3 - Existing test gear and components

I have access to equipment from work, but will try to only use a subset of my own;

Test Gear I currently have;
USB 100MHz oscilloscope Hantek DS2250. (under £150)
Digital capacitance meter (easy and cheap to make a PIC based one - £25)
Digital voltmeters
Power supplies - various
Frequency meter (easy and cheap to make a PIC based one)
I have (just) bought a HF SDR - £90 but I am hoping to be able to use it for 80% of what a spectrum analyser can do.

(as an aside, I brought an old spectrum analyser from work home - about 20Kilos in weight, carried it up the stairs to my workshop/shack/man-den and discovered it didn't work. <sigh>)

I also have an antenna analyer - rigexpert AA-30 which can measure R,C,L
I have several SWR meters and dummy loads as well as a couple of amateur radio transceivers (Kenwood TS520 and an Elecraft K2)


Components: you should build up a junk box full of stuff!

I have bought two resistor kits, one leaded and one SMT (0805 size)
I have a selection of capacitors, some old polystyrene, quite a few polycaps, electrolytics and tantalums and a few micas. I also bought 500V mica caps specifically to build a bank of low pass filters for a PA, I will need more.

I have ferrites - 25 of FT37-43, 25 T50-6 and T50-2 (red and yellow)
Lately I bought 10 each yellow and purple capacitance trimmers.

And 10 x 2n5109, 25 x MPSH10 and 10 x J310, 2 x  RD06HHF1 and 4 x RD16HHF1, I have some diodes of various types but bought 10 x1N5711.
I also bought a dozen BNC Sockets and plugs.

As a strategy I will try to avoid using unusual or unmarked parts, it should be possible for any one to follow this blog and duplicate the work. I may build two or three of something to check repeatability.

Also where I use expensive test gear I will try and research how to build cheap gear, again so anyone can repeat the project themselves.

2 - Order of building - test gear

I think at present I need to build the following;

An RF 2 tone oscillator, this should be two separate xtal controlled oscillators, each possibly pulled to be 20kHz apart (maybe a series coil in one and  series cap trimmer in the other as I don't have many Xtals in my junk box). Each of these will be built ugly style using PCB board soldered up as boxes. The two boxes must be very well screened from each other, Each will feed a 6dB attenuator and then into a return loss bridge wired as a combiner into a low pass filter, 3 coils, 4 caps. (see the separate posts)

Maybe a second RF weak signal oscillator to measure sensitivity. (see the separate post)

Actually might divert into making a grid dip meter as this would pay dividends - with jigs to measure C and L. I could build in a PIC based digital frequency meter into it as well as an analogue meter.

A switchable step attenuator. 0-70dB, low power

A return loss bridge - I'll just use this with my scope and see how I get on. I wonder how I could do phase as well as return voltage across 50 Ohm. (maybe make a more sophisticated bridge with hi-q air capacitors - assuming a two channel scope can detect zero phase (add/subtract scaled voltages - minimum if in phase)

A "sampler" to allow feeding from a 10W or 100W Linear into the SDR(acting as a spectrum analyser).

Dummy loads:  I do have ham radio SWR meters and ATUs with dummy loads as well as a Elecraft K" 10W transceiver and a Kenwood TS530 Valve Transmitter, but I will try and test with simpler (cheaper) equipment.

Farnell have 3W 1% metal film and even 30W or 100W metal film 1% (100 Ohms) FEC2396003, FEC2328286(30W/1%/100R@£2) or EC1114422(100W@£5.74)Need a heat sink on the last two, maybe <0.7degreesC/W

These should allow testing the receive path - measuring sensitivity (MDS= Minimum Discernable Signal) and third order intercept/1dB compression/IMD (Intermodulation Distortion). I will also need to measure noise figure but have yet to learn the theory of how to do that! (I have postponed that for now).

When I build the transmit chain I will have a chain of amplifiers/drivers, each of which should be 50 Ohm i/p and o/p; I would think outputs of the 100mW, 1W, 10W and finally 100W should be ok. With a 20W return bridge I can do return loss measurements of the input of the 100W amp. I will use a conventional SWR on the output, at least on the 10W and 20W.

At present I can see how to use a return bridge to measure amplifier inputs - best done at normal running power. I have read they can be used to measure output return loss by injecting signals into outputs whose inputs are grounded. Sounds risky to me, a spurious oscillation destroys the sig gen. And the test is better done at full power output, hence I think outputs should be tested just by measuring their SWR feeding into a dummy load. Measuring "SWR" of a 100mW amp can be done using a bridge - or just drive 50, 60 and 70 Ohm resistors? When I get experimenting I'll see what things look like.

1 - Starting building a homebrew HF transceiver, Linear and associated test gear

Initial thinking about building my own transceiver; actually I need a couple of 12v 100W Linear HF amps but having the transceiver first makes sense. Makes it easier to test the amplifiers, and means my early work is harder to break.

Sources of data;

I have been reading QEX, QST and RADCOM for 10 years, and built up a library of most of the ham radio books from the ARRL and RSGB. But specifically;

Eamon Skelton EI9GQ - I was inpired by his RADCOM articles and bought his book "Building a Transceiver" from the RSGB shop ( www.rsgb.org )

Experimental Methods in RF Design (EMRFD). Vital reading

I will hopefully remember to specifically quote exact references when I get into the details. I intend to use standard discrete components and avoid specialised ICs