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Allison wrote:

"For ubitx (V3 or 4) a pair of back to back 1n194/4148 diodes from K3 Pin14 to ground
is the best bet as then its only there for RX and has no impact on TX."?

If there is a possibility that these diodes could cause spurs during TX (which I doubt), then it seems the safer approach is to connect the back-to-'back diodes from K1 pin 12 to ground.? K1 pin 12 is grounded and isolated from the RX/TX circuitry connected to K1 pin 14? during TX, which guarantees that the diodes can't cause spurs during TX.? Placing the the diodes from K1 pin 12 to ground should still provide the same protection for Q90 during receive as connecting them from K1 pin 14 to ground.?

73,

Carl,? K0MWC

Guess I should have watched your video first as you said everything I just said:-(

Joel
N6ALT

I built and installed the Kees AGC kit yesterday but dang thing would not work.? Waited until today to check it out.? A close look at the board showed that every component was soldered properly with no solder bridges or other issues.? But then, I noticed that pins 1 and 2 at the top of the board hat a "J" printed above them with a jumper symbol.? ?That's when I re-read the instructions from Don that stated "if you are not installing an RF gain control you must jumper pins 1 and 2".

Well, DUH!? I chose to not install an RF gain control.? Once a jumper was soldered all is good

Posting in case anyone else has a tendency to not read instructions slowly enough......

73, Bill NZ0T

Thanks peter,

Leon at ozqrp puts these into all his rigs. I find them to be useful tools to show power output and sufficient SSB modulation.

Joel
N6ALT

William, you could consider the road that SM0JZT has taken. He installed a G4HUP buffer amplifier and uses an RTL-SDR dongle externally. This gives you the best of worlds - a low-cost transmitter and an equally low-cost SDR receiver. I have also bought the buffer amplifier, but will wait with installing it until the winter.

Just to throw in another way of specifying microphoen sensitivities . 1V/Pascal is equal to 94 dB SPL.? So you may see either terms when looking at mic specs.

Greg
K1YW

On Wed, Jul 18, 2018 at 07:52 AM, Richard E Neese wrote:

I have a ubitx v4 it was workign fine on my 12v 3 amp power brick all fo a sudden whip transmitting the unit shut off and cam back on.

Mine did that, too, because the current draw was too much for the PS, and the PS turned itself off and back and on.? That can happen (at least in my case) on lower bands with a bad antenna mismatch.

I did not have further issues like you describe.

Sadly based on the data sheet I got some MPSH10s and as reported they didn't perform as expected.

The devices I found worked better for me are:
2n2222A(to18), I tried PN2222 and they?produced less power (better than 3904).
2n2219A,? the same as 2n2222A (they are the same die in different package)
2n3866
2n5109

I also tried a pair of irf510 as drivers with suitable mods for bias and they worked
fairly well. The transformers for predriver and driver were less than optimum using
those.? ?I also tried the 2n6661As and they were about the same as IRF510 and?
for those that might consider it 30* the cost of IRF510, and 9* the cost of 2n2222A.

Others that might work if you have or can find them are:
MRF495, 2sC799, 2sc1306, 2sc1307, 2sc2166

Most of the effort to get not more power as you will get that but more even power
ended up with changing the transformers for better impedance matching at higher
frequencies.? My goal was 10W plus or minus a few and decent power at 10M.
If your pushing for more power in the 80-17M range the 2n2222A is a winner?
in the driver and pre driver along with bias changes already discussed.

Allison

You might want to check the power supply too. If something in it died, you might be getting ac on the power lead which could cause this symptom.

Mucking with RV1 could easily and quickly blow the IRF510.
Whenever adjusting RV1 (the IRF510 gate bias voltage), you should be monitoring?
the drain current into the IRF510 (12v into PA-PWR1) with an ammeter.
RV1 should be set for 100ma and no more (with no audio into the mike), it's very touchy.
At that point (100ma) the IRF510 is just starting to conduct, a little bit more and it will be several amps.
I'm a bit surprised it stopped at 1.6A, perhaps you have a weak power supply, could have been 10A.
Assuming 1.5A going up as heat in the IRF510, that's 12*1.5 = 18 Watts into a very inadequate heatsink.
Will be smoking hot.

This RV1 on the Bitx40 corresponds to RV2 and RV3 on the uBitx (there's two IRF510's on the uBitx).
Same rules apply, don't mindlessly twiddle those pots or you will blow the final.
Should be 100ma into each IRF510.

Twiddling R136 on the Bitx40 and RV1 on the uBitx adjusts the drive level into the transmit pre-amps.
Somewhat less dangerous, as it probably won't cause the IRF510's to blow across the room.
But turning up the gain too high there will cause distortion in your transmitted output
and you will be splattering across the band.
On commercial rigs, this is much like turning the mike gain up too high.

When going for more power by adjusting those pots or increasing the voltage into the IRF510 drain
or when going to long duty cycle transmissions (perhaps digital modes), a good idea to check if
the IRF510 heatsink is getting hot.? If it's too hot to hold your finger on it, that's too hot.

Jerry, KE7ER

Yes, low output when speaking or whistling into mic.

Power wiring correct AFAIK.

RV 1 set at about 30% on arrival.? Adjusting to full CCW raises draw to about 1.6 A on PTT, with no change when using mic.? Reset back to about 30%.? Also, adjusting R136 has no effect.

Hi, I am not Mr Farhan, am just a user and an advanced qrm maker. As for ' Problems: great carrier in SSB mode TX, more then modulation speech signal!' I believe you should move up or down the BFO as it seems to be within the bandwidth of the filter. Most probably your modulation would sound extremely muffled.

You might try Allard's mod to transmit CW, drive the top of C107 from 5v through a 4.7k resistor:
? ??


If that gives power to your dummy load, then the problem is back in the mike amp or mike.

Is the low output with you talking into the mic? The carrier is suppressed in SSB as you know and almost no output is expected without modulation.

I had a mic go bad on mine after a month.? ?Found a replacement in an old portable phone.

R136 with Bitx40!

1: Power connector all wires connected properly ?

2: RV1 at center ?

At 18-07-18, you wrote:

1: Power connector all wires connected properly ?

2: RV1 at center ?

Thank you for quick reply.

Re-checked soldered correctly, and confirmed continuity to board connector.

Al, check the electret condenser mic element soldering. Polarity is important.

Raj

Just finished wiring my bitx40.?

Draws ~350ma with PTT, but no change at all when yelling or whistling into mic.? (Dummy load present at all times, so don't suspect final blown.)

I see lots of discussion around this issue, but would appreciate advice on how to troubleshoot.

72/3, Al - va3iaw

That strap could cut Q90-base out of the circuit too, in case that causes RX spurs.
Probably OK to leave the back-to-back diodes in there near Q90-base (to the left of C80)
during transmit, as I doubt we have much more than 0.1vrms there.

Unfortunately, I've got a very long list of stuff to do while the weather is good.
Fiddling with the uBitx isn't on it.

Jerry, KE7ER