28 April 2014

QRP Field operations. Lessons learnt from the Kruger trip and many other field trips

Herewith in this blog are some of the practical lessons learnt on the Kruger trip and other field operations during my time in South Africa. These observations pertain to the deployment of a end-fed wire halfwave (#18 awg) and a counterpoise of 8ft 6 inches in length and the use of a tunable tank circuit as the coupler.

These comments relate to a simple operation where the aim is to get on the air easily in order to make local (South Africa wide) contacts and then to take down the system easily and quickly after a day or two of operations. It is assumed that a minimum system has been packed with very limited spares. In my case my whole station plus antenna and accessories easily fitted into a plastic container the size of a shoe box. Refer to my previous blog showing pics of the packed station.

For this type of deployment it is absolutely NOT necessary to try to get the wire up more than 15 - 20 ft in the air. Attempting to get it higher will almost guarantee difficulties in the form of multiple launch attempts, tangled cord and wire, frustration, and if it goes really badly, the loss of the whole antenna system.
  1. Be very patient when un-winding the cord and antenna wire. The total length of my 40m system is 66ft of wire with a 60 ft cord attached. If you let this get in a tangle then it can take another 20 minutes to un-tangle it. I wind this up over one hand and turning the wrap around every 10 winds or so to prevent it twisting. This can be easily un-wound by releasing each turn carefully. Once the wire and cord is lying on a nice bare piece of ground, make certain that the coils are laid so that the end of the cord is at the 'top of the pile.' It will then uncoil during the launch without incident. Use slippery plastic cord as found in the hardware store. 
  2. Make sure that the end of the wire that will connect to your radio is fixed before launching. Preferably tied to a convenient tree branch about 8ft above the operating position. Here I am assuming that the most likely deployment will be a sloper with one end up at 20ft and the other end up about 8 ft. Trust me it is no fun to watch the whole system end up in the tree. Been there done that!  
  3. If an error is made in the launch and you need to retrieve the cord then disconnect the weights before pulling the cord back through the tree. Do this every time and don't take a chance. The weights will hang.
  4. Consider a spare set of detachable weights. The chances of hanging in a tree are extremely high. The most likely is a situation where the weight and cord does not drop to the ground after the launch. Now you are forced to retrieve the cord by pulling it back through the tree. Very often the weights will snag in the 'Vee' of a branch joint making it impossible to retrieve. A good strong cord is an asset in this case because heavy pressure can be applied in an effort to try to dislodge the weight.  
  5. Spend time and be patient in carefully selecting the tree to launch over. Preferably launch over a tree as opposed to trying to select a specific branch. The tree is much easier to aim for. An ideal launch tree would be about 25 ft high. Select a tree that has smooth branches and few leaves if possible. Do not select an Acacia thorn tree! Optimize the tree selection taking into consideration the fact that you want to be QRV quickly, you want the weight to drop to the ground and you want to be able to easily recover the wire and cord after the operation.
  6. 1.3Ah battery easily lasts a week provided it is in good working order. I had many lengthy QSO's during this 5 day trip. This assumes the use of minimum power on 40m. In my experience it is easily possible to make regular QSO's throughout most of the day on +500km path lengths using 1.5Watts output power maximum. Refer to the battery power measurements below.
  7. Try to get as much of the antenna up in the air and horizontal to the ground. Ideally both ends at 20ft above ground between two trees. An inverted L with 46 ft horizontal and 20 ft vertical. It is amazing how much this configuration improves the signal strength. This is why I carry two cords. The same set of weights can be used to deploy each cord.
  8. Put some plastic putty over the joint between the cord and the antenna wire. This will allow it to glide through the tree easier.
  9. When laying the 8ft counterpoise along the ground be sure that it is not a safety hazzard. It is easy for people to trip over this wire.
  10. Pack away the radio and accessories each time after use. Leaving it set up is an invitation to the monkeys to pull the counterpoise and to try eating the battery.
  11. Take a small portable plastic table. One of those small green ones. They pack easily in the boot and allow the operating position to be set up comfortably under a tree. It can also be moved as the sun position changes.
  12. Consider using a length of coax between the radio and the tuner to avoid RFI issues. I certainly experienced RFI/common mode on this trip on one occassion when I had the tuner directly connected to the radio. I believe the end of the wire and tuner were too close to the radio.
  13. Build the coupler with a link switch so that you can connect the coax/ground to the counterpoise end of the secondary coil. Sometimes this will improve the match. Sometimes it will cause RFI.
  14. Make the coupler tunable with a small variable capacitor. The resonant point can change by up to 30pf depending on deployment conditions.
  15. If possible try to get the wire in the clear. However if it has to snake through the tree it will still work fb and no problem.  
  16. If possible have a variable power output rig so that when conditions are good you can reduce power and save battery. In South Africa the rig only needs to operate on a single frequency of  7020Khz CW. A simple DC Rx can be used with RIT and an attenuator. BCI is not an issue during daytime operations, however it is an issue during early evening unfortunately.   
  17. Always carry a Leatherman of Swiss Army type knife. Preferably with one of those spikes that used to be used to take stones out of horse's hooves. This spike can be used to loosen tight knots. The knife blade is useful for cutting off snake's heads and for general defense.
  18. Wear a hat and stay hydrated.
  19. Look after the XYL and the kids.
  20. Enjoy!

Audio Record by Jan ZS6BMN. Thanks Jan!

Audio Record by ZS6BMN.

Transcript of email received from Jan ZS6BMN.

"Hello Dick,
It was good to hear this morning that you were safely back in Fourways :-)
I have followed your Kruger Park trip/adventure all the way (with atllas and maps too) and it was obvious that you were enjoying the Park, the game and the QRP operation tremendously! Thank you for all the interesting CW operation from the Bush. I cannot recall when last there was such a lot of CW activity on 40m and also never realised how well the band was performing over these medium distances early in the evenings. Your 1.5 W Norcal did a sterling job and has often peaked at S9 on my simple setup with the small indoor whip antenna and TS-140S. Just a great pity that I was without an antenna as I have heard you calling CQ when nobody else was around and you thought that you were not getting out. Still, I have enjoyed listening and must thank you for again for providing such a lot of listening pleasure and for giving QRP operation so much positive exposure! You have even managed to get my old friend Evert to operate 40m after dark :-) BTW: I have listened on the little Rebel to his last QSO with you and then his signal was the first CW signal that could register a reading on that set's stingy S-meter - all of S2, but the reception was great and I could even hear the DX in the background. The Rebel was set up with the single band whip in the dining room while I also had the TS-140S running in the 'shack'.
I have a great recording of your first early evening's operation with Monk, Barrie and Dave all calling in. Later that same evening OM Monk, OM Peter, ZS1JX, and you were calling at different times on the same QRG and just missed each other. At that time OM Monk was putting in the strongest CW signal that I have heard to date and it has sounded like FM with 100% quieting! I have had a lucky break in that the noise was completely gone that day and the S-meter was idling at S1-S2 on background noise.
So all-in-all in the terminology of "1066 and all of that" your enjoyable weekend in the Park has been a 'good thing' for many others as well :-)
73 for now!"


MEASUREMENT                            START OF TRIP                     END OF TRIP (after 5 days operations)        
Battery Voltage Radio OFF                   13.01V                                        12.3V
Battery Voltage Radio ON                     12.99V                                        12.22V 
Battery Voltage KEYDOWN                  12.75V                                        11.92V
Current RX                                           19.9mA                                       19.9mA 
Current KEYDOWN                                                                                 190mA
Power Output                                       1.58W                                          1.4W

NOTES: Measurements taken at 7020KHz with Keithley multimeter and AD8307 Power meter using a 36dB attenuator.

1 comment:

  1. Much humour :O) and and very informative. Thanks Dick. You will be missed here in South Africa as you move back to W land but you're only a few Hertz away. Keep in touch!

    73 de Eddie ZS6BNE