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

[David Gilbert]

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
>
>
>