PAR EF-SWL grounding improvement

[oceans777]

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.

 

[prcguy]

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.

 

[nanZor]

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.

 

[oceans777]

Thanks for the spot-on insight and advice, prcguy and hertzian.
I reconsidered yesterday, understood the isolation and reasoned it may not be the best or optimal way overall to defeat the noise etc. I replaced the jumper between 1 & 2, moved the ground (still with excellent results) and will definitely install the common mode choke before deciding which config works best.

These antennas like all things PAR, continue to amaze me with their simplicity, versatility and capability. With a G13DDC or G33DDC joining the receivers soon it will be fun learning what delivers the best results.

 

[oceans777]

The common mode choke is ready to install as suggested about 12’ down the coax from the box. I temporarily went back to grounding the 2 post secondary winding with jumper out between it and coax shield because it’s so much quieter until choke goes in this week. Reading all antenna info, I understand the connections but not why grounding the secondary is so seemingly effective, especially with the jumper out. Jumper in = immediate consistent noise especially 40 meters and at/below 80 is the TV noise scene from Poltergeist.

Am I just getting less noise at expense of desirable signal going into ground in that config with secondary grounded and shield isolated? So all noise on the shield can only go to ground at the house it seems (or into the antenna?) Not good.

Interestingly -
Before grounding #2 with jumper inline shorting 1,2, the EF-SWL was pulling in more weak signal than the Wellbrook loop, but now the Wellbrook is outperforming the wire in weak signals and definitely better SNR. Weak signals (and most) on wire are much fainter in the background noise on the SDR display of the Icom IC-R8600 it feeds. The Wellbrook fed second IC-R8600 signals are very sharp and clear from the background noise. Meters don’t show much difference when both 8600’s are set to same station.

So plan is install jumper back to #1, coax shield at antenna box and #2 secondary winding to restore shield as part of antenna and path to ground for both at box. Install common mode choke..

Sorry long post and antenna 101 for many. Hanging and hoping was a fun year but learning is more fun.
Appreciate any corrections in my plan or thoughts.

 

[oceans777]

All installed and great results. Noise is down significantly and I'm grounded on the shield, jumper in at box and re-grounded at the house which was loose after gate installer hit it with his equipment.

 

[prcguy]

How much difference did the common mode choke make?

All installed and great results. Noise is down significantly and I'm grounded on the shield, jumper in at box and re-grounded at the house which was loose after gate installer hit it with his equipment.

 

[oceans777]

Oh very big difference - the appliances and neighbors local noise has really dropped out of the antenna, not getting any of the washing machine, UVerse boxes etc at all now. It definitely is the best result I've had yet in lowering noise - much appreciated! Myantennas got the chokes here very fast too. Thanks prcguy!

 

[kamylkut]

My most sensitive SWL antenna is a 160 foot inverted L fed with a 9:1 balun. Based on the performance of mine, I would say this will probably become your favorite antenna. Add more wire for better performance on the low bands. Leave as-is is you spend most of your time above 10 MHz

 

[oceans777]

I'm reading lots of praise for the inverted L and it would definitely get reception where I'd like to be and the L is a great fit for the back yard. The Wellbrook loop is performing so well I thought I might skip taking the next level wire antenna but definitely going to get one up soon. Appreciate the info.