G5RV
10 To 160 meters double size G5RV total length 204ft (102 ft a leg ) 61ft 300Ohm slotted ribbon feeder
[to make matching section] resonant on 40 meters
10 To 80 meters full size G5RV total length 102ft (51ft a leg ) 30ft 6inch 300Ohm slotted ribbon feeder
[to make matching section] resonant on 20 meters
10 To 40 meters half size G5RV total length 51 feet ( 25ft inch a leg ) 15ft 3inch 300Ohm slotted ribbon feeder
[to make matching section] resonant on 10 meters
Results for Modelling a double size G5RV (204ft) doublet mounted 10m above average ground.
This analysis looks at a typical installation of a double sized G5RV aerial mounted 10m above average ground and fed with 61ft of 300 Ohm feeder (as recommended in some web site references) followed by 32ft of RG58 Coax back to the Tx. No Balun used.
The aerial was modelled in MMANA to establish the center feed point impedances and a program called TLDetails used to calculate the feeder impedance transformation values.
Impedances at Aerial Centre
| BAND (Mhz) | Resistive Element (R Ohms) | Reactive Element (jx Ohms) | SWR in 300 Ohms |
| 1.91 | 9.59 | -362 | 279 |
| 3.75 | 341 | 1864 | 211 |
| 7.05 | 91.12 | -64.6 | 3.4 |
| 14.15 | 2939 | 326 | 59 |
| 18.12 | 738.3 | 951 | 6.83 |
| 21.2 | 145.7 | -349 | 5.1 |
| 24.94 | 600 | -1209 | 10.45 |
| 28.5 | 2103 | 808 | 8.073 |
SWR (50 Ohms) at the end of 61ft of 300 Ohm balanced feeder (Vf = 0.8, K1 0.109, K2 0.0)
| BAND (Mhz) | Resistive Element (R Ohms) | Reactive Element (jx) Ohms | SWR in 50 Ohms | Feeder Loss (dB) |
| 1.91 | 8.95 | 15.31 | 6.1 | 3.59 |
| 3.75 | 12.79 | 30.34 | 5.41 | 1.85 |
| 7.05 | 93.12 | 16.37 | 1.94 | 0.344 |
| 14.15 | 116.45 | -434.82 | 32.87 | 1.041 |
| 18.12 | 102.17 | 274.71 | 17.24 | 0.921 |
| 21.2 | 69.01 | -2.49 | 1.38 | 0.787 |
| 24.94 | 622.12 | 969.8 | 42.7 | 1.53 |
| 28.5 | 53.59 | -95.44 | 4.92 | 1.24 |
SWR (50 Ohms) at the end of a further 32ft of RG58 Coax
| BAND (Mhz) | Resistive Element (R Ohms) | Reactive Element (jx) Ohms | SWR in 50 Ohms | Feeder Loss (dB) |
| 1.91 | 23.97 | 57.65 | 5.14 | 0.780 |
| 3.75 | 151.64 | -119.25 | 5.04 | 0.401 |
| 7.05 | 32.28 | 16.04 | 1.8 | 0.519 |
| 14.15 | 4.92 | -11.31 | 10.69 | 5.21 |
| 18.12 | 12,51 | 44.06 | 7.21 | 3.84 |
| 21.2 | 61.21 | -10.87 | 1.32 | 0.75 |
| 24.94 | 5.74 | -8.8 | 8.95 | 6.84 |
| 28.5 | 119.9 | 74.2 | 3.44 | 1.99 |
Results:
At the end of the 50 Coax an ATU will be required on all bands except 15m and possibly 40m.
All other SWR values are within the range of most manually tuned ATU’s
Internal ATU’s may struggle on some bands.
The amount of Power lost and radiated due to feeder SWR values is shown in the following table: (Assuming 100Watts input)
| BAND (Mhz) | Total Losses (inc 0.5dB ATU Loss) | Power Lost | Radiated Power (Neglecting Ant Gain) |
| 1.91 | 4.87 | 67.42 | 32.58 |
| 3.75 | 2.75 | 46.9 | 53.1 |
| 7.05 | 1.36 | 26.9 | 73.1 |
| 14.15 | 6.75 | 78.87 | 21.13 |
| 18.12 | 5.26 | 70.22 | 29.78 |
| 21.2 | 2.03 | 37.34 | 62.66 |
| 24.94 | 8.87 | 87.03 | 12.97 |
| 28.5 | 3.73 | 57.64 | 42.36 |
The most efficient band is 40m where 73.1% of the power is radiated
The worst band is 12m where only 12.97% of the power is radiated
The efficiency on Top Band is only 32.58%
G Boull G4NVH August 2009
W3DZZ Antenna
W3DZZ Antenna
Feed point
--------------***-------------------0 0--------------------***--------------
22’ 0” trap 33’3” 33’3” trap 22’ 0”
traps are 7.1 MHz.
The feed point may consist of a balun, coaxial or twin centrepiece.
It is preferable to use twin feed, with a balun at the output of the ATU, if it does not have a balanced output, but if you must use coax, then a RALCOMM balun is strongly advised. In any case the feeder length should be 75’ or 91’ feet optimum length.
The lengths given are approximate and may need to be adjusted to suit your particular location.
Using a GDO, or your transceiver, set to 7.05 MHz. adjust the inner legs to resonance. Adjust the outer legs for resonance at the centre of your favourite portion of the 80m band.
The feed point impedance will vary according to the configuration of the antenna, but will provide a good match to the 50 ohm source.
The antenna may be set up as an ‘inverted v’ or horizontal dipole, but not sloping from one end to the other. If you are short of space, the antenna may be folded once or more, but each fold should not be greater than 90 degrees.
This is taken from the instructions I had with my RALCOMM traps, purchased at a rally, but as you know from the W3DZZ
I have in my garden, some liberties can be taken and it will still give a good account of itself.
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