Advanced Controls for HF+ (take 2)

[WA7F]

Hi,
Sorry I’m new to the forum and posted a blank thread earlier.

I’m experiencing low sensitivity with an AIRSPY HF+ Discovery when using SDR Console v3.3 build 3236. Are there RF Gain, Sample Rate and Decimation adjustments somewhere in this software? If not, is there an SDR Console version that does offer these features? Thanks for any replies.

Dave - WA7F

[KA1GJU]

You should see the AGC, ATT, Preamp, and Visual Gain buttons in the 'Radio' section of the home tab. See attached image.
Typically AGC on Low or High (doesn't seem to matter), ATT OFF, Preamp OFF (or ON if on 20m and higher), and Visual Gain of 0dB.
The lastest version is 3.4 and you can download 3.4 beta, dated February 10th, 2026 Build 3972 about 3/4 the way down on the downloads page of the website sdr-radio.com

What antenna system are you using, ie coax length, type of antenna, balun(?), unun (?), CMC(?), etc.

For example in the attached photo, I have the Airspy HF+ Discovery, +170' of RG-213, 9:1 unun, and an inverted L going up about 60' and horizontally about 100'. Counterpoise directly under the antenna of +150' made from repurposed galvanized cattle fencing wire. Grounding the unun with a 3/4" copper pipe gives me a 1.5 S-unit drop in noise floor on 160m, 1 S-unit on 80m.

73 Kriss KA1GJU

[WA7F]

Thank you for the reply.

With ver 3.3 it was only showing AGC, ATT and Visual Gain. No preamp. After some reading I decided to update the firmware. That went Ok but, the cover came off when pulling some Velcro loose that was holding it in place. Trying get the cover back on I managed to poke a screwdriver inside and sheared off an inductor off the PCB. I can barely see it let alone attempt to repair it.

So that Airspy is toast and I’ll never know if the firmware update fixed the issue. I’m usually pretty good about working on things but, stuff happens.

My antenna isn’t the best (80m EFHW) but, that isn’t the issue. It actually does Ok on 20 and 15 if the lobes and null are working in your favor. My beam will go up this summer.

I am splitting the RX-OUT of a K3S with a Microcircuits splitter/combiner. One side of the splitter output goes the Airspy HF+ INPUT and the other goes to the K3S RX-IN. Both receivers are seeing same signal levels regardless of antenna performance. The K3S can clearly pull out weak signals while the Airspy doesn’t even squiggle the scope. I don’t expect the Airspy HF+ to outperform the Elecraft but, with Airspy claiming better sensitivity than the KS3 I would think that the performance would be closer. So I tried SDR++ and with the use of decimation and attenuation I was able to improve the sensitivity significantly.

At the moment I’ve replaced the Airspy with a Hermes Lite 2 and the sensitivity is pretty close to the KS3. However, with my resent bad luck, I’m not crazy about having a TX capable SDR connected to the RX out port of my K3S. (Even though the HL2 TX is disabled.)

So I’m looking for another SDR. I’ve had a couple of SDRPlay/RSP units and never got them to work right. They both had issues with mirrored spectrums and other artifacts. I’ve been happy with the Airspy for the most part but, ordering one means shipping on a slow boat from China plus tariffs.

What firmware version are you running on your Airspy? It is the HF+ Discovery, right?

[Max]

I’ve been happy with the Airspy for the most part but, ordering one means shipping on a slow boat from China plus tariffs.

iTead say on their website on the "Purchase" information page that US orders are shipped from within the USA. However, on their shipping information page they don't say that, so which it is I have no idea.

I will only say that when I ordered mine from iTead a few years ago to be shipped the UK I had no issues at all. Postal service from China was fast (about a week I seem to recall) and no duty to pay.

https://itead.cc/product/airspy-hf-discovery/

I have not seen any of the sensitivity issues you say you see, but you could check this for yourself by trying one of Kriss's many remote HF+ Discoverys. If you have SDR Console already installed it literally tales about 30 seconds to add a remote definition from the V3 servers in the Radio Definitions list.

73

Max

[WA7F]

Thanks, Max.

I also didn’t have any issues when ordering Airspy products through ITEAD a few years ago. However, US imports from China are now complicated with tariffs and delays.

My tests so far have shown me that the HF+ Discovery is capable of better sensitivity. I think the missing gain control in SDR Console was due to older firmware.

I would be interested in testing an online HF+ Discovery but, it’s not clear to me how to do this. If you can offer some pointers that would be great.

Dave - WA7F

[KA1GJU]

Try this tutorial I wrote a while back. Say's v3.3 but will be the same for the most part on v3.4

[KA1GJU]

BTW... every November there's a Black Friday sale, I stock up during that time and plan on the next location.
No surprise tarifs on my last purchase, and was at my door about a week and a half later (lot's of sales due to the 20% off I assume).
I have only one SDRPlay (RSP1A model) in my fleet of 19 SDR's, and thanks to it's issues with local AM BC stations (images appearing all the way up into 40m), I had to install an AM BC filter on that site to tame it down. The AGC likes to pump with a strong CW station in the operating bandwidth, so I run manual -35dB IF Gain, not automatic -35dB.

You might be able to find a replacement on QTH.com, QRZ.com, Facebook Marketplace, etc.

[Max]

I would be interested in testing an online HF+ Discovery but, it’s not clear to me how to do this. If you can offer some pointers that would be great.

Dave - WA7F

Kriss's PDF guide that he linked sums it up perfectly. Just to quickly summarise, you are just adding a server definition in exactly the same way as you would add a new hardware radio, except to add it you choose a server from the V3 Server list. Each server can be hosting several hardware radios, and you just select the server you have "added" and hit "Connect" then select one of the radios from the list on the server and hit Start. Job done. Probably takes about a minute to add the server to the definitions list and being up and running with one of the remote radios. Very straightforward. The most time consuming bit is choosing which servers to add from the long list.

Sadly the quality of the antennas on some of the offerings varies greatly, but you soon get to know which work well and which don't. Basically if you choose from one of Kriss's many offerings you will not go wrong as they are all excellent ad also he has almost exclusively HF+ Discoverys. Without me counting, how many is it now Kriss?

Max

[KA1GJU]

Max,
I think it’s at 19. Mostly Airspy HF+ Discoveries, a few SDR-iq’s, two Airspy Mini’s for those VHF/UHF users, one SDR-IP that gets locked up frequently (has to be power cycled to get it back online), and one SDRPlay RSP1A.

[jdow]

Regarding a missing gain control, if you have AirSpy's AGC enabled, no gain control exists. With AGC off gain control returns. Sensitivity is a function of your antenna more than your front end tool at HF. A front end can have a half dB noise figure and behave the same as another with a 30 dB noise figure on 160 meters with a full size dipole 100' up in the air, for example. The galactic noise, locally generated noise, and noise from all over the planet that noise, that effective antenna temperature, adds to the noise from the receiver itself and utterly swamps the receiver's noise.

Stepping back from the front end noise figure issue, we can look into the local oscillator. If it has a lot of noise, that appears on top of your signal. The HF+ might have a quieter oscillator/synthesizer setup for its conversion to the IF that is digitized. That and mixer design can, if poorly done, significantly degrade receiver performance. HF+ appears to have, for the price, a top-notch set of filters, local oscillator, and mixer.

After that it's all in the SDR and basically the same for all front ends. All in your antenna is VERY likely to set your sensitivity below 10 MHz and likely even up to 30 MHz the ambient noise, even in the middle of a Kansas cornfield, is going to be high when the band is open setting your sensitivity. With a YouLoop, a very inefficient antenna, the HF+ is designed to perform very well with it. Other front ends will fall short as they have more generic designs. In general, if you switch from a 50 ohm dummy load to your antenna and the noise goes up, the receiver is as sensitive as it gets within a dB or two. Back in the late 1950s I spent carefully hoarded allowance money and bought a DowKey preamp for HF use - on 15 Meters with a beam up about 50' on our roof. I was REALLY er peaved when physics reared its ugly head at my expense. In about 1963 when I was in college I found a nice book about noise figure at a local electronics store in Ann Arbor. It explained what happened. With the prior experience this knowledge has stuck around as vividly as if it happened yesterday.

There is another receiver effect to consider, Intermodulation Distortion. If the analog portions of the front end are overloaded stray signals and noise appear. If the A/D converter is overloaded, which is hard to do with AirSpy's AGC setup, this effect very suddenly appears with a very hashed looking spectrum display. Even a single bit of overload (8191 + 1 for 14 bit samples) turns the digital world upside down - quite literally. That sample becomes minimum negative, -8192. I have a suspicion setting gain too high and getting this overload effect is how people think they have found one receiver more sensitive than another at HF.

Depending on the front end design you can get an effective notch or peak dead center on your display. Tune aside slightly so the signal you want is about an IF filter bandwidth and a half away from that center. Sometimes that can make a HUGE difference.

That said, I have one each of the two HF+ models and a raft of the UHF AirSpy units. They are not what a professional spectrum hunter might pick. But, for their respective prices they are damn good. That's why I have a half dozen minis and a couple R2s.

{^_^} Joanne had rambled on enough for now.