Dummy load power rating
 

On Tue, 23 Jan 2007 21:45:17 -0800, "Sal M. Onella"
wrote:

Nobody ever explained it. It's a wonder we didn't make more smoke than
light. [AN/SRT-14, AN/SRT-15, for those who've been there & done that.]

Hi OM,

Must've been before they were replaced with the AN/URC-32 (Collins). I
suppose there weren't enough bulbs to load 500W (much less from about
a dozen bays). All I remember where conventional dummy loads and the
time we used the shorting bar on the finals' capacitors and took out
the island's power station (forgot to throw the power switch off).

73's
Richard Clark, KB7QHC

Dummy load power rating
 

"Sal M. Onella" wrote in message
...

"Jimmie D" wrote in message
news:Ujwsh.298$ch1.65@bigfe9...
I was cleaning up today and came across an old dummy load I had that
looks
like it is made from 2 watt resistors. ITs mounted on a quart size paint
can lid and looks to be a 50 watts worth of resistors. This looks like
it
may have been a commercially built unit and I was wondering what the
power
handling capability would be if the resistors were submerged in mineral

Related, sort of:

When I was in Navy ET School in the 1960's, we had a shipboard radio
transmitter lab which used banks of incandescent lamps for the dummy
loads.
By the time we got to that phase of the school we understood the concept
of
matching to 50 ohms and I wondered then (and now) what the actual
impedance
of a bank of light bulbs would be. (Of course it changed with the amount
of
power applied, since it lit the lamps more or less brightly.)

Nobody ever explained it. It's a wonder we didn't make more smoke than
light. [AN/SRT-14, AN/SRT-15, for those who've been there & done that.]

Also, for excellent heat dissipation and no conduction, a liquid called
FC-75 is used as a heat transfer medium. They literally immerse the gear
in
a tank of the stuff and run it though a liquid-to-liquid heat exchanger.
It's totally inert. We used it in our high power pulse transmitters in
ECM
gear and it's apparently still around [
http://news.thomasnet.com/fullstory/473395 ] . No, I don't have any :-(



Yeah, I am familar with the stuff, its an inert flurocarbon. FAA did some
experiments to see if it could be use in RADAR tx oil tanks to replace PCB
type oil. I understand it worked pretty good, having better heat transfer
qualities than the oil they finally used.


After I got my ham ticket I built a little TX with a 6146 and used a light
bulb dummy load. To get an idea of how much power I was putting out I
measure the rsistance of a photo resistor with the tx keyed then applied a
variable ac voltage to the lamp and adjusted it until the resistor measured
the same and calculated power from the voltage and current measurements. I
wonder how accurate this was.

Dummy load power rating
 

On Wed, 24 Jan 2007 07:50:41 -0500, "Jimmie D"
wrote:

After I got my ham ticket I built a little TX with a 6146 and used a light
bulb dummy load. To get an idea of how much power I was putting out I
measure the rsistance of a photo resistor with the tx keyed then applied a
variable ac voltage to the lamp and adjusted it until the resistor measured
the same and calculated power from the voltage and current measurements. I
wonder how accurate this was.

Hi Jimmie,

This was exceptionally accurate. The substitution method here employs
a transfer standard. By bringing the light bulb to the same light
level (the substitution), you have removed any inaccuracy of the
detector, the photo resistor. It has been removed from the sources of
error. Further, you have shifted out of the more difficult domain of
direct RF measurement into 60 HZ where there are a world of tools
(transfer standards) that exhibit very good accuracy.

This is a form of calorimetric measurement, akin to bolometery.

73's
Richard Clark, KB7QHC

Dummy load power rating
 

Jimmie D wrote:


Next time I ask about something I will have it in my hand when I discribe
it. Dummy load is 44 each 2.2K 2 watt resistors in paralell.
I think I will rebuild it using metal film.



Jimmie D:

Perhaps they misunderstood the title of your thread and/or your original
question?

Now, I clearly heard you asking about a "Dummy Load Question"; however,
I fear some heard that as you wanted "A Load of Dummies' Answers to Your
Question."

However, you are right, be wise to ask a more concise question next time
LOL

Regards,
JS

Dummy load power rating
 

"Richard Clark" wrote in message
...
On Tue, 23 Jan 2007 21:45:17 -0800, "Sal M. Onella"
wrote:

Nobody ever explained it. It's a wonder we didn't make more smoke than
light. [AN/SRT-14, AN/SRT-15, for those who've been there & done that.]

Hi OM,

Must've been before they were replaced with the AN/URC-32 (Collins). I
suppose there weren't enough bulbs to load 500W (much less from about
a dozen bays). All I remember where conventional dummy loads and the
time we used the shorting bar on the finals' capacitors and took out
the island's power station (forgot to throw the power switch off).



The Collins AN/URC-32 was being taught at that same time, the early spring
of 1963. I distinctly recall getting a just-barely-passing grade in that
beauty because it was the last class in the school. I had my orders and I
was all studied-out after 38 weeks.

Each SRT-14/15 had its own bank of bulbs -- six or eight in a wire cage. No
idea of the series/parallel connection, though. The -14 did 100 watts. By
adding the HPA and its PS, the set became a -15 and did 500 watts.

Never performed the shorting bar trick myself but I saw the aftermath of one
of my crew doing it (AN/ULQ-6 - sometime in 1977). He converted much of the
line filter to a puddle of slag.

Dummy load power rating
 

On Wed, 24 Jan 2007 21:36:48 -0800, "Sal M. Onella"
wrote:

The Collins AN/URC-32 was being taught at that same time, the early spring
of 1963.

The Cadillac of HF.

Hi OM,

I was teaching at TI 7 years later. By then we had both added and
retired the TED/RED (VHF/UHF) with the SRC-20-21, added the URC-17c
(RTTY), and topped it off with a "systems" class (for teaching patch
panels, tuners, and encryption) to lengthen out the curriculum. That
was called A4, you probable stopped at A3 (Radar had A5 and A6
sections that I schooled in before becoming an instructor in the Comm
division). The system lab was two identical ship's comm stations
HF/VHF/UHF in all modes. One side held a comm with the other through
dummy load leakage.

73's
Richard Clark, KB7QHC