Just some info im copying and pasting from an online resource-
After a year running the PAR EF/SWL as a sloper in default configuration (#1 and #2 posts shorted together on the network box) with no ground at the box (I have a coax ground at the house near the receivers) I finally grounded the #2 post over the weekend.
I had great reception before but below 4-5 MHz was awful until very late night or early AM. Lots of nasty RF, spikes, crashing from the house and neighborhood across the bands, (ATT Uverse DVR boxes alone plagued 11 MHz unless unplugged.) 80 meters was just a noisy mess. 20 meters often had spurs every 20-40 kHz, didn't realize how bad it was.
I tested grounding the #1 post first ((SO-239 shield) with the jumper still connected to 1 & 2. Some improvement, better than it was. Then I grounded #2 (ground lead of the antenna side of the 9:1 transformer) with the short jumper removed - what a huge improvement for my area.
Easily picking up weak signals now on 80 meters and monitored through noon with no problem. Never been able to do that except on the Welbrook Loop and not with the reach/reception of the PAR. The entire HF SWL is dramatically quieter, all of the nasty stuff is gone and anything remaining is so much quieter through 25 MHz.
I reconnected the short jumper to 1&2 with #2 still grounded, and much of the noise came right back especially below 5 MHz. I think it was getting into the antenna on the outer of the coax. Never saw any real difference grounding receivers but I'll sure be grounding the other PAR antenna this week.
Just passing it along and hope it's useful for other PAR/LNR Precision HF SWL antenna operators.
Antennas like the PAR end fed use the coax shield as a counterpoise to some extent. Grounding or floating will be different for each user depending on noise flowing on the outside of the coax from sources inside the house or ?? Sometimes grounding the antenna brings in noise from whatever you are using for a ground due to noisy appliances sharing that same ground.
The best thing you can do for this type antenna is put an effective common mode choke in the feedline that will stop common mode junk from flowing up the outer shield to the antenna. You can make an effective choke by wrapping coax around a ferrite core, or just buy one specifically designed for SW receiving like this one:
https://myantennas.com/wp/product/cmc-0510-r/Placing this in line maybe 10 or 15ft down the coax from the PAR transformer should give better results than the best you've had so far changing the ground connections. There will probably be a ground connection that works better than others with the choke in line and one that connects the coax shield to the transformer will include the coax shield as a counterpoise while the common mode choke will isolate the shield from everything else down stream toward the radio and interference in the house.
Aug 28, 2018
#3
Removing the jumper from #1 and #2 physically isolates the primary and secondary windings of the transformer. You can verify this by using a voltmeter set to detect shorts and opens. With the jumper removed, you will not notice any physical connection between the input and output windings.
That's a start. But as prcguy mentions, and as I have noticed in my own projects, additional common-mode filtering and/or grounding of the shield is beneficial.
BUT, if your antenna system actually depends on the shield as being part of the antenna, then you'll want to leave the jumper in place, and deal with common-mode, rfi, etc in other ways.
It's a pretty flexible system, but if one has no preference, and just wants to try and cut down common-mode shield noise, then removing the jumper (or just pivoting it out of the way so you don't lose it) is a nice way to start. It may require further attention, but I love the EF-SWL for that kind of flexibility.
In your tests, where you removed the jumper and grounded #2, what you did was physically isolate the antenna from the shield, but provided a ground of the secondary winding, out at the ef-swl box, which seems to have improved your setup.
Plan or play, I dig that little antenna.