Best MWDX antenna?

[RobRich]

Airspy HF+D using the bundled USB cable having two ferrites along with a common USB extension cable.



Airspy HF+D using the bundled USB cable having two ferrites along with a (supposedly?) quality USB extension cable wrapped 10 turns around a Fair-Rite 0431177081 mix 31 snap choke.



Both using my 31' vertical over a radial field. 4:1 unun at antenna feedpoint. KD9SV CMC inline choke near house. Multiple coax passes through a HF-rated (mix 31, 43, whatever) at the SDR input.

[RobRich]

Second config, but on notebook battery power.



I am thinking about adding enhanced EMI/RFI filtering and maybe even metal encasing a compatible notebook power supply.

[~SIGINT~]

Try to wire an EMI / RFI filter backwards.

Have a look at PA0NHC Main Index web page. There is some good information there like "De-noising of Switched Mode Power Supplies". This is where I first got the idea of wiring the filter backwards. https://www.pa0nhc.nl/

Don't forget about your peripheral devices; I.E. mouse, keyboard, printer cable, Ethernet cable etc ... They are all sources of "noise".

Some pretty good references can also be found at the K9YC site like the "A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing" pdf: http://www.audiosystemsgroup.com/K9YC/K9YC-old.htm

EMI / RFI is a never ending battle.

P.S. Some interesting DYI construction ideas can be found here: https://www.kf7p.com/KF7P/RF_chokes.html

[RobRich]

It is the notebook power supply itself, and most likely on the DC output side.  On the AC input side is an APC Line-R.

I was more or less just pointing out the bundled USB cable with the Airspy HF+D might not have enough choking, especially at lower frequencies, for some systems despite it already having a couple of ferrites. ;)

If I ever bother with EMI/RFI filter mods to the particular supply, initially it probably will be a few caps and a inductor on the DC output side. The next step would be additional AC input filtering and mounting the whole thing in a metal enclosure if actually needed.

For an example:

http://ka7oei.blogspot.com/2014/08/completely-containing-switching-power.html

BTW, that is my quiet 150w HP notebook supply. The noise falls off relatively fast above longwave. Conversely I have another later revision of the model that might as well be a wideband transmitter. o.0

About the ferrite, the Fair-Rite 0431177081 is a rather large mix 31 snap choke capable of winding numerous USB cable passes. I could have done more than 10 passes, but I would have needed an even longer USB extension cable for my current setup. Arrow Electronics currently has the model for around $10 plus shipping, or free shipping with a free perks membership and an $100+ order.

[~SIGINT~]

I have an IBM Thinkpad which is just as brutal of a hash generator!

[RobRich]

Belden RG-11 and connectors arrived. Still waiting on a new F connector compression tool, as my existing one is limited to F connectors for RG-6/59.

I suppose first on the priority list should my usual "go to" HF antenna these days. Moving the 31' vertical to an elevated install should not be a huge issue at least logistically. It works fine ground mounted right now, but I would like to get rid of the radial field in the backyard.

I already have a couple of cemented 4x4 posts, four cemented guy stays, and brackets to install the mast from a previous 11m antenna project. I should have room for at least a couple of opposing elevated ground radials, assuming I do not try a singe radial for a little potential directivity.

[RobRich]

Might be a decent radio day here. Been listening to various regional 2m ops via my 31' vertical. o.0 Yeah I know, but it is the only working feedline routed to my Airspy HF+D right now.

[RobRich]

Had help available today. :)

Nearly all of the old bulk RG-6 coax feedlines and on-ground radials are out of the yard. The 148' LoG built using RG-6 is still in the woods, so that might be a task for another day.

The 31' vertical is down and being prepped to be mast mounted. 4:1 unun, various clamps, mast guys, and two 31' radials are connected. The vertical antenna might get deployed today, though the two radials might just run down to the ground for tonight. I really could use a couple of eye bolts for the far ends of the radials, but I am not finding any large enough in the parts bins.

[RobRich]

We got the 31' vertical on about 21' of mast and the guys done.

Dropped a temp feedline to the house. Turned on the SDR, and normally strong signals are barely above the noise floor. Troubleshoot it tomorrow I guess.

So I am down to temporary vertical on a tripod in the yard for now.


Did a NanoVNA sweep at the base of the mast. The problem is somewhere up the mast. Either the feedline, which I checked earlier, or perhaps the unun that was previously working.

[RobRich]

The 31' vertical is back in business. It is dropped down to just ~10' of mast, that way the feedpoint can be serviced without having to take the mast and guys down.

The 4:1 unun probably has a broken connector or wire inside. Something to perhaps check later. I had an 1:1 in the parts bins, so I am using it for now.

Next up for twice the fun, despite earlier testing okay, the RG-11 appears to have a bad connector or similar. Figures. My coax stripper does not do RG-11, so just guesstimated it by hand with wire cutters. I have a stripper for RG-11 on order. I replaced the coax temporarily with a run of RG-6 I had already.

I removed the two 31' horizontal radials to simplify things. I just connected the balun ground to the mast and guys lines. Whatever, as it is just a receiving antenna anyway.

Did a NanoVNA sweep. SWR dips right above the 40m band and the third harmonic as expected. The cheap RG-6 has enough loss to somewhat smooth out the impedance from MW through 30MHz anyway. ;)

Net result? I doubt performance is much different than when ground mounted, but at least it gets the numerous 31' on-ground radials out of the yard.

I would have looked at the active antennas, but oddly enough, it seems I am out of RG-6 coax. ?!


Quickly skimmed 10m. A net in California, an op in Brazil working DX, and a few other signals. No preamp. Not bad IMO.

[~SIGINT~]

Rob, if the guy lines are metal / conductive, you could do what we do on AM towers and that is to put insulators in-line with the guy wires. This should give you working radials. If you look closely at guy lines on AM towers somewhere along the way you will see an insulator. There is a formula for it but in a nut shell, less than a 1/4 wavelength of the operating frequency so that the guys do not resonate. In your case you want it to resonate so, insulators at both ends and bond them together at the top. A little hard to explain but I think you get the idea.

[RobRich]

Sure enough. Before I have had a upper-HF vertical antenna using the guy lines with insulators as radials.

No insulators on the guys for this deployment. Using 14ga galvanized electric fence wire as guy wires since they are only lightly loaded with a 10' mast. The vertical lobe at low angles might not be ideal if modeled, but it is working okay enough (for now) for casual listening.

Better than the temporary 12' vertical on a tripod I am still using for the nightstand receiver. I am thinking possibly using an active miniwhip there.

[~SIGINT~]

I'm using one of my mini-whips on the nightstand receiver, the ICOM IC-R75, and I am not very pleased with it, mind you, it's inside hanging from the curtain rod and well camouflaged by the curtains. I had limited success with 2nd mini-whip which was externally mounted on the communication mast at my prior location. I have yet to install one outside at my new location to see how it performs. It was -11 F this morning so no thank you ... not until it get warmer out.

[RobRich]

Do you RF ground your indoor miniwhip? A ground wire even to an outlet ground might help. I have done it before in a pinch for a temporary setup. Huge YMMV depending upon electrical system RFI.

Could you hang it from an eve or gutter? Snake some RG-179 or RG-316 through the window. I have done that with the coax under the closed window in a piece of un-shrunk heatshrink tubing to get a feedline outside.

I often use those inexpensive eBay 75-ohm "flat" coax jumpers under windows. Most are not really flat, but more like probably RG-179 or similar inside the casing. They are typically less than 1' long, so losses are no big deal at HF and lower.


Since the 31' vertical feedpoint is readily accessible, I intend to replace the 1:1 balun with another unun to flatten the multi-band impedance curve at the feedpoint at little. Balancing losses at the feedpoint versus losses in the feedline. Yeah, I know is not a big deal for receiving, but I do not mind experimenting a little with the deployment during cooler weather.

I was considering another basic 4:1 unun, but I kept thinking about what G8JNJ did after analyzing the Comet CHA-250B match.

https://www.g8jnj.net/cometcha250b.htm

I considered building one, but then I stumbled across a similar dual-ferrite unun on eBay. :)

https://www.ebay.com/itm/303018040561

It is a little different design, but the same idea. I am not entirely sure how it will fare under 80m, but "whatever" as long as S is decently over N considering the usual noise levels down there anyway. Either way it probably will perform no worse than a simple 4:1 unun, so again, a "whatever" for my purposes. Something different to try I suppose.

At some point I might try the even simplier G8JNJ approach to multiband vertical matching using a bifilar winding on an iron powder core. It is further down the previously linked page. I still have an S9v18 vertical in storage.

[~SIGINT~]

The mini-whip is just floating with about 20 or so feet of coax and a choke at the radio end (between the bias-t and the receiver). I can try coupling to the AC ground and see what happens. Getting through the patio door is a challenge, specially when the temperatures are -10 or lower at this time of year. I should have got some of those flat ribbon pass-through the last time I was at the store. If anything, it would have been worth the test. Even when I had this mini-whip hanging outside it performed just ok, not that great. I'm actually surprised that it picks up as much as it does. I might hang the YouLoop in the patio door instead and see what happens.