Re: NDB - Airspy HF+ DIscovery versus Hermes Lite 2


Heh, me be injuneer. Alas not hairy chested for some reason. So MY R390A has been tweaked a little. It goes down into that frequency range. I used it a little. I moved back to 20 meters SSB talking with folks in Oz after dinner here. (nice folks.) At that time I had a TH6DXX at 70'. Gone with the divorce. And I still think I won.

I also built in a hang AGC system and rewired the demodulation processes so that for SSB and CW I used a 7360 tube.  Heaven forbid you'd think I'd leave it unmodified. Hm, I also had a nice vernier knob on it. I forget the exact ratio. I get something like 2 kHz to 5 kHz per revolution. It has an PLL synchronous AM demodulator that I'm not fond of. It needs tweaking and was not worth it. Its a superb SSB receiver. I used it in actual communications service rather than SWL.


On 20211224 02:01:22, Allan Isaacs wrote:

The R390A is one I still need to try out. It is somewhat of a lightweight pound for pound though compared with say the DST100 which tunes down to 50KHz and uses a VP41 RF amplifier to handle 10V RMS signals without distortion or so they claim. Is this the ultimate valve receiver I wonder, although for VLF maybe the CJD wins.

Alas mine is yet persuaded to work so I cannot tell.

Allan G3PIY

From: [] On Behalf Of jdow
Sent: 24 December 2021 08:07
Subject: Re: [SDR-Radio] NDB - Airspy HF+ DIscovery versus Hermes Lite 2


I suspect you are not running them correctly.

I have listened to the best of the best analog. In fact I still have my R390A; but, it is retired just before I redesigned it for semiconductors. (I've been planning that for decades now. The earliest and most complete set of notes comes from the 1970s.) The basics of the designs for noise and dynamic range are basically the same. And the very basic detail that on large antennas attenuators on the receiver front and are an exceptionally good thing at MW and HF. Most SDRs have headaches from hitting their heads on their A/D's ceiling. The more bits of resolution (and precision) from their A/D converters helps. You may be suffering from a nearby large signal radio. For most (all) other front ends run the gain up until one of two things happens. The first thing, the good thing, is you reach a point where the signal to noise ratio does not improve. You can see that on the spectrum display. The second thing, the bad thing, is the display very suddenly shows a whole lot of signals you had not seen before. Go to a much higher gain and work down until these spurious signals become invisible. That's the best you'll get out of that front end.

For any AirSpy HF+ leave its internal AGC on. You lose the ability to calibrate it. But you get the best possible dynamic range that way.

Once you get good settings it should be as usable as any other radio for these frequencies and more usable than most because of digital only features.

{^_^}   (Poor thing. She only has 63 years experience and a couple college degrees as a result.)


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