I would certainly trust this data from the two undergraduate college
students LOOONNGG before I'd trust W6LG to tell me the correct time of day.
You can calculate the power dissipated within their connector at 1750
MHz (through-loss of -0.17277 dB) as 3.9% of 1000 watts, or about 39
watts. No wonder it failed after 28 minutes...
I've felt an N connector passing 1500+ watts at 432 MHz from an 8938 get
hot enough to be very uncomfortable to hold. Assume an N connector has
0.05 dB loss (higher than what the undergraduates measured for
PL259/SO239 combo, but this connector was well-used); that's 1.15%.
1.15% of 1500 watts is 17.4 watts. (Since this system had to be 100%
reliable, we switch to type LC connectors instead.)
Steve, K0XP
On 6/17/2024 11:41 AM, David Gilbert wrote:
That's really interesting data. I'm currently thinking about an array
of helical antennas for weather satellite reception at 1700 MHz that
would need a phasing harness. Your results suggest that since all I'm
concerned about is reception, I could get away with even UHF
connectors without too much loss involved. I have a bunch of LDF1-50
heliax for the cable, and I found that it works fine with a PL-259 ...
I just solder the center conductor to the pin and the shield to the
barrel. It all fits like a glove.
Thanks!
Dave AB7E
On 6/17/2024 9:53 AM, Kimo Chun wrote:
From the archives when I posted in 2012. All credit to my friend K7FR.
This subject comes up from time to time. I believe this is possibly
definitive proof.
73, Kimo KH7U
*Fromk7fr@ncw.net <k7fr@ncw.net> (Gary Nieborsky) Mon Sep 16
17:18:20 1996*
From:k7fr@ncw.net (Gary Nieborsky) (Gary Nieborsky)
Subject: Cable Attenuation Question
Message-ID:<199609161618.JAA02127@bing.ncw.net>
Tom,
35 watts = pencil soldering iron.
Your comments made me go out and dig through the College Archives.
Back in senior year at Washington State U (W7YH, Go Cougs!) we had
to do a
measurement project in Measurements Lab. Since there were two hams
in the
Lab we decided to measure losses in coax connectors (the Prof was a ham
too). We set up a calorimeter and measured I**2R losses from DC to 2
GHz
for a PL259/SO239 combo (did it for BNC and N too...hey it was a senior
project).
Here are some of the results from my Lab Notes:
Input power = 1,000 watts (100V, 10A @ DC, homebrew 4-1000 .1-30 MHz,
borrowed USAF signal source 30-2,000 MHz (black box from Fairchild AFB),
Bird dummy load)
(We used a kW because neither of us had ever run more than 100
watts...power
trip!)
f (MHz) Loss (W) dB
0.1 1 -0.00435
1 1.2 -0.00521
10 1.3 -0.00565
20 1.5 -0.00652
30 1.8 -0.00782
50 2.2 -0.00957
100 2.6 -0.01131
200 3.5 -0.01523
300 5 -0.02177
400 7 -0.03051
500 10 -0.04365
1000 15 -0.06564
1250 18 -0.07889
1500 28 -0.12334
1750 39 -0.17277**
2000 100 -0.45757**
** Connector failed before calorimeter stabilized.
We attributed the steep upswing after 100MHz to the finish on the
connector,
not the connector design. Nickel plating seems to exhibit non-linearity
above 100MHz. The N and BNC runs were much better. BNC went flakey
above
600MHZ (RG-58 size, RG-8 BNC went to 1000 MHz). We were able to isolate
cable loss from connector loss by building a teflon box around the
connector
body and only "viewing" the inside of the box with the sensor. The
Department Chair was not at all happy that this teflon box cost $750 to
build (teflon was rare in 1977).
As you can see from the table we experienced two failures. Both were
due to
the solder melting in the probe part of the connector. The 1250 and
1500
watt runs showed discoloration but no melting. The values for 1750
and 2000
MHz were the calculated values at the time of failure. Each run took 1
hour, these two failed 28 and 17 minutes into the test.
We experienced a failure of an N connector at 2000MHz. We ran the
output
up in 100 watt steps until we observed a sharp up turn in losses. We
were
able to boil the water in the calorimeter at 15,000 watts and at 17,100
watts the fingers inside the connector relaxed and started arcing.
Before this experiment I was paranoid about my connectors. Since then I
have only been concerned with the quality of the assembly and water
ingress.
My take on it.......
73 Gary K7FR
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