Amateur Radio Homebrew (Shack Culture)

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Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 31 Oct 2012, 22:00

As my interest in Amateur Radio is building again with the ultimate objective of re-establishing my station or "shack" I thought it would be a good idea to open up a few new threads within the category to record activity. This one is intended for all the homebrew or self built bits of kit and projects. I will start it off with a few examples of what I built when I was first licenced.

The first offering is what I posted in the mystery objects thread and was so ably identified by Tripps. It's a RTYY (Radio Teletype) TNC (Terminal Node Controller). The bit that allows you to connect a computer to a radio transceiver and send and receive text based messages from the keyboard.

Image

The complete setup emulates the actions of the earlier mechanical teleprinters.

Next photo is with the lid off. I built this from a circuit in Radcom (RSGB Members Magazine). All was made on the bench including the PCB's for the design. It is all built using passive components on a fibreglass single sided PCB. I'ts mains powered and back in the 1980's was used to interface between my BBC Model B Computer and my transceivers of the time. With terminal software on the computer the TNC generates the timing signals, shifts and tones that make up the Baudot code that RTTY is based on. This is then fed to the transceiver and used to modulate a signal. Incoming RTTY transmissions are fed from the receiver into the TNC and then onto the computer for decoding and display.

Image

You can see on the filter board that I built this in 1984, I etched it into the board during manufacture along with my callsign.

Image

This was all before the days of the PC and computers with inbuilt sound cards. Nowadays the role of the TNC can be emulated in software and the soundcard or built in audio can be programmed to generate all the tones. More or less any transceiver manufactured from the mid 90's (and many from before) can be interfaced directly with virtually all types of personal computers all you need is the correct software and away you go.

I will pinch Whyperion's Googled link from the other thread as a source of further information on the transmission mode:

RTTY

Many of the modern applications available for various platforms can handle a miriad of different transmission modes used in amateur, commercial, military and marine radio. RTTY, AMTOR, Packet, PACTOR, ASCII, PSK31 and many more. A lot of these modes had elements of what ultimately was developed into the email protocol that we all take for granted nowadays.

Revisiting the various data modes 30 years on, it certainly seems that I will need a computer in the shack if I want to dabble in that area again.
Ian

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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 01 Nov 2012, 04:36

Well over my head but I know a tidy job when I see one! Isn't it amazing how many skills there are out there built by ordinary people of whom it has been said "they aren't intelligent enough" to understand 'complicated' legal and political matters. I wonder how many of the detractors could build this? I wouldn't know where to start!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Bodger » 01 Nov 2012, 11:27

I recall someone on the old site starting to build a wireless, but do'nt remember if it was ever finished ?

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Re: Amateur Radio Homebrew (Shack Culture)

Post by Bodger » 01 Nov 2012, 11:37

which reminds me , as an apprentice engineer at Hepworth Iron Co. i spent one day /week in the drawing office, in the cricket season i was ordered by the chief draughtsman to sort out the catalogues etc on the top shelf of the library, amongst the books was a crystal set and headphones, my job, perched on a ladder was to relay the score to the lads in the office, one of whom would keep a lookout for the chief engineer approaching, there was no sanctioned entertainment for workers.

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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 01 Nov 2012, 14:41

Bodger wrote:I recall someone on the old site starting to build a wireless, but do'nt remember if it was ever finished ?
You're right Bodge, it was me and yes it is not finished. It's one of those things that has been put on the back burner a few times. Not to worry, I tidied a cupboard the other week and came across all the bits I had accumulated for the job. I know where they all are and will make an effort to complete the job. I think urgent family matters down South put the mockers on it first of all and then a couple of grandchildren came along .......

Here's the list of stuff as a reminder of what we need.

I have a bit of wood to mount on, I have wound the coil and decided on a method of mounting it. Coil tapping bar is sorted, I have two lots of razor blades now which hopefully will be coaxed into a detector. The first are 7 o'clock razor blades which are un-blued and were donated from Stan's magic garage (not our Stanley but Dulciesdad on the site). These have potential as they have oxidisation (rust) blemishes on them which could offer good rectification properties. The project has never been completely out of mind as I managed to pick up some Blue Gillete blades from a table top sale that I came across whilst on holiday in Norfolk, these will be tried also.

I have bought contemporary headphones for the project from Ebay which need a little TLC but I have high hopes for them. It all basically needs screwing together which I will endeavour to do. The design will then just need the longest bit of wire I can find to use as an aerial and a decent earth connection. If i can get it all to work, I will then need some method of displaying it on here to prove the point, have to think about that.

Here are all the bits:

Image

And a close up of the razor blades that I will try as part of the detector:

Image

This will not be a pristine project. The basic object is to cobble it all together only using what might have been available in the field and coax it into receiving a signal. I have used the centre of a toilet roll for the former for the coil, ends are secured with insulation tape. The tuning bar is made from a wire coat hangar although any piece of stiff wire would suffice. The razor blades are what would be in use at the time as are the headphones. Wire of course is wire, anything will do to connect it all together, connection points will be simple screws and washers to provide a compression joint. I still have to fashion the "cats whisker" side of the detector. I shall address that once I have all the other bits mounted up, probably using a bent safety pin and a short pencil or pencil lead.

Thanks for the reminder Bodge, time it was sorted out.
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Bodger » 01 Nov 2012, 18:41

Looking at your bits and pieces, it appears to the uninitiated just a simple matter to build a reciever, makes me think of POWs in camps who produced remarkable units from virtually nothing !

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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 01 Nov 2012, 19:37

Indeed Bodge, it is amazing what has been used to create various versions of receivers particularly the ones constructed under conditions of duress. In many cases, headphones (or a substitute for same) had to be created in addition to the radio. Necessity is the mother of invention in these cases. The Foxhole or trench radio does have the advantage of being constructed from easily scrounged stuff that could be sourced on or near to the battlefield. POW radio's generally did not have this benefit.

The rudimentary principle is that you only need something to gather and magnify the signal a bit (aerial and coil), something to convert the signal into a dc current (detector (rectifier) AKA cats whisker) and then something to convert that DC to audio (the headphone or substitute). The basics of radio are very simple although it was quite a journey for the early experimenters until the penny dropped with Mr Marconi. He was playing around with lots of different ideas pioneered by his predecessors and using his own developments as well. Like any other discovery once it is proved to be functional further development comes along in leaps and bounds as more interest is generated and more people become involved adding their ideas to the mix.

War tends to focus the attention somewhat and if you look at the technological leaps that were made during the First and Second World wars the tally of invention and development is staggering.

Back to our little squawk box, I have started and the coil is mounted. I'm looking for a suitable way to add a bit of compression to the coil tuning arrangement. It's fine when it's in the middle of the coil but it loosens off as it moves in an arc from one end of travel to the other, A couple of compression washers might work. I'm going to tidy up the headphones, I'm keeping them original but they need the braided leads sorting and maybe some new terminations putting on and a bit of a clean up on the drive units. I have also sussed how I'm going to do the whisker arrangement. Work is in progress.
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 02 Nov 2012, 06:19

When I was at Lancaster we found that we could get reception from the university radio station using a metal waste paper bin but I forget how we did it. Best inadvertent radio reception I ever got was on an un-shielded lead while trying to record a local old music group rendering Lillibulero for Pendle Heritage Centre. As a back-up I had my Uher running on one microphone. Good job, the main recorder picked up the local taxis and Nordwest Deutche Rundfunk!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 02 Nov 2012, 16:47

A bit of a set back with the Foxhole Radio, no sooner started but a spanner in the works or more to the point an open circuit in the mix. I set about refurbishing the 1930's set of Brandes headphones that I managed to obtain from Ebay. I bought them as they are contemporary with the project.

They are a high impedance set of headphones with braid covered leads. The individual headphones have an impedance of just over 1000 ohms and they are wired in series. They disassemble quite easily, the headphones are just held in clips from the headband assembly. Wiring to the headphones is via small threaded terminals on each unit, the two wires to each phone are secured with 4BA nuts so the wiring harness can be removed quite easily.

I stripped then down last night and gave each of the headphones a clean up. I have already established that each of the headphones are sound. No problems with the coils, magnets or active discs in each unit. I have never checked the leads though until today, there was no problem with the terminations at the headphone end but the leads needed stripping back at the other end. This is where I started to run into problems. I got the meter out and tested the leads from end to end and could not get continuity. I stripped back the braided cable a few inches because the braided and twisted centre copper conductors showed signs of oxidisation. I still could not get continuity either from end to end or from the series link between the two headphones so it looks like the lead assembly is past its best.

It would be a little more than coincidence if there were two breaks in the lead. The braided construction is quite robust but what I think has happened is the the inner conductors have oxidised, possibly over the whole length. Although the braided cable would be pretty much state of the art at the time it has not really fared very well over the last 80 years. Not surprising really the inner copper conductors are only covered with a double thickness of braided material not even rubber inner conductor. 80 years of moisture and air ingress has done the rest. Pity really, I would have liked to keep them as original but there is no option but to rewire. I will see if I can find some modern cable that is at leas sympathetic with the design.

Actually this is probably a gift as although it's disappointing, if I had just re-terminated the leads and attached them to the finished radio I never would have stood a chance of resolving a signal!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 12 Feb 2013, 20:59

I have not forgotten the foxhole radio but have decided to wait until I have my radio station up and running before continuing with it. I intend to install a work area in addition to my operating position for the station. This will make construction and repair projects considerably easier and also by that time I should have a reasonable antenna and earth systems to connect to for testing.

So to continue the thread I am posting another of my homebrew projects built around 30 years ago.

This is a Transmatch ATU (Antenna Tuning Unit). Actually ATU is a bit of a misnomer as devices such as this do not actually tune the antenna, what they do is provide an impedance match between the antenna and transceiver. This ensures maximum power transfer between the transceiver and the load made up from the feed line and the antenna. This allows a single antenna to be used on a broad range of frequencies.

The optimal length of any given antenna is determined by the frequency that it has to operate on. As the frequency gets higher the length of antenna needs be shorter, if you lower the frequency the antenna length needs to be longer. Clearly, you cannot have a single antenna that will operate on a wide range of frequencies so most are constructed to operate in the centre of a given band. At the design frequency the antenna will provide a perfect match for the transceiver.

Modern transceivers are designed to operate into a 50 ohm impedance. As any given antenna can only be resonant on one frequency, at which point the antenna will provide a perfect match, the further you tune away from the design frequency the greater the mismatch will become. Antennas that cover more than one band present a huge range of differing loads and varying impedances so an ATU is essential to ensure that the transmitter can deliver maximum power at any particular frequency that you wish to use.

I built the Transmatch in a nice extruded aluminium equipment case that I picked up at a radio rally. Not sure what the case was used for previously but it has cut outs in the front and in the rear of the case. I put new aluminium plates inside in the front and back and then filled the cut outs with perspex. White card is sandwiched at front and back between the new plates and the perspex to carry the decals.

Image

Rather than Antenna Tuning Unit the device should really be called an Antenna Matching Device as this is what it actually does. The device operates by introducing variable amounts of capacitance and inductance into the feed line. This allows it to match the variable range of impedances presented by the antenna and feed-line to the fixed impedance of the transceiver.
Here is the front view showing the two Vernier slow motion drives that are connected to the variable capacitors. The centre knob is connected to a variable inductor. This is known as a rollercoaster. This is a multi turn device and so it has a counter fitted so that you can record any given position of the inductor. The counter range is 0 to 1300.

Image

This is the back of the unit. The Transmatch design can handle antennas fed with different types and impedances of cables. Single wire, open (dual) wire feeders and coaxial cable. The unit is connected to the transceiver using 50 ohm coax. The antenna is connected to the other terminals depending on feeder design. You can see that I finished building this in February 1985.

Image

The next picture shows the internal view of the design looking from the back. You can see the counter unit mounted above the drive shaft for the rollercoaster inductor. All three drive shafts have insulating couplers on the shafts. This isolates the shafts from the front of the unit and stops interference from hand capacitance affecting the tuning. It also isolates potential high internal RF voltages from appearing at the front of the Transmatch.

Image

Here is the view from the front, you can see that all the components are mounted on insulated spacers mounted in the bottom of the unit. This is to isolate the components from earth. Large voltages can develop inside the unit depending on the amount of power being used at the transmitter. All connections are kept to minimum length and are wired point to point in insulated cables. The spacing between the vanes of the variable capacitors determine how much power you can run through the unit without risking RF flashover problems between the vanes. I have used this particular unit at 100W but it would not really be suitable for higher output powers.

Image

The problem with tuner such as this is that it is a manual device with infinite combinations of settings. Once you have found a match for a given antenna at a given frequency you have to make a note of the settings so that you can retune the unit again easily when you next need to use the same frequency. With experience you pick up how to set the controls somewhere near depending on the band and frequency you are using but you do end up with tables of settings for the finer adjustments.

So there we go. I gathered all the components for this at various radio rallies the previous year and then built the device for use with my first HF transceiver. I also entered it into the annual construction contest that we held at The Rolls Royce Amateur Radio Club each year. We used to get members from other local radio clubs to come along and judge our efforts. I think I came second with this effort. Feedback from the judges said it was nip and tuck with a lovely engineered straight Morse key made by our club secretary Les Logan. I upped the anti the following year and pushed all the boats out with a design for a different device that took me the best part of 9 months to build. I will post this later.
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 13 Feb 2013, 04:59

Fascinating.....
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 21 Feb 2013, 00:51

Not fully homebrew like the previous offerings but an example of what can be achieved with a little ingenuity.

Image

It is another bit of kit that I will keep and give another airing to once I have some antennas up. Anyone who operated on the CB Bands may recognise this or at least have a little feeling of deja vu. This started of it's life as a Hy-Gain V (2795DX) multimode CB transceiver. It has 120 channels in total, 40 each on what was known as Low, Medium and High Bands by the CB fraternity. There is a link below to the original specification on the Rigpix database.

Hy-Gain V (2795DX)

The transceiver originally covered 26.975 - 28.305 MHz and can operate in AM/FM and SSB and was not licensable for use in the UK. Plenty of these and many other multimode models of CB transceivers were imported though from the USA and Europe and traded in the UK. Many of the CB DX chasers would attach large linear amplifiers (burners) and operate wherever they wanted using any mode at their disposal with no regard whatsoever to band plans and the like.

Once CB was legalised in the UK with 40 Channels FM with a maximum power of 4W, the DTI who administered the bands at the time would have occasional purges on owners of such kit and take a few to court to make an example to deter others from use of illegal transmitting equipment. It was also illegal to sell on kit such as this, so the upshot of this along with the perceived threat of prosecution from the DTI would see transceivers like this being offloaded to many an amateur licence holder simply to avoid a potential fine.

Because these transceivers operated very close to (and sometimes overlapped into) the 10M (28MHz) Amateur Band it was possible to convert these and turn them into a fully functional transceiver covering a good range within the 10M amateur band.

This one came my way totally free gratis sometime around 1986, the guy that gave it me had been an illegal operator since the mid 70's but had become paranoid about a potential knock on the door and was quitting CB. It became my 1986 Winter project.

The transceiver operating frequency is determined by a PLL (Phase Locked Loop) Frequency Synthesizer IC used in conjunction with a crystal controlled oscillator circuit. In the original configuration it used three separate crystals, one each for Low, Medium and High Band. Low and Medium ranges were within the European and USA CB Band and High band strayed into the bottom portion of the UK 28Mhz Amateur Band in the area allocated for CW (morse) operation and propagation beacons.

PLL Synthesizer Operation

Frequency selection was via the 40 channel selector switch on the front panel. This provides a different binary code at each position which in turn is fed to the program input lines on the PLL IC and in conjunction with the selected crystal oscillator and various mixer stages in the transceiver determines the final operating frequency of the transceiver. Here is the circuit diagram.

Hy-Gain V Circuit Diagram

The conversion up onto the 10M band could be achieved by swapping out the mixer crystal for one of a slightly higher frequency and introducing some method of reprogramming the output of the channel selector. Once this was achieved the rest of the mixer and output stages in the transceiver could be re-aligned to move the input and output frequencies up onto the 28MHz band.

As the channel switch is a mechanical device the binary outputs from the switch are fixed. The solution was to change these outputs by using a pre-programmed EPROM (Electronically Programmable Read Only Memory) and inserting this between the fixed outputs from the switch and the PLL. The EPROM was programmed so that each setting of the switch would output the new desired binary code from the EPROM and apply this to the PLL synthesizer IC in place of the original code effectively shifting it's output to the new higher frequency that was needed.

The first picture shows the transceiver with the bottom cover off. You can see the channel selector switch at the bottom right and it's associated board that produces the fixed codes for each position of the switch. The next board to the left is the Crystal Oscillator board. This board originally had three crystals but now only has one as we only need one to cover the portion of the 10M band we are moving the transceiver on to. You can see where the other two used to be in circuit.

Image

The close up picture shows the boards a little better. The next board contains the additional circuitry introduced to fool the PLL Synthesizer IC using the EPROM. It's built on Veroboard and bolted to the side of the case. I produced the EPROM using a programmer that I built for my BBC Model B computer. I think it was an 8K EPROM from what I can remember. There is a bit of support circuitry on the board for voltage stabilisation and level control of the output lines from the EPROM. The board is inserted into the existing wiring between the channel switch and the PLL IC. You can see that I referenced the mixer crystal frequency and the final frequency range that the EPROM would shift the transceiver on to along with the date of the conversion.

Image

Frequency coverage is now 28.510 - 29.700 MHz all within the 10M amateur band. I renamed the transceiver Flare Chaser as this particular band is one where propagation is greatly affected by sunspot and solar flare activity. I quite enjoyed doing this conversion as it involved computing skills in programming the additional EPROM as well as the radio side of things. The last time I used it I managed to make contacts into Europe through some of the 10M repeaters and over into the Eastern USA when band conditions allowed. It will be nice to give it another outing.
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 21 Feb 2013, 05:04

Spaghetti junction!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 21 Feb 2013, 09:37

Not really Stanley, only working to plan, most of the wires were already there in the loom. The thing I liked most about this project is that it only cost a couple of quid for the components to convert this up for legal amateur use. The build quality of the original transceiver is not as good as what you would find in a transceiver produced for the amateur market even though they retailed for a similar amount within the CB fraternity. Lots of CB users now buy amateur HF equipment that can usually be very simply modified to work on the 11M CB band and elsewhere! The TS 140S HF transceiver I bought will do this. The extra band coverage is provided simply by lifting one end of a diode conveniently placed for easy access. Not a lot of technical ability required to achieve the end result. All fully documented on the internet.

Lots of the latest transceivers attempt to provide every possible feature you could ever need (and a lot you will never use). In my view using a sledgehammer to crack a nut but always appealing to the more knobs must be better operators. Check out the link below for the latest offering from Kenwood:

Kenwood TS-990

It retails at a little over £6,500.00 - hows that for overkill!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 22 Feb 2013, 06:54

Look here Ian! 3 wires is my limit!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 22 Feb 2013, 09:07

Somehow I just don't quite believe that Stanley :wink:
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Re: Amateur Radio Homebrew (Shack Culture)

Post by Tripps » 22 Feb 2013, 10:55

TS - 990S That looks like a lot of fun. How long till one's on Ebay? :smile:
Born to be mild. . .

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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 22 Feb 2013, 19:55

It's only available to order at the moment Tripps. It will be a long time before it comes into my price range. The predecessor TS140S I bought came to me at just over £200.00 and will do exactly the same job. All funded from stuff I don't use any more. More stuff I don't use any more will fund the auto ATU I have my eyes on. A bit of wire over the roof will complete the HF side of things and will allow me to communicate around the globe.
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 27 Feb 2013, 18:20

A few posts ago I mentioned that I used to enter my homebrew projects in the annual construction contest that we ran at the Rolls Royce Amateur Radio Club. Here is the design that I won with after a previous years close second to an engineering project.

This is what is known as a Transverter and is used to enable a transceiver that is designed for one particular frequency band to operate on a completely different band or multiple bands. The first picture is a general view of the completed Transverter.

Image

Here is a view of the front panel showing the very minimal controls (the fun is under the lid). There is the on/off switch, the band selector switch with six bands and a pre-selector control associated with each of three channels. You can see I colour coded the switches to co-ordinate with the relevant pre-selector control. I fitted a Perspex front to the aluminium fronted case to protect the annotating decals which were made using Letraset rub down lettering.

Image

This is a view of the back of the case which is fitted with stand off's to space the connectors away from the wall. There are SO239 sockets for the connection from the driving transceiver and the antenna input/output from the transverter. A 2 pin DC input socket completes the connectors on the back. You can see that I annotated the unit with details of the design which came from one of the amateur radio magazines of the day. The transverter was featured across two monthly editions in August and December 1983 of Ham Radio Today. Each of the designs was for 3 band devices, the first article was for a transverter design covering the 1.8 MHz (160M), 3.5 MHz (80M) and 7.0 MHz (40m) bands and the later one covered the 14 MHz (20M), 21 MHz (15M) and 28 MHz (10M) bands. The original articles gave instructions for two complete units with 3 band coverage from each. I decided to adapt the design and put the whole lot in one box with modifications to the associated switching but ultimately producing a combination design that would give full coverage of all six of the main amateur HF bands from one unit.

Image

The transverter operates from VHF to HF and HF to VHF and interfaces with any low power 144 MHz (2m) transceiver. It converts the transmitted output from the VHF transceiver into the corresponding frequency on whatever HF band is selected.
For example: The 3.5 MHz amateur band (80M) covers 3.5 MHz – 3.8 MHz. To produce this range from the transverter the driving transceiver should be tuned from 144.5 MHz – 144.8 MHz to transmit on corresponding frequencies in the 80M band. Incoming signals on the 80M band will be transverted to their corresponding frequencies between 144.5 MHz – 144.8 MHz for reception on the transceiver.

In transmit mode it is converting downwards in frequency. On receive, it takes the incoming HF signal and converts it upwards in frequency, back to the 144 MHz band for reception on the drive transceiver. Input to the transverter should be limited to a maximum of 1W p.e.p (peak envelope power), it will produce the same power level at the transverter output, and this in turn can be used to feed into an HF linear amplifier to provide higher output power if required. The transverter will operate in any mode that the interfaced transceiver is capable of.

Here is the inside view with the top cover removed. I added a central shelf to the project case I selected for the design. This was to allow a mirrored layout arrangement. The pre-selector control is connected to a variable capacitor which in turn is connected to the board at the front which has the associated pre-selector circuitry; this effectively acts as a narrowband filter to the incoming HF band signals before passing them on to the Intermediate Frequency mixing stages on the same board. You can see that there are a number of relays on the board; these operate to switch in the correct oscillator frequencies for whichever band is selected (160M/80M/40M) by the front panel switching. The crystal oscillators for each band are situated on the board at the centre back of the unit. The small relay section at the top left operates to switch the transverter circuitry between transmit and receive modes.

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The next picture shows the underside of the unit where the boards are mounted on the reverse of the centre shelf. The boards on each side of the case use common mounting studs with spacers. This layout maintains a continuous ground plane within the unit. It is an exact copy of the top but the board circuitry and oscillators now cover the other three bands (20m/15M/10M). There are minor differences between some of the coil assemblies as they cover different frequencies.

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The blank circuit boards were only available through the magazine for about a year. It was two years after the articles had been published when I decided to have a go at the project so boards were no longer available. I had all the equipment to produce the boards although I had never attempted a double sided ground plane board before. Fortunately the layouts were fully documented in the articles with 1:1 artwork. As this device operates at RF frequencies the boards are designed to minimise instability by removing as little of the copper as possible and so maintaining an effective ground plane for the various sections of the circuit. The boards are double sided with only feed through holes cleared on the top component side, any interconnecting circuit tracks on the reverse.

A few close up pictures to show various features. All of the wound toroid’s (the rings on edge), the coffin feed through ferrite's (square flat), the small bead ferrite's and the open coils were all hand wound. They are all wound with various gauges of enamelled copper wire. The toroid coils are varnished to hold them in place.

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Here is a close up which mainly shows the crystal oscillator section. The tuning coils with the ferrite slugs were off the shelf types. The inter stage screening was produced from tin plate sections which were edge soldered to the ground plane on the boards. Screening is required to cut down cross modulation between the different sections of the design. The transistors on the mixer and RF output board are all fitted with heat sinks. Any interconnecting cables between boards use screened cables and are kept to minimum length.

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The next photo shows the front switching arrangement. The original design used a simple 3 position rotary switch for each transverter. I wanted to use push buttons so I had to develop a board that would support the interlinked 6 band switching arrangement. I mounted the interconnecting switches on Veroboard and then attached this to a right angle bracket for mounting. The Veroboard allowed me to create a common ground point for the array and bring out the shielded connecting cables neatly. The switches are mutually exclusive so you can only select one band at a time. They are break before make so it is impossible to cross drive the mixer and oscillator stages.

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The last two pictures are close up views of the top side boards. It’s the first time in about 25 years that the covers have been off this unit and it still looks like the day I produced it.

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It took 3 or 4 months to gather all the required parts together from various suppliers and amateur radio rallies. There are quite a few size critical components that cannot be substituted due to the board designs. Actual construction and alignment took a further 6 months or so steadily away. I think it cost about £70 - £80 for all the components back in the mid 1980’s. The cost of the time though cannot really be accounted for although it would almost certainly be in excess of what a commercial HF transceiver could be bought for at the time. That’s not the point though.

This effort represents the pinnacle of my home construction skills and designs. I had a lot of fun putting it together. It works very well and gives full 6 band HF coverage from a 2M low power multi-mode transceiver. I still have my multi-mode 144 MHz transceiver to drive this with so it will get another airing at some time in the future. I don't have an HF amplifier so I will see how far I can get with the bare 1W output.
Ian

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Re: Amateur Radio Homebrew (Shack Culture)

Post by Stanley » 28 Feb 2013, 04:17

" The cost of the time though cannot really be accounted for although it would almost certainly be in excess of what a commercial HF transceiver could be bought for at the time. That’s not the point though"

I understood that bit.....!
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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 16 Jul 2013, 08:52

I posted a mystery object in another thread which was an Iron Dust Toroid. I said at the reveal that this was to be used in a wire antenna design that I was going to try. The design is one originally conceived by Ivan James G5IJ and has been subject to some controversy over the years as to how it actually works.

It consists of 20M of twin cable or ribbon feeder fed via a transformer. The design offers multi-band capability from a length of wire normally associated with single or maybe dual band capability. Despite the stunted physical dimensions of the design it would seem that it does indeed perform right across the spectrum and I have glowing reports of the design from other local radio amateurs who are already using the design.

So as this is the homebrew thread, here is the construction process starting with the transformer:

The design uses a TO200-2 Iron Dust Toroid, here it is with a reel of 20swg enamelled copper wire which will be used to form the secondary winding of the transformer. This will be wound on first and overlaid with primary winding in the finished design.

Image

Here is the toroid with the finished secondary winding which consists of 27 turns bifilar wound on to the core. I have used a couple of cable ties to temporarily secure the ends of the windings. You can see that the winding is created with a doubled up length of wire so we have a loop at one end and two separate wires at the other. The coax I will use for the primary winding is shown alongside.

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The primary winding consists of 12 turns of 50ohm coaxial cable. I have used UR43 cable as it is what I have to hand. It is 50 ohms impedance and of the right diameter to get the 12 turns needed. Its hard to see in the photo but the inner conductor at the end of the coaxial cable is connected to the loop end of the bifilar winding along with the outer screening of the coax after 12 turns on the toroid. The coaxial primary winding will be connected to the transceiver. The two wire ends of the secondary winding will be attached to a choc-block connector shown in the picture and this will be used to attach the twin lead or ribbon cable radiating element.

Image

Now that all the windings are in place and secured the last cable tie will come off when the connector block is fitted. The transformer will be installed in a suitable small plastic box. I am going to use 300ohm twin ribbon feeder to make the radiating element which will be connected into the block. It is quite thin so it will be relatively easy to bring it out of the box via the edge of the lid. I need to source a suitable ABS plastic box and get a length of 300ohm ribbon but the hardest bit of the design is now done.

I will post again when I get the other bits.
Ian

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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 18 Jul 2013, 08:02

300ohm slotted ribbon cable for the radiating line ordered along with Paracord 550 (tm) nylon cord for the supports at each end. Paracord is military specification and is available in dozens of different colours and outer jacket effects. I have ordered digital camouflage. I hope I can see it when it comes!
Ian

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Re: Amateur Radio Homebrew (Shack Culture)

Post by Bodger » 18 Jul 2013, 08:58

Panbiker, you may be interested in this, some clever precision machining of piezo crystal for war use

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Re: Amateur Radio Homebrew (Shack Culture)

Post by PanBiker » 18 Jul 2013, 12:42

Thanks for the reminder on this Bodge. I saw it when you posted the link in another thread but have yet to watch it.

Later edit: Happy Birthday, just seen it on the front forum page.
Ian

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Re: Amateur Radio Homebrew (Shack Culture)

Post by Bodger » 18 Jul 2013, 18:55

Thanks, i will get my teeth done and i will be catching up on Stanley !!

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