Antennas

H
ere is some information on my antenna projects. I am no expert on anything to do with Amateur Radio, but I have had a lot of experience in getting odd-ball ideas working, experimenting and translating esoteric theories into practice.


Doublet for NVIS on 40m band

I rate this antenna as "Good - but noisy"

Configuration

  • 80m band doublet fed with 12m of 300 Ohm ribbon plus a G Whip 4:1 current balun (coax to rig)

  • 5m above ground level and orientated N-S. 

Performance

  • Can be matched with the internal tuner in my TS-570D on all bands from 80m to 10m. Will not match on 60m with a TS-590SG!

  • On 40m at short range (up to 100km) signals received with the doublet are c.1 to 2 S-points higher than with the OCFD.

  • On 40m at a distance of c.100~200km this aerial is about the same as my (higher) OCFD.

  • On 40m, for distances over 200km the doublet is 2 or more S-points less sensitive than the OCFD.

  • This indicates it is a little better for NVIS but . . . . . .

  • Noise (QRN) is higher than with the OCFD (approx 2 S-points).


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'Explorer-1'

I rate this antenna as "Very Good"

This is a mainstay multi-band antenna used for most of my one or two day portable operations, and for many Phoenix RG events, etc. It requires only one (9~11m) FG pole, but it does need a substantial support at the base. This is essentially the main antenna recommended by SGC for use with their Smart Tuners.

Configuration - Inverted 'L'

  • 23m wire running vertically up the FG pole and then sloping down from the top.

  • Aerial is raised using a pulley and halyard.

  • Single 31m radial on ground.

  • SGC SG-231 Smart Coupler. This is often positioned 1-1.5m above ground using electric fence posts, etc.

  • Earth spike (essential for the SG-231).

  • Single radial as long as possible and preferably longer than the antenna.
  • RF choke.

  • Barenco tripod base or drive-on plate.

Performance

  • The SG-231 does most of the hard work and, apart from occasional RF feedback issues, tunes quickly on all bands from 80m upwards if the antenna is long enough.

  • Mixed vertical and horizontal polarization is an advantage for inter-G contacts.

  • This antenna system has been used successfully for Special Events and other 'DX' activities.

  • Performs about the same as an Inverted Vee at the same height.

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'Explorer-2'

I rate this antenna as "Good"

This is a more compact version of the Explorer-1 which dispenses with the SG-231 Smart Coupler thus saving some weight and the need to power the coupler.

The version described here is a starting point for similar configurations

Configuration - Inverted 'L'

  • 16.1m (50ft) above ground element. 7~9m is vertical and the rest slopes down from the top of a FG pole.

  • Radials are used - on the ground - as follows:

    Antenna Band Radial 1
    Radial 2 SWR Typical


    Explorer-2
    16.1m Inverted 'L'
    7 MHz


    8.2m
    3.5m 1.2
    14MHz None 1.5
    18MHz 3.5m 1.1
    21MHz None 1.6
    25MHz
    3.5m
    1.3
    28MHz 2.2
 SWR measured at c. 50 Ohms using an MFJ Antenna Analyser
  • Earth spike – used as necessary.

  • 9:1 un-un close to ground (0.3 - 1.2m).

Performance

  • Polarization is mixed.

  • SWR (see table above) and impedances on 40m through to 10m are all within the matching range of my Icom IC-703, Kenwood TS-570D and are easily matched with the Yaesu FT-897D and LDG AT-897Plus and with a Yaesu FT-857D and FC-30 Tuner.

  • Stations that are S-9 on the OCFD are S7~S8 using this aerial, but this depends upon distance.

  • The small 'footprint' makes this a pretty stealthy antenna.

  • Efficiency is not going to be very high, but that is not the point of using this type of antenna.

  • Experiments with ground radials and over ground counterpoises continue.

'Schematic' for the Explorer-2 antenna

Click image for larger view



Please read the explanation above.

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'QD Explorer-1'

I rate this antenna as "Just Adequate"

I have used this QD antenna for QRP use with my Icom IC-703. It was a spur of the moment 'lash-up' using available materials. It works at QRP levels (10watts) but it isn't a top choice compared to either of the other 'Explorer' antennas. See the much better 'QD Explorer-2' below.

Configuration - Vertical

  • 5.2m spiral wound active element. Wire is very flexible, silicone rubber coated, which makes it easy to wind helically on to a 3m vertical section of FG pole. The rubber coating grips the pole nicely.

  • Fed at ground level with a 9:1 un-un, against one or two long radials (5m and 12m, or more).

  • Earthing is very helpful on most bands.

  • Supporting the short FG pole is not difficult.

Performance

  • SWR on all bands 80 to 10m is within the range of the ATU in my Icom IC-703.

  • This antenna is probably not very efficient - but that isn't the point.

  • Fuller testing is needed to evaluate performance in the field, but back garden tests show that it performs adequately:

  • S9 report from HB9 with 7W on 20m
  • S9 reports locally in the East Midlands (<50 miles) on 40m.


  New    'QD Explorer-2'   New
August 2015

I rate the antenna as "Good"

This is my latest QD antenna for QRP use with my Icom IC-703. It is much better performer than the QD Explorer-1.

It is still being tested, but initial results are encouraging, with some good "59" (some were genuine) reports from around Europe (using 10W and an Icom-703 during a very busy contest).

Configuration - Vertical

  • 9m active element.

  • Fed just above ground level (0.3-1.2m) with a 9:1 un-un.

  • One or two long radials - on the ground- are used as follows

Antenna Band Radial 1 Radial 2 SWR Typical

QD Explorer-2
9m vertical
7 MHz


8.2m


3.5m
1.2 – 1.6
14MHz 1.4
18MHz 1.3
21MHz None 1.8
25MHz 3.5m 1.3
28MHz 1.8

 SWR measured at c. 50 Ohms using an MFJ Antenna Analyser
  • Earthing is unhelpful on most bands.

  • Supporting the short FG pole is not difficult.

Performance

  • SWR (see table above) on all bands 80 to 10m is within the range of the ATU in my Icom IC-703.

  • This antenna is probably not very efficient - but that isn't the point.

  • This configuration is quite directional on the 40m band.

  • MMANA-GAL plots:

7.15oMHz


14.150MHz




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Off-Centre Fed Dipole for 80m to 10m

I rate this antenna as "Excellent"

Configuration - Dipole

  • Based on a 'Carolina Windom' off-centre fed dipole.

  • A third short (3.9m) length of wire, in parallel with the longer element gives 17m operation which was not possible with the 'straight' version. (Some people also lose the 15m band). 18mm dia.water pipe is used as spacers ( 150mm in length).

  • Capacity hats, just 100mm diameter were added to the ends of the antenna bringing the SWR on all bands down compared to the 'straight' configuration. The most significant effect of this has been to extend 80m coverage to the whole band (previously just the top 200KHz) and to reduce the SWR on 80m from 8:1 to <5:1.

  • The 100mm diameter capacity hats (still prototype versions) are fabricated from the ends of a large 'tin can' (canned grapefruit was the best choice) with a S-shaped hook brazed/soldered in the centre.

  • As an alternative to adding capacity hats, the two sides of the antenna can be 'linear loaded' by folding back about a metre (or more) spaced approximately 100m from the main wire. This shortens the antenna a little, which may also help to reduce the sag caused by the feedpoint balun.
  • Fed with 7m RG58 into a 200W G Whip 4:1 balun (originally an LDG shown in the photo) at the feed point. RG-213 is used elsewhere in the feed line.

  • Clip-on ferrites are used to control common mode currents (feedback) along the coax. Air-core choke coils are used just outside the shack.

  • Height above ground is 14 – 10m sloping to the south.

Performance

  • The antenna SWR is significantly less than 3:1 on 80, 40, 20, 17, 15, 12, 10 and 6m bands.

  • This means that the antenna was easily 'tuned' (i.e. matched) with my FT-897D and LDG AT-897Plus automatic ATU (and even a Yaesu FC-30 ATU).

  • A Kenwood TS-570D will also will 'tune' (match) using the internal auto ATU on all bands (including 80m).

  • Naturally, performance on 80m is limited by the relatively small length of the antenna, but on all other bands performance leaves little to be desired.

  • This antenna has been used regularly with very good results. Overall it seems 'well-behaved' with no particular issues or problems.

  • An antenna analyser is indispensable for setting up.




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