[minima] Re: Minima V1.0, what AF levels at diode mixer needed?
- From: allison <ajp166@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Sun, 04 Jan 2015 13:43:35 -0500
The typical level for that form of mixer is 5-10 db less than the
oscillator injection. So if the diodes are
driven with about 7dbm the audio drive should be about -3dbm possibly as
high as 2dbm. We are
talking about .22 to .4V p-p.
Generally its good to inject a signal and see what leve the waveform (or
power) tends to flatten out
and distort. Then go a few (3) db) less as a maximum. This would be at
the modulator output. This
gets the best carrier (suppressed) to message level. Care is needed to
insure the level out of
the IF amp does not reach overload and if so reduce IF amp gain as
needed. Again the mixer
after the filter must not see a signal greater than its input capability
it also can be tested for the
maximum undistorted output capability. Again if the input to that mixer
is then too high
the IF gain should be adjusted as needed.
Myself I'd expect more than -16dbm at the mixer output. I feel that is
at least 10db lower than
possible.
Allison/KB1GMX
On 01/04/2015 11:24 AM, Jochen Wander wrote:
>
> 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).
>
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>
> 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
>
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> *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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