Instrumentation for radio amateurs
You will not get around it - at some point you want to know why an antenna is not working, or an amplifier is not amplifying, and then you have to take measurements. Measuring means certainty and reliable knowledge about the state of a system. Doesn't it? Yes, it's a long story...
What kind of instrumentation equipment does a radio amateur need?
Let’s start very gently, without high-frequency technology - a multimeter would be useful. It doesn't have to be anything super-fancy, but it should be able to measure the current consumption of a small device. Or the voltage of a power supply. Voltage measurement is still easy, but with current it gets more difficult above 10 A. In many cases you might need special measuring equipment, for example a current clamp meter. Such a device is already something you will not buy easily due to cost. But maybe it would be a good purchase for the local radio club, where every member can borrow the meter?
Should it be a digital or analogue multimeter?
As always - it depends. If you want to measure changing values, an analogue display is unbeatable because you can see trends much faster (value increases, value decreases, etc.) If, on the other hand, the exact value is more important, a digital instrument is easier to read.
And - an older analogue instrument can offer another advantage: Namely, a much higher internal resistance than a digital multimeter. This is important when you want to measure very small voltages at sources with low load capacity. With a high internal resistance, the instrument hardly loads the source and the measured value is not influenced. Say on the other hand, you want to measure the battery voltage of a rechargeable battery, it doesn't matter that much. This battery has a low internal resistance and can also cope with a load from a measuring instrument with low internal resistance.
So the first recommendation would be a simple digital multimeter with a continuity tester (beeper). This makes it easy to find faults in the circuitry and in the power supply cabling of your station. An analogue multimeter is often very helpful for those who build their own electronics.
And what about high-frequency stuff?
The most common measuring instrument for radio technology is a standing wave meter, an SWR meter. It measures the forward power that is sent from the radio to the antenna and how much of it is reflected by poor matching and comes back to the radio. In other words, the ratio of outgoing and return power, which is why it is called the "standing wave ratio". More precisely, we speak of VSWR, Voltage SWR, because we actually measure the voltage on the coaxial cable. Now, if you also know the impedance of the cable, you can easily convert to the power, which is what the SWR meter shows.
So the typical application is monitoring the antenna. Does it have a good matching or not? Even if you don't do your own antenna experiments, you should keep an eye on the SWR. A bad match leads to high reflected power, which can damage the radio in extreme cases.
But every radio has an SWR meter built in, why an external device?
That's right, radio manufacturers have been integrating SWR bridges into their radios for many years (more precisely: since the use of transistor amplifier stages). The reason for this is to protect the final amplifier stage. This way, if too much energy is returned, the transmitting power is reduced, in extreme cases to almost zero.
The catch with the built-in instrument: you don't always have it visible, because the display can often be switched to other measurement values, for example, output power or the degree of compression. Further, if you have a power amplifier following the radio, the built-in SWR meter is almost completely useless. This is because it only 'sees' the (hopefully) perfect match of the power amplifier, but not that of the antenna. That's why an external SWR meter is often much more flexible and suitable for daily use.
How do I choose an SWR meter, according to which criteria?
Firstly, according to the required frequency, and secondly, according to the maximum power you want to measure. A switchable maximum power range would be very nice. Next selection criteria are the type of connections (N or PL), how small it is (take it with you to your vacation, does it have an easy-to-read instrument, backlighting, etc., etc.
Typical SWR bridges have a frequency range from shortwave to the lower VHF range (2m, VHF, up to 150 MHz). The maximum power is usually limited to 200 W. So you can get through your amateur radio career just fine if you limit yourself to these bands (short wave, 2m) and don't use a lot of power.
Talking about high and low power: Don’t develop too much expectations about the accuracy of simple SWR meters. The reading is often not more accurate than up to an error value of 5 to 10% of the maximum reading. This means that an SWR meter that can measure a maximum of 200 W can show an error of 10 to 20 watts! This is not a problem, as long as the person making the measurement takes this fact into consideration. For QRP it is therefore essential that you can switch the meter to smaller measuring ranges, because otherwise the 5 W transmitting power will simply be lost in the error of the display. If, on the other hand, you can switch the SWR meter to max. 20 W, then the measurement error is negligible.
For higher frequencies, the measuring technology usually becomes more complex, and this is also true for an SWR meter. Starting with the 70 cm band, a separate device is necessary. Making measurements up to the GHz range quickly becomes expensive and difficult to find a suitable instrument. This is also due to the low power levels used at higher frequencies. An SWR instrumentation bridge for several hundred watts is easier to build than one for a few milliwatts. In any case, the SWR meter for higher frequency ranges should definitely have N-type sockets.
Some special SWR instruments have remote sensors. This makes station wiring easier, the display of the SWR meter no longer has to be close to the antenna cable, but can be placed anywhere. Other devices offer a very precise measurement, not only for the power but also for the modulation level and other values. Such measuring instruments are, of course, more expensive and are no longer available in a wide selection.
Besides a multimeter, a useful, simple SWR measuring bridge belongs in every shack, at least for the most important bands and adapted to the power requirements. Higher-quality devices are only needed if you build a lot yourself or have very high demands on the cleanliness of the signal, for example as a large multi/multi contest station.
Beyond SWR meters
Technical progress has made it possible for us to own instrumentation systems, that were as expensive as a mid-range car just a few years ago. We are talking about so-called network analysers, especially vector network analysers (VNA).
Until a few years ago, this domain of measurement technology was almost exclusively reserved for the large instrumentation equipment manufacturers such as Rohde & Schwarz, Hewlett-Packard, Tektronix or Wandel & Goltermann. The reason was the very complex sensor and processing technology. Of course, these companies still exist today (mostly) and they have their justifiable market which they serve. But 80% of the typical HF measurements in amateur radio today can be done with devices that sometimes cost less than 100 €. The reason for this radical change is the progress in semiconductor technology. For one thing, chips for high frequencies are now much cheaper to produce and easier to use than before. In addition, we now have much more powerful digital processors, which allow us to perform complex metrological tasks and calculations quickly and in a power-saving way, even in small, battery-operated devices.
VNAs conquer the market
Around the 2010s, the first network analysers came to market, priced in a range that made it possible for most radio amateurs to afford something like this at home. These were mostly devices that required a PC with special software for analysis. An example is the "MiniVNA" from Mini Radio Solutions in Italy. In Germany, the trade journal "Funkamateur" offered (and still offers) its own developments such as the FA-NW. These devices were initially excellent sensors with a suitable interface to the computer (via USB). The actual calculation and display of the measured values was done by software on the PC.
But the technological development didin’t stop here. In the meantime, devices like the NanoVNA are on the market that also work without a PC. They have their own display, usually a touch display, and work completely independently with a battery. The USB interface serves only to charge the battery and to occasionally download the measurement results to the PC for archiving.
These vector network analysers are suitable for so-called quadripole measurements, i.e. measurements that feed a self-generated signal into a measurement object, e.g. a filter, and on the other side pick up and analyse the potentially modified signal again. This means that a signal generator is also built in. Such analysers can be recognised, among other things, by the fact that they have two HF connectors, one for the output of the measurement signal, a second for the recording of the output signal (simplified). Quadripole measurements have been standardised in RF instrumentation technology for many years; these measured values are called scattering parameters (S-parameters). The typical and standardised measurements measure factors such as the reflection at the input or the transmission of a cable or filter and are described with designations such as S11, S21 etc. Standardisation makes it easy to compare these measured values and process them in other software. In addition, other data can be conveniently calculated from these parameters, for example the complex impedance 'Z'.
You will only need a VNA if you want to dive deeper into HF technology and also want to home-brew devices such as filters, amplifiers, mixers, etc. Of course, you can use a VNA also for very simple measurements like for cables with it, but that would be overkill. Or you can measure an antenna, the SWR and the matching/reflection. But this can be achieved much easier.
Convenient and easy-to-use antenna analysers!
The same reasons that have made general RF instrumentation technology smaller and cheaper have also led to the development of lightweight and easy-to-use antenna analysers. Because in order to determine the matching of an antenna, one does not need the often somewhat more elaborate and complex measurement technology of a vector network analyser. In most cases a much simpler and easier to use device with only one socket is sufficient. This way, the generated signal and the measurement of the resulting value are carried out via the same connection. Although this does not permit a quadripole measurement from the input to the output of a cable, filter or amplifier, it is still very useful. Instead, the two-pole measurement that now takes place is much easier to handle and perform.
These measuring instruments were mainly developed with the aim of easy and quick operation. After all, the goal here is to quickly find the cause of a fault outside at the antenna. Especially in bad weather, you want to do this quickly and easily without having to handle a sensitive VNA.
A typical representative of this type of instrumentation is the analogue MFJ-259, which has been around for many years and still finds friends today because of its simple operation. On the other hand, completely digital devices, with colour display and analytical tools up to the display of a Smith chart, are now offered by RigExpert from the Ukraine. Here, a large selection of portable analysers is available, which differ mainly in terms of the maximum usable frequency and features such as colour display, Bluetooth, etc. MFJ now also offers digital analysers, for example the MFJ-225 or MFJ-226.
Conclusion - so what is recommended now?
Instrumentation technology is complex, and you can still spend a lot of money on top technology. By no means have we discussed everything here. For example - what about an oscilloscope? When is an MSO/DSO useful? Who needs a spectrum analyser?
But as we said, by now even an amateur radio budget is enough for most HF measurement tasks.
- A digital multimeter with continuity tester for simple troubleshooting of wiring and power supply is a must for every radio amateur.
- An analogue multimeter with high internal resistance is required only if you build radio stuff by your own.
- Today, an SWR meter belongs to every amateur radio station. You don't always have to have it looped into the antenna line, but it's good to have at least one in the drawer.
- A VNA like the NanoVNA-F V2 is extremely helpful if you want to measure a lot on cables and filters, or if you build or adjust amplifiers yourself, or if you want to automate recurring tasks (cable length?). Not strictly necessary, but good to know it is out there if one needs it.
- An antenna analyser is a must have for every radio amateur who experiments with antennas or wants to adjust and measure commercially built antennas. Think of the holidays when you want to install and adjust a working portable antenna, very fast. In many cases you can help yourself with an SWR meter, but that is rather cumbersome.
Measuring in HF technology is fun and brings certainty where before you were just guessing. The fascination of these devices lies in the fact that they usually use the best and latest technology the industry has to offer. As a radio amateur, you can get by for a long time without very special measuring equipment, some even for a lifetime. But at some point, it begins. And at that point in time good advice is important, as WiMo offers it on the phone, by email or here on the blog.