开云体育

I am guessing here, but it seems like the signal generator is being loaded down by T2.? That might explain why you are getting better results when further up the LPF.? If there is a problem, then I would look at T2.? Inspect it closely for any leads being shorted (i have read that was a problem for another person's board).

Beyond inspection, I would not have another way to test that part.? Maybe someone else has an idea or suggestion on how to test.?

To support the above, when you inject the 12mhz signal at T16/17 are you getting a very load tone out of the audio speaker/headphone?? I am not sure what the .1PP measurement should be, and my board is down for spurs and harmonics correction surgery, so I cannot test it.? Trying to isolate in my mind if the problem is in the RF or AF sections of the receiver.? My current hunch is more on the AF side,? If you have an audio amp that can work at microphone input levels (computer amplified speakers would not have the input sensitivity) then you could try that.? You could build an audio preamp with an op amp ic, assuming you have the parts for that kind of construction.? One based on a 741 op amp has been listed in one of the threads on BITX20.

73
Evan
AC9TU

I redid some tests

7.150MHZ
TP2 - 100uv gave 88mv p-p, 200uv gave 144 p-p - estimated those may be a little high given my frequency generator only put out 2.4v when set at 3.5v and can't measure just calculating uv.

TP1 - 900uv gave .1 p-p

TP13 I tried 3rd harmonic at 17.383 since my generator only goes to 25MHZ I couldn't get a tone. but if putting in estimated 2900uv got .1p-p

From my previous tests:
TP17 at 11.99 or so I could get a tone 480mv gave .1v p-p
TP16 same freq at 50mv got .1v p-p

Q70 pin 1 is 0.65v
pin 2 - 0 volts
pin 3- 1.7 v

Q71
pin 1 - 2.06v
pin 2- 1.38v
pin 3- 4.48

Q72
pin 1- 5.66
pin 2 - 5.07
pin 3 - 11.92

Q73
pin 1 - 4.46
pin 2 - 5.07
pin 3 - 0.00

Measuring in circuit so might be off:
R72 shows on the schematic as 10k I measure 2.2k it's 103 so should be 10k
R73 shows 1.79k supposed to be 2.2k

Rob,
Thank-you for verifying that the connections as shown do work.? Would you know the reason for C211 in the original circuit?? I would have thought that Ashhar Fahran would have only installed one if the other was not needed.

73
Evan
AC9TU

Scrape off the toplayer of the underlaying trace and solder them there.
Works fine.
Rob PA0RBL

On 12/24/2018 12:31, d balfour wrote:

Woody
Did you every science out why the power seems low?

Have you tried an alternate mic?

-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.

I have not yet tried to trace the signal path or a different microphone.?? Output power varies by band.? Strangely, it is lowest on 40M and 80 M, at 3-4 watts.? On 30M the power increases to over 10 watts.? From 30M up, the power decreases slightly (as expected) to about 7 watts? at 10M.

This happens with both SSB and CW.? Power is generally lower with SSB but the trend is the same.? I have my rig set up for digital / PC sound card feed also.? I can over drive with the sound card if I try, so do not think audio level is the issue.

Given the symptoms, I think the loss is likely in the output filters.?? I need to open the box and trouble shoot more!

Woody - KZ4AK

Thanks Evan I was not understanding that but got it now.? Appreciate all the great info and ideas/diagnostics here.

TP17 at 11.99 or so I could get a tone 480mv gave .1v p-p
TP16 same freq at 50mv got .1v p-p

Woody
Did you every science out why the power seems low?

Have you tried an alternate mic?

Too bad Evan. Your loss.

Your question made me go back and look at the picture.? L5 looks correct, as it is in the circuit as was the original (L5 and C215 in series with the filter).? L7 is directly connected to T4, removing C211 from the circuit.? Not sure if that is intentional, so good question!

Hopefully someone can answer your question, I do not know for sure.? Based on the values, I would assume that it is for DC blocking that may not be needed on both sides of the filter.

Evan
AC9TU

I tested with an RF Explorer SA and found that I had the harmonic issue on 40m, even on ssb.? I did not see the issue on 20m or 10m.? I have not had any success with those bands, mostly due to conditions.

I need to replace the relays and verify again before I use 40m.? I do not have an antenna for 80 (MFJ-2010 40, 20, and 10 only).? I could do 20m, however the band has been pretty bad over the past month, so now is the time to replace the relays.

73
Evan
AC9TU

Dave,
By the time the signal from the antenna gets to TP17, it has been converted to the audio on a 12mhz carrier.? Said another way, the signal by now has been converted to 12mhz +- the audio tone, not the base? original received frequency.

Injecting a pure 12mhz signal at TP17 (or TP16) should produce an audio tone that is 12mhz - the BFO frequency at TP20 (input to the audio amp).? From previous posts I believe that you stated the BFO as 11.996 mhz so you should have an audio tone of 4khz at TP20.

Evan
AC9TU

AT 60mV you should a really loud sound from your speaker. Check all the resistors and report on
DC voltages at the audio transistors.

Raj

Injecting 1khz tone 2.4v at pin 3 of q71 (should feed into q72 and q73) produced .1v p-p

Also interesing at the base of Q71 injecting 1khz signal at 60mv gave a .1 mv peak to peak signal but I could not hear any tone on the speaker.? It wasn't until injecting 300mv could I faintly hear the tone and that produced 444mv peak to peak.

I checked the boards solder joints with a magnifying glass but it's really hard to tell.? probably need to find a way to test specific suspect points.

I tried to check the toroids in the load pass filter I think they all look good from what I can tell.

K3 pins 12 and 14 get a tone for continuity.


Tp21 shows 10.85k ohms to ground.

The Koss cs100 has an electret element and works well. I have one that I have used. Someone else on this board put me on to it. They are now about $20, but not long ago were much cheaper.?

Sorry that was for Q70