|
Changing out L5 & L7 in UBitX for Spur Fix
Guy WB7SZI
just desoldered L5&7 to get ready for the placement of the SMD inductors.?
From the image I can see where to solder the inductors to where the toroids were but can¡¯t see where to solder the other ends. It looks like the traces below L5 & L7 were exposed to solder the other side. Is this right? thanks Guy WB7SZI? |
|
Re: Tracing receive signal for low signal
Jim, all you mention is good for this problem and then
toggle quoted message
Show quoted text
I thought of something else: What if it's not just one thing on that list but a couple of them at the same time? In this case, it's not so much looking for a problem, it's making sure all is well at all those points before proceeding to the next one. Gray line here but it is sometimes better to verify circuits are working properly instead of concentrating on what may be wrong. At least this will provide some encouragement as you go along the circuit path. And, also, when you find one problem, it may "fix" the problem to some degree while another problem is waiting to be found. Bob ¡ª KK5R -------------------------------------------- On Sun, 12/23/18, jim via Groups.Io <ab7vf@...> wrote:
Subject: Re: [BITX20] Tracing receive signal for low signal To: [email protected] Date: Sunday, December 23, 2018, 1:39 PM Well ..so far, at least you have something on al the test points ...useful for reference if for nothing else ... the situation at TP 17 indicates to me bad/misaligned 12 mhz filter? or defective 12 mhz mixer? or messed up clk0? or defect in Q70 stage or open contacts M1/M2 or Q74 shorted/turned on (conducting)?? or ....?? One step at a time progressing at this point from front to back .. I prefer going back to front but we are where we are Jim On Sunday, December 23, 2018, 8:21:06 AM PST, Dave Space <davesspacebar@...> wrote: Thanks I'll try those new measurements tonight.? Do the measurements so far say anything?? Seems like it's taking a lot more to get .1 vp-p output than jim's board from all test points.? The weird thing though is it mostly gets worse (requires more power to get .1v p-p audio) further along the receive path.? For those other questions: Yes everything on the radio seems to work, display, etc.? Tapping on components doesn't seem to change anything connections at least seem stable.? before changing the BFO I could hear only the strongest of signals but they were so faint and almost completely unintelligible.? Changing the BFO I can now pick up only really strong signals faintly and they are a bit more intelligible.? It's clear from the signal tracing it is taking a lot more power to get my audio to .1v p-p so clearly something interesting is going on here.? The real interesting part is the farther away from the antenna on the board the more power it takes to produce a .1v p-p audio output for the most part. I have a tiny bit of experience using my signal generator / scope on a working fm/am radio kit I built recently? (An nice little kit building the radio in sequence and testing each stage, teaches quite a bit) |
|
Re: Tracing receive signal for low signal
RE:
toggle quoted message
Show quoted text
"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" Sounds like it's time for a good magnifying glass to examine the joints. Some poorly soldered or defective joints are hard to see and the person who did the job may not have caught the problem. I did this on IBM 224 recorder boards for several months and it takes too much time looking for a bad joint so some slip through the inspection process. Bob ¡ª KK5R -------------------------------------------- On Sat, 12/22/18, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Subject: Re: [BITX20] Tracing receive signal for low signal To: [email protected] Date: Saturday, December 22, 2018, 7:57 PM 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: 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 |
|
Re: Quick question
The ones for telephones are condenser type. The last one for PC I had was also condenser mic.
toggle quoted message
Show quoted text
Raj At 24/12/2018, you wrote:
You all have seen those computer headsets like the VTIN with boom microphone. Does anyone know what kind of microphone those use.Eg. condenser , dynamic etc. If I open my junk drawer I may use it on the Ubitx. |
Bob Lunsford
Raj vu2zap
_Dave_ AD0B
Michael Shreeve
