Best MWDX antenna?

[RobRich]

Mine is working about as expected thus far, though I tend to have a low almost rural-like noise floor much of the day and pretty much most nights. Beyond local noise field coupling, area SNR is a big consideration with amplified low-frequency antennas.

Admittedly, RF noise does vary somewhat with neighbors' activities. For example I suspect someone nearby might have a plasma tv, but it is generally intermittent and seems limited to day time hours when present. Even the quite limited noise blanker on my old Kenwood R-2000 usually cleans up most of it, so I tend to just ignore it. Now if it was there all day.... :/

Currently my miniwhip is grounded to a 10.5' mast, with about 3' in the soil.... well, more like sand here. I am thinking about adding a few ground radials to the base of the mast given the local sandy soil. Kirchhoff's first law still applies even to active e-field probe antennas. IIRC, the one at Twente is grounded against a large metal roof. ;)

If interested in perhaps trying another miniwhip in the future, you might find the following document a worthwhile read:

https://www.dst.defence.gov.au/sites/default/files/publications/documents/DST-Group-TR-3522.pdf

Otherwise, speaking of smaller antennas, I find my unamplified 9' vertical can be a decent "general-purpose" antenna for local MW BCB, casual HF, and even local FM BCB. It is a typical CB steel whip with spring section on a mobile window mount, u-bolted to a copper pipe driven in the ground. It has just four 9' ground-mounted radials and a few snap-on ferrites on the feedline.

IIRC, the US Navy once published a study suggesting an unamplified 6' whip was typically more then enough for basic HF reception when contrasted against atmospheric noise. However I am unsure what, if any dedicated ground plane was considered. Might have been grounded to an entire ship, or it might have simply been common mode on the feedline and receiver. YMMV.

[~SIGINT~]

Ack the roof at Twente. If you read their documentation they even mention that the only reason the antenna works so well is because of the large metal roof. Both of my Mini-Whips are this one: https://www.ebay.com/itm/MiniWhip-Active-Antenna-HF-LF-VLF-mini-whip-shortwave-sdr-RX-portable-receiving/332818922997 and are well built. They look identical to yours. I purchased one fully assembled and the second as parts so that I could see how it was built and play with it i the shop. I later installed the antenna in a PVC pipe.

I'm sure you have seen Fundamentals of the MiniWhip antenna: http://www.pa3fwm.nl/technotes/tn07.html and Grounding of MiniWhip and other active whip antennas: http://www.pa3fwm.nl/technotes/tn09d.html

Try moving your ferrites closer to the house. These do not do much at the antenna base. Ferrites at the antenna protect the antenna from becoming a victim of coax noise. This is the typical placement of ferrites when you are transmitting into the antenna. If you want to remove noise picked up by the coax the ferrites are more effective at the receiver. The best way to view this is to think of it as "source" and "victim". In the case of a receiver, the "source" is the coax and the "victim" is the receiver. The entry point to the house is a good place as it removes noise generated by electrical wiring etc ... You would be surprised how noisy wall surfaces can be. Ferrites at both ends are ideal. Mix 77 (100 kHz - 10 MHz) is a good choice or you can slip some mix 77s and mix 31s (1 MHz - 300 MHz) together. All of my ferrites are outside at the entry point and I have a common mode noise choke at the output of the antenna switch. Ferrites are not weather sensitive so no need to seal them etc ... For the Mini-Whip, the coax forms part of the antenna system so it has to be routed away from noise sources.

[RobRich]

Sure enough that is PA0NHC-derived design, too.

Thankfully I have not had much issue with common mode noise ingress on even my cheapest RG-6 feedlines, though I usually have some type of ferrites or chokes on both ends of my various feedlines. There also is the factor of having a concrete-block stucco house. The stucco is applied over wire mesh, and the house is electrically grounded to the rebar in the concrete foundation.

I have KD9SV common mode chokes closer to the receivers on some of my HF receiving feedlines. The model is rated supposedly for 3000-ohms+ common mode resistance at 0.5-10MHz. I suspect mix 73, 75, 77, etc.; but they are potted, so no real idea on my part.

https://www.dxengineering.com/search/brand/kd9sv-products/product-line/kd9sv-products-sv-cmc-common-mode-choke/part-type/hf-receive-antenna-system-devices

IIRC, the only outside antenna I have deployed currently without choke ferrites at the feedpoint is my 31' vertical. It has a 4:1 unun between it and the coax, then back to one of the KD9SV common mode chokes near the receiver end.

[RobRich]

Deployed the second active miniwhip about 40' to 45' from the first one. Took a quick skim on upper mediumwave. So far phasing them can help with noise when tuning a single station. The better test should be tonight to try nulling and peaking simultaneous signals on the same frequency.

[RobRich]

Quick-and-dirty example. I cycle the phasing unit a couple of times. Watch the noise level in the waterfall.

https://www.youtube.com/watch?v=zqYjeREnnJQ

Local MW conditions are extremely rough right now with an elevated noise floor, static crashing, etc.

[~SIGINT~]

Rob, remarkable difference in the noise level. I was also thinking about your grounding. As these types of antennae use the shield / braid from the coax as a counterpoise, perhaps the addition of a real counterpoise vs. a ground at the mast may yield some extra benefits.

Have a look at this article: How to properly install a Mini Whip antenna in an noisy urban environment
https://swling.com/blog/2020/10/how-to-properly-install-a-mini-whip-antenna-in-an-noisy-urban-environment/

[RobRich]

Currently the coax feeds are grounded at the top and bottom of the 10.5' masts, with 3' of the masts in the ground and choke ferrites as the coax cables leave the masts.

Elevated counterpoises are out for now due to limited height, but I have thought about adding a few on-ground radials at some point. Alternatively I thought about using metallic guylines for added counterpoises if I ever bother adding another 10.5' section to each mast.

I can listen routinely to signals from the Middle East, interior Asia, Oceania, etc. on HF with just one miniwhip when propagation cooperates.

I am just too close to the tropics for decent mediumwave summertime reception, especially with these active antennas. Elevated noise floor and near constant static crashing. ;)

[RobRich]

Second active miniwhip is way down on gain versus the first one. I should have checked that when deployed, but just noticed it when swapping around feedlines.

I checked impedance at the feedline. It matches the good one, so it is unlikely to be feedline or output stage related.

I will try taking a look at the antenna board later.

[RobRich]

Went ahead and just ordered a replacement antenna board, too.

[~SIGINT~]

I did a couple of very unscientific lab test on one of mine. Essentially, I swept the antenna with a tracking generator / spectrum analyzer. I was curious to see what frequency bands the antenna responded the best to. I will go back and dig out the data and present it later.

[RobRich]

Replacement board arrived. Need to swap it out.

Meanwhile my 31' vertical is offline. Had some trees trimmed, so wondering if they did not run over my feedline or similar. Fun stuff.

[~SIGINT~]

The joys of the hobby. As a side note, I am currently listening to Drunken DJ Radio 6950 USB 0138 UTC 05 JULY 2021 with the Belka-DX and telescopic antenna while sitting in the basement from a location 500 miles North of Toronto, Ontario Canada. The receiver is working like a charm.

[RobRich]

Receiver aside, that is a good demo of what actually good propagation can do. Hopefully conditions will improve further as we progress into the current solar cycle.

I have almost ordered the Belka a few times, but I keep talking myself out of it. I have several portables largely going unused as it is.

Been thinking about the 31' vertical. After resolving whatever the issue is, I might change the feedpoint setup. Right now it has a 4:1 unun to help with high-impedance excursions like around the 20M band where it is near a half-wave vertical, but I know that 4:1 transformation could be hindering performance below 40M where the antenna is already low impedance. A remote preamp might be better, especially for extending low-frequency performance. Decisions.

................

No 31' vertical for my usual Kenwood R-2000 tonight, so I have been experimenting a little.

Listened to an 11m opening via the 18' end-fed vertical, then DX from France on 20m via the 148' LoG.

The interesting part IMO is the preamp. I typically use a MFJ-1020B (~20dB) with that radio if needed, but I am trying an eBay "60dB" preamp since my current upper HF noise floor is rather low. I am not interested enough at the moment to actually measure much of anything, but it probably does deliver like 40dB+ (or more!) of gain at 12v. Naturally, high noise floors need not apply with such ridiculous gain. o.0

I am sure the eBay preamp's noise profile likely is horrible, but I can foresee a few possible uses when the noise floor is already *very low* and wanting extreme gain for a BoG, LoG, or similar.

................

Leaving the inexpensive preamp inline for awhile, but I did move it to the more proper location between the MFJ-1030B and the receiver. The 1030B is back to being a preselector and gain controller if needed.

....And now a 20dB attenautor between the preamp and receiver. Got tired of tweaking the receiver's own attenuator.

Probably will put it back to normal later today. Just playing around until sunrise. Planning to swap out that active antenna board this morning, plus maybe take a quick look at the 31' vertical.

................

Combined a few posts. ;)

Swapped out the active antenna board. Quickly tested each active antenna with a Tecsun 310 using a couple of local mediumwave stations for steady groundwave signals. They are about the same. Like 1-2 dBu difference; if that. Yay!

I did note one regional station with a slightly higher dBu difference, but I suspect it is due to the positional differences and/or perhaps the storage building in between where the two antennas are mounted. Basically typical stuff when dealing with active e-field antennas.

................

Put the antenna phaser inline. I just do not have enough local noise or the need for nulling for it to do much on HF during the day. I can get a mild gain bump through combining and/or maybe slight directivity, but I have not found it useful as of yet. Maybe it will fair better at night on MW, but otherwise I suspect the two active antennas will feeding two receivers more than feeding the phasing unit. ;)

[~SIGINT~]

With regards to propagation, yes, the SSN has been very high over the past few days. 81 yesterday, which I have not seen in a while. For the mini-whip antennae, I do believe there are all kinds of factors which can affect their performance. I as well use a step attenuator to balance gain vs. noise.

[RobRich]

Sometimes you can change the performance of an active e-field antenna just by moving it a few inches.

Put the Kenwood R-2000 back to normal.

Glanced at the 31' vertical. I straightened some ground-level radials, but otherwise it looked okay. I need to check the antenna-side connectors at the unun. I might have broken one when shaking the fiberglass vertical lose from a nearby limb awhile back.