K0CQ CSVHF 2010

Low impedance parallel transmission lines

Back about 1964, I struggled to design a low impedance balanced line to match an array.

By 1966, my research showed the common formula was incorrect for low impedance lines.

So I wrote the article reproduced in the proceedings as it was published in The VHFer.

Low impedance parallel transmission lines

Back about 1964, I struggled to design a low impedance balanced line to match an array.

By 1966, my research showed the common formula was incorrect for low impedance lines.

So I wrote the article reproduced in the proceedings as it was published in The VHFer.

This QST

This was on page 61 of the April 2010 QST by QST's technical editor

Low Z TL

I have to admit only about half the professional references mention the restriction on the simple formula and no ARRL resources mention that.

The close spaced formula comes from work of Harold Wheeler about 1939 where he found that the charges on close spaced wires concentrated where the gap was smallest and that affect the

computation of the distributed capacitance leading to the inverse cosh formula.

Low Z TL

The earliest handbook I had with the full formula dates from 1943, an early edition of the Federal

Telephone and Telegraph Radio Handbook. It was copied from a Standard T&T handbook probably

printed about 1942.

ARRL publications have missed the update.

FT-8x7 TX-INH line

Typo in the fourth line second paragraph. Needs a closing parenthesis after “turn that transistor off.)”

Adjusting the FT-857 for transverter service

I've found evidence to indicate there is a similar menu for the FT-817, but I don't know if the values

or the menu entries are exactly the same.

It is handy to align the transmitter gain to absolutely prevent spikes and to keep the power minimized for transverter service without needing to go to the transverter mode. Because depending

on transverter mode allows full IF power to the transverter if that mode switch is missed.

Using TX-INH and DEMI TC for simple sequencing

Power Amplifier Protection Concepts

Typo, third paragraph third line, “loss, So the”

PA Protection

➔ We aren't using surplus parts so often.

➔Even Russian tubes are getting more expensive.

➔Exotic SS devices can run a kilobuck each now or can't be bought at all.

➔Voltages and currents rise in picoseconds in UHF and microwave amplifiers.

PA Protection

●The best protection comes from using devices that can stand a high SWR.

●The second best protection comes from using an output circulator.

PA Protection

●What to detect?

● Excess supply current.

● Excess SWR.

● Excess device RF voltage.

Collins 821A-1

821A-1

821A-1

821A-1

●Tripped off on high plate current.

●Tripped off on arc detection.

●Saved many tubes and vacuum variables from destruction.

Post 821A-1

Series switch tube also use for pulse width AM.

Saves much energy and power supply damage.

P TYPE FET circuits to follow

In these schematics the pass FETs are drawn wrong! Input is to source, load connected to

DRAIN.

PA Protection circuits

S D

G

CircuitsS D

G

G

D

S

CircuitsS D

G

S

GD

Steam power

Safe Tapping in Soft Metals

While machining handbooks say if the threads are the length of the screw diameter, a 50% thread

cutting depth is plenty, most tap drill charts are for a 75% thread which often leads to binding and a

broken tap.

For years I have gone to a number drill two or three sizes larger than the standard charts, but a

true 50% chart is better and is in this paper.

Safe Tapping

I have been thinking the threads extrude into the clearance space when tapping soft metals. So I

bought some alloy 1100, soft and gummy to show that. I've failed. But my experiment has vividly

shown the value of lubrication.

Safe tapping

Safe tapping

Safe Tapping, drills

Safe Tapping, Drills

Drills

Drills

Drills

Hole punches

Big hole punches