RadCom April 2024, Vol. 100, No. 4

20 April 2024 Regulars than a full-wave vertical antenna. Figure 4 shows the configuration of our modified vertical antenna. As we can see, there are now, in effect, three traps for this antenna. One is tuned to just below the 10m band to ensure that 10m operates as a half- wave. The 15m trap ensures the same for that band, albeit as a slightly-shorter antenna than a conventional half-wave. We also still have our 32-35 µ H coil which operates as a 20m trap and inductively loads 40m. Note that the overall length of the antenna is now shorter than our three-band original. Indeed, as I used un-insulated wire in the modelling, I would expect its final dimensions to be within the length (or very close) of a 10m fibreglass pole, thus enhancing its portability and reducing its visual impact. As we can see from Table 1 , through being further shortened to a length of just over a quarter- wavelength, 40m performance suffers a little, with gain reduced by a further 1.5dB. As 20m is also shortened through the loading effects of both the 15m and 10m traps, its gain is reduced slightly. However, the big advantage here is the transformation of 10m performance back into that of a half-wave vertical antenna, with low-angle gain subsequently improved by 3.6dBi. The 15m performance of this antenna, slightly shortened by the 10m trap, produces a respectable -6.1dBi gain at the 5° elevation angle. So, overall, this is a useful antenna for portable or small-space operating. The 40m performance is undoubtedly a compromise, but still compares favourably with base-loaded mobile whips or shortened ground verticals. Its performance on the 20m band is the shining star of the three bands, and, with some tweaking, we might be able to operate on the 15m band and improve 10m into the bargain. Signing off I have enjoyed writing antenna articles for RadCom, and would like to thank the editorial team for their help and encouragement over the past twelve months. I am now stepping aside from being the regular author of this column, and would wish that the next author enjoys the process of putting their thoughts into print as much as I have. If you are interested in writing this column, please email radcom@rsgb.org.uk Reference [1] Coil inductance calculator: https://66pacific.com FIGURE 4: The outline for our adjusted vertical, now incorporating 15m. Contest Calendar April 2024 RSGB HF Events Date Event Times (UTC) Mode(s) Band(s) Exchange Sat 6 - Sun 7 Apr FT4 International Activity Day 1200-1200 FT4 1.8-28 Report Mon 8 Apr 80m Club Championship 1900-2030 CW 3.5 RST + SN Wed 17 Apr 80m Club Championship 1900-2030 SSB 3.5 RS + SN Thu 25 Apr 80m Club Championship 1900-2030 PSK63, RTTY 3.5 RST + SN Sat 27 - Sun 28 Apr UK/EI DX CW 1200-1200 CW 3.5-28 RST + SN (UK/EI also send District Code) Mon 29 Apr FT4 Series 1900-2030 FT4 3.5-28 Report RSGB VHF Events Date Event Times (UTC) Mode(s) Band(s) Exchange Tue 2 Apr 144MHz FMAC 1800-1855 FM 144 RS + SN + Locator Tue 2 Apr 144MHz UKAC 1900-2130 All 144 RS(T) + SN + Locator Wed 3 Apr 144MHz FT8 AC (4 hour) 1700-2100 FT8 144 Report + 4-character Locator Wed 3 Apr 144MHz FT8 AC (2 hour) 1900-2100 FT8 144 Report + 4-character Locator Tue 9 Apr 432MHz FMAC 1800-1855 FM 432 RS + SN + Locator Tue 9 Apr 432MHz UKAC 1900-2130 All 432 RS(T) + SN + Locator Wed 10 Apr 432MHz FT8 AC (4 hour) 1700-2100 FT8 432 Report + 4-character Locator Wed 10 Apr 432MHz FT8 AC (2 hour) 1900-2100 FT8 432 Report + 4-character Locator Thu 11 Apr 50MHz UKAC 1900-2130 All 50 RS(T) + SN + Locator Tue 16 Apr 1.3GHz UKAC 1900-2130 All 1.3G RS(T) + SN + Locator Thu 18 Apr 70MHz UKAC 1900-2130 All 70 RS(T) + SN + Locator Tue 23 Apr SHF UKAC 1830-2130 All 2.3G – 10G RS(T) + SN + Locator Sat 27-Sun 28 MGM 1400-1400 MGM 50, 144 Report + 4-character Locator Best of the Rest Events Date Event Times (UTC) Mode(s) Band(s) Exchange (Info) Mon 1 Apr IRTS 70cm Counties 1300-1330 FM, SSB 432 RS + SN (EI & GI also send country) Mon 1 Apr IRTS 2m Counties 1330-1500 FM, SSB 144 RS + SN (EI & GI also send country) Wed 3 Apr UKEICC 80m 2000-2100 SSB 3.5 6-character Locator Sat 6-Sun 7 Apr SP DX 1500-1500 CW, SSB 1.8-28 RS(T) + SN (SP send Province code) Sun 7 Apr UKuG Low Band 1000-1600 All 1.3G-3.4G RS(T) + SN + Locator Sun 7 Apr WAB Data 1000-1400, 1700-2100 Data 3.5-14 RST + SN + WAB (two periods) Wed 24 Apr UKEICC 80m 2000-2100 CW 3.5 6-character Locator Sat 27 - Sun 28 Apr SP DX RTTY 1200-1200 RTTY 3.5-28 RST + SN (SP send Province code) Sat 27 - Sun 28 Apr UK/EI DX CW 1200-1200 CW 3.5-28 RST + SN (UK/EI also send District Code) Sun 28 Apr BARTG Sprint 75 1700-2100 RTTY 75Bd 3.5-28 SN For all the latest RSGB contest information and results, visit www.rsgbcc.org Ian Pawson, G0FCT