Dear Alberto,

Here are some further comparisons (bearing in mind I don’t own a R75!):

The RA1792 has flat sensitivity from about 100kHz – 30MHz (about 0.3uV for 12dB SNR in SSB bandwidth), and rolls off about 20dB down to 10kHz, so works quite well for VLF. The R75 only tunes down to 30kHz, but does also cover 30MHz – 60 MHz; I don’t know what the LF sensitivity is like, although I think it is reduced below 1MHz. The R75 has various preamp and attenuator settings, while the RA1792 has fixed front-end gain (although you can link out the RF amplifier). The RA1792 has no preselector, although it seems to cope well on HF.

The RA1792 has, as standard, 300Hz, 1kHz, 3kHz, 6kHz and “bypass” 16kHz bandwidths (for some reason, mine has a 150Hz filter instead of the bypass setting), plus dedicated USB and LSB filters. The bandwidths are specified as -3dB rather than -6dB as is normally the case for amateur rigs, so they would be slightly wider in amateur terms. The BFO can be set to +/- 8kHz in 10Hz steps. So, if the RA1792 audio output is to be processed by DSP, it is quite flexible - for example, you could use a 6kHz BW and have audio output from 2 – 8kHz. The R75 has 2.1kHz, 6kHz and 12kHz as standard – I think CW filters are an extra. You can only set the BFO offset between 300 and 900Hz.

The skirt selectivity of the R75 should be good, since it has cascaded 9MHz and 455kHz filters. Signals a few kHz off tune are only suppressed by about 60-70dB on my RA1792.

The R75 has an RS232 port and there is remote control software available. The RA1792 has a non-standard interface that can be wired for RS232 or RS422 – apparently, there is some software available for download, though I have not tried using it.

The RA1792 has 455kHz IF output, reference frequency input/output, audio line out, muting, agc and various other things on the back panel, so it is easier to get at the internal signal paths if you plan to do hardware experimentation.

The R75 is quite compact and runs off 12V DC. The RA1792 is in a 19” rack case and requires AC mains, so much less portable!

The 0.5ppm TCXO is an extra on the R75, the RA1792 has a 0.1ppm OCXO as standard.

The only real complaints I have about the RA1792 are the ergonomics of the controls and display – Even after using it for years, I still find I often press the wrong button and suddenly find it on a completely different frequency and operating mode!

Cheers, Jim Moritz

73 de M0BMU