[minima] Re: Minima V1.0, what AF levels at diode mixer needed?
- From: "Jochen Wander" <jochen.wander@xxxxxxxxxxx>
- To: <minima@xxxxxxxxxxxxx>
- Date: Sun, 4 Jan 2015 17:24:44 +0100
I checked that one (desired) side frequency coming from mixer, generated by
AF injection, is sure in filter passband.
BFO frequencies are adjusted +/- 1.3 kHz away from filter center frequency.
TX chain diode mixer/amplifier/KISS mixer/LPF looks ok (Bidir amp gain
~16dB).
Can someone please help me with some own measurement results, what AF level
at diode mixer input leads to the mentioned RF -16dBm ( ~100mVpp) at LPF
output,
and what should be the proper gain of MIC amplifier? I measured ~2 (6dB), it
seems to be pretty low.
73, de Jochen, Dl1JWA
Von: minima-bounce@xxxxxxxxxxxxx [mailto:minima-bounce@xxxxxxxxxxxxx] Im
Auftrag von allison
Gesendet: Freitag, 2. Januar 2015 20:55
An: minima@xxxxxxxxxxxxx
Betreff: [minima] Re: Minima V1.0, what AF levels at diode mixer needed?
On 01/02/2015 04:38 AM, Jochen Wander wrote:
Hi guys,
meanwhile I had some good progress with my minima V1.0.
I got the digital board running, and I built up also main board (with PP2KR
V1.1 PCBs, pls. see attachment).
My goal is to get an real travel companion, as mentioned in Farhan's basic
document.
Crystals, JFETs and mixer diodes are selected carefully.
I implemented also the mods coming from HF signals web page.
Receiver is working properly. I only found that 15m is also attenuated by
20M notch.
All stages are working also during transmit, but I need help again.
I'm not able to establish suitable transmit signal in CW mode.
When I'm injecting 800Hz 0.25Vpp at mic jack, push PTT, I get AF level
0.2Vpp at diode mixer (D4, D6) input (0.1uF cap).
The RF output signal (LPF output jack, tested at 7 MHz) is 0.1Vpp at 50
ohms.
I have 1.6Vpp 20M BFO output at T3 input to diode mixer.
The gain of mic amplifier Q19 is <2, is that correct (I measured Ic=8mA)??
What microphone input level is expected here?
In CW mode, I have big AF swing (6,4Vpp) at collector of side tone generator
Q20, but the AF signal coupled out via the 10 ohm resistor in emitter
circuit is only around 10mVpp.
With that arrangement I cannot detect any RF output in signal chain from
diode mixer to LPF output jack.
Has someone tried out CW mode successfully? What are the AF levels we must
inject into diode mixer, why we couple out such a weak AF signal?
I guess I should increase the 10 ohm resistor to get some output?
Thanks in advance, for any help.
Happy 2015 and 73 de Jochen, DL1JWA
It is possible you have enough signal but the frequency of the carrier
oscillator is far enough down the slope of
the crystal filter that very little is making it though.
Allison/KB1GMX
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