{"id":279,"date":"2020-02-14T23:22:23","date_gmt":"2020-02-14T23:22:23","guid":{"rendered":"http:\/\/bytewyse.org\/?page_id=279"},"modified":"2020-02-15T13:48:49","modified_gmt":"2020-02-15T13:48:49","slug":"4-band-trap-inverted-v-antenna","status":"publish","type":"page","link":"https:\/\/bytewyse.org\/?page_id=279","title":{"rendered":"4-Band Trap Inverted V Antenna"},"content":{"rendered":"\n

Introduction<\/strong><\/p>\n\n\n\n

This trap antenna is\ndesigned to cover the 10m-15m-20m-40m bands and resonate on the PSK31\/FT8\nfrequencies [1] and Table 1 with operation on SSB QRP frequencies desirable.<\/p>\n\n\n\n

The building of the\nantenna was inspired by [2] and [3].<\/p>\n\n\n\n

Summary<\/strong><\/p>\n\n\n\n

The write up here\nrepresents the third iteration of the design. \nIn the first iteration the traps were wound for resonance a few 100’s of\nkHz below the edge of the higher band and weren’t particularly well matched for\nresonant frequency.  The antenna\nresonated low on all bands and the elements required significant trimming to\nget resonance anywhere near the FT8 segments of the bands.  This, combined with the fact that the VSWR\nwas still unacceptably high on 15 m \nmeant that another iteration was required.<\/p>\n\n\n\n

For the second\niteration I adjusted the traps to resonate within a few kHz of the lower edge\nof the higher band and made sure that each trap pair was resonant to within a\nfew kHz.  The measurements for the\nadjusted traps are shown below in Figures 1 to 3.  The antenna was re-constructed and due to the\nexcessive pruning from the first attempt the antenna was now measured to be\nresonant at too high a frequency on all bands with unacceptably high VSWR on\nthe FT8 frequencies.<\/p>\n\n\n\n

It was calculated that simply replacing  the 10 m elements with the original calculated length would bring all bands to resonance at the lower end of each band. Plots of VSWR and |Z| having replaced  the 10 m elements are shown below in Figures 5 to 8. <\/p>\n\n\n\n

Trap Construction<\/strong> <\/p>\n\n\n\n

The traps were built\nusing T106-6 Iron Powder torrid cores [4] wound with the appropriate number of\nturns of 14 SWG wire [5]. Calculation of the number of turns required was from\na spreadsheet created by myself [6] to analyse “what-if” for different\ncores and inductor\/capacitor ratios. Resonance was achieved by using 100 pF\nSilver Mica capacitors [7] in series\/parallel combination to give between 50 pF\nand 200 pF as required to achieve resonance on the desired band.<\/p>\n\n\n\n

Resonance just below\nthe bottom of each band was chosen for the reasons outlined in [3]. Furthermore\noperation off the resonant frequency reduces the circulating voltages in the\nresonant circuit and hence the voltage requirement on the capacitors.<\/p>\n\n\n\n

Trap Measurement<\/strong><\/p>\n\n\n\n

Traps were measured on the SARK110 using |Z| and <Zs as described on the SARK110 website.  SARK Plots was used to control the SARK110 with the results of the measurements being saved to Excel for importing into Zplots [9] for additional analysis. The figures below show the resonance for each trap pair:<\/p>\n\n\n\n

\"Machine
Figure 1: Resonant frequencies 27.952 MHz & 27.980 MHz (delta 28 kHz) <\/figcaption><\/figure>\n\n\n\n
\"Machine
Figure 2: Resonant frequencies 20.968 MHz and 20.967 MHz (delta 1 kHz) <\/figcaption><\/figure>\n\n\n\n
\"Machine
Figure 3: Resonant frequencies 13.992 MHz and 13.986 MHz (delta 6 kHz) <\/figcaption><\/figure>\n\n\n\n

Variation in |Z| between trap pairs is likely down to slight variations in the winding and construction of the traps but they are resonant within less than 30 kHz difference between each pair.<\/p>\n\n\n\n

Having tuned the traps using my SARK-110 vector impedance analyser the cores were then mounted on bases cut from FR4 PCB drilled appropriately as per the template diagram below [8]  to accept the core and antenna elements.<\/p>\n\n\n\n

\"80.00
Figure 4: Drilling Template for Trap Mount <\/figcaption><\/figure>\n\n\n\n

Antenna Construction<\/strong><\/p>\n\n\n\n

The antenna centre\nis an LDG RBA 1:1 balun mounted on “T” piece mounded from Polymorph\nplastic appropriately drilled to mount the balun and thread the antenna wire\nthough. Antenna elements are constructed from coated Flexweave style wire from\nNevada Radio (UK). The initial element lengths were calculated for a standard\nwire dipole in the knowledge that there would be some significant trimming to\ndo to compensate for the loading effects of the traps.<\/p>\n\n\n\n

\n FT8<\/strong>\n <\/td>\n PSK31<\/strong>\n <\/td>\n SSB QRP<\/strong>\n <\/td>Length per leg (m)<\/strong> <\/td>\n Delta (m)<\/strong>\n <\/td><\/tr>
\n 7.0740\n <\/td>\n 7.035\n <\/td>\n 7.090\n <\/td>\n 10.08\n <\/td>\n 5.01\n <\/td><\/tr>
\n 14.074\n <\/td>\n 14.070.150\n <\/td>\n 14.285\n <\/td>\n 5.07\n <\/td>\n 1.68\n <\/td><\/tr>
\n 21.074\n <\/td>\n 21.080.150\n <\/td>\n 21.285\n <\/td>\n 3.38\n <\/td>\n 0.84\n <\/td><\/tr>
\n 28.074\n <\/td>\n 28.120.150\n <\/td>\n 28.360\n <\/td>\n 2.54\n <\/td>\n 0\n <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

 Table 1:  FT8\/PSK31\/SSB QRP Frequencies (MHz) and\nCalculated Antenna Element Lengths<\/strong><\/p>\n\n\n\n

Antenna Tuning<\/strong><\/p>\n\n\n\n

The plots were saved on the SARK-110 and downloaded to a computer for further analysis in Zplots by AC6LA [9].  The antenna is tuned starting with the 10m elements checking for lowest VSWR on the SARK-110 for the frequency of interest and progressing to each lower frequency.  Plots below for each frequency:<\/p>\n\n\n\n

\"Machine
Figure 5: 10m VSWR<\/strong> <\/figcaption><\/figure>\n\n\n\n
\"\"
Figure 6: 15m VSWR<\/strong> <\/figcaption><\/figure>\n\n\n\n
\"Machine
Figure 7: 20m VSWR<\/strong> <\/figcaption><\/figure>\n\n\n\n
\"Machine
Figure 8: 40m VSWR<\/strong> <\/figcaption><\/figure>\n\n\n\n

Analysis<\/strong><\/p>\n\n\n\n

10 m, 15 m and 40 m\nare slightly low in resonance and 20 m is \nabove FT8 frequency.  Trimming 10\nm will likely bring 15 m to resonance on FT8 frequency and move 20 m slightly\nhigher, 40 m may require additional trimming.<\/p>\n\n\n\n

\n F1 (MHz)<\/strong>\n <\/td>\n F2 (MHz)<\/strong>\n <\/td>\n Delta (MHz)<\/strong>\n <\/td><\/tr>
\n 27.721\n <\/td>\n 28.000\n <\/td>\n 0.279\n <\/td><\/tr>
\n 20.967\n <\/td>\n 21.128\n <\/td>\n 0.162\n <\/td><\/tr>
\n 14.040\n <\/td>\n 14.120\n <\/td>\n 0.080\n <\/td><\/tr>
\n 6.875\n <\/td>\n 6.991\n <\/td>\n 0.116\n <\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

On-Air Results<\/strong><\/p>\n\n\n\n

On-air results using\nFT-8 and a maximum of 10 W of power has been encouraging on all bands with\ncontacts into South America and the Middle East. Indonesia and Australia have\nalso been heard but I have, so far, been unsuccessful in establishing contact\nwith these countries.<\/p>\n\n\n\n

References<\/strong> <\/p>\n\n\n\n

[1] PSK\nFrequencies<\/a>.<\/p>\n\n\n\n

[2] Lightweight Trap\nAntennas – Some Thoughts, Doug DeMaw W1FB, QST, June 1983.<\/p>\n\n\n\n

[3] Sotabeams HF\nAntenna Traps<\/a>.<\/p>\n\n\n\n

[4] Link\nto power magnetics website<\/a>.<\/p>\n\n\n\n

[5] Scientific Wire Co. Retail Site<\/a>.<\/p>\n\n\n\n

[6] Spreadsheet.<\/p>\n\n\n\n

[7] Farnell\npart 1264880<\/a>.<\/p>\n\n\n\n

[8] Drawing of PCB\nmount.<\/p>\n\n\n\n

[9] Zplots<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

Introduction This trap antenna is designed to cover the 10m-15m-20m-40m bands and resonate on the PSK31\/FT8 frequencies [1] and Table 1 with operation on SSB QRP frequencies desirable. The building of the antenna was inspired by [2] and [3]. Summary The write up here represents the third iteration of the design.  In the first iteration […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":7,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-279","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/pages\/279","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bytewyse.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=279"}],"version-history":[{"count":10,"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/pages\/279\/revisions"}],"predecessor-version":[{"id":303,"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/pages\/279\/revisions\/303"}],"up":[{"embeddable":true,"href":"https:\/\/bytewyse.org\/index.php?rest_route=\/wp\/v2\/pages\/7"}],"wp:attachment":[{"href":"https:\/\/bytewyse.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=279"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}