Hi Walter,

In MY kitchen I have two workhorses, comprising the -

Autek Research, RF Analyst, Model RF-1, Frequency range 1.1 - 36 Mhz

and the -

MFJ, HF/VHF SWR Analyser Model 259-B, Frequency range 1.8 - 170 MHz.

Both were made in the USA. I bought the 2nd one in the hope it might be
better than the first. It wasn't. Nevertheless, between them they are the
best things since sliced bread.

The last measurements made using them were of soil impedance vs frequency,
in the kitchen sink, on samples from my backyard.

And the accuracy of any instrument depends on how it is used rather than on
what the manufacturer says about it.
----
Reg, G4FGQ

================================

"Walter Maxwell" wrote
And Reg, in conjunction with the HP-8405 Vector Voltmeter, the HP-778D
dual
directional coupler can measure SWR from 1 MHz to 1 GHz with no
transmission
line whatever. This combination is the workhorse of my RF Lab.

Walt

Walter, W2DU wrote:
"Is it possible that Geoff`s business is a spinoff grom Gates?"

Harris Intertype Corporation, predecessor of Harris Electronics,
axquired Quincy, IL`s Gates Radio in the 1950`s, I believe. Then Harris
really hit the acquisition trail. It acquired R.F. Communications, a
2-way radio manufacturer. It also acquired a telephone and SCADA
equipment manufacturer, which had a government equipment and
semiconductor division in Florida. It acquired Farinon Electric a
microwave manufacturer in California. There were other acquisitions,
Lanier which made office equipment such as duplicators. It acquired a
hardware manufacturer which made 19-inch equipment racks among its
products. I don`t about other shuffles in Harris` portfolio of
companies, but the companies it bought were among the best at what they
did at the time of acquisition.

Best regards, Richard Harrison, KB5WZI

In brief, how can you have a conjugate match with the source impedance
hopping about trying to follow the load? ;o)
----
Reg, G4FGQ

Reg, I have a myriad of measurements which prove that when the pi-network
is
adjusted to deliver max power for any reasonable drive level into any
reasonable
value of load, the source impedance is the conjugate of the load
impedance. When
adjusting the load control of the network for max output the output
resistance
equals the resistance of the load. And when the plate tuning is adjusted
for max
out the reactance injected into the network equals the reactance opposite
to
that in the load. To be practical, be assurred that the tuning and loading
controls are alternately adjusted continuously until they converge and the
max
power is delivered.

Having performed these measurements many, many times, I assure you that
the
resulting data isn't a series of coincidences. So instead of the source
impedance 'hopping about trying to follow the load', when the network is
correctly adjusted, the source impedance 'finds' the load and stays put
until
the load is changed and the network readjusted to accomodate the new load.

Walt
================================

Walt, forgive me for stating the obvious, but when operating under
non-linear conditions, as tubes and transistors are, I think you'll agree
that when the load resistance is changed, the tubes operating conditions
also change, and so does the tube's internal resistance.

I don't know exactly how you have conducted your measurements. But I suggest
that when you change the load you automatically force the internal
resistance to change with it.

But in any case, whichever way the source changes, the basic idea of a
conjugate match to an unstable source is itself not very sound.

The best way of determining source impedance is to mathematically model and
calculate it. It need not be accurate. It is necessary only to show that it
does change.
----
Reg, G4FGQ

"Walter Maxwell" wrote
If you question my statements above see the data from my measurements
using
professional grade instruments in either QEX, May/Jun 2001, Chapter 19 in
Reflections II,

============================

The accuracy of measurements depends on who uses the instruments rather than
on what the manufacturer says in his sales catalogue. I'd much prefer just
to take your word for it, Walt. The manufacturer's type number is
superfluous - it sounds like a gratuitous advert.
----
Reg, G4FGQ

Walter, W2DU wrote:
"A conjugate match can be obtained for any loading you choose."

No doubt. A conjugate match permits maximum power transfer. No other
load can extract as much output as a conjugate match. Were I designing a
broadcast transmitter for a 50-ohm or a 75-ohm load, I would want my
money`s worth from the output devices I`ve selscted, consistent with a
long useful duration.

I`d design for a conjugate match at the rated load and include overload
protection for an output short circuit or near short. For solid-state
I`d provide overvoltage protection.in addition to overcurrent
protection.

Harris solid-state medium wave transmitters have a number of amplifiers
supplying the output and a faulty amplifier can be easily removed from
service while the remainder continue operation almost as if nothing had
happened, if I read their internet pages correctly.

Best regards, Richard Harrison, KB5WZI

Reg Edwards, W4FGQ wrote:
"---when the load resistance is changed, the tube`s operating conditions
also change, and so does the tube`s internal resistance."

I would think that change in operating conditions result from
readjustment of the amplifier, not from changing the load on it.

Most of the output impedance of a Class C power amplifier tube does not
come from the saturation resistance when switched on, but comes from the
duration of the period in which it is switched off. Until you readjust
drive, the on and off periods and even the saturation resistance of the
tube remain unchanged.

Best regards, Richard Harrison, KB5WZI

"Richard Clark" wrote about the specs for Harris Broadcast Txs:
As for the specification for output impedance gone missing :-)
MW-10B SPECIFICATIONS
RF OUTPUT IMPEDANCE: 50 ohms, unbalanced.
Other output impedances available on special order.
Harris Platinum Z FM transmitter
100 ohm output impedance (unbalanced)
HARRIS SW-50 A
RF Output Impedance 300 ohms balanced, 2.0 to 1 maximum VSWR
Well, instead of reciting their complete catalogue, it is easier to
simply say I could not find any product that did not specify an output
impedance, much less that others were available on special order.
_____________

I won't try to soften this: your conclusion above doesn't just _appear_ to
be wrong, it IS wrong. 100% wrong. The impedance published by Harris is the
expected load impedance, not the tx source impedance -- which is the
convention used by all OEMs of broadcast txs (at least).

How do I know? I was the author of all of the brochures and technical data
sheets for Harris' entire FM product line for the ten years before I
retired. That any published value of impedance applied to the load
impedance expected was/is universal across the product lines: AM/FM/TV.

Your post above showing 100 ohms for a Platinum Z FM tx also is wrong. It
is designed for a 50 ohm load. Here is a link to an on-line brochure for
the current 10kW model:
http://www.broadcast.harris.com/prod.../HAR173569.pdf
Observe the statement at the bottom of the right column on the last page
thereof, which I quote below for your convenience:

"All specifications referenced to any single output frequency
(87.5-108MHz),
nominal rated output power, and 50 ohm, isolated, non-reactive load."

No other RF impedance spec is given in the very detailed list of specs
contained in these brochures.

Kindly recant your accusations.

RF

"Walter Maxwell" wrote to R. Fry:
I'm not at all familiar with the circuitry used in solid-state
amps, please interpret my comments accordingly.
__________

Understand, and will keep that in mind. However I won't be
reading/responding to anything for the next few days, as I'll be taking a
short "R&R" trip.

RF

"Walter Maxwell"
When I bought the tx for new BC stn WCEN in 1948
it was from Gates Radio in Quincy. Is it possible that
Geoff's business is a spinoff from Gates?

Yes, Harris-Intertype (later just "Harris Corp") bought Gates Radio, lock,
stock and barrel -- not a spinoff.

Don Peterson, developing the use of TDR for finding discontinuities
in RF feed lines for TV. He developed a kit for use in the field for
locating ghost problems in the lines connecting the tx to the antenna.
Were you aware of Don's work in this area?

Vaguely. My primary contact and mentor was Dr Matti Siukola, lead engineer
at RCA's antenna lab and test range at Gibbsboro, NJ. Under his direction I
was responsible for updating and improving the VHF and UHF RF pulse test
sets used by RCA Field Service.

RF

Hi Richard,
I don't have anything to do with broadcasting, but when I first ran across
their DX line of AM transmitters, it really blew my mind. It seems though,
that it is really hard to find detailed info on them. Do you have a link
that describes what happens in some detail. The best I have been able to
come up with was anecdotal data let to from the WLW web site. There must be
some article that was published in some trade magazine. My questions a

The 50 KW transmitter supposedly has 60 some modules of about 1KW each. How
does this jive with being able to get the 200KW PEP that is required for
100% upward modulation? Does the combiner add voltage or power? Seems like
it would be voltage, but then the impedance a module sees would depend on
how many are active at a given time.

What is the digital sampling rate? Seems to me they need a high power
bandpass filter to get rid of the sampling frequency after the combiner.

BTW, I think a lot of people are going to confuse this with Digital AM.

Tam/WB2TT

"Richard Fry" wrote in message
...
"Richard Clark" wrote about the specs for Harris Broadcast Txs:
As for the specification for output impedance gone missing :-)
MW-10B SPECIFICATIONS
RF OUTPUT IMPEDANCE: 50 ohms, unbalanced.
Other output impedances available on special order.
Harris Platinum Z FM transmitter
100 ohm output impedance (unbalanced)
HARRIS SW-50 A
RF Output Impedance 300 ohms balanced, 2.0 to 1 maximum VSWR
Well, instead of reciting their complete catalogue, it is easier to
simply say I could not find any product that did not specify an output
impedance, much less that others were available on special order.
_____________

I won't try to soften this: your conclusion above doesn't just _appear_ to
be wrong, it IS wrong. 100% wrong. The impedance published by Harris is
the
expected load impedance, not the tx source impedance -- which is the
convention used by all OEMs of broadcast txs (at least).

How do I know? I was the author of all of the brochures and technical
data
sheets for Harris' entire FM product line for the ten years before I
retired. That any published value of impedance applied to the load
impedance expected was/is universal across the product lines: AM/FM/TV.

Your post above showing 100 ohms for a Platinum Z FM tx also is wrong. It
is designed for a 50 ohm load. Here is a link to an on-line brochure for
the current 10kW model:
http://www.broadcast.harris.com/prod.../HAR173569.pdf
Observe the statement at the bottom of the right column on the last page
thereof, which I quote below for your convenience:

"All specifications referenced to any single output frequency
(87.5-108MHz),
nominal rated output power, and 50 ohm, isolated, non-reactive
load."

No other RF impedance spec is given in the very detailed list of specs
contained in these brochures.

Kindly recant your accusations.

RF