More Mini-Whip Testing

The latest field outing to test the PA0RDT and generic Chinese mini-whips against one another gave good results for both.

Connecting up in the field. Chinese unit on the left.

 

I'll spare myself the time-consuming process of uploading each and every video of the stations listened to and will give you the plain results instead! Blue background simply highlights the strongest signal, if any. SDRConsole produces probably rather optimistic signal strength data, so take the accuracy of the numbers with a pinch of salt and rely simply on the comparison between units.

60kHz, time signal, Anthorn UK:

PA0: S9+34dB; Chinese: S9+35dB 

77.5kHz, time signal, Germany:

PA0: S9+19dB; Chinese: S9+15dB

153kHz, Alger Chaine 1:

PA0: S9+18dB clean; Chinese: S9+19 with broadband noise.

3.985MHz, Unidentified, Spanish:

PA0: S9+26dB; Chinese: S9+26dB

15.400MHz, Interradio Romania:

PA0: S9+48dB; Chinese: S9+48dB

Clearly, there is no enormous difference between the two units, though the PA0 unit is a significant, 4dB stronger on the 77.5kHz DCF signal. The Chinese unit is only ever 1dB stronger on any signal.

This 1dB occasional advantage for the Chinese unit, though tiny and perhaps non-existent, given the variability of lower frequency signals, is undermined by, for example, the clear case of 153kHz, where the Chinese unit was suffering from some kind of broadband noise. Looking at the wider spectrum, I can see this extended along the whole LW spectrum. If this was being received from the laptop, it was certainly not being heard on the PA0 unit at all and the addition of a choke on the feedline did not reduce the noise. In this case, even though the Chinese unit was 1dB stronger than the PA0 unit at this frequency, the noise was distracting and, where it would coincide with a desired, weak signal, be significantly detrimental to reception of that signal.

I'm reminded that the SNR figure is more meaningful in such comparisons, though this is a little more difficult to obtain as the varied signal is always changing and a reasonably long sample time is needed to get a feel for what the maximum signal can fairly be said to be. But I tried it, using SDRUno, noting a much longer test on more signals is needed:

60kHz, Anthorn time signal:

PA0: 42dB; Chinese: 52.3dB

77.5kHz German DCF time signal:

PA0: 24dB; Chinese: 31.2dB

225kHz, Polskie Radio:

PA0: 23dB; Chinese: 8.9dB

252kHz, Alger Chaîne:

PA0: 23.3dB, clean; Chinese: 23.3dB, with broadband noise

9.690MHz Radio Exterior España:

PA0:46.5dB; Chinese: 42.9dB

 

Overall, and whilst more testing is definitely required, I think the PA0RDT mini-whip, though double the price of the Chinese units (but still cheap at ~£50, delivered), is of much better, more durable build quality and can be much quiter than the Chinese units, which may become a much more important deciding factor if you like listening to distant NDBs or such like; I may conduct tests on those at some point. Sadly, it takes a lot of time to carry stuff out into the field and do the tests and the weather is often wet at the moment.

Poor-quality phone shot of the laptop screen, showing the broadband noise at LW with the Chinese unit.

The probe ('antenna') of the PA0 unit is less than half the size of the Chinese unit, though this is almost certainly because the Chinese have tried to impress by simply enclosing a similarly-sized circuit in a longer PVC pipe!  The PA0 DC supply is smaller, but it does lack a DC (on/off) switch and has no socket for attaching a grounding wire; the Chinese unit, much more conveniently, has both these features. But they are relatively inconsequential differences. Though most information - and the theory of operation - says that grounding is essential, my own tests in the field, at an RFI-free location (noise floor of below -120dBm), show there is no discernible difference when the grounding is disconnected. But I will check this in future on very weak signals.

Both units, however, fail to take weather fully into account!  Whilst the probe circuitry is safely enclosed in PVC pipe (the PA0 has minute vapour/pressure equalisation holes on the base, the Chinese has none), the BNC connectors that both use at the base are unprotected and, for a permanent outdoor installation, will quickly become very wet and lead to connection and coax cable corrosion. All that needs to be done to avoid this is to find a short length of PVC pipe and attach it by glue or sealant to the base of the whip housing, such that it shrouds the connector from water ingress whilst still allowing hand access to the connector. It should be done as standard, but isn't!

PA0RDT kindly supplied me with an audio recording of SAQ's 24/12/2023 transmission as heard at his QTH with his mini-whip (roughly 850km from SAQ, as opposed to roughly 1000km for a typical central-UK receiver), which you can listen to here.

 

Mini-whip shoot-out!

Interest in the remarkable mini-whip antennas - actually e-field probes, rather than antennas in the usual sense - continues here in now rather cold north Wales, where mountain waterfalls are currently frozen solid.

Today saw the arrival of the PA0RDT mini-whip system, which I bought because of its reputation for high-quality build and out of curiosity with how a generic Chinese mini-whip, widely available on e-bay, would compare with it.

Now, the Chinese circuits are perfectly well manufactured to good quality standards and can't fairly be thought of as inferior products. The Chinese unit I bought cost £23 delivered, and it arrived within 6 days from China, even though I ordered it on Xmas Eve. The PA0RDT system, with delivery, costs twice this amount and took 7 days to arrive from the Netherlands.

The two whips, prior to deployment in the night sky. The PA0 probe is less than half the size of the Chinese probe.

 

With the easterly winds lower and the temperatures a bit warmer this evening, I took-off to the lakeside woods, a quiet rural setting free of as much electrical interference as it's possible at low frequencies.

I mounted the probes ('antennas') on separate fibreglass poles. Though there is no interaction as one gets with true antennas, I kept the one not under test at near ground level whilst the one under test was up at 7m and then repeated with the next probe. 

Each system had the sheath of the coax feed connected, via slightly different mechanical means, to an independent ground stake in very moist/wet ground (the PA0 system has a jumper to allow common or independent grounding).

Whilst the Chinese system has a separate grounding connector on the DC supply box, the PA0 system doesn't and you have to, rather less ideally, croc-clip an earth connection to a coax plug. The reception was by the same coax cables and the same RSP1a SDR.

Because my interest is mainly SAQ reception, I listened to low frequency signals for this comparison. They are also much steadier signals than, say, SSB at 80m or something like that.

Let's look at the evidence. First, the PA0RDT system, receiving the UK's Anthorn time signal in Cumbria (and therefore a good ground wave signal at my position, just down the Irish Sea from the transmitter):

And this is how the generic Chinese mini-whip did, a steady 3dB stronger than the PA0RDT system:

Next, let's look at DCF77, the German time signal as received by the PA0RDT system:

And how DCF77 was heard by the Chinese mini-whip, being a full 4dB weaker than the PA0 system:

I'm a bit tired for now to post more videos, but on the local ground wave 198kHz (BBC Radio 4), the PA0 system was 2dB weaker than the Chinese system. But on Algerian radio at 252kHz, the PA0 beat the Chinese system by the same, 2dB.

So it seems on this limited test that the PA0RDT is better by between 2 and 4dB on more distant low frequency signals than the generic Chinese system. I'll do more testing as time allows, hopefully during the early morning, when some South American stations can usually be heard at low frequency.

Mini-whips: junk, right?

I still have little time for radio these days. When I do get some time, I've tended to develop the listening side of things over on the MW, LW and VLF frequencies, herded there by recent efforts to receive SAQ, which have been successful.

For the 17.2kHz SAQ signal, I first tried the standard solution of a 3m-circumference coax sheath loop (RG-213) with a nice amplifier made by George Smart (WellGood). This yields good, strongly directional reception, though I found SAQ was only weakly heard from a domestic location. It would, of course, be better from a quieter location.

Early tests of the amplified loop (rear) and unamplified (passive) loop. The passive loop is pretty useless for SAQ, at least at my distance from it.

 

A later SAQ transmission was due, and I packed the loop in the car, ready for some beach deployment. Unfortunately, I forgot the battery and had to return home, which I did just in time to connect-up a very much larger, 18m-long coax loop, slung in loose vertical arrangement in a hedge.

The signal from this was very good, even in a noisy domestic environment, hitting a steady S6. I made a recording of the full transmission, which you can see and hear, here.

To avoid the noise for the next SAQ transmission, I headed for the local lakeside, just a few minutes away. The large loop was slung from the densely-branched evergreen trees, and the signal was again around S6, but with none of the noise. You can hear that event, here.

Windy and threatening rain for the Xmas Eve 2023 SAQ event - hence the tent!

 

I did the same for the Xmas Eve, 2023 event and again, S6 or just under. 

Then I started wondering if there was an alternative to lugging a big loop of heavy RG-213 around to the woods and spending several minutes setting it up. So, on Xmas Eve, I ordered a generic Chinese amplified 'mini-whip' system for the grand total of £23, delivered. Just six days later, it arrived - amazing! But would the performance be equally impressive?

Just six days from China to Wales, even over the Xmas period!

 

Well, I will wait until the next SAQ transmission to compare the mini-whip against the large coax loop. But I did manage to get out during a brief spell of dry weather, at night, to test the 3m-circumference amplified loop against the mini-whip.

Test conditions for the amplified loop were: centre height of about 1.5m, WellGood amplifier boards via ~10m RG8-X coax, coax-wound choke known to have extremely low return loss at the lower end of HF (>>46dB), SDRPlay RSP1a receiver and a laptop running SDRConsole, CW peak enabled where a CW signal was in contention and synchronous AM for commercial AM stations. The loop was aligned by compass on great circle paths to the relevant transmitters, determined earlier via Google Earth.

For the amplified mini-whip, mounting was at roughly 4m atop a PVC pipe installed in a plastic ground screw; the coax sheath was grounded at the base of the pipe via a ~30cm copper pipe of 15mm diameter. Feed arrangements the same as for the loop. Ground conditions are very moist ground, almost freshwater due to the peaty lake shore location.

The results were very surprising, at least to me, where I hadn't expected much from the mini-whip at all. Overall, it was giving the loop a good run for its money and gave a better signal on some stations, and you can see the evidence for yourself in this hastily-assembled sequence of clips from the evening.

Testing the mini-whip on the Anthorn (UK) time signal at 60kHz.

Very much encouraged, I ran a very quick test of the mini-whip at 2m and then 4m height. The signal from DCF77 time signal in Germany during daylight showed an increase from S9+9dB at 2m to S9+13dB at 4m. It was about to rain again and I took the wrong keys for the field shack, so I couldn't get it up any higher. I've ordered a 9m fibreglass pole, which fits nicely into a standard clothes line plastic ground screw and from which the very lightweight antenna unit can be hung at around 7-8m up. 

Stay tuned for the next, increased height tests and, maybe around February, a 'Grand Comparison' between the mini-whip, 18m coax loop and a terminated 50m Beverage! I've also ordered the 'original' PA0RDT miniwhip, to see how well that compares with the Chinese edition. There is always so much to do, and so many ways to keep the 'anorak' image alive!

Some very useful and reliable resources on the mini-whip can be found here and here.

Autumn Equinox Beach WSPR

Yes folks, the equinox that, from this point on, takes us into winter, is upon us again!

I always try to do some WSPR receiving down at the beach, facing the incoming signals along the morning long path, whenever I can at the quinoxes. During the pandemic lockdowns - I shudder to remember them - the ability to get out onto the beach and meet some local people was part of my survival strategy.

Nice, but a bit showery, at the beach this morning.

 

The set-up, for 14MHz, is simple: an elevated 1/4 wave vertical, with two sloping elevated radials, installed on saltwater-saturated sand at the water's edge. On this run, I was using a SDRPlay RSP1a receiver, with a Raspberry Pi 4B doing the business on the WSPR signals.

Whilst it was geomagnetically fairly quiet during the test, it had been slightly rough the previous later evening. This does tend to degrade my performance at 53.2 degrees north (e.g. WSPR signal broadening is common here during rougher conditions, whereas it may not occur at all a bit further south).

A particular station of interest for me is VK3QN, a fixed long-path (to Europe) 14MHz array that is optimised for low-angle radiation. It's owned by Ian, VK3MO and transmits 5W every ten minutes.

I found Ian's signals were not being decoded, once they reached a good signal strength. I had the decode depth on 'normal', whereas 'deep' seems, oddly, to work much better on very strong signals; VK3QN is a solid, saturated line on the waterfall whilst transmitting.

VK3QN fixed long path (Europe) 2 x 6-ele 14MHz array. (C) VK3MO, with permission.

 

In any case, my reception of VK3QN was very good, but the typically-excellent performance of the likes of 2E0PYB, who I think is still using a vertical phased array, not too far from the sea and in a low noise environment, was doing a bit better. That said, the usual disclaimer has to be issued, in that we often don't know (and some won't tell!) what antenna is in use on any given day. We also have to be mindful that, being well east of me, 2E0PYB's long path will peak about 15 minutes earlier than me, so my curve has to be mentally shifted to the left.

VK3QN being heard by various UK stations, 21/09/2023

Feeling a bit deflated that my effort to get up at 5am and brave heavy showers and a cold wind didn't seem to be bringing home the goods, I turned my attention to analysing the signal from VK2DAY. This restored a bit of faith in beach operation, with something around a 9dB typical enhancement over even the excellent stations of 2E0PYB and GB0SNB(/SDR). Nobody else in the UK could hear VK2DAY in this period.

VK2DAY reception, 21/09/2023.

How about VK7JJ, which wasn't being heard very often by anybody in the UK? Turns out I wasn't quite as good as the other two 'big cheeses', but still there with the only three who were hearing him.

VK7JJ reception, all UK stations hearing him, 21/09/2023.

Turning to VK4PK, again only three UK stations hearing him in this period and where I was definitely above 2E0PYB and, overall, about level with G6MC/K.

VK4PK reception by all UK stations hearing in this period.

Where the beach did very well for me was in hearing stations that nobody in the UK - not even 2E0PYB and GB0SNB - could hear during the test period. These included ZL2KR (-21dB/2500Hz, 05:08UT), VK2WQ (-24dB/2500Hz, 06:40UT) and JA5YLT (-23dB/2500Hz, 07:18UT) - though G4HSB, whose data I could not access for some reason, was also reported as hearing that station. With the detection limit for WSPR being about -34dB, this implies at least 13dB enhancement for these stations, relative to the other best stations in the UK - and much more than this, compared to a typical UK receiver.

Zl2KR spots, heard only by me in the test period.