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Author Topic: XLR8 7/14/15 receiving antenna comparison: PA0RDT vs RF Systems EMF via Palstar  (Read 8977 times)

Offline Lex

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When XLR8 came on Monday evening I just happened to be testing a version of the popular PA0RDT active antenna that Chris whipped together for me to try out.  It works so well I might not send it back.  Or maybe I'll send back an empty paint can and claim the NSA and USPS stole the guts.

I compared the active antenna against the excellent compact RF Systems EMF - a clever thing that's quick and easy to rig up for temporary receive only use.  It's made of RG174 shielded coax for both the main antenna and feedline/counterpoise, along with some fancypants impedance transformers on both ends, including one that seems to help with non-directional MW reception.

To get as far as possible away from the usual suburban noisemakers I set everything up on batteries on a metal picnic table in the back yard of our apartment complex - fortunately it's the size of a football field and the middle is around 30 yards from the nearest power lines and flickering metal halide lights that infest the streets and parking lots.  I figured the metal table wouldn't hurt the performance of the active antenna, which reportedly does better with a good ground or at least a ground plane for capacitance.

Overall I'd say this variation of the PA0RDT fares as well as the RF Systems EMF across the MW and HF spectrum I tried.  However the active antenna needed a little help so I clipped a 6' length of ordinary twisted copper wire to the antenna stub, and either clipped the other end to an overhead tree or just draped it across the ground - the latter actually performed a bit better, with a little less signal and a lot less noise than the vertical orientation.  I also draped the RF Systems EMF antenna across the ground to minimize local noise pickup.  Too much wire clipped to the active antenna will overload and cause intermod from the local MW flamethrowers like WBAP 820, which broke though a few times on 6950, 6754 aviation weather and 3330 CHU.

A couple of notable examples where the active antenna seemed to fare better than the RF Systems EMF or my usual random wire outdoor antenna: 20m was so quiet on the active antenna I thought it was deaf on that band until I heard the usual hamsters loud and clear, minus the usual noise floor; and WWV on 2500 was unusually clear before dark (around 0130z, 8:30 pm Texas time in summer), much clearer and with less static than I've ever heard on a summer evening with any wire antenna.

I haven't had time to edit the videos I shot while switching between the antennas, and one is 25 minutes long.  I was chattering over the videos hoping to avoid having to type in captions later, but there's some wind noise picked up by my video camera because I forgot the wind screen.  But it should be an adequate demonstration.



YouTube video demonstrations:

PA0RDT active antenna vs RF Systems EMF with Palstar R30C (2 of 3) - 25 minutes long.  Skip ahead to 8:30 mark for WWV on 2500 comparison; and 14 minute mark for the rest - you won't miss much.

PA0RDT active antenna vs RF Systems EMF with Palstar R30C (3 of 3) - Only a few minutes, toward end of XLR8 broadcast.  Signal had faded a bit but still audible.



Anyway, the PA0RDT design has a lot of potential.  Very quiet noise floor compared with older style active antennas I'd tried.  It's broadband so no tuning is needed - a big improvement over my older style active antenna.  But it does need a quiet location.  Fortunately just moving a few yards or feet in any direction may find that sweet spot in a noisy urban/suburban location.  The advantage to a short whip or wire is that it won't pick up every bit of local RFI in the area.  The disadvantage is less wire in the sky leads to more fading, but it's a fair trade off.
« Last Edit: July 15, 2015, 0038 UTC by Lex »
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline Lex

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And a few photos of the homebrewed PA0RDT style active antenna in a paint can.
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline Lex

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Only needs a little artwork or a few friendly stickers so cops don't mistake it for a bomb.

That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline Oliver

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Attached are some pictures of my PA0RDT.
I purchased the kit via known auction site for $20.
The assembly that was left to do was done with in 1 hour including the tubular housing.

So far my experience has been pretty good.The only down turn is the enhanced noise and overload on local station.

It was worth the investment, and I could recommend the PA0RDT to anyone especially if you have room limitations.




RX: Elad FDM-S2, Grundig Satellite 700 & Yaesu FRG-7
Ant.: HDLA 3 (Active Loop), EWE @ 270, ALA 100LN, MiniWhip
QTH: JO31 (Germany)

Please send eqsl to: oliverinusa[at]yahoo.de

Offline Oliver

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Attached is the original PA0RDT information from Roelof Bakker for those who are interested in some more details.

The extended version can be found here:
http://dl1dbc.net/SAQ/Mwhip/Article_pa0rdt-Mini-Whip_English.pdf
« Last Edit: July 20, 2015, 2115 UTC by Oliver »
RX: Elad FDM-S2, Grundig Satellite 700 & Yaesu FRG-7
Ant.: HDLA 3 (Active Loop), EWE @ 270, ALA 100LN, MiniWhip
QTH: JO31 (Germany)

Please send eqsl to: oliverinusa[at]yahoo.de

Offline Lex

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Thanks, I'm encouraged enough by the paint can version to tackle building one myself.  Unfortunately I sold or gave away all my electronics hobby stuff including soldering iron 10 years ago, just before the SWLing bug bit again.  I probably had everything I needed except for the amp.  But this project looks fairly easy and the kits are affordable.

Ideally I'd need a design that's easy to hoist up a tree for temporary use, mostly on weekends, so I'd need a different on/off switch, or just leave it on full time and swap batteries as needed, using rechargeables.

I've noticed that at least this paint can version shares a characteristic with the built-in whips on my portables -- I can find a sweet spot between the RFI-infested patches with relatively low noise.  That's harder to do with random wire and dipoles in my neighborhood.

BTW, what's the blue wire on yours, opposite the feed line?
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline Oliver

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Lex,
the Blue wire is around 2 feet of wire which is serving as external antenna. This length has proven to work best for my setup.
RX: Elad FDM-S2, Grundig Satellite 700 & Yaesu FRG-7
Ant.: HDLA 3 (Active Loop), EWE @ 270, ALA 100LN, MiniWhip
QTH: JO31 (Germany)

Please send eqsl to: oliverinusa[at]yahoo.de

Offline Lex

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Thanks, I wondered about that.  I tried 6' of wire on the paint can version and it overloads when vertically oriented.  Much better draped across the ground, still very sensitive.

Have you found any need for a ground with yours?  I've noticed the University of Twente web SDR gets outstanding broadband reception with theirs.  Their info blurb says it's mounted to a metal rooftop, which may serve as a ground or ground plane.  None of the other web SDRs using the PA0RDT can touch it for overall reception quality, and most are swamped with RFI at regularly spaced intervals.
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline skeezix

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I made a Mini-Whip according to Roelof's design last fall, incl running power up the coax. Its been mounted in a short PVC pipe with end caps. Even survived our winter without a problem. Used to have a ~80' random wire running out back, but that was always mediocre.

Comparing the two, the Mini-Whip is vastly superior on MW & lower part of HF. It has a bit less noise than the wire.

Been listening to it tonight- was listening to MW earlier (WXYG 540 kHz, 250W station about 50 miles away) and now WTWW on 5085, waiting for Art Bell to start the new show.

I made a second one that I put in a glass jar. A friend thinks its really cool electronic art. I said its a real antenna... friend insisted its art. Compromise: Its living art.   Still need to make a power supply for that one (I think, unless I already did and forgot where I put it).

Have enough parts to make another 4-5 of them. The plan was to make them and put them all around the house to have for nearby rooms. The current problem is that don't have a good ground plane and there is stupid noise coming from neighbors and underground services. A month ago one noise went away, but then a week or two ago, a new noise showed up. Just can't win. Ever.

Dear Uncle Charlie, want to save radio? CLEAN UP THE NOISE.  >:(

Minneapolis, MN

Offline Lex

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Quote
"A friend thinks its really cool electronic art. I said its a real antenna... friend insisted its art. Compromise: Its living art."

Heh!  One of my neighbors makes pinatas.  Best I've ever seen.  I tell her they're art.  She laughs, says she can't get her customers to pay what they're worth, usually around $75.  I tell her she doesn't charge enough.  Call 'em art and charge $10,000.  They'd love her at Art Basel in Miami.

For a makeshift ground plane, try clipping on various lengths of free dangling wire.  I've done that until I found a combination that works on the funny bands.  It may increase noise on other frequencies, but as long as it decreases noise on the desired freq it's okay.

Meanwhile I've had good results with a homebrewed vertically oriented loop mounted on a nearby wooden fence.  It's about 1/8 wavelength for 40m - no room for anything larger, and the smaller loops were best for MW, not HF.  This most recent homebrew is very compromised - TV cable and balun, but it works well enough that I'll try again with better cable and a proper impedance transformer for HF.
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline skeezix

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Call 'em art and charge $10,000

I like it. Need to make more and bring one into work and see what happens. Hopefully will get some that will buy them for some outrageous amount.

I'll try hanging some wire off of it and see if that helps. Tried to ground it to my gutter, but no effect at all.

Also have a Wellbrook loop. Works very well, but it also picks up stray noise (even though its ~80 from the house in the shed). I'm using 100+' of TV cable as well, but its direct bury for part and quad-shielded for above ground/indoor. TV cable seems to work fine and far cheaper than 50-ohm stuff (and I want to say that Wellbrook recommended the 75-ohm, maybe).

Minneapolis, MN

Offline Lex

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Yeah, I was a little surprised about the Wellbrook loops.  A few years ago there were several online receivers with Wellbrooks, and none of them was really a magic bullet.  Broadband, sure, but they seemed to be just as vulnerable to local RFI as any antenna.  Very expensive for what they offered.

I've tried several homebrewed passive loops and most were good at MW but only fair on HF.  The most recent loop I described above has been the best on HF, and the simplest.  Remarkably resistant to the heavy local RFI from our flickering parking lot and street lights.  It's best from 4-8 MHz, but that's good enough.  That's in the range my smaller homebrewed Villard loop couldn't reach.
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com

Offline Zazzle

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Hey,

hah, funny that this topic popped up. I've just build a PA0RDT MiniWhip myself last week. I used the "reloaded" version, which uses more modern/enhanched FETs basically. Like a BFG591.

 However the active antenna needed a little help so I clipped a 6' length of ordinary twisted copper wire to the antenna stub, and either clipped the other end to an overhead tree (...)

Heh, same here. But honestly? I didn't expect a small pice of copper of approx 1,5x2" to perform like it was touches with the magick Radio Wand by the dear Mr. Tesla himself. In my case I added a thin 1 meter steel wire (that points straight up) and after that it performed like a charm. Overall, I think the PA0RDT MiniWhip is basically just an active Antenna with a pretty good low noise Pre-Amp that benefits from the fact that the Pre-Amp is a close to the signal source (Antenna) as possible.

The Antenna I used for comparison is an Inverted V, with each dipole being 6,5 meters. Both, the Dipole and the PA0RDT are mounted 8 meters above the ground and approx 5 meters away from the house. The Inverted V is still way more sensitive but I've to amit, that the PAR0DT picks up a little less noise. So far I can't tell which performs better on which band. But I plan to run more test on the upcomming weekends.

That's how my version looks like. I got no picture from the fully mounted version... yet :)

Btw: I'm the only one reading "PARROT-Antenna" all the time? :D
Trans-/Receivers: JRC NRD-525,  ICOM IC-R72,  YAESU VR-5000,  YAESU FT-897D
Antennas: 80M Halfwave Dipole,  40m Inverted-V,  5/8λ Groundplane,  20M Longwire,  misc. UHF/VHF Scanner Antennas.

Offline Lex

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I tried the paint can amplifier again outdoors tonight to compare the Sony 2010 and PA0RDT outdoors with the Palstar indoors with outside 1/8 wavelength passive vertical loop.

Quietest reception with least QRN was with around 40' of my thinnest spool of magnet wire stretched horizontally, just a couple of feet above the ground, feeding the PA0RDT via inductive connector - a ferrite tube wrapped with several loops of magnet wire but without any direct electrical connection.  Much quieter with stronger signal than the Sony 2010 on built-in whip at maximum gain, which tends to exaggerate both QRN and local RFI.

Generally better signal than the Palstar with outdoor 1/8 wavelength passive vertical loop, which still picks up some white noise due to proximity to apartment building.

Getting an antenna as far as practical away from the apartment building and nearby utility lines and parking lot/street lights makes the most difference.  Even a portable with built in whip can sometimes get the best reception when I find a sweet spot with little or no RFI buzzing or white noise.

This may be the real key to optimal results with the PA0RDT - finding that sweet spot.  The amplifier seems quiet enough to take advantage of boosting faint signals without equally exaggerating RFI.  That's the major difference I'm hearing compared with my older Radio Shack amplified antenna, and the 1990s era Tiny Tenna (which was fairly quiet too).  
« Last Edit: July 22, 2015, 0511 UTC by Lex »
That li'l ol' DXer from Texas
Unpleasant Frequencies Crew
Al: Palstar R30C & various antennae
Snoopy: Sony ICF-2010
Roger: Magnavox D2935
(Off-air recordings.)
Email=my name at hotmail dot com