Best MWDX antenna?

[alpard]

Thanks for your info. 

I am planning to make a vertical RX antenna covering LW and MW and HF too.  I have a fibreglass  flag pole extending to 7m height = 21ft?
I also found 3x old slinkies in the shed which I am planning to join them all together making into one Slinky, and attach it to the pole.
I am thinking of either feeding via 9:1 balun with no ground input (just radiator input) or  the other balun which has ground input making unbalanced coaxial feeding (which will feed some sort of ground wires).

I also have a MFJ preamp 1020C / Active Antenna which covers 300 kHz - 30 Mhz (actually covers from 250 kHz), which will be using to power the GP.
I am not sure the total length of the stretched 3x Slinkies, but it surely will be higher than 21ft the pole height when stretched due to its wound wire length. Hopefully it will cover from LW to 30 Mhz when powered by the preamp.

[alpard]

I implemented this Slinky Vertical with 9:1 balun, and it seems working OK on LW MW and 60m tropical band.
It seems definitely working better on MW than long wire.  Good to add another antenna to switch over to, when one antenna gets noisy for the night.

A few videos added into my youtube and twitter channel RXing with the DIY slinky vertical.

[RobRich]

In theory you probably have a end-fed normal-mode helical antenna there. "In theory" because helical antennas can be a huge YMMV depending upon diameter, turns, spacing, etc. "End-"fed" assuming no ground radial field is present. In other words, it is huge YMMV on impedance curves and resonance.

That said, the bigger problem with the standard slinky is the metal. AFAIK, most slinkies are high carbon steel, which has poor conductivity compared to copper and aluminum.

https://www.thoughtco.com/table-of-electrical-resistivity-conductivity-608499

Given the helical design considerations and metal conductivity issues involved, performance likely would fair better by simply running a copper wire up the vertical support. ;)

I suggest deploying a radial field under your vertical as well. Just a few on-ground radials of whatever lengths you can fit should suffice for receiving. If your balun does not have a ground connection, then it is probably an unun, so you could connect the ground radials to the coax connector shell on the input side. If you do not want to deal with soldering, a mechanical connection with a hose clamp should suffice.


Previously I used a simple 9' vertical over four 9' on-ground radials for quite awhile, especially back when I was using a portable receiver on the nightstand. No feedpoint baluns or transformers, though IIRC, I did have a few snap-on ferrites of whatever mix on the coax near the feedpoint for whatever they were doing; likely little to not much. It worked quite nicely (IMO) for MW through VHF, plus it even occasionally pulled double duty on a scanner for local 800MHz pulbic safety traffic. SNR was decent because it was away from the house. Gain was not a consideration, as most portables tend to overload easily anyway.

[alpard]

Good point.   I was a bit uncertain about conductivity of the slinky spring material, so I got out my DMM, and checked for the conductivity after joining 3x separate slinky to 1 single long slinky.  The conductivity of the slinky shown on DMM was excellent with loud beeps from the end to the end.  But that doesn't mean it has perfect conductivity I fear.
But it seems doing the job of RXing MW, and even LW, and some portion of HF ok.   It is definitely better than the longwire on some frequencies, but not all.  There are parts of the band, the slinky vertical gets very quiet, when LongWire copies well.   

Great advice on the radials.  Yes the balun is a 9:1 unun, and has only 1 connection post for the radiator, so perhaps some substantial radial wire will have to be added via the coax outer socket via soldering or a crocodile clip.

Through time, I will try getting different balun - with 2x separate connecting posts for the radiator (one for the radials), and keep experimenting.

[RobRich]

SDRangel running on a Samsung A7 Lite tablet. Airspy HF+ and active miniwhip antenna. Audio to a BT speaker.

 

SDR++ on the same config.




Added the low-pass + shelving filter to my nightstand radio. More commentary here:

https://www.hfunderground.com/board/index.php/topic,118112.0.html

On a related note, I found a possible issue with a short RG-6 jumper when changing out connectors to install the filter.

Mostly just a reminder to occasionally check feedlines and connectors even if everything *seems* okay.


Estimated 148' loop-on-ground deployed. Could be closer to ~150' as I did not measure close. At least it is generally symmetrical for whatever that actually might benefit.

It is solid copper pet fence wire this time instead of RG-6 coax likely previously. It is also moved to a different position. Much of my old LoG is still floating under the surface where it was located. Not sure I want to bother finding it.

Deployed a LDG 1:1 balun at the feedpoint approximately halfway along a side. I fed my previous LoG on a side as well, so "whatever" IMO. Typically there is not enough directivity feeding a basic LoG at an apex to really matter IMO.

I was going to put a common-mode choke on the feedline near the house, but I did not feel like dealing with it tonight. Likewise I did not even bother with new run of RG-11 feedline. I found a long enough piece of bulk RG-6 with connectors in a parts bin for now.

Suppose I should get around to a basic NanoVNA sweep sometime. I did not even check the feedlines, though it all seems to be working okay.


As previously noted, I am once again thinking about moving the 31' vertical back to being ground mounted over a radial field. There is not much difference in performance for my receiving purposes other than the annoyance of ground radials. Then instead maybe look into finally deploying a small loop and lightweight rotator on the mast mount.


The new 148' LoG is not significantly better to sometimes even worse than my usual 31' vertical for EMI/RFI, at least so far tonight for MW/HF below 7MHz. I suspected that might happen, as it is closer to the house than my previous LoG and constructed with a single wire instead of my previous "shielded" coaxial design.

I can go ahead with adding a RF choke on the feedline near the house, though I doubt it will do much. Also I might look into changing the 1:1 feedpoint balun to perhaps a mix 73 isolation transformer. I suspect the 1:1 balun toroid might be a mix 43 given the size and power handling spec, but LDG does not publish the ferrite mix used.


^Merged a few posts.

[RobRich]

Added a RF choke on the 128' loop feedline near the house and a few snap-on ferrites below the balun at the feedpoint. Seems to have helped somewhat.


On to bigger MW/HF issues for me at the moment. The baseband noise filter in SDR# mitigates whatever the latest local RFI is for now, but I suspect it is time for a decent small loop. Tested my ~36" passive hula hoop loop with a portable in the backyard. There is considerable directivity to the particular RFI as I was able to null out most to practically all of the noise depending upon the band.

[~SIGINT~]

The Cross Country Wireless HF Active Loop Antenna v4 has been peaking my intereset for the past little while. Adding their HF Multicoupler to the setup would also be a nice touch.

https://www.youtube.com/watch?v=lD3ta2j7_ps
https://www.youtube.com/watch?v=gK07qkeBl84

[RobRich]

The RFI dropped out. I would suspect perhaps solar panels in the area, but it was dark well before the noise dropped. Hmmm.

Anyway, I dug out my antenna phasing unit in the meantime just in case.


Yeah, the CC v4 with multi-coupler is a good price IMO. I might have to take a serious look. I certainly have enough SDRs to potentially feed.

I skimmed some of the other usual suspects. Pricing for the W6LVP and MFJ-1886 loops seem to be holding decently.

Meanwhile the DXE RF-PRO-1B has jumped to ~$675 at some point. o.0

There is also the MFJ-1888, but I am not inclined to gamble $500 on a MFJ active antenna. o.0 o.0

I am hoping to score a KiwiSDR 2. I will want a decent low-noise antenna for it, especially if putting it online.

[~SIGINT~]

Nothing against MFJ but I would not invest loads of money on their product. There is a catch phrase for MFJ "Mighty Fine Junk". I have owned some of it in the past and was never pleased with the quality of assembly etc ...

My name is also in on the pre-sale of the KiwiSDR 2 and think the CCW antenna would be great with it. I'm curious about running it horizontally for an omni-directional pattern. This is not something I can do with my Wellbrook or any other large loop.

[RobRich]

Thus the part about gambling on a $500 MFJ product.

Thankfully I have had decent luck with MFJ products, but most of those products were not hundreds of dollars, either. Checking for solder blobs and cold joints is a good idea with MFJ purchases.

The basic MFJ tuners tend to be decent, though prices there have increased as well. I like the MFJ-901B, but for $80-$90 a few years ago versus about $150 these days.

[~SIGINT~]

Checking for solder blobs and cold joints is a good idea with MFJ purchases

You hit the nail on the head. I had a manual tuner once from FMJ (which was a knock off of the Barker & Williamson tuner) and the assembly was horrible. I ended up re-working the entire tuner. I also had one of their early antenna analyzer that was, well, ok, but not that great. The artificial ground box / tuner worked ok if you know how to use it properly.

[RobRich]

KiwiSDR 2 ordered. I not sure where order numbers started. Anyway, given how far I am likely down the list, I suppose that gives me awhile to work on an improved low(er)-noise antenna solution.


I used to occasionally hear what sounded like a plasma television during the day. I am not sure it is the same TV (or whatever), but it is back with a vengeance on my 31' vertical today. Has the plasma TV sound. The frequencies are a little different, but it has the double peak signal profile as well.

https://www.dxengineering.com/techarticles/lightningandrfiinfo/plasma-tv-mother-of-all-rfi-producers

It is highly attenuated on my 148' loop-on-ground. A little filtering pretty much knock it out there.


Thankfully the noise is gone now. Much better.


Continuing to poke at further mitigating imediately local noise.

I have (err, now had?) a storage box of TDK snap-on ferrites. Deployed many of them. They are better suited for VHF but still have some RF resistance down into HF.

Interestingly I was able to knock down some LW noise on my 31' vertical.

Notebook on mains:


(click to enlarge)

Notebook on battery:


(click to enlarge)

I will spare the MW screenshots. Daytime would be better a test there, but anyway, there is a slight difference currently at the very bottom of the MW band. Rest of MW through HF seems largely negligible either way.

A single ferrite on an indoor RG-6 jumper to the 31' vertical did most of noise mitigation on LW and low-MW. Again it was not even a typical low-frequency ferrite mix, but FWIW, there are now four of those ferrites on that jumper. ;)


Still cleaning up RFI. Moved my both cable modem and router to a linear regulated power supply, deployed more ferrites on their various cables, and tidied up the wiring mess.

Admittedly, this is my usual notebook on battery, but a quick look at the VLF band.


(click to enlarge)

Moving up to LW, spotted Medi 1 with the notebook on its usual power supply. Some static crashing, but a listenable copy.


(click to enlarge)

Skimmed through the usual NDBs, and I still have annoying but expected RFI around 380KHz running on the notebook PSU. Moving up the band, thankfully the previous RFI on lower MW appears to be mitigated at the moment.

[RobRich]

148' loop-on-ground to a ~$30 Msi SDR with LDG 1:1 balun at loop feedpoint and KD9SV common mode choke near house entrance. Notebook on power supply.


(click to enlarge)

After adding an 1:1 choke wound as a 4:4 on a mix 73 binocular core near the receiver. No changes in SDR app settings.


(click to enlarge)

[~SIGINT~]

Nice clean up with the 4:4 (1:1) UNUN.
For those who have not been following the entire thread, to recap, below are some of the effective frequency ranges for the various ferrite MIX values.

MIX 31 - 1 MHz - 300 MHz
MIX 43 - 25 MHz - 300 MHz
MIX 73 - < 50 MHz
MIX 75/J - 150 KHz - 10 MHz

[RobRich]

Yeah, more or less an isolation transformer due to using galvanically isolated windings. I have used them previously on other antenna projects.

I like the small mix 73 binoc cores for MW/HF receiving purposes, especially for the cost. Add enameled magnet wire and a couple of cheap F connectors. Maybe an $1 or so in build materials.

I have been needing to build more, but that means soldering, which is not exactly on my list of favorite activities these days.