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Author Topic: Best MWDX antenna?  (Read 2074 times)

Offline alpard

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Re: Best MWDX antenna?
« Reply #60 on: April 27, 2021, 0841 UTC »
After reading all the posts again, and doing some research, I feel that best option I could try out is,

1. Phased antenna setup with 2x separate active loops (I do need another Wellbrooks or MLA30 and MFJ-1026 or the Chinese QRM Eliminator)

2. WOG (Wire on the ground?  Get a drum of wire of 200m long, and just spread out along the garden fence and on the ground going along the fence and coming back making many layers of the wire on the ground), or making it into a loop?  = This might give good DX reception?  This is something that I have never tried before.

I have come across a few  Radio and  SWL blogs describing  this type of antenna for good LF RX performance.  But I was wondering, if the wire is lying on the ground, doe it not pick up the ground noise?  http://www.kk5jy.net/LoG/

This one is a loop, but looks interesting and the blogger says that it works very well on MW TADXing.
http://www.ve1zac.com/A%20New%20Homebrew%20Magnetic%20Receive%20Loop%20at%20VE1ZAC.htm

I wonder what your thoughts are on these options, and would be interested to hear especially if any one has been / is using this type of antenna on MW DXing, and reviews on them.
« Last Edit: April 27, 2021, 1022 UTC by alpard »

Offline RobRich

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Re: Best MWDX antenna?
« Reply #61 on: April 27, 2021, 1052 UTC »
There are fundamental differences in a BoG versus LoG.

The biggest being a beverage-on-ground can be unidirectional if long enough and properly terminated. It is a traveling wave antenna. More info:

https://en.wikipedia.org/wiki/Beverage_antenna

The loop-on-ground is largely omnidirectional. To be pedantic, it can be fed to have some directionality, but it is not enough front-to-back to make a significant difference in most cases.

Both of these antennas are designed for optimizing the signal-to-noise ratio, otherwise they can trend towards substantial negative gain. A receiver with good dynamic range, plus potentially adding an inline preamp, are potential requirements.

I have used an 148' LoG constructed in a "shielded" format from RG-6 coax for quite a few years now. It works on MW, but it has no directivity, so many frequencies are a jumble of stations at night. Not exactly ideal. Of note, it also works for longwave BCB broadcasters when DX permits.

Another prospect is simply a longwire antenna on the ground. It will be bidirectional off the ends assuming it is fed at one end and not terminated on the far end; plus long enough. Think length in terms of multiple wavelengths. It might be something you could try at a local park, field, or similar.

I used an 148' longwire-on-ground antenna on HF for several years before deploying the LoG. It did have some bi-directional directivity, but again, only where it was like twice or more the received frequency's wavelength. Otherwise it as largely omnidirectional below a wavelength or so.
« Last Edit: April 27, 2021, 1105 UTC by RobRich »
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals

Offline alpard

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Re: Best MWDX antenna?
« Reply #62 on: April 27, 2021, 1336 UTC »
Yes, directivity seems critical factor in MW DX antennas. Because usually MWDX signals tend to get buried under the strong local or nation wide AM Tx signals.
But then I am not sure how MWDXers with the vertical antennas cope or manage the QRMs.

A couple of questions for you. When you say "Longwire not terminated at the other end" - then how does it then left?  Just free on the ground not connected to anything?  What do you mean by "terminated"

You have a "Shielded" loop. How is it different from unshielded in its performance. What does the "Shielding" antenna does for you?

Offline RobRich

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Re: Best MWDX antenna?
« Reply #63 on: April 27, 2021, 1410 UTC »
Basically just a longwire antenna on the ground.

Radio --> Coax --> Transformer --> Longwire
                                   |
                               Ground

The wire lays flat on the ground. You can start with usual longwire lengths, though putting the wire on the ground is going to detune the wire, so it is not critical IMO. For mediumwave, put as much as wire in a straight line as possible in the direction of interest. YMMV on the transformer. I have run longwire-on-ground antennas before without a transformer when common mode noise was not an issue or a concern.

By termination, I mean the far end of a beverage-style antenna. One end of the wire is fed by coax via a transformer. The other end is "terminated" to a ground rod and/or radials via a resistor. Note one side of the transformer is grounded, too. Actual technical aspects aside, think of the wire as being one side and the ground (earth) as being the other side of a "loop."

Radio --> Coax --> Transformer --> Beverage Wire --> Resistor
                                   |                                                 | 
                               Ground                                        Ground

About the "shielded" loop, the typical claim is helping "shield" against near-field noise. The reality is more like the design *might* help balance the currents in the loop, and a better balanced loop *might* fair better with limiting common-mode noise from the coax. Usual YMMV stuff. I built mine as "shielded" due to having lots of RG-6 coax available; not for much technical reason.

More info on magnetic loop design and feeding here:

https://w8ji.com/magnetic_receiving_loops.htm
« Last Edit: April 27, 2021, 1607 UTC by RobRich »
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals

Offline alpard

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Re: Best MWDX antenna?
« Reply #64 on: April 27, 2021, 1628 UTC »
Great info !! Thanks.

Yeah, I think it seems easy and simple antenna to put down (not up :D) , and would suit my garden pretty well.
If it performs well for TA MW DXing, that would be fantastic.

For directivity, so far the standard Active Loop such as MLA30 or Wellbrook seem most directional.
To increase the DX pulling power of Active Loops, perhaps some sort of Phasing would work?

Offline RobRich

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Re: Best MWDX antenna?
« Reply #65 on: April 27, 2021, 1731 UTC »
Do you have the space for wire on the ground at mediumwave frequencies? Note it will need to be multiple wavelengths to have any directivity.

The upper end of MW is 175 meters. Figure like 1.5x to 2x that to get any meaningful directivity, so around 1000' to 1500' or so of wire, which is similar to an 160m amateur radio beverage.

The bigger issue is the lower range of the band. That is more like 565 meters. That would be pushing 1/2 to 3/4 of a mile. o.0

----------------

If we are back to the small backyard, what other low-frequency receiving antennas have you considered? If you do not mind building one, a pennant or a flag antenna might be worth considering.

https://www.qsl.net/wa1ion/index.html

----------------

You already have a Wellbrook loop, right? Being straightforward, that might be hard to beat for a single antenna setup in a small yard. So you have an excellent place to start IMO.

Phasing *might* help assuming your predominate noise or interference source is largely from a single direction. I would not buy a second Wellbrook for phasing before investigating other options if trying an antenna phaser. Many find a basic longwire or small wire loop work fine enough for the noise source antenna.

I suppose the bigger issue is a phasing unit with MW support. You can build one, or modify a MFJ model. Otherwise, you likely are looking at serious money, for example the DXE NCC-2. o.0 At $850+, think I could listen to WebSDRs instead. ;)

----------------

Let us see what you can do to maybe improve your existing loop before running down to the hardware store for a mile of copperweld wire. How is the receiver grounded? Could you describe your antenna grounding configuration? What type of coax are you using? Are you running chokes on the feedline? How is the feedline routed?
« Last Edit: April 27, 2021, 1801 UTC by RobRich »
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals

Offline alpard

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Re: Best MWDX antenna?
« Reply #66 on: April 27, 2021, 2023 UTC »
Yeah, my yard is only 25 x 25 meters, which is not great.  Even that is too optimistic size, because there are plants and sheds and storage boxes dotted around in the yard.  So my plan was to run wire all along the fence, and then when it reached to the end, turn back do another run, and do a few runs in layer just to get the length spread out.  It will not give any directivity, or maybe it will I am not sure.  I was really looking to be lucky, but luck is scarce thing when needing it.
But it is just a little project to try when I have absolutely nothing to do but kill time one day or weekend just for testing.

But you are right, I think Flag or Pedant antenna seems really getting sworn by many MW DXers.  The thing I am not sure about these type antenna is that, it is not easily rotatable or moveable once set up.  And if they can, then it would be hassle to move or turn all the time when you want different direction for incoming signals.  So, I might be actually making a smaller mini version of Flag, and set it up on a stand with wheels, so it could easily be turned around. Still would imagine it would be hassle to run out to turn it when trying to listen some radio at night.  So, yes, this is another project in the list.

And you are right. The Wellbrook and MLA30 are actually quite decent Active Loops, which work fine.  I was keep looking into making them more DX hungry antennas, so they will pull weaker and more interesting TA DX or rare DX etc.

Phasing loops - I read it on the blogs, and know it utilises usually MFJ-1026 or some QRM eliminator, but not fully understand how they exactly work.  And of course, I don't wanna spend lots of money for the hardware, so I will need to read or watch the youtube videos on this for learning more about it.  There seems other ways to  increase RX antenna gains by stacking or lining up the parasitic elements just like multi element Quads or Yagi antennas in ham radio.  Again, I am not sure how it works, and implement it properly, so that it will work nicely.

=====
For my current set up, I am mostly using MLA30 and Wellbrook Loop antenna. I also have a copy of PA0 mini whip too.  I have a long wire in the garden, but it is not currently used. It is just random length of wire of about 40-50 meters which goes round the fence.  The wire directly comes into the room via the window, and it goes into the back of my Yaesu FRT7700 ATU, and the coax from the 7700 goes into 3 way antenna switch 2 of them is occupied by the Active Loops, and to my radios.
I also have a washing line (insulated copper wire actually) which is about 20 meter long forming a loop in delta around the 3 metal poles in the ground. The wire is then wound on one of the metal pole in the ground for magnetic connection to the ground, and then it comes into the radio room via the window, then to the FRT7700 Earth connection.  The FRT7700 has suspected short or connection problem on the output wire, which I must look into before it is set inline again.
« Last Edit: April 27, 2021, 2027 UTC by alpard »

Offline RobRich

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Re: Best MWDX antenna?
« Reply #67 on: April 27, 2021, 2315 UTC »
If the fence completely encloses an area, you might try a horizontal loop. Nothing for directivity, but it might make for an interesting low-frequency antenna experiment.

Also I know it is not going to do much for your desired MW DX, but a loop-on-ground in your space might be interesting for improving MW to mid-HF regional listening if that is something you might want. It looks like you might able to do 250' to 300' total in a square or similar configuration. I would be tempted to experiment by tossing out the wire and connecting it straight to coax without a transformer or preamp. If it does not work in some beneficial way, you just pickup the wire and try something else. :)

----------------

About the grounding, the reason I ask is that I am wondering about common-mode and similar noise. I am curious if you have a high noise floor, and if so, what we might can do to help mitigate it.  For example, grounding your feedlines and applying RF chokes *might* knock down some noise to further improve the signal-to-noise ratio (SNR).

Try this during the day. Tune to a open MW frequency. What is your S reading without an antenna connected, and then with the antenna connected?
« Last Edit: April 27, 2021, 2319 UTC by RobRich »
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals

Offline alpard

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Re: Best MWDX antenna?
« Reply #68 on: April 27, 2021, 2330 UTC »
Yes, we have 3 fences 2x are hedge plants, and 1x is wooden fence.  I tried a horizontal delta loop one time, and as you said, it had no directivity at all.  I was receiving multiple stations on the same frequencies often. 

I will definitely try a wire thrown on the ground straight connected to a coax just for testing.  If it didn't work, always can change it to something else.

I do have a few RF chokes and 9:1 baluns and also 4:1 balun. Whenever I put up a new antenna, I would try these chokes and baluns. If it helps with the RX, then I tend to leave them on. If not, take off, and just run  the antenna.  RFI and QRN, it is not too bad, and sporadic here. 

I just saw this Phased Array antenna presentation, and found it interesting. 
https://slideplayer.com/slide/17837705/
« Last Edit: April 27, 2021, 2338 UTC by alpard »

Offline RobRich

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Re: Best MWDX antenna?
« Reply #69 on: April 28, 2021, 0629 UTC »
I have been thinking about smaller outdoor antennas with possible directivity down into mediumwave and having relatively simple construction to save on time and costs.

Start with an inverted U, then add termination towards the direction of interest. That is an EWE antenna!

http://www.dxing.info/equipment/ewe.dx
http://f8afc.weebly.com/full-size-ewe.html
http://www.radiodx.com/articles/technical/antennas/it-had-to-be-ewe/

You probably even could fit two or three EWE antennas in your space for multiple directions.

No guarantee it would outperform your existing Wellbrook loop, but an EWE is unidirectional unlike a bidirectional loop, which could help if you need more front-to-back separation in a particular direction.
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals

Offline alpard

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Re: Best MWDX antenna?
« Reply #70 on: April 28, 2021, 0825 UTC »
Great links, thanks !!

How would you compare EWE antennas with Flags?
How are they different?  First impression from the diagrams tells me that
EWE is grounded at both ends, and Flags look like a type of Loop.

Offline RobRich

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Re: Best MWDX antenna?
« Reply #71 on: April 29, 2021, 0009 UTC »
The flag and pennant antennas are related to the EWE. :)

The EWE uses earth to complete its "loop," while the other two use lower wires to complete their loops.

A flag or pennant theoretically should have better directivity and maybe even gain compared to an EWE.

The thing about the EWE is it being earth terminated, which I suspect might help more with local noise versus a raised loop. YMMV, of course.
« Last Edit: April 29, 2021, 0108 UTC by RobRich »
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals

Offline ~SIGINT~

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Re: Best MWDX antenna?
« Reply #72 on: April 29, 2021, 0110 UTC »
Some nice options although one of those links showed the BALUN constructed from a MIX 43 ferrite core. I would not use a MIX 43 core. This is a Nickel-zinc (NiZn) ferrite core with a frequency range of 2 MHz to several hundred MHz. I would use a Manganese-zinc (MnZn) ferrite core, I.E MIX 31, 73 and 75. A MIX 31 is good for 1 MHz - 300 MHz and a MIX 75/J is good from 150 KHz - 10 MHz. MIX 31 cores are common and readily available.

Offline alpard

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Re: Best MWDX antenna?
« Reply #73 on: April 29, 2021, 0737 UTC »
Great info. Thanks !!

Came across this old post on MLA30, and also found quite interesting.
https://www.hfunderground.com/board/index.php?topic=59386.45

Modify MLA30 with a smaller loop, and attach it  to the  larger loop for magnetically coupling, and tune the larger loop with
a variable capacitor?   Problem with this type of modification would be that, it will not be for outdoor operation at all. Indoor use only?
What about possibility of all the RFI and noise pick up in the room?
How has it been working for MW DX?

Gosh I am in the thread too. Totally forgot about that :D
That was the time before I got my MLA30.
At the time, I was not sure if MLA30 was a toy or real antenna :))
« Last Edit: April 29, 2021, 1024 UTC by alpard »

Offline RobRich

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Re: Best MWDX antenna?
« Reply #74 on: May 03, 2021, 2217 UTC »
You can remote tune a variable capacitor, but starting with a MLA-30 as a coupling loop is not ideal IMO.

Being realistic, while there are much worse MW/HF antennas than the MLA-30, its design relies upon a single two-stage video amp. That is far from ideal for signal-to-noise ratio (SNR), which is what you are going to need to optimize for pulling out stations at the noise floor.

Your tuned loop is a good idea. Make it passive a you can add a preamp later if needed. As noted, the loop can even be remotely tuned outside. You do not even an expensive vacuum varicap since you will not be transmitting. Copper pipe, the proper range varicap, a stepper motor, and an inside control for the stepper. It can be homebrewed assuming you do not mind a little soldering.
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
148' "Shielded" Loop-on-Ground | 18' End-Fed Vertical | 9' + 31' Verticals