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.