Making Waves Power supplies.

November 10, 2017 Leave a comment

I was sat wondering what I should propose as a winter project this year – after all we all know how these winter months can drag on with long nights and cold wet days – and looking through some old notes I have decided on building myself a new PSU.  We all know the importance of having a good PSU in the shack, whether it be a switched mode type or linear regulated type, to power our radios and various peripherals.  I personally don’t like the switched mode ones so very much as they do tend to be rather noisy in the HF spectrum where most of my activity occurs.

So a standard linear regulated power supply it will be then.  Surprisingly very few components are needed for this although a good metal case with ventilation will be a must.  Let’s look at a layout plan.

Rectified_PSU_transformerfig.1

In its simplest form A is a fuse unit for the input to prevent any mains surge from damaging the transformer, B is a double wound transformer to convert 240V to 12V (still AC), C is a full bridge rectifier and D is a smoothing capacitor.  The output is then 12V DC.

With the above assembly we should expect to see the following outputs when measured on an oscilloscope:

AC_Sinewave fig.2 AC sinewave.

The AC sinewave should be seen at the output terminals of the transformer.

Rectified_Waveform fig.3 rectified AC

Tis is what we should expect to see at the output terminals of the full wave bridge rectifier.

Regulated_DC_Output  fig.4 Regulated DC output

And this is what we would expect to see across the output terminals all being well.

Obviously, the size of the transformer depends on how much current you wish to draw and an inline fuse between the unit and the equipment you will be powering will also be necessary in case of any surges (or faults with the equipment).  I shall now attempt to source components and will report back later with progress.

 

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Making Waves – 2m Quad

October 16, 2017 Leave a comment

The M0CVO High Gain 4 Element Quad for 2M

The antenna I am now going to describe is one that I designed some time ago. It is a high gain quad beam for 2M (144 – 146 MHz) band. The forward gain of such an antenna is approximately 11.5 to 12dBd, that’s approximately 10.6 to 10.8 times the output power from the rear of your transmitter. For example, say you were operating a 10 Watt txr, the effective radiated power (erp) would be 10*10.6=106 Watts.

All this power and still a relatively small antenna; the boom is a mere 1 metre in length and may be constructed from 1” (2.5cm) square, weather treated, wood. The elements are constructed from 2.0mm diameter enamelled copper wire (ecw), the dimensions of which are shown in Table 2.

All the dimensions were calculated using the formulae in table 1, which was, admittedly gleaned from “The Amateur Antenna Handbook” by William I Orr, W6SAI, although the beam is of my own design.

Table1

Polarisation
For horizontal polarisation feed from bottom for vertical polarisation rotate by 90◦

Table2.PNG

Fig 16

To strengthen the elements of the quad a 2nd support can be fitted which will also make it easier to attach to the boom.

Making Waves – The Shorty Forty

September 17, 2017 Leave a comment

I was taking part in a Twitter conversation today with someone building the helical antenna published in this month’s RadCom, the RSGB member’s magazine, and having issues with the matching of it.  He was trying it out due to lack of space and a poor earth (clay) at his QTH.

I set to thinking and remembered an antenna design that I used to hand out to Foundation and Intermediate Licence trainees when I was mentoring them through their studies and assessing their practical assignments.  This was the Shorty Forty antenna because we don’t all have the requisite 20.28m of free space to string a dipole across.  I shared the plans with him and later thought “Why not share them for everyone?” so here goes:

The Shorty 40 – Helical Whip for 7MHz

So you want to get onto 40m but don’t have room for a dipole (20.28m)? Then this could be just the answer if you have a little time on your hands and enjoy home construction.

The Shorty 40 is a helical whip for 40m wound on a 3m long, 32mm diameter piece of PVC tubing (the sort available in most DIY stores). You will need 21m of 1.2mm diameter enamelled copper wire, 80cm of 2mm diameter ECW and 10 or 15m of 1.5mm diameter insulated copper wire (the sort used for lighting circuits or earth wire). You will also need a SO239 connector and a piece of angled aluminium.
ShortyForty

The picture says it all really but, just in case, begin by winding the 21m of copper wire along the length of the pipe, using tape or adhesive to secure it along the way. Cut the 80cm of 2mm ECW in half and push through the holes drilled in the top of the pipe. Solder together in the centre and solder the end of the coil here also. Drill a 16mm hole in the aluminium bracket for the SO239 socket and then attach it to the pipe using machine screws. Then solder the other end of the coil to the centre pin of the socket. Connect pipe to mast and connect two or three 5m radials to the solder lug on the aluminium bracket. Attach coax, raise mast and away you go.

Disclaimer  I cannot claim to be the first person to develop an antenna such as this but I have researched ideas on the internet and in books on the subject – from ARRL, PW Publishing and RSGB publishing – and changed them to suit modern metric measurements and make them easier to understand and build. 

 

Making Waves – Antenna Polarisation Issues

June 8, 2017 2 comments

 

Someone asked me to explain why he was unable to hear some horizontally polarised stations on his vertical even though the vertical operates at 360degrees.  This was the explanation I gave him:

Dipole1fig.1

Fig.1 shows the radiation pattern of a 1/2 wave dipole, showing strong signals off either side with nulls towards the ends.

Dipole2fig.2

This is better shown in fig.2.  Assuming that the antenna runs from north to south in a straight line, any station to the east or west will be able to hear / work it but if they are located north or south of it they will struggle to hear or be heard.

Vertical1 fig.3

fig.3 shows the radiation pattern of a vertical antenna.  A vertical antenna, when placed over a good earth, will radiate evenly in all directions and so can be heard/worked by any station in any direction that is either vertically or horizontally polarised.  However, those who are horizontally polarised must have their antenna running in the correct direction for the reasons outlined above.  There is also a 3 – 6dB loss in signal due to the change in polarisation although this effect is only true in a vacuum as scatter caused by other objects and reflection changes the polarisation of the radio waves anyway.

 

 

 

 

 

 

 

 

Making Waves, 23cm and infinity

As I have stated previously I purchased a 1296MHz transverter from SG-Lab in Bulgaria.  Anyway, upon applying power to it and testing the transmit (with an IF of 145MHz at 2.5W from my FT-817) I noted that it was not working as described.  Upon opening up the top of the case I noted that one of the components was raised and obviously burnt.  I contacted Hristiyan, LZ5HP, at SG-Lab and sent photos of the faulty component in situ.  He immediately identified it as a short in the choke having caused the problem and I returned the unit to him.  Two weeks later it was back with me in full working order with a replaced choke.  This time when I applied power and some IF it worked as it should.

I also mentioned that I would look at constructing a DL6WU Yagi but, unfortunately, work has got in the way and I just haven’t had the time.  I looked online for suppliers and, after much deliberation, decided to purchase one from Dual Antennas in Serbia (www.antennas-amplifiers.com).  This was down to both price and quality.  Although there are manufacturers both in England and in Germany, Dual seemed to offer the best deal.  For a 13 element Yagi it cost me 59€ plus shipping.  there was the other issue that when it arrived in the UK it was held by customs for a week whilst they added import charges and VAT but that only came to £19.15.

23cm-Yagi--Antenna-Rear-Mount-PA1296-13-R-420x200The 23cm Yagi from Dual.

So now I am fully operational on all bands from 80m – 23cm (except 4m currently).  I have not yet had a QSO on 23cm although I have put out a few CQ calls, so maybe next Thursday evening during the UKAC contest.

23cm Yagi

The 23cm Yagi up at CVO Towers

M0CVO QRP Setup

The transverter visible in operating position below the X1M HF QRP set with the FT-817 providing the IF to the left.

Making Waves – Higher Bands, Transverters and Kanga.

January 12, 2017 3 comments

c1zrqflxeaaoreu The SG-Lab 23cm Transverter

So I finally bit the bullet and decided that it was time to extend my amateur radio boundaries beyond 433MHz.  I read various reviews and product descriptions and decided on purchasing a SG Lab 1296MHz transverter. I sent an e-mail to Hristiyan, LZ5HP in Sofia Bulgaria who constructs these units enquiring about pricing.  He promptly replied with a return e-mail and a PayPal invoice for 145€ (£132GBP).  I paid up (cheaper than expected) and within two days had tracking details and confirmation that it was on its way.  It actually arrived surprisingly quickly (about 1 week) using Bulgaria Post and then Royal Mail when it arrived on our shores.

The unit supplied is enclosed in a smart tin case and comes complete with an HB9CV “test” antenna printed on FR4 laminate. Both are shown in the picture above. There is also a DC plug (you need to supply the wire and solder this yourself) for the power.  You will also need a BNC to SMA pigtail lead to connect to whatever you choose to use as an IF.  I am making use of my mostly redundant FT-817 for this.  The IF is from 144 -148MHz.

c16nd2kxaasorva

For a test antenna, the supplied HB9CV demonstrates a rather good match as can be seen from the above Smith Chart produced by my MiniVNA Tiny.  With 3.2dBd gain it has quite promising performance as a suitable antenna for local ops too.  The instructions are available online at http://sg-lab.com/amateur.html and these will be needed for setting up the unit.  Nothing too complex though but you will need to remove the top cover and possibly use some long nose needle pliers. for setting jumpers.

20170112_083920

The picture above shows the transverter with the top cover off for the purpose of setting up using the jumpers.  Output power (up to 2W) can also be adjusted here using the trimmer visible on the left.

20170112_083932 Most functions can be monitored using the LEDs at the side.

After purchasing this then discovered that the completed units are stocked in the UK by Kanga Products (www.kanga-products.co.uk) so I could have obtained it possibly faster and cheaper but we live and learn.  I may look at the 13cm (2300MHz) transverter at a later date – also from SG Lab and I will look then to see if Kanga have it first.

Now I am going to build a DW6LP type Yagi Beam for 23cm so I can put the unit to full use.

 

 

 

 

 

Making Waves – Fundamentals of radio Antennas part 2

November 20, 2016 Leave a comment

Standing Waves

Assume that it is possible to have a wire conductor with one end extending infinitely, with an RF transmitter connected to this wire.  When the transmitter is turned on, a RF current in the form of sine waves of RF energy moves down the wire.  These waves of energy are called travelling waves.  the resistance of the conductor gradually diminishes the amplitude of the waves, but they continue to travel so long as the line does not come to an end.

The antenna, however, has a finite length.  Therefore, the travelling waves are halted when they reach the end of the conductor.  Assume that the RF transmitter is turned on just long enough for one sine wave of energy to get on the line (Fig.4A).  This travelling wave is moving down the antenna toward the end.  When the wave reaches the end of the conductor, the current path is broken abruptly.  With the stoppage of current flow, the magnetic field collapses.  A voltage is induced at the end of the conductor that causes current to flow back towards the source as in Fig.4B.  The wave is reflected back to the source and , if a continual succession of waves is sent down the line, they will be reflected in the same continual pattern.  The wave moving from the transmitter is known as the incident wave and its reflection is known as the reflected wave.

4

Fig.4 Travelling waves on an antenna and typical resultant wave.

A continuous flow of incident waves results in a continuous flow of reflected waves.  Because there is only one conductor, the two waves must pass each other.  Electrically, the only current that flows is the resultant of both of these waves.  The waves can reinforce or cancel each other as they move.

When they reinforce, the resultant wave is maximum; when they cancel, the resultant wave is minimum.  In a conductor with a finite length, such as an antenna, the points at which maximum and minimum occur (Fig.4C) are stationary.  In other words, the maximum and minimum points stand still, although both the incident and reflected waves are moving.  Because of this effect, the resultant is referred to as a standing wave.

The development of the standing wave on an antenna by actual addition of the travelling waves is illustrated in Fig.5.  At the instant in A the incident and reflected waves just coincide.  The result is a standing wave having twice the amplitude of either travelling wave.  In B, the waves move apart in opposite directions and the amplitude of the resultant decreases but the points of maximum and minimum do not move.

When the travelling waves have moved to a position 180 degrees phase difference, the resultant is zero along the entire length of the antenna, as shown in C.  At this instant there can be no current flow in the antenna.  The continuing movement of the travelling waves, shown in D, builds up a resultant in the direction opposite to that in A.  The in-phase condition of the travelling waves results in a standing wave, in E, equal in amplitude but 180 degrees out of phase with the standing wave in A.

5

Fig.5 Development of standing wave from travelling wave.

If the progressive pictures of the standing wave are assembled on one set of axis, the result is that shown in Fig.6.  the net effect of the incident and reflected waves is apparent.  The curves are lettered with reference to Fig.5.  As the travelling waves move past each other, the standing wave changes only its amplitude.  The fixed minimum points are called nodes and the curves representing the amplitude are called loops.

The concept of the standing wave can be applied to the half wave antenna with reference to either current of voltage distribution at any instant.  This application is possible because there are travelling waves of both voltage and current.  Because voltage and current are out of phase on the half-wave antenna, the standing waves are also found to be out of phase.

6

Fig.6. Standing Waves

 

Part 3 to follow.

NB. This collection of items was first produced as an adaption of information from a US Army training manual on antennas and radio propagation.  This manual is no longer in print.