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RW3XA’s 9 Band HF Vertical Antenna

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ANTENTOP- 01- 2005, # 007

RW3XAs 9 Band HF Vertical Antenna

 

L

Diameter
mm

Wire Diameter

mm

Coil Length

mm

Turns

Tap

L1*

35

4

45

7.5

3

L2*

35

4

55

8

4.5

L3

40

1.8

â/â

47

-

L4

40

1.8

â/â

35

6/11

L5

36

2.5

52

18.5

8.5

L6*

35

4

55

9

8.5

L7

32

2.5

50

13

4.5

Tuning.
  Tuning the matching network was achieved with help of AEA HF SWR Analyst and transceiver Yaesu FT-990AC with a priority of CW parts of HF bands. All initial adjustments were made without feed line, right at the out connector of the matching box. The Analyzer was used in general adjustment and selection of circuit types. It is necessary to bear in mind that the analyzer makes measurements at very small signals, accordingly, it is very sensitive to even greater signals coming from the air, so that can result in chaotic distortions of diagram of SWR. The adjustments of SWR were checked with transceiver finally, but they only have confirmed that all have been properly adjusted by means of the analyzer. The measurements with coax feed line showed even lower (approximately 10 percents) SWR due to the coax losses. It always is possible to adjust SWR down to 1:1, it only depends on how accurate you are and time spent. In my case SWR was down to 1:1.1/1:1.2, which seemed to be quite sufficient for the time being, hoping to improve it to best SWR later on, but this time hasn't come yet :-) Results. Though the theory predicts of low efficiency (especially on 1.8Mhz) and rather high radiation patterns in a vertical plane (on 18Mhz and above), operating experience has proven (I operate all HF bands since 1997 with this antenna) to be a success! It's hard to make impartial assessment to the quality of the omnidirectional aerial because it depends on too many factors, for example: propagation, output power, experience of a HAM and so on.

But those who used to chasing DX up to 2004 (I am not too active since than due to non HAMRADIO reasons), should remember my callsign, their assessment would be more convincing than my own... A direct comparison with other aerials in my case is impossible, since I have only one. However, indirect comparisons while poking pile-ups show high efficiency on all HF bands. 322/CW out of 325 countries by DXCC are worked with this aerial and 100W (> 90 % QSO, the others by means of 3xGU50-200W out amplifier only on 3.5/7/14MHz) since 1997 and up to 2004. Here (http://www.feerc.obninsk.org/rw3xa/ant/rw3xa.txt)

is my LOG quote. On lower bands the near field certainly is weaker (in comparison with the neighbour HAMs using horizontal antennas). The difference was especially appreciable at indirect comparison with R7000+, not in favor of the last. I took the matching box several times during field test with me, connecting it to the mast of similar size, but different diameter aluminum tubing (approximately in 1.5 times less). The aerial was erected right on the ground with an insulator and same radials as I use "on the roof position". In comparison with the aerial set up on the roof of 9 stores block of flats, SWR differed by 20 to 30 percents due to insignificant shift of its resonance. SWR tables of the aerial (on top concrete roof cover of the 9 stores block of flats) on separate HF bands are resulted below. In addition, lowering the signals by 10-20db of the other bands (i.e. if the network is switched to the other band) makes additional attenuation much useful: especially when the heavy QRM from my neighbour RA3XO while he is operating even the other band but his vertical is near my antenna, 12 meters apart. Here (see page 38) is RW3XW matching network box picture. This is the same idea, but his antenna is 18 meters high, though more effective on lower bands, but LC network is different, of course.

 

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August 3, 2016 16:41

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