Ideal height and polarisation of MLA30 for best DX performance?

[alpard]

I have put out my MLA30 outside in the garden. I also replaced the stock wire like element to thick earth wire type element and made it into a perfect circle.  And I put it horizontally for the omni directional reception, but about 2ft from the brick patio on the plastic box.

I have been monitoring the usual DX signals on various freq. and bands, but DX performance from that MLA30 in that location and position and height is disappointing.  I couldn't hear any signals from South America on the tropical bands.

But it seems working better for 6065kHz Voice of Hope signal from Lusaka Zambia. This is one of a good DX signal to catch, and on this new setup of MLA30, that was the only signal which was a little better than before.  But the rest was all very dismal.

I am wondering if there is ideal height and polarisation for better DX performance for the MLA30, or any active loop antenna in general.

Previously, the MLA30 was vertically polarised and was tied into a defunct coat hanger in the radio room upstairs. It was not the best, but about similar to what it is now = in the garden outdoor horizontally polarised on the plastic box 2ft above the ground.

[alpard]

Anyone using MLA30 and how high is it set up? And how does it perform on DX on SW?
I noticed last night and this evening that my 20 meter long wire in the garden was performing far better than the MLA30+ horizontally mounted and 2ft above the ground level for copying KBS WORLD Radio.

[ThaDood]

Well, not having one myself, so I doubt that I could really answer this. So, I'll ask, do you have a tree that you can put that loop in? Maybe try 10ft, (3 Meters), up it. Do you have a very low S/N Ratio with that antenna? If so, can you try a MW and HF preamp? Just some passing thoughts there, since a smaller loop antenna is almost always a compromise to a 1/2-wave dipole, or even a random length wire antenna. 

[alpard]

Thanks Dood.

Well, I have a few trees in the garden, but they are far away from the house. The feeder of the MLA30 is not very long about 3-4meters? My radio room is upstairs in the house, and when the feeder comes out the window, it really does't stretch far away until it runs out. So, it is sitting on the patio on the plastic box 2ft above ground.

But you know what? I saw a DXer who uses Wellbrook loop and his loop is actually hammered into the ground, and he catches all the good DX with it. So I was under impression that with the loop antenna, they don't need much height.

But my MLA30 was not copying great DX.  It copies very nice if the signal is not DX and in good strength from all over Europe. It copies beautifully.  But I was trying to copy the weak DX signals Txed with 1 - 10 KW from South America, and they are not heard.
I know the signal is there under the noise, but cannot read what it is with this MLA30.  So, I thought maybe it needs height? And would it be better with vertical polarisation? I was asking these questions to myself, but wondering how other DXers use the MLA30 for their DXing. 

I now concluded that one thing definite in this game is that, it doesn't matter what radio you have. It is the antenna which will make it or break it as far as DXing is concerned.  I think your DX-440 or my D-808 will copy that DX signal no other radios costing 20 - 30 times more can hear, if they were fed with good efficient DX antenna set up with right height and location.

[RobRich]

If opting for horizontal polarization, you need to get it as high as possible due to incurred ground losses, especially weighted against the already small capture area.

My advice? Vertically polarize it to minimize ground loses for now, as it can be rather low to ground and still work okay. If you do not have a rotator, your best bet is probably pointing it to null local noise as best as possible. Turn to the noise floor hopefully drops to its lowest, then set and forget.

BTW, low horizontal loops can work. In fact the design of my loop-on-ground works in part due to ground losses, but it is also 148' in size.

[alpard]

I am gonna try vertically setting the MLA30 up this weekend.
I will need a pole and some tripod type stuff making it stable.

I didn't know that RX antenna will suffer from the ground loss. Is it not the case for TX antennas only?
But maybe it does. The MLA30 horizontally lying on the plastic box 2ft above the ground, was not copying any DX signals at all.

On the tropical bands at night, the band noise increased with the MLA30, but no signals were heard.

I had to switch back to the long wire, and it sounded more pulling the weak signals than the MLA30.

[JCMaxwell]

I have a W6LVP.  From my research, I mounted it about 10 feet off the ground, vertically.  Hope this helps.

[alpard]

I have a W6LVP.  From my research, I mounted it about 10 feet off the ground, vertically.  Hope this helps.

Thanks for your info.

This evening I moved the MLA30 and put it on the ladder shaped as a long A.  On the top of the A shaped ladder, I could VERTICALLY hang the MLA30 element made of hula hoop with thick earth wire all around it kindly donated by my xyl.  The height is now about 7ft off the ground.

It seems working really powerfully well on 11 - 15Mhz.  But from 9Mhz and below is full of MW stations breaking in. The worst is 4Mhz.  On 6, 7 and 9 Mhz it is sparse break through from the MW stations. But on 4 Mhz, every part of the freq is filled with some strong MW stations.

I am not sure if that is due to the fact that the hula hoop is a about twice of the diameter of the original wire element, and also the supporting ladder is made of aluminium, and it is making the MLA30 about 4 - 5 times larger element than the original one, and causing horrendous overloading on 4 - 9 Mhz?  Worst being the 4 Mhz.

Will keep experimenting with this trying to get best from the MLA30, but I am not sure if that is the limit.

[ChrisSmolinski]

It seems working really powerfully well on 11 - 15Mhz.  But from 9Mhz and below is full of MW stations breaking in. The worst is 4Mhz.  On 6, 7 and 9 Mhz it is sparse break through from the MW stations. But on 4 Mhz, every part of the freq is filled with some strong MW stations.

I am not sure if that is due to the fact that the hula hoop is a about twice of the diameter of the original wire element, and also the supporting ladder is made of aluminium, and it is making the MLA30 about 4 - 5 times larger element than the original one, and causing horrendous overloading on 4 - 9 Mhz?  Worst being the 4 Mhz.

Will keep experimenting with this trying to get best from the MLA30, but I am not sure if that is the limit.

The amplifier is being overloaded.

Here's the problem (both in this case and with many active antennas in general):

Because the actual antenna element is small, the output signal from your shortwave DX station of interest is small. If your receiver is not very sensitive, you need an amplifier before it, to amplify that weak signal. But... local MW stations (and maybe even FM stations) still produce a strong signal. And that gets into the amplifier also, and overloads it, causing images all over the place.

What's the solution?

One solution of course is a larger passive antenna, but you don't have room for that. What's another solution? Well... it's a better receiver. For example, the AirSpyHF+ / Discovery can work surprisingly well with a small passive antenna, such as the YouLoop. (Note I am referring in this case to this specific receiver. This is not generic for all SDRs.)

You could perhaps try putting some filters between the antenna and amplifier to alleviate the overloading/images, but 1) that might be difficult based on the design and 2) you're rapidly approaching what I like to call "lipstick on a pig".   

[RobRich]

Most things considered, RX and TX are reciprocal for antennas. :) If you have high losses for TX, then you will have high losses for RX; be it ground losses or whatever. Same goes for gain, directivity, take off angles, and lost of other factors.

The difference is RX losses can be easier to overcome, like via the preamp in your active antenna, plus modern-era receivers have incredible gain. In other words, as long as there is a signal to discern, you can typically turn up the receiver volume to compensate for the lack of antenna gain.

As Chris noted, an amp in your RF chain likely is being overloaded. It is probably the inexpensive amp in the active antenna. You might try a smaller loop to limit capture area, thus lowering the input into the amp. First try going back to the factory-included wire loop IMO.

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

Admittedly getting into the lipstick-on-the-pig territory, a few of many possible options in increasing order of expense:

* The receiver could be overloading, too, thus overrunning its own selectivity. If the receiver does not have an attenuator or RF gain feature, you can toss together a cheap 10-20dB pad attenuator with a few basic resistors: four for a pi network or three for an even simpler tee network. Like a couple of dollars or less. It is also a good basic RF building project. Lots of designs on the net. Drop a search.

* There also is the option of a high-pass filter to heavily attenuate the MW band to essentially "knock out" AM broadcasters. You can get a basic model via eBay for under $20, but do not expect miracles, especially if it is the active antenna preamp overloading. Ideally the filter needs to be *before* whatever is being overloading, which again I would suspect is the active antenna preamp.

Assuming you actually do live next door to an AM broadcaster, there are better high pass filter options to build or buy. Personally I can attest to the build quality of the PAR BCST-HPF, which uses a 7th order elliptic filtering network, but it also costs ~$70 new.

* A potentially more comprehensive solution could be a preselector, though that can get into serious annoyances due to keeping its tuning in sync with your receiver as you change frequencies. Again, though, it really needs to be before whatever is being overloaded, so it is not really where I would start with your current situation.

I have used various revisions of the MFJ-1045 as preselectors for years, especially with portable receivers. Such active preselectors tend to include preamp, attennuator, and preselector features in a single package. There also are passive models without integrated preamps, which can be preferable when needing extra gain is not an issue, as there is no active circuitry to generate more RF. Either way, the biggest downside IMO? Cost if buying instead of building. Most decent models are around $100 to $150 new.

[alpard]

Great info & advice. Thanks.

Yeah, all true.  I have tried different receivers with the new set up of the MLA30. They are the Tecsun S2000, Sangean ATS-803A, D-808 and a vintage Yaesu FRG-7, and they were all the same, serious overload throughout  4 Mhz.

What I have done at that moment was inserting a 0.001 uF capacitor between the antenna and the receiver, and Voila the Images disappeared.
I was wondering if it made the receivers deaf too. But it was copying Radio Havana 5025 kHz and 5040 kHz very well. So that wasn't the case.

Again I was wondering if high grade SDRs such as AirSpy or SDRplay duo, or even the new RX666 or RX888 would perform better with these images problems.

Anyhow, I failed copying the target DX signals (the  low powered BC stations on the tropical 4 Mhz band from South America) last night with every receivers and antennas I tried. Maybe there were no propagation?  I am going to try again tonight, but this time, I will set the MLA30 horizontally on the A shaped ladder. I think it will anchor at around 3ft off the ground on the A shaped ladder.  If it still overloads, then I will go back to the original wire element.

If it works well, I wouldn't mind even putting on bikinis to the pig

73s

[ChrisSmolinski]

What I have done at that moment was inserting a 0.001 uF capacitor between the antenna and the receiver, and Voila the Images disappeared.
I was wondering if it made the receivers deaf too. But it was copying Radio Havana 5025 kHz and 5040 kHz very well. So that wasn't the case.

IIRC you are using an active antenna. *Where* was the capacitor placed? Between the DC power inserter and receiver, or antenna and DC power inserter?

[alpard]

What I have done at that moment was inserting a 0.001 uF capacitor between the antenna and the receiver, and Voila the Images disappeared.
I was wondering if it made the receivers deaf too. But it was copying Radio Havana 5025 kHz and 5040 kHz very well. So that wasn't the case.

IIRC you are using an active antenna. *Where* was the capacitor placed? Between the DC power inserter and receiver, or antenna and DC power inserter?

I have a capacitance box with different capacitance settings. It has 2 alligator clips for clipping things onto. I have clipped one to the wire antenna input of the FRG7, and the other clip to the antenna.  The FRG7 is fed with a cable one end has two clips and the other end has a stereo  3.5mm input jack.   The two clips go to the antenna and earth input of the FRG7, and the female stereo jack is inserted with the MLA30 ant. output.

[Ray Lalleu]

This evening I moved the MLA30 and put it on the ladder shaped as a long A.  On the top of the A shaped ladder, I could VERTICALLY hang the MLA30 element made of hula hoop with thick earth wire all around it kindly donated by my xyl.  The height is now about 7ft off the ground.

It seems working really powerfully well on 11 - 15Mhz.  But from 9Mhz and below is full of MW stations breaking in. The worst is 4Mhz.  On 6, 7 and 9 Mhz it is sparse break through from the MW stations. But on 4 Mhz, every part of the freq is filled with some strong MW stations.

I am not sure if that is due to the fact that the hula hoop is a about twice of the diameter of the original wire element, and also the supporting ladder is made of aluminium, and it is making the MLA30 about 4 - 5 times larger element than the original one, and causing horrendous overloading on 4 - 9 Mhz?  Worst being the 4 Mhz.

AFAIK, there should be no metal parts inside or near the loop, except the connection. All successful receiving loops are supported with wood or plastic braces and poles.

The polarisation is of no importance for receiving SW skywaves as they are of mixed polarisation, but it can be used to cancel direct wave interference (or RFI) - as well as orientation in vertical or slant position. Close to the ground, probably the loop should be left vertical.

Any screen around a loop should be open, not being a closed loop. Then it should be balanced too, not to become part of an antenna near the loop. Before using a screen, try without any screen or metal parts near the loop!

[RobRich]

Regarding the inquiry about propagation, yeah, it has been in a deep hole in the past day or so. There was a geomagnetic store with a residual high Kp index for many hours.

Ray also offers sound advice. There should be no metal objects near your active loop. Get a plastic pvc pipe, wooden broom handle, or similar to mount the antenna.