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Use scope to check audio input level to D4D?

Adrian B
 

Hi All. I'm curious if there's a point in the D4D circuit that would allow for an easy check of the input audio level using just an oscilloscope. Can one look for clipping (or some other symptom) that indicates an overload of the D4D's audio input circuitry? I realize that it's possible to look at the RF output for signs of trouble but I'm wondering if it's possible to do so further upstream in the circuit.

Jim WB2LHP in MI <jmarco1955@...>
 

I've been working on this issue also Adrian...Right now I'm testing two solutions...The first is to incorporate the KD1JV resistive divider mod...I use a 33K/1K combo to get the level I want...The other is simpler...Replace C6 with a 0.1uf cap and C5 with a 10uf electrolytic...This capacitive divider ratio should accomplish the same thing and keep the mixer from saturating...Expect your power output to be significantly lower but with much greater spectral purity...Without the mods, the signal is about 75KHz wide!...I'll report on my testing later after I have access to the spectrum analyzer and wattmeter again...Jim  WB2LHP

On Sat, Nov 2, 2019 at 5:53 PM Adrian Boyko <adrianboyko@...> wrote:
Hi All. I'm curious if there's a point in the D4D circuit that would allow for an easy check of the input audio level using just an oscilloscope. Can one look for clipping (or some other symptom) that indicates an overload of the D4D's audio input circuitry? I realize that it's possible to look at the RF output for signs of trouble but I'm wondering if it's possible to do so further upstream in the circuit.

Adam Rong
 

If you don’t have RF test equipment like spectrum analyzer, you can use WSJTx spectrum to make rough judgements. Transmit with D4D and receive with other rig and observe the received spectrum. The overtones in audio range will reflect the distortion.

You will have to find a balance. The recommended modifications will give you good balance.

Thanks,
Adam

在 2019年11月3日,上午6:12,Jim WB2LHP in MI <jmarco1955@...> 写道:


I've been working on this issue also Adrian...Right now I'm testing two solutions...The first is to incorporate the KD1JV resistive divider mod...I use a 33K/1K combo to get the level I want...The other is simpler...Replace C6 with a 0.1uf cap and C5 with a 10uf electrolytic...This capacitive divider ratio should accomplish the same thing and keep the mixer from saturating...Expect your power output to be significantly lower but with much greater spectral purity...Without the mods, the signal is about 75KHz wide!...I'll report on my testing later after I have access to the spectrum analyzer and wattmeter again...Jim  WB2LHP

On Sat, Nov 2, 2019 at 5:53 PM Adrian Boyko <adrianboyko@...> wrote:
Hi All. I'm curious if there's a point in the D4D circuit that would allow for an easy check of the input audio level using just an oscilloscope. Can one look for clipping (or some other symptom) that indicates an overload of the D4D's audio input circuitry? I realize that it's possible to look at the RF output for signs of trouble but I'm wondering if it's possible to do so further upstream in the circuit.