Monthly Archives: September 2001

THE MUSEUM COLUMN. OCTOBER 2001.

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by a Staff Reporter

Well! It’s a bit difficult to write something for a Column like this if you haven’t got anything to write about! Here I sit, in the land of museums (UK) and I can’t think of anything to write about either. I should be careful about complaining but there are several museums in South Africa with attendant and interested Hams who could supply info. for this Column.
Please forgive me for saying “They do like this in the UK …….. etc.” It’s annoying but to me what’s even more annoying is that the people of South Africa, especially we radio amateurs, could just as well! The lack of funds shouldn’t hold us back either! Many museums have surplus equipment, not suitable or appropriate for any particular display (or having much cash value attached to it!) which may be used for demonstration. Just about all the museums I’ve seen have a children’s section which is geared up for the young to fiddle with bit and pieces and learn something about certain physical properties. One such display caught my fancy, a section of an aircraft was clearly marked “Touch Here” . Another was a number of tubes of the type used for cleaning pools, all knotted with their beginnings and ends marked! The idea was to show the tube allows one to talk to some in another position without causing interference to some other conversation. The section was appropriately named, “Explorers’ World – Interactive and Science Centre”!
Another point, a very big point, that was very evident was the availability of pamphlets and brochures which were available at various points where the interested could see them clearly, railway stations, bus stations, tourist bureaux, etc. Even the individual museums had brochures of others in same area!
The standard thought seems to be …. “If its old keep it, preserve it and make it interesting to look at” . Above all, a small charge to see it won’t chase anyone away.
Judging by the attendance most of these places of interest are doing fairly well especially in the shops where novelties relating to the museum are sold.

I have just been watching a short TV documentary about nations who were invaded and conquered by barbarians. Occasionally the “take-over” was, in a way, a good thing and brought a new and better way of life. Other times it was a total “take-over” with the older and probably better ways being absolutely replaced by something quite foreign. The main reason for the defeats seems to be the lack of co-operation between the defenders! Perhaps we, as hams, should take note of these ancient battles, invasions, etc., etc., etc. because to me that’s what seems to be in our SA Ham circles is that we are running around in circles and not standing together to defend and protect what we’ve got! A pretty good amateur radio system! Yes! There are a few dents and blemishes, here and there, to clean up but we do have a very good working system!

 

If you think this Column is too Euro-centric you’re probably correct! Then whose fault is that??? For a more South African oriented feature please send your contributions to P.O.Box 77, Irene, 0062, or Fax/phone 012-667 2153 or be really un-museumlike use the ultra-modern e-mail to davegemmell@BMKNET.co.za

THE QRP COLUMN OCTOBER 2001

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QRP
THE ———- COLUMN OCTOBER 2001
80/40
by DAVE GEMMELL and
the Low Power Bunch

Well! Here I am typing your Column in Surrey, merry England! Yet I have a tale of woe! As I’ve no correspondence from you chaps I have to resort to I have to resort to
Ye Olde Thumbe Suck to fill this, your Column with goodes fit to be read! Nevertheless here goes! Hey Nonny Nonny!

Well, I got a homebrew QRP rig together and put it in a padded envelope which was then put into the pocket of my anorak which I wore on the flight to the aforesaid merry England. It took me a few days to get the necessary wire for the antenna and other items together before I could “get-on-the-air”.
The main problem was actually the 12 volt power source for the home brew QRP transceiver followed by a means of checking whether the main power transistor was going it’s job or not!

Fortunately the scullery was close enough to the back door and the garage so that
the 12 volt car battery could be used as the main power source. The problem of a safe connection between battery and equipment was solved by using the cord from an old power supply, the type that is plugged directly into a wall socket.

The antenna was made from “twin-flex” which is normally used for bedside lamps, etc. I wanted to operate on 40 metres which means the actual dipole section had to have a length of 20,2 metres, ie. A half-wavelength at 7.05MHz less 5%. We must get it clear in our minds that dipole and feeder line are formed from one length of cable!
This type of cord has a figure-of-eight cross section, the insulation forms the “8” bit with the two conductors the centres of the loops! Now to “make” a dipole for
7.05 MHz you take the one end of the “twin-lead” split the conductors apart for a length of 10,1 metres, ie. Quarter-wave length at the “design frequency” and you have an dipole of insulated wire, 20,2 metres from tip-to-tip with the feeder connected in the middle! That’s the reason for original piece of cable being one quarter wavelength plus the required feeder length! So be careful when choosing your operating position and where your antenna is to be erected.

The antenna section, when erected in a “straight line” and high enough always has a terminal impedance of 72 ohms. In the set up I used the two legs of the dipole were at about 90 degrees to each other so bang goes to 72 ohms especially at a height of around two metres.

Another point, still to be investigated, is that of the characteristic impedance (Zo) of the “twin-flex”. The calculations I made to find Zo gave a result of about 83 ohms which wouldn’t be a bad match at all but I would like to try it out on someone’s
MFJ-259 VSWR analyser, just to check.

It’s nice to know that the SWR is more a less within limits! This is not serious for receiving but can be very important even when transmitting one watt. Certain transistors, such as my ancient 2N1711, can give up the ghost quite easily and completely!

Perhaps, in some future issue of RADIO-ZS, a kind contributor to this Column will
send in a design of a light weight combined voltmeter /dummy load/power -/ SWR meter suitable for taking on holiday, etc. Dare say, the SWR part could similar to those found in certain CB rigs which operate an indicator on the front panel when there is a poor connection to the antenna or even an antenna problem.

This type works on the principle where an iron dust toroid is fitted over the lead to the antenna socket, most times on the PC board itself at the last point. This acts as the primary winding of the transformer. Another winding around the toroid is the secondary and is connected to the diode network which actual distinguishes between the forward and reflected voltages! A relatively simple circuit but the component count will be significant compared to the average QRP rig. We do like to keep these sets of ours fairly simple and that’s why I suggest an “add-on” that’s part of a multimeter type instrument.
I’m ashamed to say I didn’t make any contacts but I did call CQ CQ DE M/ZS6AAW
a few times, with little success, on two Saturday mornings, 8th and 15th September 2001. Very pleasant hearing other call signs like GM4OEC, G4PYW and a chap from Brussels ON4LBL.
So, at least the receiver section works quite well but I had to remove the PC board from it’s temporary box. This action seemed to cut out a lot of AF feed back with which this design is plagued. It’s my favourite design with transmitter, receiver and AF section all on one PCB so it looks like I’ll have to have another look at this layout, possibly putting each section on a separate PCB.

Before I close this Column and word about licencing! (Again!!) I did contact ICASA about the required HAREC certificate for me to operate in the UK. I left the arrangements a bit late but Elna, the lady at ICASA was very helpful and FAXed a copy of the necessary two pages to me very promptly. On my arrival I phoned the Radioauthority (RA) and the Radio Society of GB to be polite. Another lady at the RA helped me and it seems that for a short stay of up to about one month the HAREC Certificate is sufficient, anything longer than three months you have to apply for a temporary licence and pay £15-00. The HAREC Certificate is merely confirmation that you have successfully completed the RAE IN South Africa which equivalent to the corresponding UK one.
Please be patient those of you who have sent me e-mails and have not received any reply! Hopefully on my return I will get to grips with all facets of the e-mail system and send replies.
Well that’s it again. The bottom of the Column! Please send all contributions of your Low Power activity to the usual address: P.O.Box 77, Irene, 0062 , FAX or Phone 012 – 6672153 or e-mail …. davegemmell@MBKNET.co.za

RADIO SCOUTING. OCTOBER 2001.

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By Dave Gemmell and
the Broomstick Warriors.

PLEASE NOTE THAT ALL JOTA/JOTI IN FORMATION IS TO BE FOUND ON THE WEB. PLEASE CONSULT LAST MONTHS ISSUE OF RADIO-ZS FOR THE CORRECT WEB ADDRESS.

Well, it’s the October issue and it’s being written in the middle of September!
Hopefully, when you read this column most of the Guides and Scouts will either be busy on the JOTA week-end or busy with their final preparations. I hope all those stations taking part have registered as educational station so that the girls and boys can talk on the air or send messages using morse code.
Now here’s a thought!!! I suppose all JOTA stations which have packet radio, RTTY, SSTV, and so on., must also register as educational stations before the non-licenced will be allowed to use these modes? Your comments please, ladies and gentlemen!!!

Before I left on holiday I did submit the form to advise the SARL that JOTA would be taking place on 20th – 21st October 2001 and wanted to assume that one of these forms would be sufficient but as it required a callsign . Now I’m not so sure.
So please, chaps, fill in and send both forms.

I haven’t been around in SA to hear what’s going on radio-wise on the Scouting scene neither is there much news here in the UK mainly as I’ve yet to meet some Hams and scouting types.
Perhaps I will come across something or other in the next week or two.
At the bottom of this Column again with the major yearly plea for reports of the goings-on and happenings at your JOTA and JOTI stations. Hams, don’t wait for the scouts and girls and girls and boys don’t wait for the Hams to send in the report.
If individual hams, guides or scouts would like to send in separate reports please do so! These all help for the National JOTA Report which must be sent to World Scout HQ in Geneva. Please include attendance figures even “guestimates” will do. I would like to have these before 30th November 2001 as the completed report must get to HQ by 31st December 2001.