Best MWDX antenna?

[alpard]

Good point on MLA30, and DIY mods.

It is just I saw the old thread about MLA30, and one of the poster showed his modded MLA30 with the extra larger element magnetically coupling to the MLA30, and also tuning the larger element with variable cap. 

He seems very pleased with the increased performance on DXing with the mods, and I was wondering about the increased performance on MLA30 DX capabilities after the mod.  As you say, I would have been doubtful to see the active antenna coupled to a larger element loop for possible overloading.

[RobRich]

Received my phasing unit from Ukraine.

https://www.ebay.com/itm/284239070097

Usually I have a moderately low local noise floor anyway, so I have been using it more for peaking and nulling signals instead of local noise. IOW, another radio toy with knobs to turn. :)

It rolls off into MW, but I have found usable phasing with my antennas down to approximately 1000KHz or so, at least for strong signals. YMMV for weak signals, especially as frequency decreases.

I have been phasing my 31' vertical against my 148' LoG, and the setup can help separate some overlapping MW stations. For a test I am currently listening to music on 1110 by significantly phasing out WBT from North Carolina. It is not perfect, but it can help turn a jumble of stations into something listenable. Thing is it might not always be the specific station you want to peak or null out from the two or more present. ;)

Two matching antennas would be preferable for the type of phasing I am doing, or maybe even three with the center antenna grounded. Not sure I would want to bother deploying another 31' vertical with a ground radial field, but I might toss out another LoG sometime. Alternatively, I have an affordable active vertical collecting dust, so I could consider ordering another to deploy a pair. Decisions for another day IMO.

[RobRich]

Quick demo of the 1110AM station. You can hear WBT mixing into the music with the phasing unit off. Also added receiver attenuation to hopefully drop the now much weaker WBT towards or even into the noise floor.

https://youtu.be/SgkZhl0IrKE

[~SIGINT~]

Thanks for sharing. It seems to give a nice null. I'm going to have to think about one of these.

[RobRich]

Welcome. :)

Here is the flip-side of the above. Nulling the music on 1110 to hear Coast to Coast AM on WBT.

https://youtu.be/yK13MTGLTKU

[~SIGINT~]

That is very nice. I like it. It makes a world of difference. With all of the antennae options alpard has this would probably greatly enhance his MWDX reception. It probably doesn’t even have to be identical antennae. We still use similar technology in direction finding where there is a centre whip (omni) and a bunch of directed antennae pointing at the various compass headings. You null the directors against the whip until the signal disappears. That null represents the direction in which the signal is emanating from.

[RobRich]

Yeah, matching antennas are not a requirement, especially if using phasing for local noise reduction. I was surprised my vertical and LoG was able to achieve such results given their vastly different characteristics.

Otherwise I was thinking more about using phasing to help steer an antenna array. Ideally that would be two similar antennas with the same polarization and similar impedance characteristics. Staggered parallel beverages, two verticals, etc.

Active antennas typically have wide bandwidth (low Q) and hopefully somewhat stable broadband impedances. Since I would be doing the project on the cheap, I already have one the following miniwhips on a shelf doing nothing and could order another:

https://www.ebay.com/itm/222469570201

I will think about it. In the meantime I might try phasing a couple of simple wire verticals or whatever if/when I feel like deploying them.

A three vertical array for additional enhancement might be possible as well. Probably phase the two outer verticals and ground the center vertical to the radial field. YMMV.

[alpard]

Great info, thanks.
I have been working on decorating my radio room, and all the radios and antennas are offline for the time being.
Hopefully it will not be too long until it will all get finished and get back on rxing soon.
Working on the walls and ceilings of rooms with plaster can be very tough job taking long time for a lone DIYer
And then it will need to get sanded, and painted

[RobRich]

Ordered a second active miniwhip for further adventures in antenna phasing.

[alpard]

It would be interesting to compare the performance for MWDX between Flag Antennas vs.  Phased Active Loop.
I am on the way to set up a DIY flag for MW and HFLF soon in the garden in the near future.
Phased Active Loop also sounds interesting, but having to buy a new phasing tuner box puts me off, as it will add into the extra expenses.

[RobRich]

I received a couple of the <2GHz 60dB preamps floating around Amazon, eBay, etc. It is basically a 2-chip cascaded version of the similar inexpensive 30dB preamps.

At first flance I suspect the listed upper voltage limit could be incorrect. 12v probably will not damage them, as I have ran that through the older 1-chip 30dB preamps for short periods, but most of these cheap MMIC-based preamps without voltage regulators likely are rated for more like 4-7 volts to optimize the noise factor.

Anyway, having upwards of ~60dB gain might prove interesting if deploying a high-loss antenna designed for SNR like some of the designs we have discussed here.... assuming the local noise floor is low, the preamp noise factor is not ridiculous, and there is a decent impedance match on both sides of the preamp.

[~SIGINT~]

It is definitly the principle behind the mini-whip antenna. PA0RDT design documents are open source from the author. Pa0nhc has done a very good job at explaining this in a youtube video. His page also includes the Pa0nhc active wideband receiving loop 15 kHz - 30 MHz and the pa0nhc 80m-20m Symmetrical dipole antenna with coax END feed. Don't forget to check out the section on common mode chokes.

http://www.pa0nhc.nl/

[RobRich]

True enough, though the preamp in mini-whips tend to pull double duty as both a matching device and gain amplifier. Someday I might actually try a VNA plot of a like 6" strip on HF and lower, though I already can imagine the extreme loading characteristics.

Most of these cheap eBay preamp boards appear to be MMIC-based chips. I was looking at the INA-02184 for a potentially close match to the 60dB boards I received. Actually probably more like clone chips of an INA-02184 or similar MMIC amp, but anyway.

https://www.qsl.net/n9zia/metricom/ina02184.pdf

The gain and noise factor profiles are rather flat under ~300MHz. Rated voltage max also is 7v, which also seems rather typical for these cheap MMIC amps despite sellers claiming 12v. ?! Yeah, 12v might slam the gain, but the NF tends to improve at lower voltages as many of us have already found. No wonder.

I had been using 9v batteries for temporary deployments of the single-chip 30dB preamp model, but think I will drop voltage further down in future testing of both single- and two-chip models.

[~SIGINT~]

Over the years I have tried to switch everything over to Mini-Circuits components (splitters, amps). I am a big fan of their products and there is no shortage of them on ebay. They are a prime supplier of components to the military comms equipment manufacturers. You just need to be persistent and patient on ebay to pick something up at a decent price. For example, there are currently some Mini-Circuits ZFL-1000LN 0.1-1000MHz SMA RF Low Noise Amplifiers (20dB) available for $75.00. A little bit on the high side, but like I said, you just need to keep an eye out for a bargain. I have also found that the Mini-Circuits chip baluns have the best specs out there so far.

[RobRich]

20+ years ago I likely would have been there with ya' regarding hardware. :)

Radio is a part-time hobby for me these days, with HF as my only significant particular interest. That is before even factoring costs versus diminishing content and increasing noise floors; both local and environmental.

Admittedly, at VHF and above I too would be more inclined to spend money on better hardware. Just not much that interests me up there.