F-Troop questions & answers
New radio amateurs are invited to submit their questions via email to ftroop@amateurradio.com.au
Basic antennas book
The QSL bureau
The QSL bureau - a quick run-down
Slim Jim antenna information
Dual-band 2m-70cm antenna
After testing and exploring the design of an antenna sold by an amateur radio group, plus research has come up with one that really works on both bands.
The initial antenna worked on 2m but was disappointing on 70cm. Using aluminium foil to try and change the radiation pattern of antennas and computer modelling software led to further developments.
Anyway to cut a long story short, after much messing around with diameters and lengths I came up with dimensions that afforded an excellent match and good radiation pattern on both bands.
The antenna gave good results when compared to others including a 5/8 wavelength ground plan on 2m.
The observed performance matches the theoretical results in every respect. Although only three have been built to this specification so far, all have performed excellently.
- Dave Parslow VK3AIF
Understanding emission modes
The International Code for Radio Emission Modes came into being on 1 January 1982 replacing the former simple three characters used for modes such as A1A for CW.
It came about to more accurately described emission modes as they became more complex in terms particularly in terms of their modulation and bandwidth.
A full designation has nine characters although the first seven are mandatory and the most often used.
Ben Crnojacki VK3KBC has set out an explanation of the emission designators which can be found at http://www.radcomms.net/index.php?option=com_content&view=article&id=67:...
Portable antenna talk
Antenna continue to be a popular topic of discussion. On the F-Troop nets on 8 and 15 June mention was made of the MiniBac, a microlight backpack antenna for portable operation.
Another suggestion for portable antenna ideas is Ham Radio Fun which has several yo-yo antennas. This unique product uses yo-yo shaped winder reels to neatly store the antenna wire, and good quality PL259 centre-pieces.
Are the D-STAR radios compatible with ordinary radios?
The only D-STAR radios, hand-helds, mobiles and base stations currently available in Australia are made by Icom. These will transmit/receive both digital D-STAR and analogue (ordinary) FM.
I have put out a few calls (using a D-STAR radio) but not received a response or heard anything
The band plans have just been revised. Check them out and until D-STAR repeaters come on air the centre of activity in Melbourne appears to be the national simplex frequencies 145.125MHz and 438.900MHz.
Why do Australian callsigns begin with the letters 'VK'
When amateur wireless experimenters began in the late 1890s, it is thought they used
'handles' or just two letters. No licences were necessary until the Wireless Telegraphy Act of 1905.
By 1914 there were more than 400 callsigns that began with the letter 'x' which stood for 'experimental'. All those stations were closed during World War 1. When transmit licences were issued after the war the callsign series included state numerals and two letter suffixes.
The next change to callsigns came in 1923 in response to the long distance and international contacts being made by radio amateurs, and the first callsign prefix 'OA' was added to callsigns. O stood for Oceania and A denoted Australia.
The International Radio-telegraph Conference in Washington, in October-November 1927, decided on callsign blocks for countries and this required Australia to adopt VK from 1929.
It is believed that the VK, and other callsign blocks beginning with the letter V at the time, were chosen for many British Commonwealth Countries because of the reign of Queen Victoria.
Question
Ross, First of all, thanks for the opportunity to gain experience ( of which I need a lot of - dropping the foxtrot prefix, of which I apologise for ).
Second, the tuning of the Ringo Antenna. I have had some advice from a couple of members at EMDRC, and also an associate connected to VK3 SCP. However, they have come up with same type of ring set-up as you were describing - the sliding-adjustable arm on the ring.
As mentioned, the VSWR at 146.000 is 1 to 1.2.. At 147.995 it is 1 to 2.8.. The VSWR meter I am using is a Diamond SX200 (1.8 - 200 MHz range) - purchased, brand new from Strictly Ham.
I've a couple of photo's of the ring set-up. Your suggestions are most welcome. Regards
John VK3FZAC
Answer:
There does not appear to be any adjustment on the ring section of your ringo, I can only suggest if the aluminium sections slide easily it may be possible to shorten or lengthen the overall antenna to tune it to the desired section of the band.
The feed appears to be fixed and should not be altered. You cannot expect that all antennas will cover the entire 2m band with a low SWR.
It would be normal for an antenna to have a low SWR at band centre and rise as you go to each end of the band.
As an after thought when you change frequency you should re calibrate your SWR meter just to make sure as sometimes this can give funny readings.
VK3FCE
Question
Thanks for the "F" Troop initiative last Sunday. I have a question regarding the Inverted "V" Dipole antenna, I've constructed a dipole for 80m but am limited by space, it's been suggested that the "V" type of antenna might be a solution to my space problem.
I have a 20m TV antenna pole and I'd like to know how the feed line when coupled to the balun is positioned on the top of the pole, eg. does it have to be mounted clear of the pole by some means or can it be attached? also, at what distance should each leg of the wire be from each other i.e.. is there a minimum and maximum distance between wire as each leg will have to travel forward at approx 45 degrees as opposed to immediately left and right of the pole? I hope this question makes sense.
Richard VK3FFRS
Answer:
Richard,
The best way of setting up your inverted V would be to arrange a rope and pulley at the top of your antenna pole then you can attach the balun to the rope and run it up and down at will.
The way I have set up my dipoles is to have a common coax feeding a balun to which I have attached three dipoles (80,40,20). The dipoles are evenly spread out around the mast so as to minimise interaction with one another, there is a little interaction and is best to check and adjust SWR on 80 first then 40 etc.
You don't have to be particular arranging the dipoles, one of the legs of my 80 metre dipole comes down and then runs along the fence without problems. If you have to do this to fit it in your block the theoretical length will change so check and tune as necessary.
If you haven't a balun as yet you can wind 6-10 turns of your feeder into a loop approx 6 inches in diameter cable tie together and that makes a good choke balun placed at the top as close as possible to the dipole legs.
Ross VK3FCE