Archive for the 'Field Operating Tips' Category

“Homebrew” Balanced Line Support

You can build your own multi-purpose balanced line antenna feed point support in just a few minutes using readily available “off-the-shelf” parts.  Balanced line transmission lines should be securely attached at antenna feed points to prevent breakage due to “wire fatigue” caused by the flexing effects of wind and the weight of ice loading.

The most common types of balanced line used as antenna transmission lines are show below.

imageThe balanced line antenna feed point support discussed in this article consists of two parts.  The top part is a modified plastic dog bone insulator.  The bottom part is a “sandwich” type clamp made of durable lightweight weather resistant material.  The clamp is attached to the modified dog bone insulator with a stout plastic zip tie.

Top Part

You can make the top part of the support by drilling a hole (slightly larger than 3/16” diameter) through the center of a plastic dog bone insulator.  The next step is to insert a 3/16” diameter stainless steel eyebolt through the hole and secure it with a stop nut.  It’s a good idea to use flat stainless steel washers on either side to bridge the ridges in the insulator.

image

top part

Bottom Part

The bottom part “sandwich” clamp can be made from weather resistant lightweight composite material such as 3 1/2” wide rigid landscape edging available in 20’ rolls.  Other materials such as Plexiglas can be used to make the clamp.   It turns out that a single clamp can be made by cutting a 9” long piece of edging and ripping it exactly in half (1 3/4” wide).  If you go with the edging,  be sure to use a bi-metal or ceramic saw blade because of the abrasive properties of the material.  Also be sure to wear eye protection and a mask when cutting the edging.

 

rigid landscape edging

The next step in constructing the bottom part is to drill holes for the nylon bolts that will secure the two halves of the clamp and cut two threading slots.  Since we want the clamp to work with any of the three types of balanced line discussed above,  hole/slot placement is important.  Drill an appropriately sized hole at the top of the clamp for the zip tie that will secure the clamp to the modified dog bone insulator.  Lay a section of each type of window/ladder line on the clamp and mark the spots (centered) where the top edge of the line will catch a nylon bolt.  Drill two holes at the spots slightly larger than the diameter of a 10/24 nylon bolt.   Drill two additional holes (same diameter) near the bottom of the clamp.  These two holes and the hole (second from top) will accommodate the three nylon bolts needed for configuration #1 shown below.  Lay a section of TV/FM twin lead on the top half of the clamp and mark the spots where the slots will be cut.  Use a drill and appropriately sized bit to cut the two slots.  Allow enough spacing between the slots so the TV/FM twin lead is not bent up at a sharp angle as it passes through the slots.

Configuration #1 (300 ohm TV/FM twin lead)

image

300 ohm TV/FM twin lead

Thread the TV/FM twin lead through the slots and tighten the clamp using three nylon bolts and wing nuts.

Configuration #2 (300 ohm & 450 ohm window/ladder line)

 

image

300 ohm window/ladder line

image 

450 ohm window/ladder line

The window/ladder line is placed in the clamp so the two nylon bolts catch the top edges of the gaps in the line.

image

Tighten the wing nuts to secure the window/ladder line snugly between the two halves of the clamp.

Hanging the support

To hang the support, secure the clamp to the top part (modified dog bone insulator) with an appropriately sized plastic zip tie.  The ends of the wire radiators are inserted through the ends of the dog bone insulator and appropriately secured.  To connect the antenna, strip the ends of the transmission line and the ends of the wire radiators, and join the corresponding ends of the transmission line to the radiators.   Be sure to provide enough slack in the connections so the strain on the transmission line is at the zip tie junction and not on the wire ends.

image

zip tie used to secure clamp to modified dog bone insulator

TIPS:

(1) Keep a spare balanced line support handy as a template for future use.  You will be able to lay the template over the material to be used and mark the spots for the holes and slots.

(2) To lower visibility of the finished antenna, use black THNN coated wire for the radiators, black dog bone insulators, black zip ties, and spray paint the bright metal, nylon bolts/wing nuts and clamps with camouflage dull black paint.

It won’t take you very long to make several of these supports so you will be ready for future antenna projects.

Field Operating Tip – Length Measurement Jig

Looking for an easy way to hold the ends of your tape measure and a length of wire, ladder line, coax, etc. while you measure out required lengths.  You can make a simple little jig that will simplify length measuring tasks.  Attach a couple of alligator clips to a short piece of metal angle stock using short bolts and nylock nuts.   One alligator clip secures the end of your tape measure and the other alligator clip secures the material being measured.

 image

measurement jig

If you have tree near where you are measuring, you can wrap a piece of chain around it and attach the jig using the snap hook.  If you don’t have a tree or post nearby, you can position a portable cement utility block and attach the snap ring to the embedded eye bolt.

 

imageportable 25-lb cement utility block

 

KI4PMI describing length measurement jig

The jig enables one person to easily make accurate length measurements.

73.

NC4FB & KI4PMI

 

Field Operating Tip – Portable 12 VDC Cooling Fan

Ever wish you had a cheap light weight portable 12 VDC fan to cool you and your equipment while  you are operating at a Field Day or similar event?  Cruise by your local Wal-Mart store and pick up an O2 Cool 10" Battery or Electric Portable Fan for about $16 + tax.  This 2-speed fan will operate using power from (8) D size batteries, a 12 VDC wall adapter (L size coaxial plug) or you can wire up a plug and connect the fan to your 12 VDC power supply or 12 volt battery.  The fan is very light weight, has a folding carrying handle and a folding base that can be tilted.  If you are operating in a tent, you can suspend the fan above the table and enjoy the cooling effect.

image

O2 10" cooling fan

If you plan to wire up a power plug, you will will need a size L (Tip size: 5mm O.D. x 2.5mm I.D.) coaxial plug.  Radio Shack sells them in a 2-pak for $3.19 + tax.

image

Size L coxial DC power plug

This little fan is very quiet and moves quite a bit of air.  It can really help keep your equipment operating on those hot days in the field.  We tested the fan under operating conditions and it did not introduce any noticeable noise into the equipment.

KI4PMI explaining the O2 8" cooling fan

73.

NC4FB & KI4PMI

All-band Doublet Antenna (40-6 meters)

Looking for a simple, cheap, easy to build, easy to put up, all-band horizontal wire antenna?  Take a look at a 40-6 meter doublet antenna fed with 300-ohm twin lead.  The antenna performs well at a height of 25 feet.  Tune the antenna (40 m) by adjusting the radiator lengths.  An antenna tuner is required.

Materials List

~66’ antenna wire (#14 black THHN stranded wire works well)

(2) insulators (antenna ends)

(1) twin lead connector/support (antenna center)

300 ohm twin lead (transmission line)

4:1 current balun

short length 50-ohm coax cable (balun to tuner)

antenna rope

 

image

 

The antenna performs reasonably well for 40 – 6 meters.

EZNEC models (40 – 6 meters) can be downloaded from the link below.

all-band doublet EZNEC models

Field Operating Tip – WiFi signal BOOSTER

Ever been in a Field Day event equipped with a portable WiFi network where the signal to the WiFi card in your laptop wasn't strong enough for you to login?  How would you like to get a 10X signal boost at your laptop giving you solid connectivity up to half a mile?  Well, you can by adding a WiFi X 10 Booster.  Software installation is a snap.  The unit plugs into a USB port on your computer and gives you the needed signal BOOST.  Power to the unit is supplied through the USB port so  you can operate your laptop completely in battery mode.  When the unit is unplugged from the USB port, the internal WiFi card in your computer handles connectivity.

My shack is located at the back part of my yard far enough away from the home WiFi network router that my netbook will not connect to the network using its internal WiFi card.  The WiFi X 10 Booster gives me excellent signal strength and 54 Mbps transfer speed from my shack.  I use the unit in my shack and at events that provide a WiFi network.

73.

NC4FB

 

 

 

 

 

 

 

 

 

ARRL National Field Day 2011

Ki4pmi-nc4fb

KI4PMI (left) –  NC4FB (right) operating during Field Day

KI4PMI confirming contact during Field Day

My friend KI4PMI and I had what we consider a very successful Field Day.  This year we constructed four different types of antennas and used them during Field Day.  Although we didn’t officially participate in the competition, we did make mumerous contacts.

Our primary goal was to evaluate and document the performance of the antennas we built.  A secondary goal was to offer a “learning experience” opportunity for Technician class licensees to participate in National Field Day as operators and to ask questions about antennas, equipment, operating procedures, etc.  We had several Technicians participate and the feedback we received indicated they learned quite a bit and really enjoyed themselves in the process.

The most interesting and complex antenna that we built and used was the 6–band N4GG array. The antenna system was originally designed to cover 6, 10, 15,  and 17 meters.  While analyzing the system with an AIM-4170C, we discovered surprisingly good SWR curves for 80 and 40 meters on the 15 meter antenna hence the designation “6-band.” The system performed exceptionally well on all bands including 80 and 40 meters.  A number of contacts were made on all the covered bands even in the midst of heavy “pile-up” conditions.  The only time an antenna tuner (Palstar AT-500) was required was when the 15 meter antenna was used for 80 and 40 meters. Perhaps the most interesting characteristic of the antenna system was that you could place the parallel radiators only 1′ apart at the same height with almost no interaction between antenna elements.  Although the 17 meter band was not part of Field Day competition, we did make a number of contacts using the 17 meter antenna element.  The QTHs of the two most distant 17-meter contacts that we made were located in New Mexico and Italy.

N4gg

N4GG Antenna Array System

Note: The three antennas to be discussed below were all suspended “in line” at a height of about 25′ feet with antenna rope separating each antenna.

The second most interesting antenna was the G7FEK compact nested 1/4 wavelength Marconi designed to cover 80 – 10 meters.  It took a little work to get it properly tuned but it performed very well during Field Day.  We were able to make contacts on all the bands covered by the antenna.  A good manual antenna tuner (Palstar AT-500) was required for bands other than 80, 40, and 20 meters. Perhaps the most interesting thing about this antenna is the 80 meter band coverage in only 46′ and the use of ground radials.

G7FEK

lower end of G7FEK antenna (notice the ground radials);  the blue wire going upward is the 20 meter add-on element

The third antenna used during Field Day was a 20 meter delta loop fed at the lower end.  The antenna was originally designed to be hoisted to a height of 35′ above ground but the EZNEC+ v5 model predicted good performance at a lower height which better suited our mounting capabilities of around 25′. The antenna performed very well and proved to be the best overall antenna for 20 meters.  The antenna was much “quieter” than the other 20 meter antennas during band monitoring. 

20-m delta loop

 

20 meter delta loop antenna

The 20 meter delta loop EZNEC model can be downloaded from the link below.

20 meter delta loop EZNEC model

The fourth antenna used during Field Day was the “junior version” of the venerable old G5RV.  We wanted to see how the antenna would perform and also have the opportunity to compare it’s performance to the other antennas.  The antenna performed very well on 20 meters although not as well as the delta loop discussed previously.  It performed acceptably on the other bands it was designed to cover with the use of the Palstar AT-500 tuner. 

Note: Check out the useful article at the link below by VK1OD on how to properly tune a G5RV antenna.

Optimising a typical G5RV

We are eagerly looking forward to ARRL National Field Day 2012 and the prospect of evaluating a whole new suite of antennas.

Field Operating Tips – portable equipment mount + stand

Ever need a “grab and go” type of equipment mount?  Here's an idea for you.  Use an old tripod work lamp to make a portable equipment mount + stand that will hold your transceiver plus an external tuner.   The adjustable mount can be used for field activities and demos. 

Mount-1

                                      height of stand is adjustable

Mount-3

                                 sit back, relax, and operate in comfort

The “quick disconnect” feature enables the mounted equipment to be easily relocated for table top use or in a mobile environment.

Mount-2

             quick disconnect lets you easily move to a table or operate mobile

KI4PMI explains the portable mount + stand in detail.

 

73.

NC4FB & KI4PMI

Field Operating Tip – SHADE for your equipment table

Need shade over your folding equipment table without putting up a canopy or tent?  If you have an old beach umbrella laying around, you have options to provide that needed shade.  If you don't have a beach umbrella, you can buy one from Wal-Mart for around twenty dollars.

Shade

                                  Equipment table –  ARRL Field Day 2011

Option 1

Buy an EMT electrical conduit clamp that fits the umbrella pole. Drill holes in the edges of the table where you want to place the umbrella.  Attach the clamp to the table with a 1/4 X 20 TPI machine bolt and nut.  Slide the pole into the clamp and tighten it up.  The umbrella and clamp can be quickly and easily installed and removed.

Umbrella clamp

 

Option 2

Got an old C-clamp laying around?  Drill a hold through the middle of the “C” and attach a short piece of metal hanger tape to it using a 1/4” X 20 TPI cap bolt and nut.  Size the hanger tape to provide a snug fit for the umbrella pole.  Screw the clamp to the table and insert the umbrella pole.  This is a good option if you are using someone else's table because no permanent alteration to the table is required.

C-clamp-small

 

Option 3 –  (Industrial Strength)

Make yourself a detachable mounting bracket. All you need is a short piece of Superstrut®, a 1” clamp, and a couple of 1/4 X 20 TPI bolts, washers, and nuts.  All of the materials can be purchased at a local building supply outlet or home improvement store. 

                            KI4PMI explaining Option 3

Tip:  If you know an electrician, ask him if he has a short piece of scrap Superstrut® that he will give you.

Shade bracket small

                                  Superstrut® and matching clamp

Place the Superstrut® on the edge of the table and drill a couple of holes slightly larger than the diameter of the bolts through the  Superstrut® and the table.  You will probably want to center the bracket in the middle of the side. 

Umbrella 0

Attach the bracket to the edge of the table.

Umbrella 1

Umbrella 1a

Slide the umbrella into the clamp and tighten.

Umbrella 2

NC4FB & KI4PMI