Download K0CQ-CSVHF2010

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
Circuits
S
D
G
D
G
S
Circuits
S
D
G
D
G
S
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