Wednesday, March 11, 2020

New Technology for 202 ~ The Iowa Hills Software --- Hilbert Transforms

March 16, 2020 ~ Time Killer


Go to soldersmoke.blogspot.com and tune into Podcast SS #219. This is good for 1.5 hours and may help pass some of the time you now have as the USA closes down for business. 

I am having a difficult time reconciling what I am seeing on the ground and what we hear from the emperor (with an extremely small e). This is going to get worse! Note: "He is responsible and it happened on his watch!"

There was a line at the grocery store this morning at 5:30 AM and the store didn't open
until 6 AM. Friends that is 0'Dark 30!

How are your stocks doing today? Are the Russian hackers at work trying to penetrate our national health agencies? The emperor (with a very small e) probably will most likely claim it is the deep state who did this. At around 1PM eastern the DOW was down about 2000 points. So emperor (with a very small e) how is your metric doing????

This actually may be a really good time/place to pick up women. But it probably is money is the big draw moreso than the ability to cook!

Pete N6QW

March 15, 2020 ~ This Sucks!

Today in California they closed the bars, night clubs, wineries, and brew houses. That means no more watching girls pole dancing. 

Most of the public and parochial schools in the major metro areas (SF, LA, SD) are closed. I expect the senior centers will be shut down on Monday.

Gatherings are limited to no more than 50 people. We are also told that if you are a senior citizen you must self isolate yourself by not going out in public.

Today our local grocery store (Albertson's) which is one of their flagship stores was out of the following:


  • No Paper Towels or Toilet Paper
  • No Clorox Wipes or Clorox Spray
  • No Bread
  • No Butter
  • No Pasta or Macaroni
  • The Soup stock was down by 75%
  • Canned vegetables were down
  • But Plenty of Beer & Wine but given todays proclamation that too will be gone
  • Water was in short supply.

The good news story is that I have a shack full of waiting projects, lots of parts and plenty of solder.

73's
Pete N6QW


Today's Question:

Is the stable genius tanking our country? How did your 401K do today? Some people are saying his shortcomings are showing! Where is the leadership we so desperately need? Tomorrow will be another "bumpy ride" as more cases surface.


The Iowa Hills Software:  Hilbert Transforms

So what I am about to share with you comes from someone who knows very little about the Iowa Hills  Software. Yes, it is a case of the blind leading the blind.


For those of you deeply into mathematics, or a high level software architect, the subject of Digital Signal Processing and Hilbert Transforms is much like Massimo Banzai starting by saying "The Arduino is a simple tool to make things happen". Mr Banzai of course is the face of all things Arduino just so you know. Bob if you are reading this, then time to engage "the snooze control".

The Hilbert Transform dates back to 1905 so it was not invented in Silicon Valley and I encourage you to do the Wikipedia thing and look up Hilbert Transforms. It made my head hurt...

The Hilbert transform is important in signal processing, where it derives the analytic representation of a real-valued signal u(t). Specifically, the Hilbert transform of u is its harmonic conjugate v, a function of the real variable t such that the complex-valued function u + iv admits an extension to the complex upper half-plane satisfying the Cauchy–Riemann equations. The Hilbert transform was first introduced by David Hilbert in this setting, to solve a special case of the Riemann–Hilbert problem for analytic functions.

So the bottom line is that someone who wanted to do digital signal processing reached back in time and had a Eureka Moment -- use Hilbert Transforms. 

The Iowa Hills Software essentially takes all of what you see in the Wikipedia page and compresses it into a Simulator where you simply move some cursors around a graph to form the type of filter you want. 

Since we are using the I and Q approach (90 Degrees out of phase) which is processed at audio frequencies, then we must do the phase added option where we run the simulation twice. One is at + 45 Degrees Phase Added and the other at - 45 Degrees Phase Added. The span between the two is of course 90 Degrees.

But wait -- long ago and for those of you who once owned a Central Electronics 10A (with a BC458 VFO) or perhaps like N2CQR who has a pristine hallicrafters HT-37 (in addition to his restored S-38E) this idea of I and Q was done with hardware --HDR as Bill says. 

Essentially resistor and capacitor networks provided the 90 Degree shift in the audio signals. This was (and is) problematic as the hardware networks drifted over time and required a lot of constant fiddling. 

Anthony Vitale, W2EWL, came up with a SSB transmitter all fitted inside and using much of the original Military ARC-5 transmitter components to produce a compact Phasing SSB transmitter, Now that was advanced technology for the late 1950's (March 1956 QST). Many units built from his design found their way into Mobile SSB transmitters.

But now with the advent of creating phase shift networks digitally, the problem of drift and changing component values is simply GONE! 

The Iowa Hills Software now lets you create the digital filters and provide the all important 90 Degree Phase Shifted Values so that you can create nearly perfect I and Q Data Streams. Couple that with powerful microcontrollers like the Teensy 3.5, 3.6 and 4.0 with the integral CODEC board you now have a very capable SDR transceiver in a very small platform. 

Let us not breeze by that too quickly -- the same hardware used in my front end is bilateral -- so one set of hardware does all. My ADE-1's are used on both transmit and receive. 

Another simplification which I have as yet to implement (it is me having some cockpit problems making that happen) is to generate the quadrature RF signals directly from the Si5351 at the operating frequency. 

This is impactful in that you could make the Si5351 into a Two Meter SDR transceiver. Right now my Si5351 outputs at 4X and that is frequency divided by the 74AC74. This has two limitations where the 160 MHz end of the Si5351 would limit the upper operating frequency to 40 MHz and the 74AC74 drops off the radar at 95 MHz. 

Zl2CTM has provided me some code to directly generate the two out of phase RF signals. But I keep getting error messages about my variant of the Si5351 that is stashed in my library directory. Just need to fix that and test drive the higher limit frequencies possible by eliminating the 74AC74 and the 4X frequency multiplication. 

So ok what about those of you who are ardent CW operators and want a CW filter. Below is a plot of a potential CW Filter where I chose the Center Frequency of the filter to be 500 Hz and the 3 dB Band Width to be 500 Hz. 

At 60 dB down the BW is 1 kHz. If I remember this correctly the shape factor is the ratio of these two and so we have a 2:1 Shape Factor. For the purist that probably is too large and some would like to see perhaps a 1.6 to 1 shape factor. That might be possible --I just didn't fiddle with the numbers -- hey this took me all of 5 minutes. 

Note worthy along the left hand top edge are some blocks to check. The last one is Coefficients. Checking that block will produce 115 coefficients that appear along the right hand side of the plot. The normal default when you select Phase Added under the Pass Band Tab is +45 Degrees. Run the coefficients at this setting and then under the File Tab -- save the coefficients with the added title  +45. Now look at the Help Tab and just below that and to the right is the Phase Add block. Use the down arrow to make that value - 45 and rerun the Coefficients and save that with the added title -45.

These values with a bit of added information are embedded into the Arduino Sketch and instant filter 




Next week I hope to test drive this filter in a Teensy 3.5. Hopefully I will also make a video so you can listen to the filter on the air. But a real test is to find a CW contest weekend and see how well it holds up. In my mind the chosen 500 Hz BW is a compromise between having a narrow CW filter, yet not so narrow as to present some issues like ringing or significantly reduced audio volume because of a very narrow BW.

Keep in mind this is very new to me and I may have some incorrect assumptions … the long journey starts with the 1st step. The on the air test is the key. I haven't figured out how to make this transmit CW --just another day at the home office.

The value of having two Teensy 3.5's is that I can use one as a test bed and the other as "standard" when I want to operate the rig. I only need to exercise care that I plug Teensy 3.5 Pin #1 into Socket Pin #1

Ok Bob, snooze over!

73's
Pete N6QW


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