JANUARY 22, 2019

Salt Water Immersion Blows Out RF Connectors

SO-239 in Remote Relay Switchbox

Here's what happens when Saltwater gets into a RF Connection

After repeated submersion at high tides, the feedline connector finally failed. The mating PL-259 was also destroyed.

***

So today's update reveals my misdiagnosis of the NE vertical feedpoint as the source of the difficulty. Tracing the problem from this starting point led me to the remote switchbox when the NE 84˚ line checked-out good. When removing the box in order to barrel-connect the SW vertical to the feedline, I discovered the SO-239 and PL-259 connectors had ice in them which, when chipped-off, revealed major arcing had been taking place for quite some time. This explained the problem I had been ghaving for several days of RF getting into my audio back in the shack. I removed the switchbox and cables, chipping them out of the ice pack, and connected the SW vertical to a second, back-up feedline pre-installed when I set up the system. This worked and I was back on the air with a single vertical last night, with full control over my audio. I replaced the connectors in the switchbox and on the feedline, slipping some ferrite beads on the latter to further reduce common-mode noise on receive. BooM. DonE. 

New Switchbox and Feedline Connectors

Added ferrite beads to main feedline at switchbox end.

 

***

What we're going to do today is measure the length of the 71˚ Christman phasing line we ended up with and replace it with a new contiguous length of coax. This emancipates the barrel conectors presently tied-up in the lengthening of the phasing line, while making available for use several short patch cables. One of these patch cables will be used to connect the L-match to the remote relay switchbox after I mount both onto the same post.

 

OK, I just did that.

Measuring the Final Length of the 71˚ Christman Phasing Cable

We finally get to see exactly how long it ended up being.

 

***

24.5' is the final length that I ended up with to lock the system into its present performance level. Let's compare that to mathematical calculations which set the 71˚ Christman 71˚ phasing line at 22.4' for RG-8X @ 7.1 MHz. This means we are Two Point One (2.1) feet longer, which could partly be due to the actual velocity factor of the coax I am using and partly because of the soil characteristics intrinsic to the salt water installation. However, we note that we had to add 7" to the same 71˚ phasing line used at the previous, inland installation (Editor: These items were brought together into a phasing & impedance-matching system installed out in The Marsh. 

New Phasing line
& connectors 

We raised it above upcoming Super High Tides (editor: using the elevated counterpoise system shortly described in this blog). So I would say that the real-world conditions surrounding a phased aerial installation do determine the final dimensions of the Christman phasing lines. In fact, if we subtract the 7" required for our salt marsh installation, we come up with 23' 10" as teh length of the phasing line used at the inland installation which used elevated counterpoise wires. Let's step-back and check out how these numbers crunch.

• Mathematically Calculated Length: 22.4'
• Inland Installation Length: 23.8' (106% longer)
• Salt Marsh Installation Length: 24.5' (109% longer)

That's empirical data derived from our own experimental work performed over the past few years. We may not win a Nobel Prize, but we can assuage concerns perplexing others building any phased array about sticking with coaxial lengths mathematically calculated. Any installation has to be tweaked because each one exhibits final qualities unique unto itself. So don't be afraid to deviate from dimensions provided by mathematical formulas or computer modellings. Here's what else we did today.

 

Phasing & Impedance

Matching System

Waterproofing
Connectors

We installed fresh coaxial connectors and consolidated several integral systems into one mechanism. These items were brought together into a phasing & impedance-matching system installed out in The Marsh. We raised it above upcoming Super High Tides. This field work was installed this afternoon and converts the 37 Ohm j7 impedance at the remote switching box into 50 Ohm j0 along the RG-8X feedline run back to the shack. 

This reduces receiver noise resulting from common-mode ingress along this stretch of the array's cabling system. Ferrite beads were added to the feedline to further decouple it from the array. Upon returning to the shack at sunset, a European pile-up erupted producing numerous 59+10dB to 25dB signal reports and 25db to 30 dB F/B observations.

DXSummit: January 22, 2019

Initial test of system upgrades produces encouraging results.

 

***

When the system F/B was tested, the average EU report was 25 to 30 dB. I think the installation of new PL-259 connectors with reducers, soldered with an eye on making good shield connections, combined with the removal of several PL-259 & barrel connectors integrated into the phasing line when tuning the array, have improved its overall operation. Up next will be to raise the feedpoint of the NE vertical so that it cannot be shorted-out by super high tides. After that we will relocate the SW vertical deeper into the Marsh so that it becomes the NE vertical. This will allow for the deployment of both ground radial systems (30 radials) in a symmetrical fashion, bring both verticals to the same elevation and cause their ground radial systems to be swamped by salt water at high tides.