I thought I was having the same problem, but it turns out I wasn't. I use a Motorola Service Monitor for the dummy load and power meter and thought it was in dBm where it was actually in watts. I thought 14.1 dbm, that sucks. But it was really 14.1 watts.
Anyway, while I was troubleshooting I was able to confirm the same RF levels (plus/minus a bit) except, of course, the output level was a lot more.
Moving to the AF levels, I didn't measure past the mic. At the mic connector I'm getting around 3Vpp or more with the mic that's included in the kit. So you may want to start with the mic circuit. BTW, that 3Vpp was me just saying HELLOOOOOOOOOOOOOOO into the mic as measured on a Tektronix 2430A scope.
Vince.
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On 06/06/2017 06:13 PM, ekelley wrote:
I have the same problem with 2 of my Bitx40's.
Ed W0OIC
On 6/6/2017 5:29 AM, Jirka wrote:
Hello everybody.
My name is Jirka, callsign OK1IEC, and I am new in the group. Recently
I bought BITX40v3 and built it in the Al box. RX is ok, comparable
with my K2 in normal conditions. The problem is with transmitting ¨C I
am not able to reach more than about 1W of output power shouting very
loudly into electret mike. Mike change does not help, pot R136 is in
the full gain position.
I decided to do some measurements: I used Audacity software to
produce 1 kHz audio and connected it to Mic pins of BITX40 via 47uF
capacitor. I need 280mV p-p AF signal to get 6W RF output power on my
dummy load.
AF signal levels: Mic (C121): 280 mV p-p; C122: 410 mV p-p
RF signal levels: C132: 1.3V p-p; C134: 3.45V p-p; C141: 3.25V p-p;
C152: 8.6V p-p; C155: 51V p-p; Antenna: 50V p-p.
It seems the RF chain is ok but AF stage Q12 has suspectly low gain.
Components seem to be ok, Q12 Uc=10V, Ue=2.26V
Any idea or advice appreciated.
73! Jirka
Trafo T4 in BFO mixer ??? BTW I see the difference between schematic
(D15, D16, R106) and real components on the pc board.
--
Michigan VHF Corp.
