Questions, and more Questions
Joe Chester ponders the problems of local noise and how to get round them.
In case you can’t spare the time to read this piece, I can say at the outset that I’m on the 80m nets, regularly, and on one particular net every day. But should also confess that I’m a frequent user of the Hack Green, and other online SDRs (see references for web addresses) when I am working 80m. I do this because reception here, on 80m during daylight hours, is plagued with background noise.
In an earlier piece ( PW August 2020)
I said that in order to build a better 80m station, I needed to address two issues – transmission and reception. I’d not say that I have the transmit side sorted, but it’s working better than it was when I started. Reception, however, is a whole new ballgame. I can say with certainty that on the many nets I earwig day after day, the number one topic is probably the background noise level. Many operators have been saying for some time that the Openreach implementation of xDSL is a major source of some (most?) of that noise. RadCom did a major piece on this recently (May 2020), and there is ongoing work to try to address the problem.
Where I live, my station has tall houses on two sides, I would assume with fixed line xDSL broadband, and WiFi routers on every floor. Add the noise from poorly made switched mode power supplies, and it’s hardly surprising that I have high background noise levels. And this is why I listen on Hack Green and the other SDRs. But a thought struck me recently that this way of working is not new, or unusual. I suspect many of you will remember the days of separates – a transmitter and a receiver, with changeover relays. In those days it was not uncommon to use two separate antennas. Modern transceivers have the changeover relay buried in the internals, and a few now have two or more antenna connections. So, it’s not unrealistic to use separate transmit and receive systems.
The advantage is that the receive antenna can be a low noise type. One often cited solution is to use a loop for reception. The Wellbrook loop is one example of a well regarded, highly efficient, low noise, receive antenna. This has the advantage that it can be rotated to reduce the noise level. Situated away from the house/shack would seem to be the correct place to mount such a loop, up a couple of metres if possible. There are lots of reviews of the Wellbrook about. There is also a DIY group making homebrew versions of this design – called the Wellgood loop. Note that these loops differ from the Alexloop or the MFJ 1795 loops, which are also transmitting loops.
A loop receive antenna is only one possible solution. This antenna captures the magnetic component of the arriving signal. There is another approach, by capturing not the magnetic component, or H-field, but the electric or E-field component, which is orthogonal to the magnetic field. This can also be a low noise antenna, and can be easily built. It’s much, much smaller than the loop, but just as effective at signal reception. At least that’s what its proponents say. Now a slight detour into licensing conditions, before getting on with the practical stuff.
What is aValid QSO?
Setting up a WebSDR is a popular activity among licensed operators. There are WebSDRs all over the world. These can be very useful for assessing propagation conditions. I use one in the Netherlands frequently to check my signal. I don’t see any administrative issues with this. And it’s entirely legal for anyone to listen to a WebSDR. And this includes licensed amateurs. To understand the question I want to ask, let’s start with a separate transmit and receive system at the licensed amateur’s registered address. There are clearly no issues here. But what then if one or more of the components is not at the amateur’s registered address? There are two broad categories here – one is to have a distant receiver, the other is to have both transmitter and receiver at a distant location, as in remote operation.
Let’s start with the first category – a distant receiver. The tricky question is the validity of a QSO using a distant WebSDR as receiver, and a transmitter at the registered address of the licensed amateur. Now if I want to put up a specialist receive antenna at some short distance from my station, surely it’s only a minor stretch to imagine that receive antenna being a few metres away, or a few hundred metres even, or even a few (hundred) kilometres (over the internet)! And is that not what a WebSDR is? So, the question to those steeped in the administrative conditions of our operations is this – is a QSO using my transmitter and a distant WebSDR for reception a valid QSO? An example? “Callsign 1 you are 53 with me direct, but 59+ on the SDR, Callsign 2 I’m not hearing you, you are S0 direct, but 59 on the SDR”. Is this a ‘valid’ QSO? I think it’s time to throw some specific expertise at this question. Your help would be appreciated.
Now drifting into the other category briefly, remote operation is a bit of a grey area at the moment. Some jurisdictions clearly allow it, some don’t. I seem to recall being told that Ofcom is looking at this currently in the UK. The questions posed by remote operation are many – but I will concentrate on just one here. Is a QSO made by a licensed amateur via a remote station operated in accordance with the local regulations, a valid QSO, for example, in claiming DXCC?
Back to Separates
Sorry, this piece asks more questions than perhaps answers. But I want to come back to what I know is perfectly legal, in terms of the UK operating licence, a ‘separates’ system, with a receive side and a transmit
side. I’m quite certain that a separate low noise antenna, connected to a really low noise receiver is the way to go here. I have, in effect, two choices – an E-field probe, or a H-field, (or magnetic) loop. Let’s start with the E-field probe. You could also call this an active mini-whip antenna. Extensive searching has turned up limited information about using these on the amateur radio bands. Essentially an E-field probe is a short piece of conducting material (the ‘antenna’) connected directly to a low noise amplifier. Some people have put the entire probe inside a piece of conduit pipe to provide weatherproofing. They are reported to work very well on the lower bands, even down to VLF frequencies. I want to use it on 80m – so this is possibly a bit higher in frequency than its use lower down. But the theory is good at least.
The most popular of these seems to be the one designed by Roelof PA0RDT, from Middelburg, in the Netherlands (lovely place!). Fig. 1 shows the complete antenna. Nothing extra, no trailing antenna wires across the garden, is needed. You can find Chinese copies on eBay for a few quid but I contacted Roelof directly. I’ve also contacted a few of my more energetic soldering experts to see if any of them are up for a build. You might ask why I’m not doing in myself; to which I can only reply age (eyesight, wobbly hands etc). Roelof replied immediately, and said he would make one for me, for a small fee. Thanks Roelof.
So, while waiting for this to arrive, lets briefly move on to the other alternative, the magnetic loop. Everyone talks about loops, some build or buy, but I rarely hear reports of these breaking the laws of physics performance-wise. There is one exception. I’m not talking about transmitting loops – these have their own following. Where receiving loops are concerned, there seems to be only one real contender – the Wellbrook, mentioned above. There was a review by Steve G0KYA, in RadCom in January 2012. He was impressed by its performance in reducing local noise levels. Now, a little bit of a theoretical discussion. Steve explains the role of the magnetic loop in terms its rejection “of electrostatic noise and electric fields”. At first sight, this makes sense. The loop is sampling the H-field and ignoring the E-field noise. But wait a minute. Roelof, in a report on his development of the E-field probe ( Ref. 1) says that he spent a long winter making various loops, and he reports that they did not reduce his noise levels. He then went on to make measurement of noise both inside and outside his house, using an analogue voltmeter. These tests convinced him of two things. The first was that the H-field of the noise was both inside and outside his house. And secondly, the E-field component was inside, but very much reduced outside the house. So back to Steve’s review. What he says the loop does is provide a much better signal to noise ratio (S/N) than a wire antenna, like a doublet. Roelof says that his E-field probe does exactly the same, provide a better S/N response.
And in the end, it’s about increasing the local signal-to-noise ratio. So, a decision needed to be made. The E-field probe was very inexpensive, and I suspect many operators might find the loop a bit on the expensive side. Hence my e-mail to Roelof. My E-field probe is due next week. Of course, there is a bit of systems work necessary before I can test any of this. Principally, I need to make, borrow (or buy) a changeover system, so that I don’t blow the front end on my separate receiver and low noise antenna when I transmit. Any ideas, please?
So, one final question to end – will it work, and if not, why not? Of course it will!!
References
1. Roelof PA0RDT article: https://tinyurl.com/mv6tqes
Useful SDR websites
(there are a great many more worldwide) Hack Green: http://hackgreensdr.org:8901 Stafford: http://160m.net Weston-Super-Mare: http://websdr.uk:8060
( Editor’s comment: I can’t let Joe’s questions go without providing at least some of the answers! As far as DXCC is concerned, the rules are clear and can be found on the ARRL website:
a) All stations used to make contacts for a specific DXCC award must be located within the same DXCC entity.
b) All transmitters and receivers comprising a station used for a specific contact must be located within a 500m diameter circle.
c) QSOs made with legally licensed, remotely controlled stations are allowed to be used for DXCC credit.
I believe the above answers both the remote station validity question and the remote receiver validity question. For other awards and for contests, you would need to read the specific rules to get an answer to Joe’s questions. But for a day-to-day QSO where you are not applying for an award or taking part in a contest, frankly a QSO can be whatever you want it to be!
As for using a separate receive antenna, do note that higher-end transceivers have a connection for one, so there is no need for ‘separates’ in such cases. And for the popular IC-7300, there is an add-on kit to achieve the same result.)