VK1DA's Blog

Dayton Hamvention trip 2010

After reading about the Dayton Hamvention for over 30 years I decided this year I should see it for myself.

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.

Inverter Generator 1KW

The generator that caused me so much grief in the November contest was returned to the seller, by arrangement. The seller refunded my purchase price. He was unable to provide any certainty that it would be reliable for use at the altitude of the mountains I normally operate from (all above 1500 m or 5000 ft ASL).

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…

Summer 2010 VHF/UHF Field Day

The January 2010 event was much more successful for me than the Spring field day about 6 weeks earlier.

This time Dale VK1DSH and I operated as a multiop station on 50, 144, 432, 1296, 2403 and 10368 MHz.

Successes:

• Dale made several contacts on 10 GHz with Andy VK2AES operating south east of Bungendore.
• Despite leaving the feed for the 2.4 GHz dish at home, we still made a contact with Andy on that band, using a “field day special” feed constructed onsite from a piece of wire and a N type socket connected to a piece of cable through the dish centre and attached to the normal feed hardware.  Signals S9 over the 70 or 80 km path.
• Several successful contacts with Dave VK2JDS near Bathurst on 1296 MHz. Some persistence was needed for the first contact, when conditions were not so good and we had to get our beam headings right.  More power at both ends would have been a help.
• Other than that, we had a fair contact rate on 144 with many throws to other bands.
• For this event I used one of Owen VK1OD’s Roger Beep boards.  I assembled the board on the previous weekend, mounting the board into a small box with the Icom mike plugging into a socket on the RB box, and mike output to the IC910 through a short section of shielded cable. I set the CW speed to 30 wpm and selected the K option.
• Despite some thunderstorm activity in the area, we didn’t have to shut down.

Activity was a little lower than in the past.  Chris VK2DO was away on a business trip and Matt VK2DAG was roving up and down the NSW coast and unfortunately we didn’t work him once. Our score was just over 2000 points, though, with the help of the additional microwave bands. We were grateful for Andy VK2AES’s efforts in going portable on both days and giving us contacts on all bands, in particular 2.4 and 10 GHz.

VK1DA portable in VHF Field Day January 2010

The field day shack

Spring field day a wipeout for me

After lugging all my equipment for 50, 144, 432, 1296, 2400 and 3400 MHz from the car to the north side of the summit at Mt Ginini, it still took several hours to get set up and operational. I finally got on the air on all bands at around 6pm, after making some earlier contacts on 1296, 2400 and 3400 with VK1BL and VK2AES.

Later I made contacts were made with VK1BL/p and VK2AES/p on all six bands (3400 only with VK1BL) but conditions and activity from further afield seemed quite poor with only weak signals from a small number of other portable stations.

I was running my station from a newly purchased inverter generator.  This was not a name brand but an import sold by a Victorian dealer, mostly marketed via Ebay.  I was pleased that its noise performance was much better than my previous generator.  However at about 9pm on Saturday night, within 20 minutes have having its fuel topped up, it slowly ran down and stopped.  All efforts to get it going again were unsuccessful.  I SMSd the other local field stations telling them I had a power problem.  The next morning I could only pack everything up and go home.

What happens to the generator has not been resolved yet.  My confidence in this particular unit is zero.  I have not been able to restart it, despite following the advice of the dealer and changing the fuel to premium unleaded.  I can believe it would run better, but I don’t see why it would simply fail to restart on ordinary unleaded.

I did examine the spark plug and found it was fouled considerably.  The recoil starter still reveals compression is good so I don’t think the rings have given up.  I suspect ignition circuit failure.

Fortunately others didn’t have this problem and went on to make more contacts.  The contacts with Doug 4OE did not work out too well, with Ted VK1BL making only marginal contacts on 144.  Contacts on higher bands were not possible.   Conditions were simply too poor.

Better luck next time.

3400 MHz (=3.4GHz) [aka 9cm band] on the boil

For the forthcoming spring field day I expect to have a transverter for 3400 MHz on loan from Ted VK1BL.  Ted has built two transverters, one with about 15 watts output and the other with just 2 watts.  We will be conducting a communications test with these transverters on a 90 km path on Sunday 22nd November, between Mt Gray at Goulburn and Mt Ainslie at Canberra. The antennas to be used are either grid style or mesh covered grid parabolic dishes.

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.

Generator blues

My GMC 950w generator which has powered about 5 of the last few years’ VHF field days, refused to start last week when I set out to change its oil.

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.

More about the Alligator Hat

The June 2009 edition of AR carries a small article I wrote about lowering the resonant frequency of a HF helical antenna to allow me to use it on a lower frequency than its design centre frequency. My 80m helical, for example, is resonant at 3585 and provides the lowest SWR at that frequency.  At the CW end of the band, say 3520, the same antenna has a SWR of over 3:1, sufficient for the IC706 to cut back its output power to less than 10w.  To operate on the CW end of the band with this antenna I therefore need to deal with the mismatch using an ATU, or change the resonant frequency of the antenna.

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.

Myths and Legends

Recently I was reminded of a conversation I overheard between two hams discussing which type of beam antenna is best, a full size type or a multiband antenna with traps in the elements to enable it to operate on multiple bands.

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.

Why calling freqs don’t work in vhf contests (IMO)

A calling frequency is intended to provide some certainty about where stations will operate. On VHF bands activity is generally low so it makes a lot of sense for people wanting contacts to use an agreed frequency for issuing CQ calls. However if there are more than two stations wanting to use that frequency, its purpose as a calling frequency has to be respected, and anyone who is in contact should move off the calling frequency.

This arrangements works by “gentlemen’s agreement” during non-contest periods, but falls down in the heat of a contest. It is often found that a strong, well located station can dominate a calling frequency and make it very difficult for any others in their local area to use the calling frequency at all. This requires discipline on the part of all operators and the willingness of all to gently remind frequency hogs to QSY (move frequency) once they have set up a contact.

I think there is a case for abandoning the calling frequency concept during contests.

1.  If all stations want to use one frequency for calling CQ, there must be a queue.  Why a queue on a band with hundreds of KHz of free space?

2.  If just one station decides to run a contact on that frequency, all others must wait.  see 1.

3.  If there is a mixture of technical capability, ie. power, location, antenna gain, quality of fittings combining to give variations in range capability of the stations in any area, the use of the calling frequency by the stations with less technical capability makes it useless for the others.  A couple of stations running 20w to discones can make the frequency useless to everyone else until they complete their contacts.  And if they don’t hear the dx, won’t they simply call CQ again?

4.  There is also the “hidden transmitter” problem.  eg. two well located stations 600km apart are capable of a contact on 2m.  Unless they happen to call on  a frequency free of interference from lower powered/equipped stations calling CQ (randomly and without asking QRL? first) * they will never make initial contact.   So they cannot possibly use a “calling frequency” even to make initial contact, because they won’t hear each other beneath the qrm even from a city 300km away.

5.  As has been observed by many others, notably a recent vhf column in QST, most contacts made on the bands above 144 arise by “throws” from 144.  There are few random contacts made by calling cq on the higher bands.   This makes it sensible to use the same offset on the higher band as is in use on the lower band.  Eg.  contact on 144.180, then 432.180, 1296.180 etc.   if you go to 432.160 you may well run into others who moved up from 144.160.  If you use .150 you may well be QRMd by someone calling CQ and the odds are they won’t be aware of your dx contact.

These are just the beginning and I’m sure everyone who has ever been on a decent hill in one of these contests would have other examples and scenarios.

The only situation where net frequencies or calling frequencies are practical is where there is a very low level of activity, or a very low possibility of contacts, making it vital that frequencies are co-ordinated.  The EME and MS operators need coordination or they would never get anywhere (though modern SDR receivers are making that less necessary than it has traditionally been).   But for a contest, where there is a wide range of stations operating, with plenty of opportunity to work the higher and medium powered stations at good distances, a calling frequency creates QRM, sends the wrong message to new operators and hinders contact rates.

A comparison with HF operating techniques is useful. Imagine too how the operators on 40m would react to being told they need to make contact first on 7050, then QSY up the band.  They would simply say, don’t be silly, that will never work.  They would be right.

John Moyle Memorial Field day March 2009

For this year’s JMFD contest I thought weather and propagation conditions were fairly bleak.
The weather was wet and windy to say the least.  Many field stations reported having their tents and masts blown down.

The high point for me was working 3UHF on 1296 with only a single 18 el yagi, and barefoot (10w nominal).   The distance was 501 km according to the VK1OD distance calculator, using the VK1DA/p and VK3UHF locations from the VHF Logger.

I didn’t like my chances of having hf antennas stay up and didn’t want to extend the tear down process, so I limited myself to the vhf/uhf bands.  I had a car full of antennas and several extra masts but in those conditions, there is no point in trying to do too much.

The temp in the tent at 5AM Sunday morning was 3.5 C though the official overnight minimum according to BOM was 2C.   No wind gust peak data was available.

Operating techniques and problems observed.

There is a continuing tendency for operators to call and make contacts on only one frequency, 144.150.  Can everyone please tell their club operators that there is no repeater there, they are allowed to move the big knob in the middle of the radio panel.  It is ok, nothing will break, the rest of the band also works for making contacts.  It would be better to train vhf ssb operators on HF so they get to know how to operate on ssb, how to work the tuning knob and how to  tune around the band to find stations to work.  FM channels and repeaters are quite the wrong training ground for SSB but I’m afraid that the FM repeater operation mode (staying on one frequency, as if it is the only conduit to any other station) is the method many operators learn and continue to use.

It is up to the experienced operators to teach new operators better techniques.  I appreciated those experienced operators who I heard requesting a QSY as soon as initial contact had been made.

During the contest I tried many times to make contact with some stations in the greater Sydney and Melbourne areas, whose signals were perfectly readable, but whose operators seemed to want to chat to locals interminably, on 144.150.  There are bonus points for working longer distances and these operators were ignoring those chances.  eg. a contact with another local station is worth 2 points, but a contact with a station 300+ km away would be worth 50 points.  This surely would make it worth listening to a weaker signal.

We should encourage people to operate in vhf events in a manner similar to the HF bands.  Find a clear frequency (within the band plan) and call CQ.  If looking for a contact, tune the band.   If activity is low, don’t move too far from other activity (but be mindful of local interference problems – this is why I qsy 30 kHz up from 150, not just 5 kHz as I might on HF).  If activity is high, move further out.  Give the dx something to tune for.  Don’t clump up and make it impossible!

My QSO tally

All contacts ssb.  These scores are about half the corresponding number from the summer VHF/UHF field day in January.

6m – 9
2m – 54
70cm – 31
23cm – 7
13cm – nil.