29-11-2023, 10:26 PM
Hi there,
I'm building a kit, the 'easy bitx' from inkits. Been a bit of a slog, but almost there!
At one point it requires an RF probe be used to test signal on the pcb. I did find a howto but the ascii schematic is a bit unclear.
A) Am I right in thinking there's a capacitor (C1) at the tip, a diode(D1) to ground, then a 1M resistor (R1), then another capacitor(C2) to ground, with measurement taken across C2?
B) Is measurement just with a standard digital multimeter ok? Or is a moving coil type the only real solution?
C) Is there any advantage to this method over just probing with an oscilloscope or spectrum analyser (I have both)
D) Is impedance of the RF probe a concern at all?
E) Does the voltage output depend on the rf probe construction / component selection?
F) Lastly, does the paragraph
"While doing this test you would see that the meter needle if analogue meter is used and some voltage show’s up to a certain level, this is the carrier from the balance modulator which has to be made zero or null. To null the carrier press PTT with RF probe connected adjust RV2 100 ohms in balance modulator till the meter needle comes down to zero, adjust the 22pf trimmer too. So when you modulate now you want see any movement in meter apart from a ticking of 67 meter, so when you modulate now the meter will move and come back to zero when no modulation is done"
make much sense? (Taken from page 66 of the build instructions). I know where RV2 is on the board; not entirely sure how the balance modulator works but my vague understanding is that it suppresses the carrier so only the LSB/USB are present (Thanks, google). I guess my main question is what the 67 meter is; and is "modulation" in this sense just transmitting?
I'm building this thing because I want to learn, and it's been a success on that front, but now I'm at the pointy end of making it actually work...
Thanks for reading,
Scott
I'm building a kit, the 'easy bitx' from inkits. Been a bit of a slog, but almost there!
At one point it requires an RF probe be used to test signal on the pcb. I did find a howto but the ascii schematic is a bit unclear.
A) Am I right in thinking there's a capacitor (C1) at the tip, a diode(D1) to ground, then a 1M resistor (R1), then another capacitor(C2) to ground, with measurement taken across C2?
B) Is measurement just with a standard digital multimeter ok? Or is a moving coil type the only real solution?
C) Is there any advantage to this method over just probing with an oscilloscope or spectrum analyser (I have both)
D) Is impedance of the RF probe a concern at all?
E) Does the voltage output depend on the rf probe construction / component selection?
F) Lastly, does the paragraph
"While doing this test you would see that the meter needle if analogue meter is used and some voltage show’s up to a certain level, this is the carrier from the balance modulator which has to be made zero or null. To null the carrier press PTT with RF probe connected adjust RV2 100 ohms in balance modulator till the meter needle comes down to zero, adjust the 22pf trimmer too. So when you modulate now you want see any movement in meter apart from a ticking of 67 meter, so when you modulate now the meter will move and come back to zero when no modulation is done"
make much sense? (Taken from page 66 of the build instructions). I know where RV2 is on the board; not entirely sure how the balance modulator works but my vague understanding is that it suppresses the carrier so only the LSB/USB are present (Thanks, google). I guess my main question is what the 67 meter is; and is "modulation" in this sense just transmitting?
I'm building this thing because I want to learn, and it's been a success on that front, but now I'm at the pointy end of making it actually work...
Thanks for reading,
Scott