Finally, a Radio Antenna

Over the past couple of months I have been working planning, and now, this last week, installing a radio antenna suitable for Ham frequencies (in particular, 10, 20 and 40 meter wavelengths).

The antenna installation comprises:

  • A 60′ plus antenna wire, run from our cut-off chimney, then passes though a tree supported from a limb, and then is attached via a rope to a 10 foot high PVC pipe which is sunk into the ground 2 feet, which provides support for the far end (and keeps it well above my head.)
  • An antenna matching transformer that matches the relatively high impedance of this “end fed dipole” antenna to the 50 ohm impedance of the coax feed line attached to it.
  • A safety ground the leads down from the box containing the antenna matching transformer, to a metal box which connects this to the lighting arrestor ground and a ground that runs off to the inter-system ground (see below.)
  • A lightning arrestor which is installed into the feed line, and which connects to the feed line into the house.

A big difficulty with my antenna installation was grounding. An antenna must have a ground, both to “work”, but also to provide static discharge to discourage lightning strikes.

If lighting strikes a typical antenna, it will vaporize and likely damage any equipment attached to it – that is not what the safety ground is designed to prevent. Rather, it attempts to discharge pre-lightning voltage build-ups.

An ideal ground is directly below the antenna, with a 6 foot or so rod driven into the soil. However, if that is done, it is also crucially important to “bond” that ground rod with any others on the property (such as one installed by the electric company.) The reason this is so important is that if lighting strikes the utility lines, it wants to find its way to ground, and will happily do that through your house wiring to find your radio ground, if the two ground rods are not bonded. The reverse is also true if lighting strikes the antenna.

However, in my case that would have meant running the AWG 6 (!!) bonding wire through a rock wall, which was rather impractical. So, instead, I opted to run the safety ground above ground, mounted under the deck, and connect up to the inter-system ground that was installed at my electrical panel in 2017 when that panel was replaced. That connection then connects it to the utility ground rod.

Here are some photos:

Note that the antenna box in the first picture, which contains the matching transformer, attaches to the eye bolt on the chimney with two lines of different lengths. Do you know WHY the lengths are different??? Leave a comment, below.

Q: When is a Capacitor not “just a capacitor”

A: When it is acting as a simple delay line

While working on ALD page 12.65.01.1, which generates power on and computer reset signals, I noticed something that didn’t look quite right. The computer reset signal (active negative) when negative when the button push was simulated, then went back inactive, then went active again 25 microseconds later – when it was actually supposed to go active (the result of the timeout of a 25 microsecond single shot gate).

Puzzling – the logic all looked fine. What was going on? At first I thought, “so what – it is going to reset anyway — so no big deal”. But then I looked at the IBM 1410 system fundamentals document, S223-2648, page 26, which makes it pretty clear that the computer reset signal should only be active after the computer reset clock start single shot times out, indicating that the logic gate should stop at either state A or state R. But why?

Then it hit me: CORE STORAGE. If one resets the machine at the wrong time – say, in between reading a character from core (which is a destructive operation) and writing it back, bad things would happen. — the character would be erased. But, how did the actual machine avoid this problem? Sure, I have a relatively long (90 ns, with a 100MHz FPGA clock) single shot setup time to detect the rising edge of an asynchronous trigger on the single shot, but regardless, that setup time would not be 0.

Then I saw it: A 0.047 microfarad capacitor in the ALD page 12.65.0.1 between that computer reset signal and logic ground. Ah HA! A delay!

Fortunately, I had already learned how to implement a delay on an FPGA: with a “bucket brigade” delay line – whose length determines the delay. Sticking a 4 cell (120 ns) delay at that point in the circuit fixed things up just fine.

The results are shown in the simulated ‘scope trace, below. (The count signal and SSTAGE# signals below are for a different 20 millisecond single shot.)

A couple of errors in the IBM 1410 System Fundamentals manual

For starters, I should say that the IBM Field Engineering Instructional materials, which I relied on heavily when creating my IBM 1410 Simulator software are excellent, especially considering these documents were typeset in more than a decade before anyone had heard of a word processor.

Nonetheless, I stumbled into two errors in the IBM 1410 System Fundamentals manual, S23-2589, this week. Both are instances where the output signals from gates are different from what is shown in the document.

The first one I ran into was the first Single Shot that I came across in the diagrams, SMS card type DHE, part number 370262. The timing diagram shown in figure 110, page 93 of the manual shows a negative going input pulse triggering a positive going output pulse. An analysis of the electronics in the first of two SMS card manuals (which have no number) and the use of this card in an ALD, 12.60.20.1, makes it apparent that a negative going incoming pulse creates a negative going output pulse. (This was implemented in my FPGA VHDL generation by triggering a counter on the leading negative going input pulse, which then counts down to 0.)

The other error applies to card type DFZ (and its companion, DGA), which I ran into on ALD page 12.61.13.1. The timing diagram in figure 107 on page 92 of the System Fundamentals manual shows NAND logic: If both inputs are high, the output goes negative. However, analysis of the circuit for DFZ, part number 370241 makes it apparent that it is actually NOR positive logic: If either input is high (approximately 0v), then the output is low. Only if both inputs are low (negative voltage) is the output voltage high. This was “sussed out” by looking at the intended logic on the ILD.

The FPGA Simulated IBM 1410 has a “pulse”

Having spent the past few months cleaning up my IBM 1410 SMS database program, and posting it to github at https://github.com/cube1us/IBM1410SMS , I have spent the past couple of weeks focused on the HDL (currently VHDL) generation, using GHDL and Xilinx’s Vivado toolset, with an eventual destination of my Digilent Nexys4 FPGA (Field Programmable Gate Array) board.

After fixing a few bugs, and implementing the oscillator (by way of a counter/divider from the 100 MHz FPGA clock), I loaded the results into the FPGA, and as show below, my IBM 1410 now has a clock, running at the right frequency for an IBM 1410 with the accerated throughput feature, as shown below:

IBM 1410 FPGA Clock
IBM 1410 FPGA Clock

On the original machine the lower signal, on channel 2 of the oscilloscope, was derived from the first using a delay line – about 330 ns of delay. Kinda hard to do with an FPGA. 😉 So, I implemented delay lines using a series of flip flops clocked by the 100 MHz FPGA clock – so, in this case, there are 33 of them.

This signal is not simulated – it is a real signal that exists in the FPGA.

Change in Amateur Radio Call Sign — W9IYN

WPE9IYN Shortwave Certificate
WPE9IYN Shortwave Certificate

Back in “the day” Popular Electronics magazine offered certificates for what it called “Short-Wave Monitor Certificate of Registration”. In the 1960’s I wrote in and obtained such a certificate and was assigned “station identification sign” WPE9IYN.

Part of the “deal” was that Popular Electronics also worked with the FCC to reserve the id (without the “PE” in the middle) so that your assigned station identification sign could also become your amateur radio service call sign.

I had intended to work towards an amateur radio license – my uncle and cousin were Hams. I spent some time learning code, but never actually took the exam.

So, after I obtained my license in February, I checked if W9IYN was available, and sure enough, it was. So, I applied for, and obtained that call sign as a “vanity” call sign. So, my Amateur Radio Service call sign is now W9IYN.

After some 53 years, I am finally a licensed Amateur radio operator (“Ham”)

When I was in middle school, my buddy Ross introduced me to the world of electronics by lending me his Knight Kit “Ocean Hopper” regenerative radio. We also worked together building a flip-flop circuit provided to us by a “traveling roadshow” on computers when we were in 8th grade.

When I was in 9th grade – junior high at the time – I was fortunate to receive the requested Knight Kit “Star Roamer” as a Christmas gift – still have that radio today.

In 1967 I wrote into Popular Electronics magazine, which was offering “call signs” as a “Short-Wave Monitor Certificate of Registration” for non-licensed receive-only hobbyists. At the time, they also coordinated with the FCC to reserve those call signs. I still have my certificate, and will eventually post it on my site.

Fast forward to Feb, 1, 2020, when I took the Technical and General amateur radio exams administered by the Volunteer Examiners from the Four Lakes Amateur Radio Club, and passed both with perfect scores.

My call sign was originally KD9OVL. However, I also applied for an FCC “vanity” call sign – which is the same as the one issued by Popular Electronics in 1967 (without the “PE” portion, after the “W” prefix.). I’ll let you know how that turns out. 😉

UPDATE: As of 3/10/2020, my call sign is now W9IYN.

73 (Amateur Radio lingo for “Best Wishes”)