Re: Open HPSDR Hermes (14 bit ADC, EP3C25) Transceiver Card

Simon Brown

Try listening in the 80m DX window in New England – AG1J uses a ~60 year-old SSB rig. Wide hardly starts to describe it, I think it’s a phasing exciter with obligatory after-burner.


Simon Brown, G4ELI


From: <> On Behalf Of Conrad, PA5Y
Sent: 25 February 2022 09:56
Subject: Re: [SDR-Radio] Open HPSDR Hermes (14 bit ADC, EP3C25) Transceiver Card


By clean I mean - can I hear anything of sufficient magnitude to disturb the noise floor anywhere in band, and hence inhibit my ability to receive signals close to the noise floor. The noise floor in a semi-rural location on 28, 50 and 70MHz is not particularly low so I do not feel that this is unreasonable. The biggest problem with the IC7300 is the AM noise bump at 20kHz and 130kHz which is only 60dB down on the carrier when running at 30W on 28MHz. This power level is typical when driving an amplifier.  When modulated with an SSB signal this occupies a considerable amount of bandwidth.  The close in PN -s only -120dBc/Hz at 1kHz and  -130dBc/Hz at 10kHz. The composite noise is -115kHz at 10kHz, this is not what I would consider clean, even close in. The K3S( and a few others) is far better in this respect although the PA has quite poor linearity, especially on 6m.


The Hermes will do a much better job with any decent PA, even without pure signal. There are some spurs @ -65dBc which improve with a higher sample rate.  I have not checked these with the V2 firmware but I will do immediately I receive my Hermes from Apache.


I do not think that a transceiver at the IC-7300 price point has fixed pre-distortion. As you quite correctly say keeping it under control over temperature and voltage variation would be difficult. Also Icom would almost certainly have mentioned it in their advertising. What the IC7300 does well is manage audio overshoots by using a ‘look ahead’ algorithm. This is maybe where the impression of it having a clean TX comes from.


I think that the problem here is that so many transceivers are quite bad, so I can just about accept that the IC-7300 is less bad.




Conrad PA5Y


From: <> On Behalf Of jdow via
Sent: 25 February 2022 10:27
Subject: Re: [SDR-Radio] Open HPSDR Hermes (14 bit ADC, EP3C25) Transceiver Card


OK, please refresh my mind what you mean by "clean". It certainly appears to be sending something much closer to pure signal concentrated within its intended bandwidth than most other transmitters. I also understand that it is not as good as it can be with full active predistortion. Both might generate increased noise at some significant separation from the intended signal frequency. I am not sure of the mechanism by which this would take place.

As an ornery critter there is nothing I would sit down and declare "clean" without a definition of "clean". I guess I am asking for your definition of the term or even of the term "clean enough".


On 20220225 01:13:11, Conrad, PA5Y wrote:

I KNOW for a fact that the IC7300 is not clean. Please provide me some evidence to the contrary. I have measurements with a R&S FSWP Signal analyser out to a 1MHz BW. You guys are looking in an SSB BW which is fine unless you happen to be 130kHz away, then you will hear plenty of splatter from the IC7300. I tested the IC-7300 as a result of hearing this on 50MHz. In other words the lab tests were driven by on air experience.


You are spreading misleading and incorrect information.




Conrad PA5Y


From: <> On Behalf Of oldjackbob via
Sent: 24 February 2022 23:12
Subject: Re: [SDR-Radio] Open HPSDR Hermes (14 bit ADC, EP3C25) Transceiver Card


On Wed, Feb 23, 2022 at 12:24 PM, Max wrote:

I just think if we follow good design and signal chain management that superb, clean signals can also be generated without the need for PS, that's all.


I disagree. My signal is my signature. Audio clarity is admittedly important but what matters most to me is a splatter-free signal, and in that regard nothing comes close to what PS can produce. As I stated earlier, even the best Class A amplifiers only have -40dB splatter. PS starts at -60db and often pushes -70dB. That means that PS reduces splatter to less than 1% (and at times only 1/10 of 1%) of what even the best traditional equipment can produce.

I also agree with Simon that the 7300 (and also the 7610 for that matter) produces an extremely sharp-edged signal with unarguably less splatter than is achievable with any other non-ANAN radio. It was explained to me by Ray N5LAX that the reason those radios are so clean splatter-wise is because ICOM embedded an algorithm into the firmware that functions very similarly to PS in the sense that it corrects for non-linearity in the PA, but it is a fixed-value (i.e., static) correction only, not a real-time self-adjusting correction value such as is employed by PS. NOTE: I have not been able to verify that info, but that is what was told to me over-the-air by Ray when I commented that I had no idea how the 7300 could produce such a clean, sharp-edged signal. So I'm repeating it here.

IMO it's unwise and short-sighted to summarily dismiss the game-changing value that PS brings to the hobby. Its benefits are so unarguable that I (and Rob Sherwood) often wonder why the big-name radios don't offer it as a standard feature. It's free, so utilize it for goodness sake!




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