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
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
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.

Equipment sales: name your price

I have noticed some sellers of used radio equipment make life more difficult than necessary for themselves, by being quite unclear about what they really want for the gear.  ie. what is their asking price?

This is surprising because anyone who has bought equipment knows very well what they paid, knows what they got and usually has a good idea of whether they got a good deal.  You’d think anyone selling equipment would do a bit of basic research to find out what they are likely to get for a Bloggs XYZ120S transceiver.  But many people don’t do that.  You’d think their precious Bloggs transceiver was gold plated.  They should rethink what it is they are selling.

Radio equipment has a remarkably high resale value compared with most consumer electronics and certainly compared with motor cars we get huge prices for our old radio gear.  Why is that?  Before trying to answer that, let’s consider a few examples of unrealistic pricing or expectations.

One case is a Collins KWM2A transceiver with matching power supply.  These units were arguably the best you could get in their class for about 30 years, from the early 60s to the mid 80s and possibly longer.  They could barely be matched in even one respect by the best any other manufacturer produced.  The reasons – good design, simple operation, no frills, mechanically reliable and electrically hard to fault.  However this gear is now pretty old.  It uses tubes.  The manufacturer does not build these radios any more, parts are now harder to find and are becoming expensive.  Only the true fanatic will continue to maintain and use this type of equipment.  Modern equipment by other manufacturers offers much more in the way of operator conveniences apart from power and space efficiency.  So with this background we see a number of these radios being sold on the second hand market, sometimes with remarkably high pricing.  One ad even stated that since he had noticed similar equipment, together with a power amplifier being sold on Ebay for $US4000.  However he did not nominate an asking price and left it to the reader to work out what he would be prepared to accept. what should it be worth?  What alternatives are there that produce 100 watts on the bands from 80m thru 10m, with say 500 Hz dial readout and one VFO.  Well, almost none on the new market.  Even the cheapest Icom HF radio IC718 offers more facilities for around $800.  So to hope for any more than that is plainly based on the hope that there are people out there that want the equipment just for the pleasure of owning that particular brand or model.  Only the older operators will be at all interested in that thought, yet their numbers are diminishing.  So what chance does our seller have of receiving the $2500 he may think this is worth.  My feeling is, not much at all.

Another example is a portable multimode portable transceiver for the 420-450 MHz band.  This is a Yaesu FT790R.  3 watts output and modes SSB, CW and FM.  This is a curious gadget type radio, with insufficient power to make many contacts at all, unless you are located on the top of a tall hill or connected to a power amplifier.  OR it may be used as an intermediate frequency (IF) radio for higher bands such as microwave bands from say 2 to 10 GHz.  On those bands, using a higher IF is preferable to using 144 or lower frequencies as the IF.   So what is this type of radio worth?  Well, the latest version of the portable low power radio from Yaesu is the FT817.  It operates on all bands from 1.8 MHz to 450 MHz and produces 5 watts of any mode on all those bands.  It has digital readout and tons of memories, an inbuilt keyer and so on.  It is available new for just under $900 and is available on the second hand market for around $600 to $750 depending on age (5 years or 5 days).  So what kind of price should the seller hope to receive for his 20+ year old radio without warranty and spare parts availability.  Would you think $250 excessive?  So would I, but the seller in this example wanted $600 for his old FT790R (including a 10w power amplifier). In my view this is at least double its maximum value.

Another example was someone who should have known better.  A rare piece of Icom VHF/UHF equipment was advertised with a list of all the extras that had been loaded into it.   As my eyes ran over the listing, I searched for the asking price.  I found no clues given except for the amazing phrase “don’t make silly offers”.  Well, what is not silly?  How can a buyer read the seller’s mind and know what he has in mind for an unusual item like that?

In other consumer goods no-one would expect anything for a 20 year old transistor radio, or even a 2 year old MP3 player.  They get thrown on the scrap heap once the next model arrives.  Even more expensive goods like televisions and stereo gear is almost thrown out as worthless at the ripe age of 10 years.

In the case of used amateur radio equipment, you can be lucky and find equipment that has been looked after an used carefully.  The case is not damaged, the electronics inside it are all in good order.  No-one has made non-standard modifications (“improvements”) that reduce its quality of reception or transmission.  You can also be unlucky and find a radio is being sold because someone has discovered it does not work well at all.  With 20 to 30 year old equipment, the work needed to fix some problems can be quite expensive.   However there is currently a high demand for used equipment, which is artificially propping up prices for old equipment that should really be worth $50, not $300.

But what if you do think your Bloggs radio is a fabulous piece of equipment someone will love to use, and get heaps of service from?  Well, the least you can do is to look around first and see what they are selling for.  Be realistic, especially for 20 to 30 year old equipment.

But please, name an asking price and don’t expect buyers to read your mind.

VHF Field Day January 2009

As we had scheduled a house move one week prior to the January 17th VHF Field Day, I had to set aside the equipment needed for the field day so it wouldn’t get packed up and be lost for months, which can happen when you move house.
The antennas were no problem as I had to move them on the roof racks of the car. The cables were a possible problem, as were the connectors, camping gear, tent/poles, generator, power cables and distribution boards, power cables for radios, the radios themselves.

The one thing I could not put on hold was myself and I had worked very hard for 5 days straight packing and carrying boxes of household goods. The last move took ages and I had several weekends to sort through 3 garages and dispose of unwanted stuff. This time was a bit better, there was only one garage.

The upshot was that with some encouragement from Dale VK1DSH I did find the energy to pack the car early on Saturday morning and head up to Mt Ginini, a 70 km, 90 minute trip from the new QTH. It took a bit longer as I called in at the bakery and the supermarket for some essential supplies on the way.

We got the station set up by about 3pm and logged our first contacts on all bands. Right away there seemed to be antenna problems on 52 and 432 MHz. Both antennas came down, connectors checked. The 52 MHz vertical had been extended to make it work on 50 MHz on a previous field day. Removing a short length of tubing added for 50 MHz operation returned it to normal operation on 52 which was sufficient for local contacts.

On the 432 antenna, lowering that meant going off 144 as well so we had to get it done quickly. I inserted the Bird 43 meter inline with the 432 MHz feedline and first tried a dummy load on the antenna side of the meter. Perfect, very low reflected power, transmit power fine. Same with the dummy load at the antenna end of the feedline. But with the antenna, quite poor swr at about 2.6 measured at the transmitter end. Later I ran some simulations using the predicted loss in the feedline (CNT400, 10 metres) indicated that the actual SWR at the antenna was somewhat higher. This indicated the driven element of the antenna was not properly connected to the feedpoint connector. however it was sealed in epoxy and nothing I could do up the mountain to fix it. Note that I had previously used this antenna with poorer quality feedline RG/9. The increased losses of that feedline masked the antenna problem.

On other bands all appeared to be working fine, though I never made a complete contact on 1296 with Adrian 2FZ in Sydney, nor with Dave 2JDS near Bathurst. However I made a number of contacts at similar and greater distances into the vk3 area so it remains a mystery.

With Dale 1DSH operating the 6m rig and the IC910 running on 144, 432 and 1296 it was a noisy tent at times. The radios were all together on one table. The other radio on the same table was the FT290 which was the driver for the 13cm transverter.

Dale brought his 10 GHz equipment and made a contact back to Ted VK1BL on Mt Ainslie in Canberra on the Sunday morning. No other 10GHz stations were active within range. Unfortunately the power amplifier in Dale’s transverter suffered a failure so power output was limited to around 1 milliwatt.

Packing up only took 90 minutes, half what it had taken in November. A great pleasure to be on the road heading home at that time. On the way I heard Norm 7AC on 50.170 and had a 10 minute chat with him from the car. Just for a bit of extra radio for the weekend! But I forgot to get a Ross Hull contest number from him. 11 points lost from the RH log!

After scoring the log it appears we did fairly well on 2m and 432 despite the antenna problems. The log has been sent in on time so we will see what the increased activity level does to our position in the results.

Photo gallery for Summer 2009 VHF field day.

VHF/UHF Field day log pages and checklists

These two files may be of use to other entrants in the VHF/UHF contests.

The first is an empty log page which you can simply print on your own printer.  These are for handwritten logs.

The second is a spreadsheet template for the Australian VHF/UHF field days.  The first worksheet is the summary sheet and worksheets for each band follow.  There are only a couple of formulas and they are in the scoring table.

The template, if opened in either Excel or OpenOffice will create a new spreadsheet.  When you save it will be to a spreadsheet file.  The template will be unchanged so it can be reused.

Logging for field events – paper logs and spreadsheets

I use spreadsheets to record my field day log.  I don’t need to use a computer in the field – I work with computers all day and the last thing I want on a field day is yet another day of working a computer.  A paper log is quite good enough, and avoids odd things happening due to incorrect program logic, or wrong callsign recording.

In the John Moyle Memorial field day rules you need to record the grid locators of stations worked on vhf/uhf. Then you need a column for distance, then you need to work out the points earned by that contact.

I use Tiny Locator, a nice little application from ON6MU, to calculate distances from grid squares.  There are spreadsheet add-ins available for Excel, but I decided to just use an external tool and copy/paste its results into my spreadsheet. By doing the calculations only once for each callsign, the process is cut down to the minimum effort required.

I copy all the callsigns worked, with their locator codes as recorded during the contest, into a new worksheet called Grids.  Then I sort by callsign and remove the duplicates.  Then I do all the distance calculations with the help of Tiny Logger and record the distance for each station worked.

Back in the log page itself I then insert formulas into the Grid locator, distance and points earned cells of each row.

The grid locator can either be the original locator recorded during the contest, or the data copied from the Grids worksheet for that callsign.  Similarly for the distance and points data.

The formula to copy the grid locator for any callsign in the Grids sheet is =VLOOKUP($E2;$GRIDS.$A$1:$C$28;2) for OpenOffice sheet users, or =VLOOKUP($E2,$GRIDS!$A$1:$C$28,2) for Excel.

Similarly you can get the distance using the next column of the Grids sheet.

The points are calculated using a similar technique.  The score table is set up in another sheet, in the following format.

0 2
49.9 5
99.9 10
149.9 20
299.9 30
9999 50

The formula to look up the points for a distance is: =VLOOKUP(K2;$Scoretable.$A$1:$B$6;2) for Openoffice.org Spreadsheets.
Here $K2 is the cell containing the distance for the contact made. Scoretable is the sheet containing the table above in cells A1 to B6. Column 2 in the scoretable is the column containing the points to be scored. VLOOKUP returns the row containing the distance that is equal to the specified search value.  If that exact value cannot be found in column 1 of the table, it matches against the first row found that is greater than the value sought.  Thus a distance of 80 is greater than 49.9 but less than 99.9, so the row chosen is the one with a distance of 99.9, allocating 5 points to the contact.

You could continue to refine the formulas and the fine details, such as dealing with decimal points of distance correctly.  eg. what is the score for a distance of 99.999 km?  The simple table and formulas used would give the wrong result and strictly speaking the scoring table specified in the rules does not state the score for distances between 49 and 50 km, etc.  However as a way of saving typing and avoiding keying errors in distances, this approach works well enough.  Rounding the distances appropriately is also something to consider.

Summary

Using a combination of plain spreadsheets and formulas, you can ensure the grid locator, distance and point score for each contact is consistently recorded in your log sheet.

New antennas for 1296 MHz

I received the two 18 element yagis for 1296 Mhz and they appear to be strongly made. We will see whether they are any better than the previous antenna.  I have borrowed a splitter for them and will use that for the Summer field day in mid January, unless I can make my own before then.

I found a website offering data on stacking distances for yagis.  For a boom length of 1.5m on this frequency the stacking distance recommended is 2.4 wavelengths, which works out at 55cm (23cm wavelength).  The feedlines on the yagis are about 25 cm long but that’s not long enough to reach the power divider, so additional connectors and cable will be needed, eating into the stacking gain.

Next step for 23cm is to configure the power amplifier so it can be operated remotely from the tent.  I read some comments on the UK microwave reflector about power levels from IC910H not being up to the 10w level expected.  Time to get out the power meter and check mine out.

Amateur Radio, Computing and other activities of Andrew VK1DA/VK2UH