I found the following US Navy website which has a universal calculator allowing you to find this data for your lat/long which can be extracted from your iphone or any GPS.

http://aa.usno.navy.mil/data/docs/mrst.php

For readers in the northern hemisphere, the calculator does allow for north and south latitudes, as well as west and east longitudes…

Well it is a big show.  Very big.  Have a look at the Hamvention website and you’ll find maps of the covered exhibition areas and the flea market area which is described as being 9 acres.  I observed that some lanes of what is normally a car park were not fully occupied, and some discussion on the hamvention mailing list (see yahoo groups) indicated that there were many more vendors in the flea market area in past years.

There were over 200 vendors in the covered areas.  The Dayton Amateur Radio Association (DARA) conducted exams for those who wanted to take out a ham licence, or upgrade from Technician or General to a higher grade. Candidates were lined up outside the examination areas all day, Friday and Saturday.  Hundreds must have been examined.

All the equipment manufacturers you have heard of and a lot you haven’t were present with impressive displays of their wares.

New to me were the Kenwood TS590 (HF/6m 100w transceiver), the Flex 1500 (HF/6m 5w transceiver) and the Elecraft 500w power amplifier.

I also saw a rotary 80m dipole on display from Array Solutions.  It looked to be about 50ft or 15m long, with loading coils and loading sections on each end of the dipole. It may have been shorter.

In the flea market there were many hundred vintage radios, ATUs, cables, antennas, connectors, you name it.  My vote for the most unusual item was the F16 simulator.

I came close to buying several new items but eventually just picked up some small components I want for my new antennas, some microwave attenuators and a G4DDK preamp kit for 2.4 GHz.

I met G4DDK at stand 915 where he and Kent WA5VJB were displaying and selling various items including a range of Kent’s pcb antennas including log periodic and skeleton horns for frequencies from 400 MHz to 10 GHz.

The event wound up officially at about 1pm on Sunday.  After that the exhibitor’s area was closed.

I missed out on a great deal I had been offered on an SDR-IQ receiver on Saturday afternoon.  I didn’t realise how many vendors would either close early on Sunday or not turn up at all.  I’ve emailed RF Space and have received a reply already, so all may not be lost.

Dayton Hamvention: well worth going and seeing it, but only if you already have a reason to go to the US.  It’s a long way for 2.5 days of hamfest.

At the VHF weak signal group dinner on Friday night, I met and chatted with a number of other people about VHF activities in Australia and heard discussions on contest rules that were familiar issues.  Should contest points be based on distance or on grid squares, or power, or what?  In the VHF sprints they are trying a distance based formula based on 6 character grid locators.  They have found that this approach has been well accepted by contest participants.  It is now quite feasible to calculate distances based on 6 character locators, since computers are so common.  Maybe this is what Australian VHF operators would like.  The grid square bonus system is much simpler but some people think it doesn’t give recognition or incentives for longer distance contacts.

The instruction manual for the generator had several paragraphs about what should be done to improve its efficiency at high altitudes (defined as > 5000 ft ASL). Measures such as fitting a different jet to the carburettor were included in the manual, these being arranged with “your authorised service centre”. When this was mentioned to the seller he said he had never had anyone ask about that for these generators.

So fortunately my money was refunded and I only had to pay freight both ways.

Subsequently my brother decided to replace his ageing Honda generator of some 20 years with a new EU20i inverter generator. I took a look at the manual and found it very interesting reading. Including the paragraph about getting an authorised service agent to install different jets in the carburettor if the generator is to be used at altitudes above 5000 ft asl…

During the spring field day (28-29 Nov 09) we will also be attempting contacts with Doug VK4OE at Mt Kaputar near Narrabri.  The distance is about 500 km – to be confirmed.

We expect to work Doug on the lower bands (144, 432 and 1296 MHz) and will be trying for contacts on the 2400 and 3400 MHz bands as well.

Results will be reported here as well as in the WIA journal Amateur Radio.

There have been a number of GMC branded generators on the Australian market.  GMC (Global Machinery Company) was based in China, or was it just an Australian importer of various GMC-branded items?

Mine is rated 950watts, which should really be called 950 VA (volt-amperes) and is powered by a small 4 stroke engine.  My experience of it is that it is a quiet and reliable engine, and the generator produces enough power for my modest VHF/UHF portable station, which requires power for an IC910H and a TS670S plus some minor items like a 40w light globe and a couple of antenna rotators.

My only problem with it was that it produced radio noise at a quite high level, sufficient to require a noise blanker to be run on 144 and be noticeable on 432 MHz.  On 50 MHz it was S9, at a distance of 25 metres between the generator and the 6 metre antenna, an omnidirectional vertical. I tried shielding the entire generator by wrapping it in chicken wire connected to the frame of the generator.  No improvement.

Several other radio amateurs have suggested the noise from the generator is transmitted along the 240V cable.  I haven’t yet proved where the noise is being radiated from.

Last week I put oil into a new Chinese built inverter generator and started it for the first time.  It ran fine and the voltage output displayed as 237 on a DVM.

I found a small engine mechanic willing to look at the GMC generator.  He said the magneto assembly was touching the shaft and preventing it from moving.  He has readjusted it so that it runs smoothly and at about the right RPM.  I have yet to try to calibrate the speed for 50 Hz output but I have a DVM that does frequency among other things, so I should be able to take a low voltage out of my scope soldering iron transformer and see what the frequency is.  For that matter I should check the inverter generator.

The method I used was to load the helical with a capacity hat formed by a short wire, actually an alligator lead I had in my field day accessories box.  I was operating from the car and was nowhere near home at the time.

Here is the SWR curve from the front panel of the IC706, with the radio tuned to 3585 kHz.  The SWR bar-graph is small but the general shape of the SWR curve can be appreciated.  The bars represent the SWR at frequencies below and above the centre frequency indicated by the main frequency dial.  The small dot below the bar in the centre of the graph reminds you that is the measurement corresponding to the dial frequency.  The increment per measurement is 10 KHz, as set using key M2.  The white rectangle drawn around the SWR bar graph was added to the photo by me.

SWR centred on 3585

After adding the loading and retuning the radio to 3521, the SWR curve moved down the band and here it is centred on 3521:

SWR of loaded helical, centred on 3521

A nice application for the SWR indicator and sweep function in the IC706.

One of these fellows was like the experts at the pub, who can advise you on anything from what is wrong with your car to what is wrong with your computer, TV, VCR and your dog.

His opinion was that multiband trapped antennas were nothing more than rotary RF chokes. His logic was that RF chokes have coils in them, so do traps, therefore a trap is an RF choke. His conversation partner agreed with him with a bit of a nervous laugh. This was a seemingly plausible argument but a bit worrying because most people use this type of antenna and they do seem to work.

The fact is that this is a silly conclusion to draw. Every radio has coils inside it to provide essential tuned circuits. That doesn’t mean they are RF chokes, preventing the transmitter signals from emerging on the antenna connector. How could it produce 100 watts at that point if the coils were choking all the RF?

However this kind of statement, if uttered with the right level of assurance and confidence, will feed silly ideas into the heads of less well informed listeners, asking them to suspend disbelief and accept such nonsense as fact.

A little thought about the traps in multiband antennas will reveal them to be specially selected sizes with a specific calculated inductance, to do their job and allow each element to exhibit multiple resonances. They are not RF chokes. RF chokes are coils with enough inductance that they present a very high impedance at the nominated operating frequency.  Perhaps our self styled expert thinks that is how traps work.  It isn’t.

I’m Andrew Davis.  VK1DA is my amateur radio callsign, which was allocated to me by the Australian Government once I satisfied the requirements for an amateur radio licence.

For more details of amateur radio licencing in Australia, please see my VKFAQ website.