A transceiver has 4 basic modules, repeated in various guises. Oscillators, mixers, Amplifers and filters. I will describe how I tested the modules of my sctratchbuilt uBitx
The list of some of my ham shack test gear that could be used is;
DVM (even a simple, cheap one - £10 is useful but even better is to have 2 or 3)
NanoVNA (under £50 this can be used as an antenna analyser and is very useful)
SWR Meter that can measure Power can be useful once the power gets above 1W
Signal Generator - though you can use the transmitter part of a working transceiver. You could make your own but it is probably better to pick up a second hand unit as it will probably be much more stable with more accurate level attenuators. £50 to £100
Oscilloscope, even a cheap 20MHz one (£20 second hand) is useful but the more recent Digital types that pass data to a PC using the USB interface is much better - they sometimes have a very slow Spectrum display. I have a 200MHz one that cost £200.
Component testers; in the old days these might have been a substantial RLC bridge. There are some very cheap modules available on EBAY - the GM328 or LC-100A cost under £15.
Frequency Meter, older units are now available second hand form EBAY for £50 to £100. But there are new uncased PCB modules that cost under £10. They work well provided the input is at a suitable level. At a pinch you could use a working receiver.
Spectrum Analysers, old substantial units are available second hand from £300 upwards (new ones could set you back £1500+) As an alternative you can use a SDR with spectrum analyser software - I use a RSP1a from SDRPlay (£92) although you will need to build an attenuator, The SDRPLay SDR's have properly calibrated input stages that allow display of signals with accurate display of levels to within 1dB but are easily damages at inputs much above 1mW (0dBm) and distort slightly if the input is above -10dBm so keep inputs low for the most accurate readings. They are superb if you do this.
Attenuator - you will need two or three fixed ones and a switched one - I made one with 8 slide switches that can bring in 20dB, 20dB, 20dB, 10dB, 6dB, 3dB, 1dB and 1dB allowing any values from 0dB to 81dB. fixed attenuators are made up of three resistors so you knock them up as and when you need one. Be careful above 30MHz and check your homemade devices.
Return Loss bridge -If you don't have a NanoVNA you should make a simple one of these -they only have 4 components and will cost you about 50p plus a couple of connectors - I try to standardise on BNC and use adaptors to convert to and from these if needs be.
An RF Two Tone oscillator is vital for certain types of measurement such as IMD. Slightly more tedious to make, mine has a pair of two transistor crystal oscillators, each built in its own metal Altoids mint tin along with 7 pole filters, the output of each is put into a 3dB combiner/isolator and the whole assembly put in another metal case, made up spare PCB material soldered into a box shape, still only under £10 for the bits
A testbench amplifier - a broadband, well screened unit that can provide 15 to 20dB of gain, at lowish levels of under 50mW output, you might want a higher power one to drive and test 1W and 10W amplifiers - but you will be building these anyway as you build your transceiver - provided you build in the right order! you can build a couple of extra units so you will have them for later projects.
Power amplifier sampler will allow easier testing of the output of driver and PA stages. A high power attenuator would be handy too.
Of course you will also need a soldering iron or 3, desoldering braid, flux and cutters, pliers and probably a couple of magnifiers, one of which should be an illuminated light. - unless you have young eyesight!
I have more than this of course as I hoard stuff and have 2,3 or 4 of everything, but if you were setting up your own lab in the shack using this list you would probably spend £350 to £500. You should make your own gear as much as possible, but you should be prepared to spend money on your hobby. Some people spend much more than this playing golf (per year).
Now to the tests;
Filters, you will be making lowpass filters, as well as crystal filters. Some designs require bandpass filters although the uBitx does not. It has some LC circuits used as matching circuits. The things needing measured are corner frequency, passband loss, passband ripple and Slope in the stopband. All of these can be done using NanoVNA and it can also measure the inductance of any coils you need to wind. Crystal filters are a bit special in that you need to buy more than you need and then to select a group with frequencies that are very close to each other. With care the NanoVNA will suffice but you may need to make a couple of jigs (costing under £1 each) as it is quicker to use a jig and a frequency counter.
Ampifiers Most of these are low level but the transmit chain might have 4 stages of gradually increasing power, maybe 10mW, 100mW, 1W and 10W (most amplifier designs use gains of 10 or so in each stage - better to be conservative to reduce the chance of instability). We will want to measure Gain vs Frequency, input and output Impedances (i.e return loss or SWR in a 50 Ohm environment). NanoVNAs are handy for this - provided you use an attenuator on the amplifier output - taking account of the power coming out of the amp - every attenuator has a maximum power rating. Also for the higher power amplifier you will want bench amplifiers to boost the NanoVNA output as most models can only manage 1mW. Protect the NanoVNA input too, using attenuators.
The other parameters you will want to measure is the harmonic content of the amplifier output when amplifying a single signal (you can use a signal generator and spectrum analyser) and also what is the distortion when two signals close together in frequency and amplitude are fed to the amplifiers inputs. This distortion is called Intermodulation distortion or IMD. It indicates non-linearity and the biggest is nearly always due to the third order mixing of (2 * f1 - f2) or (2 * f2 - f1) . This is also known as OIP3 - When the distortion is equal to the desired signal. You look at the spectrum on a spectrum analyser and interpolate the OIP3 as you can never get the output as high as the OIP3 level. This can be a bit tedious and you also need an RF two tone signal generator and attenuators and amplifiers. As an alternative to measuring and calculating the OIP3 you can use a rule of thumb that a drop in the gain of 1dB over what the expected output happens about 13 to 15dB below OIP3 (for amplifiers made of BJTs, ordinary transistors). So we measure P(-1dB) also known as "Gain Compression" It is easier to do than measuring OIP3 directly - though not as accurate it will give ball park figures. you can use a single signal generator with an attenuator and a oscilloscope (or a simple diode probe and a DVM to measure gain
Actually the OIP3 is usually about the same as the DC power that the amplifier stage takes from the power supply - this is why increasing the current passing through the amplifier devices, either by using bigger transistors or paralleling 4 transistors is sometimes done in the early stages of a receiver - to provide better strong signal handling, important on 40m but it does reduce battery life when operating portable and may make more noise (or less!)
The remaining amplifier parameter is concerned with noise and the minimum discernable signal, (MDS). Measurement of Noise figure (NF) is difficult, current methodology is to use a calibrated noise source and you make noise measurements with it switched on and off, the ratio of these two can be used to calculate the Noise figure using the "Y-Factor" method.
Calibrated noise sources are expensive. Alternatively if you know the NF is low you can use the Hot and Cold method were you heat and cool a resistor and take two readings. Best done with boiling water and Liquid Nitrogen but Ice would do at a pinch, particularly if the expected NF is below 2, not clear (yet) how accurate noise figures of 5 or 6 will fare. One problem with this method is that you need to have the resistance keep its value as the temperature changes - a 0% temperature coefficient. Or maybe that can be fixed using mathematics - if we know the tempco. I haven't done this yet so I am being a bit theoretical. Another way to measure noise is to use a microwave dish that is good enough quality to be sure of a tightly focused beam path, you can point this at a "cold" sky.
I will leave noise measurements to the last. I may buy a preamplifer with a known NF (or send it off the someone and get it measured. Once I have that I can make a noise source and test the amplifier using a guessed Equivalent Noise Ratio (ENR) and then amend the guess until I get the right answer!. To be scientific about it I would need to calculate all the expected errors, sum the RMS errors, think about the accuracy of everything and see what the upper and lower limits are or maybe I will keep monitoring EBAY and hope (forlornly) that a dirt cheap Noise Source with a calibration certificate becomes available. By the way, there are uncalibrated noise sources that are useful accessories to a spectrum analyser - if you pass wideband noise through a filter you can see the shape of the filter's response. Such general purpose noise sources only have a few components and can be bought or built for under a tenner. Mediocre proper noise sources start at £200
Mixers In an ideal world we measure the loss, the noise and the distortion behaviour. Mixers have three ports, low-level RF is applied to one port and a mid-level oscillator is applied to another. Mixing takes place and the sum and difference of the two input frequencies appears at the third port, This describes how they are used on receivers with the RF and Local Oscillator(LO) ports combine to present an output to the IF port, When used as a transmitter the roles of the RF and IF ports are swapped. Noise is usually taken as the loss, this will be close.
To test a mixer we can use two signal generators; one strong, one weak. Then by using a switchable attenuator between either signal generator and its mixer port you can do a series of tests to prove basic functionality - using a Spectrum analyser on the IF port, the IF port must have a 50 Ohm load on it, most SAs have this built in. As well as observing the mixing process on the spectrum you can see the insertion loss, probably about 6dB below the applied RF. A lot of mixers use 7dBm LO levels but higher is better, the OIP3 is close to the power level of the LO and the IIP3 being higher by 6dB or so. Of course you mustn't overdrive the diodes. LTSpice can offer up values to try.
Measuring Distortion is a bit harder, I will focus on 3rd order IIP3 and OIP3 (they differ by the insertion loss) To measure IIP3 you need three signal generators, the Local Oscillator and a RF two tone generator for the RF port, The Spectrum analyser is used to measure the signal levels at the IF Port, there are 4 frequencies generated at the Additive frequency and 4 at the difference frequency. for example the Additive 4 are displayed as two middle signals of ToneF1+LO and ToneF2+LO and the lowest and highest of the 4 are the third order IMD products of (ToneF1*2 -ToneF2) + LO and (ToneF2*2-ToneF1) + LO.
Mixers only work when properly terminated otherwise any signals reflected from the IF port go back into mixer and get mixed with all the signals present, so a smorgsbord of signals come out the IF port where they reflect back to the mixer. This rapidly growing list of spurious tones gives the mixer the opportunity to create more IMD products near our desired signals which will be heard, or at least have an effect on the quality of the final audio signal, clearly undesirable. To get a 50 Ohm load for the mixer will require a diplexor or an amplifier with a broadband Zin of 50 Ohms. The ubitx uses Termination Insensitive Amplifiers designed with the correct Zin. A mixer's output should never feed a crystal directly as the Zin of (any) filter varies such a lot. A diplexor is a filter that passes the desired signal without attenuation and passes any other frequency into 50 Ohm resistors.
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