Portable End Fed Half WavePortable End Fed Half Wave Antenna

NO5V – Rick BonoOctober 15 2016October 15, 2016

OverviewOverview Develop a Portable End Fed Half Wave Antenna Portable and easy to deploy Multiband capability Resonant Antenna No Tuner Needed! Resonant Antenna – No Tuner Needed! Power handling limited by components

Ideally run it on 40m through 10m bandsIdeally run it on 40m through 10m bands For theory and discussion try Steve Yates (AA5TB)

website at: http://www.aa5tb.com/efha.html Many thanks for Steve for publishing his work. Much of this

presentation is based on his findings.

Voltage Current Distribution in a Dipoleg p

• A center fed dipole has it’s feed point at highest current and lowest voltage l di t l f d i t i d f d 72 Ohleading to a low feed point impedance of around 72 Ohms.

• A dipole fed on the end has a low current and maximum voltage leading to a high feed point impedance typically around 1800 to 5000 Ohms

End Fed Wire Antenna Deplo mentEnd Fed Wire Antenna Deployment• Deployed as any wire dipole• Simplifies feed line

arrangement and support requirements

• Pattern & gain is same asPattern & gain is same as the equivalent center-fed dipole configuration.

T o Approaches to the End Fed AntennaTwo Approaches to the End Fed Antenna Non-resonant Approach

Match the high impedance at the feed line with a 9:1 UNUN Match the high impedance at the feed line with a 9:1 UNUN. Use a NON-resonant length of wire i.e. the wire must not be a length

that is a half-wave multiple of any frequency you intend to use. Operates multiband with a tuner (tuner required!) See http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf for the

definitive homebrew instructions by the Emergency Amateur Radio Club in Honolulu

Resonant Approach (EFHW)Resonant Approach (EFHW) Match the impedance at the feed line with a 9:1 transformer. Use a ½ wave length of wire on operating band Operate single band at a timeg Use a variable capacitor to tune to resonance No external tuner needed as antenna is resonant (i.e., zero reactance) Focus of this presentation

Components of a End Fed Half Wave AntennaAntenna

•Radiator length is 1/2 λ of the operating frequency•Radiator length is 1/2 λ of the operating frequency.•Requires a 0.05 λ counterpoise•Transformer is a toroid with N:1 turns between primary and secondary•Capacitor should be in range to resonate at the operating frequency with the inductance of the secondary windings.

•Capacitor should be a high voltage type if running more than QRP levels

A Little MathA Little Math… We need to find the Capacitance needed to tune the

band of interest. The formula needed is based on a tuned LC tank circuit:

Basic EFHW Design SpreadsheetBasic EFHW Design SpreadsheetEFHW Matchbox DesignAmidon Toroid ParametersAl (T94‐2) 84 Min(pF) Max(pF)Al(T80‐2) 55 Capacitor (full) 9.58 310Al(T50‐2) 49

Secondary Turns T94‐2 T80‐2 T50‐2 2 Z 3 Z 4 Z12 1.2096         0.7920     0.7056                  8.22                        46.75                      6.00                        1,800.00     4.00            800.00        3.00          450.00     13 1.4196         0.9295     0.8281                  7.59                        43.16                      6.50                        2,112.50     4.33            938.89        3.25          528.13     14 1.6464         1.0780     0.9604                  7.04                        40.07                      7.00                        2,450.00     4.67            1,088.89     3.50          612.50     15 1 8900 1 2375 1 1025 6 58 37 40 7 50 2 812 50 5 00 1 250 00 3 75 703 13

T94‐2 CoreInductance (uH) Resonance Frequency (MhZ) Primary Turns Primary Turns Primary Turns

15 1.8900         1.2375     1.1025                 6.58                      37.40                    7.50                       2,812.50   5.00          1,250.00   3.75        703.13   16 2.1504         1.4080     1.2544                  6.16                        35.07                      8.00                        3,200.00     5.33            1,422.22     4.00          800.00     17 2.4276         1.5895     1.4161                  5.80                        33.00                      8.50                        3,612.50     5.67            1,605.56     4.25          903.13     18 2.7216         1.7820     1.5876                  5.48                        31.17                      9.00                        4,050.00     6.00            1,800.00     4.50          1,012.50 19 3.0324         1.9855     1.7689                  5.19                        29.53                      9.50                        4,512.50     6.33            2,005.56     4.75          1,128.13 20 3.3600         2.2000     1.9600                  4.93                        28.05                      10.00                      5,000.00     6.67            2,222.22     5.00          1,250.00 21 3.7044         2.4255     2.1609                  4.70                        26.72                      10.50                      5,512.50     7.00            2,450.00     5.25          1,378.13 22 4.0656         2.6620     2.3716                 4.48                      25.50                    11.00                     6,050.00   7.33          2,688.89   5.50        1,512.50, , ,23 4.4436         2.9095     2.5921                  4.29                        24.39                      11.50                      6,612.50     7.67            2,938.89     5.75          1,653.13 24 4.8384         3.1680     2.8224                  4.11                        23.38                      12.00                      7,200.00     8.00            3,200.00     6.00          1,800.00 25 5.2500         3.4375     3.0625                  3.95                        22.44                      12.50                      7,812.50     8.33            3,472.22     6.25          1,953.13 26 5.6784         3.7180     3.3124                  3.79                        21.58                      13.00                      8,450.00     8.67            3,755.56     6.50          2,112.50 27 6.1236         4.0095     3.5721                  3.65                        20.78                      13.50                      9,112.50     9.00            4,050.00     6.75          2,278.13 28 6.5856         4.3120     3.8416                  3.52                        20.04                      14.00                      9,800.00     9.33            4,355.56     7.00          2,450.00 29 7.0644         4.6255     4.1209                  3.40                        19.35                      14.50                      10,512.50  9.67            4,672.22     7.25          2,628.13 30 7.5600         4.9500     4.4100                 3.29                      18.70                    15.00                     11,250.00 10.00       5,000.00   7.50        2,812.5031 8.0724         5.2855     4.7089                  3.18                        18.10                      15.50                      12,012.50  10.33         5,338.89     7.75          3,003.13 32 8.6016         5.6320     5.0176                  3.08                        17.53                      16.00                      12,800.00  10.67         5,688.89     8.00          3,200.00 33 9.1476         5.9895     5.3361                  2.99                        17.00                      16.50                      13,612.50  11.00         6,050.00     8.25          3,403.13 34 9.7104         6.3580     5.6644                  2.90                        16.50                      17.00                      14,450.00  11.33         6,422.22     8.50          3,612.50 35 10.2900      6.7375     6.0025                  2.82                        16.03                      17.50                      15,312.50  11.67         6,805.56     8.75          3,828.13 36 10.8864      7.1280     6.3504                  2.74                        15.58                      18.00                      16,200.00  12.00         7,200.00     9.00          4,050.00 37 11 4996 7 5295 6 7081 2 67 15 16 18 50 17 112 50 12 33 7 605 56 9 25 4 278 13

Selected 18 turns primary and 2 turns secondary for 9:1 ratio with T94-2 toroid

37 11.4996      7.5295     6.7081                 2.67                      15.16                    18.50                     17,112.50 12.33       7,605.56   9.25        4,278.1338 12.1296      7.9420     7.0756                  2.60                        14.76                      19.00                      18,050.00  12.67         8,022.22     9.50          4,512.50 39 12.7764      8.3655     7.4529                  2.53                        14.39                      19.50                      19,012.50  13.00         8,450.00     9.75          4,753.13 40 13.4400      8.8000     7.8400                  2.47                        14.03                      20.00                      20,000.00  13.33         8,888.89     10.00       5,000.00 

Capacitor SelectionCapacitor Selection Capacitor must be selected to meet voltage

requirement and allow tuning range. A fixed capacitor can be used for single band operation A variable capacitor in the 10pF 320pF range can be A variable capacitor in the 10pF-320pF range can be

used for a multiband version Needs to handle ~650V for 100W operation

• I am using a NOS Alps from Ebay. Shi d f Th il d f $12 50Shipped from Thailand for $12.50 (surplus from my magnetic loop experiments)

•Measures 10pF to 310pFp p•Handles 650V - good for 100W

More on Capacitor Voltage RatingsMore on Capacitor Voltage Ratings

Table based on a 4 7K Ohm ImpedanceTable based on a 4.7K Ohm Impedance

Toroid TransformerToroid Transformer Amidon is your friend:

http://www amidoncorp com/specs/ http://www.amidoncorp.com/specs/ Tons of data on inductance, sizing etc

Good source for Amidon cores is http://www.alltronics.com/ Buy from their website or Ebay Storey y

For a fixed number of turns, the larger the core diameter the greater the inductance.

Recommend using a type 2 powdered Iron core for the hmatch

Iron Cores such as type 43 will NOT work as inductance of primary will be to high to tune!

For 9:1 ratio on a T94 2 core use 18 turns of #22 magnet For 9:1 ratio on a T94-2 core use 18 turns of #22 magnet wire for the secondary and two turns for the primary. Inductance will be ~2.7uH

Basic Components & Constr ctionBasic Components & Construction•Wind 18 turns of #22 Insulated Magnet wire as primary•Wind 2 turns of #22 insulated wire as secondarywire as secondary•Connect secondary to SO-239 Connector•Wire primary across Capacitor Terminals and also across a set of banana jacks.•Add a suitable knob to the capacitorcapacitor

Testing & Calibrating the MatchboTesting & Calibrating the MatchboxIf adjust your matchbox into a resistive load on the bench first andresistive load on the bench first and then adjust the antenna for a proper match then you should have a resistive match that will minimize

t th h th l dcurrent through the coupler and through the "counterpoise“ – Steve Yates AA5TB.

• Install a 4kOhm resistor across antenna terminals (for 9:1 ratio).

• Attach your antenna analyzer and adjust for the first band frequencyadjust for the first band frequency

• Adjust knob until reactance goes to zero at that band’s frequency.

• Mark knob position for that bandp• Repeat for the additional bands.

Calibration Resistor for other T rn RatiosCalibration Resistor for other Turn Ratios

Za = antenna's resistive impedance then, Turns Ratio = √(Za/50)

6:1 for Za = 1800 ohms6:1 for Za 1800 ohms 7:1 for Za = 2450 ohms 8:1 for Za = 3200 ohms 9:1 for Za = 4050 ohms 10 1 f Z 5000 h10:1 for Za = 5000 ohms

Final Trimming for 20m BandFinal Trimming for 20m Band For 20m start with a wire 468/freq(MHz) long. ~33 feet on 20m. I

am using #22 insulated speaker wiream using #22 insulated speaker wire. Cut a counterpoise that is 33/10 = 3.3 ft Attach both to match box and orient antenna as desired (I setup

ti ll )vertically). Antenna wire on the red jack and the counterpoise on the black jack.

Adjust knob to band setting previously determined for 20m Connect Antenna analyzer and measure at frequency of interest Trim length of wire until the antenna shows zero reactance at

the frequency of interestq y SWR will drop as you trim – resonance is more important than a

1:1 SWR!

20m SWR and Xs Chart20m SWR and Xs Chart

Antenna deplo ed as a Vertical on 20mAntenna deployed as a Vertical on 20m

Make a simple Common Mode choke by wrapping about six or sevenMake a simple Common Mode choke by wrapping about six or seven turns of coax at the feed point.

Portable DeploymentPortable Deployment

Stations orked D ring Initial TestingStations worked During Initial Testing•Tested portable on FT-817ND with Amplifier running 45W SSB on 20m•Made 16 contacts during Washington QSO party•Made 16 contacts during Washington QSO party. •Made two DX contacts to Brazil and Costa Rica•No real difficulty making contacts•Europe comes in clearly when propagation opens up. y g

•Was not able to make QSO as pile-ups were difficult to break on 45W•Low background noise and good reception

Multiband OperationMultiband Operation

Use barrel connectors and insulators to form links.

Engage links to make wire longer or shorter for band changes g g g gthen adjust the variable capacitor to the appropriate band

ConclusionsConclusions•Basic design goal of an easily deployed, portable HF antenna was accomplished•Easy to build and low cost resonant antennaEasy to build and low cost resonant antenna•Simplifies deployment

•Future work:R d M t hb t d t it d t d b d•Redo Matchbox to reduce stray capacitance and extend band range

•Tune additional bands using links

Thank Yo !!!Thank You!!!Questions?