry Gaffke wrote:
? Perhaps 1 or 2 dB loss through the LPF at L1,2,3,4 |
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Re: Tracing receive signal for low signal
Wow thanks everyone for all of the great info and ideas to investigate this further.? Some great details and avenues to investigate further.
I am using the stock software.? (A separate thread I need to search for is how to update and debug it.? When I tried update failed.. I was just trying to add some print statements to trace frequency changes.) I'll try to trace through all of those test points mentioned by Jim and see what I get. I will say my test equipment is a little wonky so I have to compensate which makes things a little trickier.? My signal generator has to be set at 7.147 for the ubitx to receive on 7.150 (I've confirmed it's not the ubitx as my Yaesu sees the same signal and I confirmed it by zero beat of the 1khz signal.) (Its a hantek oscilloscope with generator so not the best but couldn't beat the price to get the signal generator and scope) Evan yep I wondered about USB/LSB also but I did a zero beat of 1khz against my yaesu and seems to match from what I can hear/see)? I could try resetting to defaults if nothing else works. Also very interesting thought from Bill on the toroid windings... going to have to take a look at that. Thanks ! |
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Re: Tracing receive signal for low signal
Assuming your signal generator can correctly inject the levels shown in the chart,
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you should get rational results here regardless of the different frequencies. Namely,? ? Perhaps 1 or 2 dB loss through the LPF at L1,2,3,4 ? 6dB through the mixers ? Maybe 3 or 4 dB through the two crystal filters ? And around 10 or 12 dB through the 45mhz amp, 16dB through the 12mhz amp. I do like the way you went about the measurements though, looking only at the audio with the scope means just about any scope could be used there. Or perhaps a diode peak detector and a dc voltmeter. The signal generator could be an si5351 driving a step attenuator. Jerry On Sat, Dec 22, 2018 at 05:51 PM, jim wrote: different frequencies .... |
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Re: Tracing receive signal for low signal
On second glance, those measurements show a 30 dB loss from TP16 to TP17, not a gain.
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Also a 20 dB gain from TP14 to TP16, going through the 45mhz filter and D3,4 mixer. That one should be on the order of a 10dB loss. The only one that makes sense to me is the 10dB gain from TP13 to TP14 Very weird. Jerry, KE7ER On Sat, Dec 22, 2018 at 04:57 PM, Jerry Gaffke wrote: Though the 10dB of gain between TP13 and TP14 could well be legit, |
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Re: Tracing receive signal for low signal
jim
different frequencies ....
Jim
On Saturday, December 22, 2018, 4:58:05 PM PST, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
I'm not sure what to make of Jim's measurements. YMMV indeed! Two measurements at TP1 with a difference of 30dB? Somewhere between 10 and 20 dB of gain or loss from TP2 to TP1, depending on which TP1 measurement you choose? The nominally 16dB amp between TP16 and TP17 gives 30dB of gain? Though the 10dB of gain between TP13 and TP14 could well be legit, that nominally 16dB amp is having a very hard time doing the right thing at 45mhz given the low Ft of the 2n3904 transistors used. I would expect maybe 1dB of loss going from TP2 to TP1,? certainly not a difference of 10 or 20 dB. And would not expect a 50 ohm signal generator to significantly upset things there. Sounds like the original problem is somewhere around L1,2,3,4 and T2. Could remove L1, L4, C200, C205,? and then short TP2 to TP1. No effect on the receiver performance except that we will also receive a strong image from any FM broadcast station at 2*45mhz+(OperatingFreq). For example, when tuned to 7mhz, CLK2 is at 52mhz so that the incoming 7mhz signal gets mixed down to 52-7=45mhz by the mixer at D1,D2. However, an incoming signal at 52+45=97mhz (normally 97mhz gets knocked out by L1,2,3,4) will also produce a 45mhz result out of the mixer at D1, D2. So choose an operating frequency where such an FM broadcast station is not present. And remember not to transmit without the L1,2,3,4 filter operational.? How Dave sees more response when injecting at TP2 than he does when injecting at TP1 is a mystery.? My guess is there is a cold solder joint or some toroid has a broken wire somewhere between L1,2,3,4 and/or T2. And with cables lying about to inject 7mhz into TP2, some of that 7mhz gets coupled into the stuff around the mixer at T2 somehow. That L1,2,3,4 filter could misbehave a little when the 50 ohm signal source drives TP1, but I would be surprised if this was anywhere near as severe as what Dave reports on a properly working uBitx. Jerry, KE7ER On Sat, Dec 22, 2018 at 04:09 PM, jim wrote:
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Re: Tracing receive signal for low signal
Hi,
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I have not looked at the schematic. This problem reminds me of the failure I found in the front end of a different radio. There was indeed a broken winding on one of the inductors, one of those donut looking toroid thingies. I rewound the inductor and that restored receive operation. The signal just about vanished when the probe was in the circuit with the broken inductor, much like the description of the findings here. When I jiggled that inductor just right the signals came pouring in. Due the nature of the broken wire that was surprisng but the broken ends would make temporary contact. I was able to confirm the open with my ohm meter while the inductor was in-circuit (power off of course). I could *see* the fracture with a magnifying glass. This may be helpful or may send the OP on a wild goose chase. I hope it can help. 73, Bill KU8H On 12/22/18 7:57 PM, Jerry Gaffke via Groups.Io wrote:
---snip---- How Dave sees more response when injecting at TP2 than he does when-- bark less - wag more |
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Re: Tracing receive signal for low signal
I'm not sure what to make of Jim's measurements.
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YMMV indeed! Two measurements at TP1 with a difference of 30dB? Somewhere between 10 and 20 dB of gain or loss from TP2 to TP1, depending on which TP1 measurement you choose? The nominally 16dB amp between TP16 and TP17 gives 30dB of gain? Though the 10dB of gain between TP13 and TP14 could well be legit, that nominally 16dB amp is having a very hard time doing the right thing at 45mhz given the low Ft of the 2n3904 transistors used. I would expect maybe 1dB of loss going from TP2 to TP1,? certainly not a difference of 10 or 20 dB. And would not expect a 50 ohm signal generator to significantly upset things there. Sounds like the original problem is somewhere around L1,2,3,4 and T2. Could remove L1, L4, C200, C205,? and then short TP2 to TP1. No effect on the receiver performance except that we will also receive a strong image from any FM broadcast station at 2*45mhz+(OperatingFreq). For example, when tuned to 7mhz, CLK2 is at 52mhz so that the incoming 7mhz signal gets mixed down to 52-7=45mhz by the mixer at D1,D2. However, an incoming signal at 52+45=97mhz (normally 97mhz gets knocked out by L1,2,3,4) will also produce a 45mhz result out of the mixer at D1, D2. So choose an operating frequency where such an FM broadcast station is not present. And remember not to transmit without the L1,2,3,4 filter operational.? How Dave sees more response when injecting at TP2 than he does when injecting at TP1 is a mystery.? My guess is there is a cold solder joint or some toroid has a broken wire somewhere between L1,2,3,4 and/or T2. And with cables lying about to inject 7mhz into TP2, some of that 7mhz gets coupled into the stuff around the mixer at T2 somehow. That L1,2,3,4 filter could misbehave a little when the 50 ohm signal source drives TP1, but I would be surprised if this was anywhere near as severe as what Dave reports on a properly working uBitx. Jerry, KE7ER On Sat, Dec 22, 2018 at 04:09 PM, jim wrote:
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Re: Tracing receive signal for low signal
jim
So ....What I did on my "seasonal vacation" Quick and dirty trace thru V3 ubitx ...Test points correspond to V4 locations ... Set ubitx freq to 7.152 mhz dial indication ...Maybe off a little as WWV? 10 mhz was silent this AM Scope at VOL-H on all tests, not moved? !0x probe to 2215a Tec ...? 0.1 V P-P for reference ... ? SG at 7.152? Maybe off (just because) -50 dbm into antenna jack gave 0.1 V P-P ? at TP-17 -60 dbm (300 uV) 11.996200 gave 0.1 V P-P at TP-16 -90 dbm (10 uV)?????? ....?????? ....? ?? 0.1 V P-P at TP-14 -70 dbm (100 uV)? 44.98500 mHz gave 0.1 v P-P at TP-13 -60 dbm (300 uV???? .......... ....????? 0.1 v P-P at TP-1?? -80 dbm (30 uV)?? ...........???????????? 0.1 v P-P at TP-1? -50 dbm? (1000 uV)? 7.150 mHz gave 0.1 v P-P at TP-2 -60 dbm (300 uV)? 7.150? mHz? gave 0.1 v P-P . "Test on my bencb ..on my ubitx ..with my SG ....YMMV (your mileage may vary) All measurements made with NO effort to "match" anything with anything else SG output 50 ohm thru 0.1 DC blocking cap...To clipleads ...to whatever Z might be where-ever ...NO modulation ...I get confused easily when looking for AM modulation on SSB stuff A Serendipitous Solstice To ALL Jim
On Saturday, December 22, 2018, 2:56:26 PM PST, Dave Space <davesspacebar@...> wrote:
Actually I redid the BFO adjustment to zerobeat and at 11996.6 sounds better for 1khz, and at least the conversations are intelligible better now.? So that is a bonus. (conversation is still faint) Still a 100uv signal injection should give 2 times s9 power expected but it still sounds very faint. The strength does seem impacted by which end of the spectrum I'm at near 25MHZ seems a bit harder to hear the 100uv tone than compared to 7.150MHZ. |
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Re: Tracing receive signal for low signal
I read (and had the issue myself) where the USB and LSB seem to get reversed.? This was related to the LO being off.? It was solved for me by going back to the default after setting the BFO and then do the zero beat with WWV.? Since you have the signal generator, I would try to zero beat it with the calibration process in the setup menu.? I had the CEC memory manager by that time, so did not need to get it close the first time (good enough to be able to receive WWV) and then calibrate with WWV.
You might want to try calibrating using your signal generator on one of the upper bands to see if that changes the rigs response.? Of course, you want a pure carrier without any modulation to do that. I would also be curious if there is any effect on changing from USB to LSB or vise versa and if the characteristics of lower signal on the higher bands changes to on the lower bands. I believe that there is a "factory reset" function built into the stock code that resets the calibration to the values used in HF Signals.? If my memory is correct, it is engaged by holding in the encoder switch when turning on the power.? Of course, this will erase the BFO setting as well as the LO. BTW, I have been assuming all along that you are running the stock software and display.? Is that correct? Evan AC9TU |
_Dave_ AD0B
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