On 01/16/2018 07:29 AM, prog wrote:

On Sun, Jan 14, 2018 at 10:41 pm, drew231955 wrote:

The main break through with the HF+ is the Polyphase harmonic rejection
mixer. As best I can work out, when converting to base-band, it is an
effective filter for the desired signal and rejects even strong signals
close by with virtually no filtering ahead of the mixer.

It uses multiple phases of the local oscillator to use phasing to reject
its harmonics, but at the same time, and because it is to a 200 kHz
base-band, it rejects everything else too.

The big advantage is not needing a large number of band pass filters like
a direct sampling SDR; the IC-7300 has 15!

The best explanation I have found is a slide show;
http://icd.ewi.utwente.nl/temp_files/158b39412cff88a4181bfec0f4449c24.pdf.
It is also subject to patent;
https://www.google.ch/patents/US20110298521?hl=de. One of the authors
wrote the slide show.

There is something wrong with this url. I think it's the second / What should the character be?
--doug

Presumably the mixer is a CMOS device, but I have not found one. And the
RF cover on the HF+ is too hard to remove!

Any thoughts on this very novel approach?

Regards Drew VK4ZXI

You can see it as a "super Tayloe mixer". The problem with the original Tayloe Mixer is the harmonic responses at multiples of the LO frequency. The fix is to mathematically suppress these responses by adding more phases. The LO will no longer look like a square wave, but rather like a quantized sine wave. Basically, the more phases you add, the more harmonics you cancel.
This method is combined with narrow band filtering at the mixer itself. There is a switched-capacitor N-Path filter built into the mixer that is tuned using the same LO phases, which provides additional selectivity.
When you see it, all the ingredients required to implement this architecture can be implemented using CMOS silicon, and have a very good "horizontal" and "vertical" scalability: Horizontal with more phases (hence, less harmonics); Vertical with better fab processes (better linearity and NF).

The icing on the cake: This same technology can also work for TX.

The future looks bright!

You should be able to dig out a CW signal less than 7.6 dB above the average noise level, by ear, so you would want the squelch to be either adjustable or switchable.  (BTW, a tangential signal is 8 dB

above the noise, not 7.6, if that's what you had in mind.)

--doug, WA2SAY.

From: main@airspy.groups.io [mailto:main@airspy.groups.io] On Behalf Of blogger@...
Sent: 16 January 2018 19:47
To: main@airspy.groups.io
Subject: Re: [airspy] Online - London SpyServer

The londonhf.ddns.net is great!
Anyone knows what is this station on 560kHz?

If SDR# does get squelch, hopefully it would be a new idea like having it based on the SNR reading.  Anything below a user-set SNR reading is completely audio muted.  Say I set my SDR# SNR Squelch to 7.5 dB then any noise/signal at 7.5 dB and below would be muted.

BTJustice

On Tue, Jan 16, 2018 at 08:14 am, Sergey Abramov wrote:

Another question, how does it work:

 

# Allow clients to control the device

#

allow_control = 1

 

What functionality is available to control users? Full IQ, what else?

If there are 10 clients, all will be available control?

 

 Аll users can not tune the device anywhere within the specified min/max frequency limits for example, 80m and 40m HAM bands?

Sorry for many questions.

Control includes the device's center frequency and gain stages if there are gain stages.
When there's more than 1 client connected, the control is disabled for all.
Yes, you can specify the min/max frequency. Don't be afraid to play and experiment. It will take you much less time.