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


jdow
 

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.)

On 20211223 07:38:34, Allan Isaacs wrote:

{o.o}

I have a couple of aerials, an 80m dipole and a random long wire about 150 feet long.

I use a matching unun with the long wire. The dipole works fine as a receiving aerial on any band and gives me the least local interference due to the feed point being very high and the ends clear of habitation.

I find all digital radios are inherently very noisy compared with old valve superhets.

I suppose most out there haven’t listened to a proper receiver with proper RF tuning and without a PLL.

There’s a challenge…

Allan G3PIY


From: main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of jdow
Sent: 23 December 2021 15:01
To: main@SDR-Radio.groups.io
Subject: Re: [SDR-Radio] NDB - Airspy HF+ DIscovery versus Hermes Lite 2

 

You have a really small antenna, perhaps? If not I suspect the Andrus is not setup as nicely as it could be. With a low loss antenna system below even 30 MHz and especially under 10 MHz it is VERY difficult to make a radio too insensitive to receive anything that is out there without reducing RF input gain by 10 dB to even 30 dB due to purely natural noise sources.



 


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