A HOME BUILT HF RIG, BASED ON THE BOOK BY EI9GQ
Last update:- July 11, 2018 16Watt PA stage built
June 23rd New PCB's built, that combine some functions.
MC1496 based balanced modulator Sch added.
After building a number of HF Amateur radio rigs, including a several (7 !) Picastars, I was looking for a new project to use some crystal filters found on eBay that were given to me. The filters are KVN branded and are part of some sort of SSB device, the PCB is made by Telrad, perhaps not an actual HF rig. The filters were removed and also the MC1496 IC's (3) on the PCB. Not much else of value. There are three filters on the PCB, USB, LSB and AM filters. Only the USB & LSB will be used in the project.
Click pictures for larger view.
The inspiration for the build is a book by Eamon Skelton, EI9GQ, who writes a column in the RSGB Radcom magazine. I am unsure if Eamon still does the column, but the book appears to be a compilation of those ideas that do not appear on his own web pages. Eamon used axial components, without any PCB's. I elected to use SMD parts where suitable on my own design PCB's.
This is a partial picture of the front cover. The book was printed in 2014 & 2015. ISBN: 9781 9101 9301 3 (I have no commercial connection to the book or author, except for its purchase.) The book is not very expensive and a great read, even if just for some ideas. I imagine it's available via the RSGB or in some countries, from technical book sellers.
My project relies heavily on Eamons book but with some changes to suit parts at hand and also in some cases, to make the modules 50ohms in and out. All PCB designs are either 50x50mm or 50x100mm in size.
Since the book is Copyright, I won't publish the Schematics here, unless I can get permission to do so, or they are my own variations. But, I will show the modules I have built so far in the project. All modules were drawn up in Schematic form, then a PCB design made for them. So far I have made enough modules to get the Receiver running. For the VFO, I used the Si5351 device which is very popular, although not an ideal choice in a hi performance rig. Later, I think I will move to the AD9951 DDS chip as I have made a PCB for it and have the chip in the junk box, from Picastar builds.
Below, is a picture of the receiver side of things. The audio amp uses a different device (bottom left module) but otherwise is much the same as Eamon's except for variations as shown above. The crystal filter board and rx band pass filters (see below) are shared between Rx and Tx modes.
All pictures can be enlarged by clicking on them.
To the left, are the receiver sections. The VFO and display is not shown. Top left is Rx mixer and post-mixer amp, then crystal filters, bottom right is the IF board and AGC boards, then the demodulator and audio. (Clockwise from top left) Bottom (angled) is the 9MHz crystal oscillator board.
The heart of the receiver is the IF strip. In my build, I used the 3 stages of cascode JFET's rather than the MC1350 stages in the book. I used the suggested AGC circuit but soon discovered it was designed for the MC1350 stages, as the voltage sense was reversed. Some on-the-run changes were made and can be seen in the AGC board (left). The FET was changed to a transistor and the AGC voltage taken from the collector instead, with emitter grounded. The AGC seems to work well in listening tests but no other tests have been made yet. IF gain is around 68dB.
AGC and IF stages. BF256's were used. The 4 pin connector on the AGC board is to select AGC decay.
In some cases, as the build progressed, I had some PCB modules made in China from my designs. e.g. the filters on a new PCB compared to above picture. It turns out to be cheaper sometimes to have them made in China, compared to the cost of buying Kinsten PCB material, chemicals etc.
Two filters are used, as they are USB and LSB types. They are switched by the relays on the PCB. Unused filter being grounded. The carrier oscillator then is 9.000MHz which is crystal controlled. NOTE: there appears to be some offset in the LSB filter as it's not offset from 9MHz the same amount as the USB filter. This will have to be taken care of by shifting the 9.00MHz filter to suit. Since my VFO runs high side on all bands the actual filter functions are reversed. ie. the LSB nominal filter becomes the USB filter and vice versa.
This is a plot of the 80M band pass filter board. (Loss about 4dB in-band.) Each band is a plug in module so I can fit as many bands as required. All BPF boards are identical with on-board relay (not fitted in picture) switching, loaded with parts to suit the band required, of course.
THE TRANSMIT SIDE:
Balanced Modulator will be either MC1496 based or use a diode DBM. I have built up both types and will decide which one to use, after testing. Eamon didn't use the MC1496. In the diode Balanced Modulator I used BAT54S diodes.
Diode Balanced Modulator MC1496 Bal Mod.
MC1496 BASED BALANCED MODULATOR, Schematic. Based on the MC1496 Data sheet, plus a Microphone amplifier stage.
Either board above produces double side-band (DSB), so, to get SSB, we need to remove one sideband. This is done by using the crystal filter, as used in the receiver. A post mixer amplifier brings the level up for application to the Tx Mixer.
This is the Transmit Mixer board. It takes in SSB generated by the balanced modulator and crystal filter, the VFO and shifts the output by mixer action, to the band of interest. Not fitted at right side, is the actual mixer, a double balanced diode type JMS-1 from the junk box. Board was undergoing tests here. It's followed by the Rx BPF, switched in to the Tx side, to remove unwanted products.
Tx Mixer (actual mixer not fitted)
Following the Tx mixer & BPF, is the post mixer amplifier stage: See further down.
Then, the low level SSB signal is amplified in several stage to bring it up to a suitable power level. The modules built so far bring the level upto 1 watt.
You can see the whole tx chain here, from the Tx post-Mixer amp, right through to the 1 Watt stage.
click for bigger picture.
Following the BPF, the Tx low level amplifier brings the signal up to around 200mW.
Shown below are the post Mixer buffer amp (left) and the 200mW stage which follows the BPF. It uses a 2N5109 in the second stage with small heatsink. It drives the next stage a 1Watt amp. shown further down this page.
In testing alone, the 200mW stage was found to have predicted gain and is very flat. Input required is about -19dBm. Harmonic suppression also good, as can be seen below.
Response is 'Flat' to within 1dB from 2 - 50MHz
Next stage in the Tx side is the Tx PA driver stage which ups the level to around 1Watt. Eamons original used an RD06HHF1 but lacking one of these, I fitted the higher power RD16HHF1 device. It still puts out about 1watt in this schematic, as tested. I don't have concrete plans as yet for the PA finals but possibly something based on the G6ALU 100Watt amp might be used, as I have used it in Picastar. Then a low pass filter of course.
The RD16HHF1 FET is mounted under the PCB and bolted to a heatsink.
No doubt many of the modules could be combined to obtain an overall smaller set of PCB's. SEE BELOW !! The present method allows various sections to be change easily though. Perhaps later, I might do something to make the rig PCB's smaller overall. Right now though the intended case for the project has plenty of room so it's not urgent !
UPDATE: 20th June, 2018: I decided to make two larger PCB's 100x100mm each for the Tx and Rx parts of the project to combine some of the smaller boards.. Plus the mother board for the band pass filters (BPF) 100mm square is the 'sweet spot' for having boards made in China.
Both were received from the PCB maker and so far, the Rz audio amp has been built on the 'Rx" board and all of the sections of the Tx board have been built and partially tested.
Rx PCB. This pcb contains the IF amplifier (top left), AGC stage, Product detector and Audio power amplifier. The audio board can use either the TDA2003 or LA4425 chip (as fitted) which requires less parts, hence the blank locatations..
Tx PCB: This PCB (below) contains the Transmit Mixer, post Mixer amplifier, 200mW driver and 1 Watt driver. The picture shows the completed PCB apart from fitting of the smd Mixer component. (top middle pads) The 200mW and 1W driver stages (bottom half of PCB) have been tested and work nicely. For this build I used a 2N4427 device in the 200mW stage rather than the 2N5109 of the PCB built previously. results are very similar.
Of course there is more to the transceiver than just the two PCB's mentioned above. There is also the band pass filter board (one per band) which is shared between the Rx and Tx stages. In addition there is the Tx balanced modulator and the crystal filters which are also shared. Plus some other PCB's, not shown here.
BPF Mother Board. This board is a motherboard into which up to 7 filter boards can be fitted by plugging them in. Only one is fitted in the picture, the 80M band. There are two relays under the PCB which switch the BPF selected, between the Rx and Tx stages. It will probably be fitted into it's own shielded enclosure.
The PA Stage
EI9GQ has details of several PA's the 16Watt and also some much higher power levels. My initial needs are for the 16Watt stage so a PCB was drawn up quickly to take advantage of a free shipping, Chinese supplier deal. The PCB had to be under 2500sq mm so a board 45x55mm was designed. This is way too small of course for the complete Amplifer but I took advantage of the deal with the smaller pcb size and an 'outboard' final transformer stage.
Eamon used some toroids in the final stage that are not available in VK. Nor perhaps, in the UK as the supplier, Maplin, has ceased trading. I used some toroids of near identical size (25mmOD) but available locally from www.Jaycar.com.au (LO1234) who have a nearby store. I don't know what the ferrite type is ("L8") but since I had some of the toroids i used them. The original design calls for 25 ohm coax to be wound on the toroids. Eamon used some single core audio shielded cable which he had measured to be about 25 ohms impedance. Not ideal co-ax of course. I had none of this cable on hand so used standard RG174 50ohm coax instead with the same 6 turns.
I did make a few changes to the original schematic, adding some ferrite beads for the input supply, additional bypass capacitors, plus electrolytic caps on the supply also. I also added small value (4.7ohms) in series with each gate.
Surprisingly, I powered it up and it works. Right now I am only driving it with 0dBm signal for testing but the gain curve is very similar to that obtained by EI9GQ but where he got about 11dB gain, I am getting a few dB more. The real test will be feeding it with more input power, 500mW to 1Watt from the stage built above, should be just fine.
Here are some pictures of my PCB and the final amp. It uses RD16HHF1 FET's mounted under the PCB and heatsunk to the chassis. (click picture for larger size)
Here is a plot of the Gain using 0dBm input signal from 0 to 100MHz. It is biased at 250mA per device here, EI9GQ recommends 500mA per device.
More to come...............
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