7000DLE and RX2

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Joined: Sun Apr 09, 2017 2:42 pm

7000DLE and RX2

Postby K4KV » Fri Jan 26, 2018 8:09 pm

Does ADC2 have the same 20db preamp in line as does ADC1?

I am assuming so, therefore, I do not see a variable step-attenuator setting for ADC2. I see only a 0db, -10, -20,
and -30db attenuator selections. My inclination is to set -20db to cancel out the preamp. However, that just about kills
the RX2 receiver.

So, how does that ATT translate to the old ADC1 stuff?


Glen K4KV
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Joined: Fri Apr 14, 2017 3:47 pm

Re: 7000DLE and RX2

Postby K9RX » Fri Jan 26, 2018 8:37 pm

double click on the "ATT" word and it will change to the SATT.

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Re: 7000DLE and RX2

Postby w-u-2-o » Fri Jan 26, 2018 9:01 pm

In the 7000 both ADC channels use the exact same physical implementation: a Mini Circuits DAT-31-SP+ 31dB digital step attenuator. You can choose to use the 10dB preset steps, or you can choose to use the 1dB steps. Just double click the label on either RX1 or RX2 like Gary said.

On the older radios RX1 also has a couple of switched attenuators on the PA/RF board, one that provides 10dB, another that provides 20dB of attenuation. You can them together with the DAT-31-SP+ to obtain greater than 31dB attenuation, although I don't know why you would.

Finally, you never want to "cancel out the preamp". The preamp and ADC work together as a team and the ADC does not work well without it. That is why it is non-defeat-able.

The way I use the attenuator is to optimize where my ADC dynamic range lays relative to band noise. Pick a large, stable signal on the band. Raise the level of attenuation until you see the signal to noise ratio drop. Back it off by a few dB. That will ensure that you can still receive the smallest signals while the large signals affect you less. Then adjust your AGC gain to taste in terms of signal loudness vs. noise loudness.



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