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

Mark Cayton

On Tue, Feb 22, 2022 at 01:08 AM, Max wrote:
Never quite sure what the obsession is with Pure Signal?
I'd like to try and answer that, at least to the degree that I own and operate an ANAN 7000.

Firstly, strictly in terms of splatter the cleanness of my transmitted signal running PS is unmatched anywhere else in the amateur radio kingdom, including from the finest Class A amplifiers. Nothing else even comes close to the transmit splatter level of between -60 and -70 dB when using PS (I routinely observe between -62 and -65 dB as measured with a tap at the output of my AL-80B). A simple calculation reveals that at 1KW transmit level the total splatter from both sides of an SSB transmission at -62 dB IMD is less than 1 milliwatt. Think about that! At that level, another ham on a high quality receiver 3 houses away from mine could be listening on a frequency immediately adjacent to mine and he'd never know I was there. That's called being a good neighbor.

Secondly, the fact that I'm basically not wasting any power at all in splatter means that all of my transmitted signal is actual talk power. So my transmitted signal (and thus audio strength) is greater than it would be if I wasn't running PS. Basically, that's free power! In fact, I've read a lab review of an ANAN radio where the reviewer remarked that when he engaged PS he observed that the power density of the transmitted signal increased (I can't find that review atm but if I do I'll post a link).

Thirdly, the purity of the audio also improves, because the IMD component of the amplifier also adversely affects the audio signal as well as the RF signal. So my audio is not only stronger but also cleaner when I'm running PS.

Fourthly, the external sampling tap available on the back of the ANAN 7000 allows the PS algorithm to correct the IMD component for the entire PA train, including my AL-80B, such that the full strength of the signal being delivered to the antenna is cleaned up, not just the barefoot signal coming out of the ANAN.

Fifthly, there are a number of niche band slices in the HF bands where 4kHz ESSB is typically employed (3.870 and 7.235 are often active in the States) and other HF amateur freqs where 8kHz wide AM is employed. So it's certainly not overkill to strive for superior audio on amateur HF. I run an AT2035 mic (yeah, it requires 48v phantom) and I wouldn't trade it for any dynamic mic, because there's simply no comparison between a good large diaphragm condenser mic and any dynamic mic. True, my mic needs a quiet shack but I've gone to the effort to build a quiet shack.

Hope that helps,

Mark K1LSB

Edit: If I neglected to mention it, I'm a huuuge fan of PureSignal. PS is the main reason I bought my ANAN, and I'll never own another radio. As far as I'm concerned, every other radio runs a distant second place to the ANAN with regards to cleanness of the transmitted signal.

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