NDB - Airspy HF+ DIscovery versus Hermes Lite 2
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Max
For anyone interested. 132ft end fed antenna. 20:26 in evening. NDB is CHT (Chilterns) 277 kHz at 61 miles NE from my home QTH. As you can see I've isolated the CW sideband but that's irrelevant as the difference can clearly be seen in the waterfall.
Airspy HL2 Connected in turn to the two receivers, but conditions were very stable and results repeatable. To my great surprise (because I was expecting superior performance from Airspy at this low frequency, which is why I bought it) HL2 bests the HF+ by some way. I intend to repeat experiment tomorrow and next day on the Grimeton Christmas transmissions on 17.2 kHz. In theory the HF+ should be superior there at least. We shall see. https://alexander.n.se/en/saq-scheduled-for-a-transmission-on-christmas-eve-december-24th/ 73 Max |
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Patrick
Hi Max, It's indeed surprising. As a LF enthusiast (chasing NDB for more than 20 years), I can tell the Discovery is one of the most sensitive receiver I have ever used, if not the most sensitive (among Perseus, ELAD S1, ELAD S2, RSPduo, RSPdx I had the opportunity to test). |
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Max
On Thu, Dec 23, 2021 at 12:34 PM, Patrick wrote:
Hi Patrick I don't think this shows any issue with the HF+ Discovery, just that the Hermes Lite 2 is a quite astonishing bit of kit for the money. Actually regardless of the cost. Punches way above its weight. I did always think so but this has just confirmed it for me. Unless I have a sub-par HF+? Wonder if you managed to watch my video recordings of the NDB? Unfortunately I was not able to listen for Grimeton test transmissions today. Listening now but nothing heard so I guess too late to the game. I will be sure not to miss the main TX tomorrow morning. Max |
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Max.. I’m overhauling a WW2 R1155 and as I tuned across the long wave band a Polish station close to Radio 4 came in at a good S8 about mid day. I checked on my Andrus SDR with the same aerial and it wasn’t more than a tiny spike with no audible modulation Admittedly the R1155 has been modified with a 6AK5 RF stage… Allan G3PIY From:
main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of Max
On Thu, Dec 23, 2021 at 12:34 PM, Patrick wrote:
It's indeed surprising. As a LF enthusiast (chasing NDB for more than 20 years), I can tell the Discovery is one of the most sensitive receiver I have ever used Hi Patrick _._,_._,_
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jdow
I suspect it is an issue with the antenna match to
the receiver. One might provide better performance on any given
antenna than the other. Which one does better depends on the
antenna. And nothing says the better one cannot be improved upon
with slight changes. This is down at a frequency range where
antennas should not make any difference as far as QRM from outside
the station's perimeter is concerned. But things such as wind can
setup charges in wires it blows past. Front end impedance at DC
can have significant effects on this. It might be entertaining, if
the antenna is large (say a full size 80 meter dipole) to place an
easily obtainable T connection and 50 ohm dummy load at the input
of the receivers. If connecting the antenna raises the noise in
both receivers the performance comparison should still face the
same externally generated noise issue perhaps with less
atmospheric effects differences on the antennas. The AirSpy's
noise figure is do low that at any frequency under 10 MHz a 20 dB
pad on a dipole antenna's feed line should not materially affect
received SNR. So something else has to be creeping into the setup.
Rain static? Wind effects? Really close by really high power AM
radio station? That latter could exceed the AirSpy's dynamic range
before it would affect something with an extra bit or two of A/D
resolution. An AM band reject filter would mitigate this problem
nicely. And it might improve both HL2 and AirSpy.
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{^_^} On 20211223 06:36:19, Max wrote:
On Thu, Dec 23, 2021 at 12:34 PM, Patrick wrote: |
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jdow
One other thing - if he is not using the AirSpy HF+
Discovery's AGC he's very likely running with some gain mismatches
in the analog portion of the chain.
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{^_^} On 20211223 06:36:19, Max wrote:
On Thu, Dec 23, 2021 at 12:34 PM, Patrick wrote: |
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Tom Crosbie G6PZZ
You lucky man Allan! I almost had one around 1970. It sat at the back of the physics lab and someone had removed all the valves. Couldn’t afford them on pocket money. Never thought of hanging on to it until I started work and could afford it. That tuning dial was really smooth.
Season’s greetings
Tom G6PZZ
From: main@SDR-Radio.groups.io <main@SDR-Radio.groups.io>
On Behalf Of Allan Isaacs
Sent: 23 December 2021 14:47 To: main@SDR-Radio.groups.io Subject: Re: [SDR-Radio] NDB - Airspy HF+ DIscovery versus Hermes Lite 2
Max.. I’m overhauling a WW2 R1155 and as I tuned across the long wave band a Polish station close to Radio 4 came in at a good S8 about mid day. I checked on my Andrus SDR with the same aerial and it wasn’t more than a tiny spike with no audible modulation Admittedly the R1155 has been modified with a 6AK5 RF stage… Allan G3PIY From:
main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io]
On Behalf Of Max
On Thu, Dec 23, 2021 at 12:34 PM, Patrick wrote: It's indeed surprising. As a LF enthusiast (chasing NDB for more than 20 years), I can tell the Discovery is one of the most sensitive receiver I have ever used Hi Patrick |
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jdow
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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{o.o} On 20211223 06:46:56, Allan Isaacs
wrote:
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Alan G4ZFQ
Unless I have a sub-par HF+? Wonder if you managed to watch my video recordings of the NDB?Max, I did. It seems the Airspy is excessively noisy. Levels appear to be high. I can not believe that a good Airspy could be that much worse. What antenna? It could be that some out of band signal is causing the problem. Sometimes I use a LPF but that's not normally needed unless I TX. 73 Alan G4ZFQ |
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They’re easy enough to come by Tom. This one belongs to the son of silent key G3PNV and has lain dormant for the best part of 50 years. https://www.radiomuseum.co.uk/modR1155.html Sacriligiously the dial is now a Muirhead but even smoother than the old type 35. My first was bought from my English teacher for £3 (quite a lot of cash in those days when a good wage was £1 a day and suffice to say my parents hit the roof). Since then I acquired a few more with one coupled to a T1154. All the best Allan G3PIY
From:
main@SDR-Radio.groups.io [mailto:main@SDR-Radio.groups.io] On Behalf Of Tom Crosbie G6PZZ
You lucky man Allan! I almost had one around 1970. It sat at the back of the physics lab and someone had removed all the valves. Couldn’t afford them on pocket money. Never thought of hanging on to it until I started work and could afford it. That tuning dial was really smooth.
Season’s greetings
Tom G6PZZ
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{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
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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Tom Seeger
I wonder if you have both receivers connected to the antenna at the same time? This can cause digital noise emitted from one radio to be received by the other. Another good test is to disconnect the antenna from each radio and replace it with a 50 or 75 ohm resistor and record the base noise. It should be less than -130 dB. I measure about -135 dB on my HF Discovery at 277 kHz with a 250 Hz bandwidth.
73 Tom |
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Gedas
Tom, I do not own an Airspy so I do not know but when you say below -130 dB what are the units? dB what? Are they an absolute figure
like dBm (which is what you need) or is it a relative number
related to ADU etc ? Gedas, W8BYA EN70JT Gallery at http://w8bya.com Light travels faster than sound.... This is why some people appear bright until you hear them speak. On 12/23/2021 11:15 AM, Tom Seeger
wrote:
I wonder if you have both receivers connected to the antenna at the same time? This can cause digital noise emitted from one radio to be received by the other. Another good test is to disconnect the antenna from each radio and replace it with a 50 or 75 ohm resistor and record the base noise. It should be less than -130 dB. I measure about -135 dB on my HF Discovery at 277 kHz with a 250 Hz bandwidth. |
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Tom Seeger
I assume dBm. In any case its his Airspy vs my Airspy. So its relative and just for diagnostics.
73 Tom |
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Gedas
You might be right but I would not assume that w/o verifying first. Also, just for fun I made some amplitude measurements of my RSPdx. You might find the near end interesting. 73 https://www.youtube.com/watch?v=qHJE6wa9dVw Gedas, W8BYA EN70JT Gallery at http://w8bya.com Light travels faster than sound.... This is why some people appear bright until you hear them speak. On 12/23/2021 1:13 PM, Tom Seeger
wrote:
I assume dBm. In any case its his Airspy vs my Airspy. So its relative and just for diagnostics. |
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Max
Before I made the videos I spent quite a while on the Airspy tweaking all settings of AGC, then AGC off and multiple different gain settings. The recording I showed was the best result I could get. With the HL2 I just plugged it in, started it and tweaked nothing. Actually there are almost no controls to tweak anyway. Just LNA which is adjusted to prevent overload as per the front panel LEDs. In fact I don't remember the last time I needed to change that. Then there is just Visual Gain, which I usually adjust for -125dBm with no antenna connected. Admittedly I forgot to make the visual gain adjustment on the Airspy so that probably explains the HF+ looking very noisy. The background noise level with this setup is actually about S3 as you can see from the HL2 recording. For the Airspy I set sampling bandwidth to the minimum of 192kHz to give it the best chance. With the HL2, although I made the recording with sampling bandwidth set to 48kHz it gave identical results on all sampling bandwidths up to it's maximum of 384 kHz. No difference whatsoever.
So here's the question. Which is the better receiver? The one which anyone can just attach antenna, turn on and it just works perfectly with no issue or the one we need to make multiple excuses for this that or the other not being adjusted correctly? I know which I'd rather have. Anyway, I did not set out to pick any faults with the Airspy. Why would I? I just paid good money for it! Just thought an interesting comparison given that the Airspy is always hailed as the "best thing since sliced bread" as we say here in the UK. It's just I was therefore quite surprised that the HL2 easily bettered it on the first test. I am sure there are other areas where the Airspy will outshine the HL2. As I said before, I'm very interested to see results on 17.2 kHz tomorrow. For info, I do have a local quite powerful AM station (about 8 miles away) and this certainly causes severe issues with my SDR Play RSP2Pro and I can also see signs of it being an issue that needs careful tweaking with the Airspy too (nothing like as bad as the RSP though). But it does not cause any issues whatsoever with the HL2. For me at least on the first few tests the HL2 is just considerably better on the frequencies it covers. Of course no VHF FM (for example) on the HL2 so it's horses for courses as ever. Max |
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Tom Seeger
Max, I do not need to do any of that with mine. I use HDSDR and just leave the AGC on auto, and the preamp OFF. If you need to do all that then I would suggest there is something very wrong with your unit, or your driver, or perhaps the Airspy is being seriously overloaded by an out of band signal. On longwave mine is far superior to my WinRadio receiver, my ICOM, and SDRPlay. I'm not saying that it should be much better than your Hermes, but based on your videos, it should not be that much worse.
Have you tried an LPF or even just a 10-20dB attenuator? Tom |
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jdow
I suspect you are not running them correctly.
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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:
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jdow
Exactly dB what. They are a measure of how far down
you are from when the front end overloads. With the AirSpy HF+
further calibration is not really possible last I knew. For most
other front ends calibration is possible and remarkably accurate
and linear.
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{^_^} On 20211223 09:41:40, Gedas wrote:
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jdow
Assume dB relative to full scale for the A/D
converter.
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{^_^} On 20211223 10:13:42, Tom Seeger wrote:
I assume dBm. In any case its his Airspy vs my Airspy. So its relative and just for diagnostics. |
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