Thank you, Mike. I will check the output of the 51J-4 on my scope. The
IF output is from the last stage and there is an output amplifier that
might have some gain, so I better measure it and add an attenuator if
needed.
73,
Victor, 4X6GP
Rehovot, Israel
formerly K2VCO
CWops #5
On 19/07/2025 20:09, Michael Carter via Elecraft wrote:
Hi Victor,
There was some old discussion on the Elecraft forum about output levels from
the KXV3 IF output port. The P3 designer, Lyle KK7P, indicated that the IF
output level is about the same as the signal input level at the K3 antenna
port. I've not encountered S9+60dB signals very often, and that may be beyond
what results in saturation of the P3 input circuit. You're probably safe up to
200 uV into the P3 (S9 is -73 dbm or 50 uV into 50 ohms, so S9 + 12 dB
equivalent signal level).
The P3 RF input circuit does not have any level-protective elements - an
optional preamp is switched into that circuit, but otherwise the RF goes
straight into the A/D converter via a transformer (single-ended to differential
drive converter). The A/D converter, an LTC2205-14, specifies maximum analog
input voltage of [-0.3 V -- Vdd + 0.3V]. The P3 uses 3.3 V for Vdd for that
A/D converter. The A/D converter does have internal clamp diodes that limit
voltages to prevent damage, but I would still put an inline attenuator from
your 51J-4 output to the P3 as insurance.
The P3 frequency coverage is specified from 455 kHz up to 21.7 Mhz, so your
studies of the 51J-4 IF filters should be OK at 500 kHz.
73,
Mike, K8CN
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