Ham Radio Programs

Three programs of use to radio amateurs.

• HASH TABLE: A program to keep track of calls during a contest
• TB: A program to compute distance based on LAT / LONG of endpoints
• CHIM: A program to compute cable impedance

“CHIM”, calculates the characteristic impedance (Z₀) of five transmission-line types—single coaxial, balanced shielded, two-wire, parallel strip, and two parallel lines with sheath return—using standard RF engineering formulae involving natural logarithms and square roots of the relative dielectric constant.

“HASH TABLE”, implements an open-addressing hash table for amateur radio contest duplicate-call detection, hashing six-character callsigns by summing their character codes modulo 1000 and using linear probing for collision resolution.

“TB”, computes the true bearing and great-circle distance between two geographic coordinates entered in decimal degrees, outputting results in nautical miles, statute miles, and kilometres using spherical trigonometry (ATN, ACS, SIN, COS, TAN).

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Program 1: CHIM — Characteristic Impedance Calculator

The program prompts for a transmission-line type (1–5) and a relative dielectric constant, then dispatches via GOTO 100*A to one of five calculation blocks at lines 100, 200, 300, 400, and 500. This computed GOTO is a classic Sinclair BASIC dispatch idiom that avoids an explicit IF–THEN chain.

Transmission-Line Formulae

Type	Line	Formula
Single coaxial	150	Z = (138/√E) × log₁₀(D/R)
Balanced shielded	270	Z = (276/√E) × log₁₀(2V(1−S²)/(1+S²))
Two-wire	360	Z = (276/√E) × log₁₀(S+√(S²−1))
Parallel strip	480	Z = 377×H/W/√E
2 par. lines, sheath return	570	Z = (69/√E) × log₁₀(V/2/S²×(1−S⁴))

Natural logarithms (LN) are converted to base-10 by dividing by LN 10, since the standard RF impedance constants (138, 276, 69) assume log₁₀. The subroutine at line 600 collects geometric parameters H, D, and R, with branching at lines 630 and 640 to skip inapplicable inputs for types 3 and 4.

Error handling stores the offending section’s starting line number in L and jumps to line 720, which prints “ERROR, REENTER” and then executes GOTO L to re-enter that section. After a successful calculation, control returns to line 25 to re-prompt for the dielectric constant, allowing repeated calculations of the same line type.

Notable Anomaly — CHIM

Line 37 validates that A is an integer between 1 and 5, but the check IF E>0 THEN GOTO 100*A at line 55 only verifies the dielectric constant is positive; it does not catch zero or negative-but-not-entered values that might have been left from a previous run, though in practice INPUT always replaces the variable.

Program 2: HASH TABLE — Contest Dupe Checker

This program maintains a 1000-element string array A$ of six-character callsigns, initialised to ****** as a sentinel, to detect duplicate (“dupe”) calls in an amateur radio contest. It uses FAST mode during the slow initialisation loop (lines 6–31) for speed, then returns to SLOW for interactive use.

Hash Function and Collision Resolution

The hash is computed by summing the CODE values of all characters in the padded six-character callsign (lines 55–65), then taking the result modulo MAX (1000) using H - INT(H/MAX)*MAX (line 70) — the standard Sinclair BASIC modulo idiom, since MOD is not a keyword. Collisions are resolved by linear probing: H is incremented (line 85) and wrapped (line 90) until either the callsign or an empty slot is found.

• Input strings shorter than six characters are padded with spaces (lines 47–49) using a GOTO-based loop, since FOR over a dynamic length would require a variable already set.
• The sentinel value ****** is safe because no valid amateur callsign consists solely of asterisks.
• The array is printed in hash-table order (not insertion order) at termination (lines 120–135), so the output listing is not alphabetical.
• There is no deletion mechanism; the table fills permanently for the duration of the contest session.

Program 3: TB — True Bearing and Great-Circle Distance

The program converts decimal-degree inputs to radians (multiplying by PI/180) and applies spherical trigonometry. Longitude difference L is normalised to the range (−π, π] at lines 130–140 to ensure correct quadrant handling.

Bearing Calculation

Lines 150–230 compute the true bearing using the four-quadrant arctangent method. Because Sinclair BASIC provides only single-argument ATN, quadrant correction is done manually:

1. Compute a raw angle C = ATN(1/CC) (line 170).
2. If L > 0 and C > 0, no adjustment is needed (line 180 → 230).
3. If L < 0 and C < 0, add 2π (line 220).
4. Otherwise, add π (line 200).

Distance Calculation

Line 250 uses ACS (SIN A*SIN B + COS A*COS B*COS L) — the spherical law of cosines — to find the angular separation, which is then converted to nautical miles (×60), statute miles (×1.1508), and kilometres (×1.852).

The FAST call at line 112 speeds up the trigonometric computations before displaying results. Convention is unusual: West longitudes are positive and East negative (opposite to the ISO standard), matching the comment at lines 14–16.

Potential Issue — TB

Line 160 computes CC = (1/TAN L) × COS(A+PHI) / SIN PHI. If L = 0 (same meridian) or SIN PHI = 0, a division-by-zero error will occur with no guard. Similarly, ATN(1/CC) at line 170 fails if CC = 0.