[TowerTalk] How lossy are PL-259s at HF?

[Steve Harrison]

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 at ncw.net <k7fr at ncw.net> (Gary Nieborsky)  Mon Sep 16
>>> 17:18:20 1996*
>> From:k7fr at ncw.net  (Gary Nieborsky) (Gary Nieborsky)
>> Subject: Cable Attenuation Question
>> Message-ID:<199609161618.JAA02127 at 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
>>
>>
>>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
--
See my QRZ.com page at *https://www.qrz.com/db/K0XP*