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Author Topic: Active loop or two verticals?  (Read 9382 times)
AK7V
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Posts: 267




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« on: April 11, 2017, 04:57:58 PM »

I've been thinking of setting up a better receive antenna.  Right now I use a Butternut HF-9V vertical as my only antenna for RX and TX.

Two ideas that have caught my attention are an active magnetic loop, like something from Wellbrook or the DX Engineering RF-PRO-1B.  The other idea is a pair of active verticals with a variable phasing controller (DX Engineering sells one, along with a couple of short amplified antennas in a set - "Active antenna phasing system").  They also have systems that phase 4 or 8 verticals, but the cost gets prohibitive for me up there.

As far as system complexity goes, it seems like the two verticals have more components and "stuff" to run out into the yard (2 antennas, 2 ground rods, 2 feedlines w/ power), but there's no mechanical rotator to deal with, as there would be with the loop.

Does anyone have experience with both of these who can describe differences in performance?  My main interest is being able to reduce local, man-made noise from homes in the area.  I have a 2 acre lot but I don't really want to fill it up with wire.... ok, I do, but XYL might not.  Wink
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G4AON
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Posts: 1019




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« Reply #1 on: April 13, 2017, 04:30:49 AM »

Jason, several of us use PA0RDT active antennas, they are very easy to make using only two transistors... A J310 FET and 2N5109 bipolar. They are very effective at minimising local electrical QRM by being small and easily installed some distance from the house and associated wiring. You do need an effective feedline choke near to the antenna and an earth rod. The antennas are best placed on a fibreglass pole around 18 or 20 foot high. The earth rod grounds the outer of the coax on the antenna side of the feedline choke. The choke can be 12 turns of RG316 on an FT240-31, or similar.

There are several articles on the PA0RDT antenna around on the web, I made a more effective dc injection box that is shown in a pdf file at:
www.qsl.net/g4aon/pdfs/pa0rdt_v2.pdf

A simple afternoon project!

73 Dave
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AK7V
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Posts: 267




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« Reply #2 on: April 13, 2017, 12:17:01 PM »

Thanks Dave!  It looks like a pair of those would work with a phasing system to try and null out local noise. 
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G4AON
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Posts: 1019




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« Reply #3 on: April 13, 2017, 02:03:03 PM »

Thanks Dave!  It looks like a pair of those would work with a phasing system to try and null out local noise. 
Most of us find local noise drops significantly once you get an antenna well away from the house, the ground rod and choke need a short wire between them to make sure any mains/house noise on the coax outer is routed to earth.

A useful page on active antennas is:
http://www.g8jnj.net/activeantennas.htm

I've built a couple of the active antennas by Chris Trask, including his 7 transistor one (fig 12 in the PDF article below). Neither worked as well as the simple PA0RDT one, indeed the fig 12 one drew quite some current and virtually cooked two of the FETs... those 100 Ohm source resistors, R3 and R4 need increasing to around 470 Ohms.

http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdf

Plenty to experiment with. 73
Dave
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NO9E
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Posts: 711




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« Reply #4 on: April 14, 2017, 04:36:05 PM »

I have one active vertical and one Wellbrook loop. I can phase them against other antennas using NCC-2. The active vertical picks up lots of noise, 20db more than the loop. The active loop is a whole lot quieter but has trouble hearing DX. I also have a triangular active vertical array, and it is pretty good, especially if local noise is not strong.
For phasing I would use active verticals but would have diminished expectations if they are close to local noise.
Ignacy, NO9E
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KD8IIC
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Posts: 648




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« Reply #5 on: April 17, 2017, 08:19:14 AM »

 With the information you've given, likely you will be better served by using a noise cancelling antenna like the MFJ1026. There have been some you tube videos made by those who use these and they are very impressive.
I HAD 2 Pixel active loops on rotators and the DXE-NCC-2 set up.
The system is now dis-assembled after being very un-impressed with the performance vs investment of cash and time.
 The Pixel and Pro loops are not very directive above LW and BCB (190kHz - 2kHz) to start with, above 80m you notice a drop in gain vs dipole.
 I'd wanna see you try something less expensive es simpler that will actually work. I think JPS makes a noise cancelling ant too.
 Best of luck OM es 73.  de n8aft  sk  ..
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KD8IIC
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« Reply #6 on: April 17, 2017, 08:22:52 AM »

   190kHz - 2000kHz.
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VA3VF
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Posts: 766




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« Reply #7 on: April 18, 2017, 11:19:43 AM »


There are several articles on the PA0RDT antenna around on the web, I made a more effective dc injection box that is shown in a pdf file at:
www.qsl.net/g4aon/pdfs/pa0rdt_v2.pdf

73 Dave

Hi Dave,

I use the RA0SMS version of the mini-whip, and I'm very happy with it up to about 15 MHz. Above 15 MHz, a random wire offers the same performance. Do you see the same behavior with your version?

Thanks and 73.

Vince, VA3VF
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AA4HA
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Posts: 2381




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« Reply #8 on: April 25, 2017, 07:53:18 AM »

Phased vertical antennas are very band-specific and if you use a phasing harness (cable) you will need to be swapping that out as you change SWL bands.

You may be better off with a loop antenna like a Wellbrook.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f
KD7RDZI2
Member

Posts: 216




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« Reply #9 on: May 03, 2017, 02:44:33 PM »

The correct answer is 2 Active loops and 2 verticals Grin
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SHORTWIRE
Member

Posts: 109




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« Reply #10 on: June 30, 2017, 07:49:01 AM »

I only have experience with the Wellbrook, apart from wire antennas.

It works well in horizontal mode, where it is omnidirectional, and also picks up less noise.

The loop is a 90/10 solution!
You can hear 90 percent of the stations that the big guns can hear, with 10 percent of the effort, size and cost..
 Cool

Only you can decide if this is enough for you..
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ZENKI
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Posts: 1421




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« Reply #11 on: September 29, 2017, 11:11:37 PM »

Some useful information on RX antennas.

http://fenu-radio.ch/en-index.htm

There is  english section if you cant read  German!
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AUSSIE
Member

Posts: 50




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« Reply #12 on: September 30, 2017, 04:22:08 PM »

I been using the wellbrook active loops for a long time main intrest for me is monitoring aircraft around the globe it took me a long time to get the right distance from the house and height which sometimes the higher you go the less you receive did get good reception but always thought wire antennas cut at the length for aircraft frequencies would do a better job in fact my first PK Loops dipole was out perfroming the loop by a long way at 6 metres high bought another 3 PK loops dipoles and reception was excellent did have 4 wellbrook loops sold 2 and recently since they werent getting used thought i will try running them on a battery to my surprise went hf aero hunting down the beach and hooked up to a 3 metre tripod and a 500mm pipe to a bracket my fiance welded for me bolted on the towball so the tripod slips in can pick up gander,new york,san fransisco,shanwick and others booming in but still prefer the wire antennas at home and for the price of one loop i can have 4 antennnas.


Regards Lino

Regards Lino.
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WA8ZTZ
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Posts: 242




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« Reply #13 on: October 01, 2017, 05:12:45 PM »

Another vote for the MFJ 1026...
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KC4ZGP
Member

Posts: 1637




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« Reply #14 on: October 03, 2017, 10:40:20 AM »


Active loops have amplifiers?

Amplifiers amplify?

What might they amplify?

Use tuned antennas.

Kraus
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