Archive for the 'amateur radio aids' 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.

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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)

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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)

 

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300 ohm window/ladder line

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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.

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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.

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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.

40-meter Rectangular Loop Antenna

Looking for a 40-meter antenna that provides good local and regional coverage during the day and good DX capability at night?  Build yourself a 40-meter rectangular loop antenna.  It performs well at a height of 25’.  Each side is 57’ 3” long and the ends are 8’ wide.  The antenna uses 300-ohm twin-lead transmission line and is fed at the mid-point of one of the long sides.  A 4:1 current balun is connected to the transmission line at the source end.  An AIM-4170C was used to analyze the completed antenna.  The results are included below the predicted SWR curve produced by the EZNEC modeling program.

Materials

  • (2) 1 X 2 X 8 treated furring strips (end supports/spreaders)
  • (8) 2 1/2”  long 1/4″ X 20 eyebolts + nuts (galvanized or stainless steel)
  • (2) double-ended swivels (galvanized or stainless steel)
  • 300 ohm twin-lead (transmission line)
  • 4:1 current balun
  • (4) insulators
  • ~ 131’ #14 AWG THNN stranded wire
  • antenna rope

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An EZNEC mode of the antenna is available at the link below.

EZNEC model 40-meter rectangular loop

An EZNEC model of the antenna turned vertically is available at the link below.

EZNEC model 40-meter rectangular loop (vertical)

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KI4PMI operating with 40 meter rectangular loop antenna

40-meter Tall Horseshoe Antenna

Really short on horizontal space but still want to operate on 40 meters?  Have some trees in the back yard with least 25 feet between them?  Take a look at a 40-meter “tall horseshoe antenna.”  The antenna performs relatively well at a height of 35’.  If you have at least 40’ between trees, a variant of the antenna performs even better.

Materials

~ 70’ #14 AWG THNN stranded wire

(2) insulators (ends of horizontal radiators)

(2) weights (ends of vertical radiators)

antenna rope

(1) 1:1 current balun (antenna feed point)

50-ohm coax transmission line

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An EZNEC model of the antenna can be downloaded from the link below.

40 meter tall horseshoe antenna

A variant of the 40 meter tall horseshoe antenna antenna is described below. 

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An EZNEC model of the 40 meter tall horseshoe antenna variant is available at the link below.

variant 40 meter tall horseshoe antenna

Want to add 20 meters?  Take a look at yet another variant of the antenna.  Add a 4’ spreader to each end of the antenna and use antenna rope to center the 20 meter portion.  Separate the 20 meter configuration from the 40 meter configuration by 3’  horizontally.  Feed each antenna separately with 50-ohm coax transmission line. If you use a coax switch, you can eliminate the 1:1 current baluns at the antenna feed points by placing a coax line isolator between the coax  switch common port and your antenna tuner.  Be sure to properly orient the line isolator (appropriate end toward antenna) per manufacturer’s instructions.

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An EZNEC mode of the 20 meter addition is available at the link below.

EZNEC model for 20 meter addition

 

 

 

 

 

 

 

License Exam Questions with Diagrams

Use the link below to concentrate on exam questions that refer to diagrams.

exam questions that refer to diagrams

HF Tape Measure Horizontal Dipole Antenna

Looking for an interesting low-cost project?  How about building a dipole antenna using two measuring tapes? The antenna can be manually adjusted for good SWR curves covering 6 meters through 40 meters without being lowered.  During the calibration step, the optimum tape lengths for each band are recorded.  The recorded lengths are used to adjust the antenna when bands are changed. A piece of string is attached to the bottom of each tape carrier to act as an indicator of extension length.  Markers are placed in the ground under the antenna for each band.  When the string length indicator is aligned over the band marker, the correct length for the band has been selected.  The completed antenna has a 1:1 current balun connected at the feed point and uses a 50' RG-8X coax transmission line.

Antenna-resized

HF Tape Measure Antenna

Mt4-resized

HF Tape Measure Antenna (6 meter configuration)

Several important mechanical factors should be addressed in order to make a functional antenna from measuring tapes.  Weight is important!  Keep the total weight of the components as low as possible.  Tapes sag after they are extended a few feet from the case.  Provision should be made to provide enough support over the tape span to handle the sag.  Retraction can be an issue if tapes with weak springs are used.  Be sure to test each tape measure to insure complete extension as well as retraction can be smoothly accomplished before using them.

We found that 33' X 1” steel measuring tapes (Item # 41255) from Harbor Freight Tools, Inc. were good choices for the antenna. The tapes were purchased at a cost of $3.99 + tax each.

Tape

Item # 41255 (source: Harbor Freight Tools, Inc.)

Carriers for the tape measures need to be fabricated.  We started with metal rafter ties and used a vise to bend them into the proper shapes to make carriers.  Pieces of flat aluminum stock were cut to size and riveted to the lower ends of the shaped pieces to make bottoms.  The top ends of the shaped pieces were drawn together and secured with short bolts through clothesline pulleys.  The pulleys ride on the antenna support rope that suspends the antenna.  A continuous loop of string was attached to either ends of each carrier to provide a way to extract and retract the tapes.

Carrier-resized

Metal rafter tie shaped into 1/2 of tape measure carrier

Carrier-2

Tape measure carrier with pulley

The next item to be addressed is the antenna support system.  We used 1 1/2” diameter Schedule 40 PVC pipe to make (2) end supports and a center support.  Metal eye bolts were used to provide “tie points” for the ropes.  An adjustable sleeve for the connection points between the antenna radiators and the balun leads was made by slicing a 2” diameter piece of Schedule 40 PVC pipe into two pieces that fit snugly around the center support.  Metal hose clamps secure the sleeve to the center support at the proper point to insure horizontal alignment with the carriers.  Eye bolts were attached to the bottoms of the end supports and the center support to provide “tethers”  for additional stability in high wind situations.  Four plastic shower curtain rings were used on each side to provide support for the tapes as they are extended.  The rings were threaded together with string so they deploy to provide support as the tapes are extended.  Be sure to size the loops between the rings to insure horizontal alignment.

Center-support

Center support with adjustable alignment sleeve

End-support

End support

Mt0-resized

Shower curtain rings for support

YouTube Movie Clip – Construction Details

Antenna Analyzer Results
(AIM 4170C analyzer; AIM-486 software release)

40 meter SWR curve

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17 meter SWR curve

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10 meter SWR curve

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6 meter SWR curve

6m-swr-11-02-2011-resized

The completed antenna met our design objectives.  It covered 6 meters –  40 meters with good SWR curves and can be adjusted for each band without being lowered.  We found the antenna to be exceptionally quiet on all bands compared to the wire antennas that we have previously constructed.  Apparently due to the unextended portions of tape, the lengths to achieve optimum SWR curves for all bands except 40 meters were shorter than they would have been for wire antennas cut to the correct lengths.  The antenna can also be used in OCF configurations.  

During a brief operational testing period, the following SSB contacts were made running 85 – 100 watts of power.

17 meters:  Abergavenny, Wales; Oberlin Park, KS;  Las Vegas, NV

10 meters:  Puntarenas, Costa Rica

If you build a tape measure antenna for yourself, Email us and let us know how you like it.

73.

KI4PMI & NC4FB

 

Technician License Exam Study Plan

Need a study plan to help you get ready for the Technician license exam?  This study plan will prepare you to pass the exam in approximately ten weeks?

The Technician license exam consists of 35 questions selected from a pool of 396 questions.  The question pool is divided into 10 subelements (T0–T9).  Subelements are further divided into a total of 35 groups (topics).  One exam question is randomly selected from each group. You must answer a minimum of 26 questions correctly on the exam to obtain your Technician license.

The NCVEC technician license exam question pool can be viewed at the link below.

NCVEC technician license exam question pool

The syllabus for the technician license exam can be viewed at the link below.

technician license exam syllabus

The diagrams referred to by technician license exam questions can be viewed at the link below.

technician license exam diagrams

The following table shows the number of questions in each subelement and the number of exam questions randomly taken from each subelement.  Do not attempt to memorize the questions and answers as they appear in the NCVEC question pool.  The questions and answers will be shuffled on the actual license exam.

T1 T2 T3 T4 T5 T6 T7 T8 T9 T0 TOT
68 33 33 22 45 47 47 44 22 35 396
6 3 3 2 4 4 4 4 2 3 35

STUDY PLAN

Week 1

Generate listings of the questions and correct answers for subelements T0 and T9 using the link below.  Read over the listings several times.  Then generate listings of questions and all answer choices including correct answers using the same link.  Read over the listings several times.

generate subelement questions & answers

SYLLABUS STUDY APPROACH: If you decide to follow the exam syllabus, use the link below to view group flashcards. The difference between the group flashcards and the subelement flashcards is the number of questions contained in each.  Groups contain smaller numbers of questions than subelements. Open the exam syllabus in a separate browser window and refer to it as you view the group flashcards for subelements T0 and T9.

syllabus group flashcards

When you complete each group, test yourself on it using the link below.

syllabus group tests

SUBELEMENT STUDY APPROACH:  If you decide to study at the subelement level, use the flashcards at the link below to view the questions and correct answers for subelements T0 and T9.  There are options to view the questions and all answer choices including the correct answer or the question and only the correct answer.  Use the check my answer option for graded flashcards.

subelement flashcards

Regardless of which study approach you elected to use, when you are ready to test yourself on subelements T0 and T9, use the link below.  Continue testing yourself on the subelements until you are consistently scoring 85 or higher on the tests.

subelement tests

BOOST your license exam score

Accumulate the missed question numbers from subelement tests in a file named subelements.txt.  At the end of the subelement tests, a list of missed + unanswered questions is displayed.  Copy and paste the question numbers (one per line) into the review file for later use with the question review facility at the link below.  Don't worry about duplicate question numbers, the review facility will eliminate them.  Just keep adding missed question numbers to the file.

question review facility

Example:  You miss the following questions on a subelement T0 test.  The missed question numbers appear at the bottom of the test.

T0A04
T0A07
T0A09

Copy the question numbers and store them in the review file.  When you are ready to review the questions, open the file, copy the question numbers, and paste them into the form provided with the review facility.

Weeks 2–9

Repeat the same steps used during week 1 for weeks 2–9 using the schedule in the table below.

Week Subelement
2 1
3 2
4 3
5 4
6 5
7 6
8 7
9 8

 

Week 10

Week 10 is dedicated to taking sample Technician license exams using the link below.  Continue taking sample exams until you are consistently scoring 85 or higher on every exam.  Accumulate the missed question numbers in a file named Tech.txt.  Periodically use the question review facility to test yourself on the missed question numbers. 

sample technician license exams

Use the link below to concentrate on questions that refer to diagrams.

tests with nothing but questions that refer to diagrams

When you are consistently scoring 85 or higher on every sample exam, you are ready for the Technician license exam.

Good luck on your exam.  Be sure to Email me and let me know how you did on the exam.

 

73.

 

Compact Restricted Space
40 Meter Wire Antenna

Need an inexpensive easy to construct compact 40 meter wire antenna that will fit in a 20 feet by 20 feet space?  One that can be squeezed into a suitably sized attic? The antenna requires a good tuner, provides a useable SWR curve over most of the 40 meter band (7.0 MHz –  7.3 MHz), and has a good radiation pattern and gain at a height of 25 feet.  A 1:1 current balun is needed at the feed point which is located 12.1′ (see diagram below) along one of the sides connected to an angled end.  The transmission line is 50 ohm coax.

If you primarily operate CW, the SWR curve can easily be optimized for (7.0 –  7.125 MHz) by shortening the angled ends.  The antenna is also useable on the 15 meter band (21.0 –  21.45 MHz).  A variant of the antenna can be installed in a backyard with the addition of end supports/spreaders.   Check the description of the variant at the bottom of the article.

40m-compact-view

Compact Restricted Space 40 Meter Wire Antenna Diagram

40m-swr

Compact Restricted Space 40 Meter Wire Antenna SWR Curve

40m-pattern

Compact Restricted Space 40 Meter Wire Antenna Radiation Pattern

The EZNEC v.5 model for the antenna can be downloaded from the link below.

EZNEC model

Variant –  Compact Restricted Space 40 Meter Antenna

The variant utilizes drooping ends instead of angled ends.  The other dimensions and feed point placement remain the same.  The variant exhibits a slightly better SWR curve over the 40 meter band.

The end support/spreaders can be constructed using treated 2” X 2” X 8′ treated furring strips, bolts, and eyebolts.  A total of (8) furring strips will be needed. Four strips for each end.  Two furring strips are used as center supports/extenders for each end support/spreader to achieve the required width. Bolts are used to join the furring strips.  Eyebolts are used to connect the insulators for the radiators and to provide hoist points on the ends of the supports/extenders to raise the antenna.  Eye bolts can be attached to insulators to weight down the drooping ends of the antennaBe sure to use galvanized or stainless steel hardware.

Variant –  Compact Restricted Space 40 Meter Wire Antenna Diagram

40m-variant-swr

Variant –  Compact Restricted Space 40 Meter Wire Antenna SWR Curve

Variant 40 meter pattern

Variant –  Compact Restricted Space 40 Meter Wire Antenna Radiation Pattern

The EZNEC v.5 model for the variant can be downloaded from the link below.

EZNEC variant model

 

 

Center-Fed Wire Dipole Antenna Tuning Calculator

Ever need a way to estimate the amount of wire to add  to or remove from a center-fed wire dipole antenna to achieve resonance at a desired frequency?  If your antenna analyzer indicates a resonant frequency below the desired frequency, the antenna is too long and needs to be shortened.  If the analyzer indicates a resonant frequency above the desired frequency, the antenna is too short and needs to be lengthened.  A good rule of the thumb when constructing center-fed wire dipole antennas is to cut the radiating arms a little long so they can be trimmed for resonance at the desired frequency.  It is easier to remove wire than to add it.

How do you estimate the amount of wire to add or remove to achieve resonance at a desired frequency?  Follow the steps listed below.

  1. Calculate the radiator length for the upper limit of the band using the formula 468/upper limit frequency in MHz.
  2. Calculate the radiator length for the lower limit of the band using the formula 468/lower limit frequency in MHz.
  3. Calculate the difference in lengths between the upper and lower limits of the band by subtracting the upper limit frequency length from the lower frequency length.
  4. Calculate the frequency width of the band by subtracting the lower frequency limit from the upper frequency limit.
  5. Divide the frequency width by the length difference yielding kilohertz /unit of length.
  6. Calculate the difference between the desired resonant frequency and the observed resonant frequency by subtracting the desired resonant frequency from the observed resonant frequency.
  7. Divide the frequency difference by the kilohertz/unit of length yielding the estimated amount of adjustment needed to achieve resonance at the desired frequency. A positive value indicates the amount to add and a negative value indicates the amount to remove.  Be sure to divide the estimated value in half and make the adjustment to both radiators.

Note:  A diagram of the amateur radio bands (courtesey of ARRL) is available at the link below.

ARRL ham band diagram

Example:  You want your antenna to be resonant at a frequency of 7.2 MHz (40 meter band).  You observe a resonant frequency of 7.05 MHz on your antenna analyzer. The observed resonant frequency is below the desired frequency which indicates the antenna radiators are too long.  The upper limit for the 40 meter band is 7.3 MHz and the lower limit is 7.0 MHz.  The calculated radiator length at the upper limit of the 40 meter band is 468 / 7.3 or 64.110 feet.  The calculated radiator length at the lower limit of the 40 meter band is 468 / 7.0 or 66.857 feet.  The difference in lengths is 2.747 feet or 32.964 inches.  The frequency width of the 40 meter band (7.3 MHz –  7.0  MHz) is .3 MHz or 300 KHz.  The kilohertz per unit of length (inches) is 300/32.964  or approximately 9.101.  The difference between the desired frequency and the observed frequency (7.2 –  7.05) is .15 MHz or 150 KHz.  The estimated amount of adjustment needed is (150 / 9.101) or 16.482 inches.   Divide 16.482 inches in half (8.241 inches) and adjust each radiator by that amount. Note: You should remove at least 5% less than the estimated amount from the radiators and check the antenna again with your analyzer.  It is easier to remove wire than to add it.  Continue incremental adjustment of the radiators until resonance is achieved at or near the desired frequency.

Use the tuning calculator at the link below to compute the estimated amount of adjustment needed to achieve resonance at a desire frequency.

center-fed wire dipole antenna tuning calculator

Good luck with your antenna projects.

73.

NC4FB