{"id":46,"date":"2019-01-09T15:25:17","date_gmt":"2019-01-09T15:25:17","guid":{"rendered":"https:\/\/fletch.scot\/wp\/?p=46"},"modified":"2020-08-29T16:03:15","modified_gmt":"2020-08-29T16:03:15","slug":"satellite-aerial-link-budget","status":"publish","type":"post","link":"https:\/\/fletch.scot\/wp\/?p=46","title":{"rendered":"Satellite Aerial Link Budget"},"content":{"rendered":"<p>I\u2019ve had a little luck transmitting to a satellite. I\u2019m using packet as I can use the 2m Cebik Moxon aerial for both transmit and receive. To see if the ISS should be able to hear my signals I wrote a link budget program in <a href=\"https:\/\/racket-lang.org\">Racket<\/a>. There\u2019s a few assumptions in it but it seems to confirm the ISS should have no problem hearing me on 2m. The program shows:<\/p>\n<pre><code>Transmit power (W)?\n5\nFrequency (MHz)?\n145.825\nElevation (\u00b0)?\n40\nTransmit power:   5 W (36.99 dBm)\nFrequency:        145.825 MHz\nSatellite height: 403 km\nElevation angle:  40\u00b0\n\nSatellite is 5396 km away\nSignal at satellite is 9 dB above noise\n<\/code><\/pre>\n<p>This seems borne out as I do receive what seem to be digipeated packets just after I transmit them. But I can\u2019t confirm on the ISS site that they are real and not just an echo from somewhere.<\/p>\n<p>70cms doesn\u2019t look as good:<\/p>\n<pre><code>Transmit power (W)?\n5\nFrequency (MHz)?\n435.255\nElevation (\u00b0)?\n40\nTransmit power:   5 W (36.99 dBm)\nFrequency:        435.255 MHz\nSatellite height: 403 km\nElevation angle:  40\u00b0\n\nSatellite is 5396 km away\nSignal at satellite is -0 dB above noise\n<\/code><\/pre>\n<p>Increasing the power to 25W might work:<\/p>\n<pre><code>Transmit power (W)?\n25\nFrequency (MHz)?\n435.255\nElevation (\u00b0)?\n40\nTransmit power:   25 W (43.98 dBm)\nFrequency:        435.255 MHz\nSatellite height: 403 km\nElevation angle:  40\u00b0\n\nSatellite is 5396 km away\nSignal at satellite is 7 dB above noise\n<\/code><\/pre>\n<p>I\u2019m currently building the 70cms version and will try some FM voice contacts.<\/p>\n<p>Here\u2019s the link budget program:<\/p>\n<pre><code>#lang racket\n; link budget for Cebik Moxon in attic\n; Andy Fletcher Jan 9, 2019 \n\n;\n; definitions\n;\n(define (get_user_input prompt)\n  (begin\n    (displayln prompt)\n    (string-&gt;number (read-line))))\n\n(define (log10 n)\n  (\/ (log n) (log 10)))\n\n(define (watts2dbm w)\n  (* 10 (log10 (* w 1000))))\n\n(define (degrees2radians d)\n  (* (\/ pi 180) d))\n\n(define (square x)\n  (* x x))\n\n; distance to satellite in km\n(define (satellite_distance e_degrees height)\n  (let* ([e (degrees2radians e_degrees)]\n         [earth_radius 6371]    ; kms\n         [r (+ height earth_radius)] ; distance between geocentre and satellite\n         )\n    (sqrt (+ (square (* earth_radius (cos e))) (square r) (- (square earth_radius)) (- (* earth_radius (cos e)))))))\n\n; free space path loss\n(define (fspl f d)\n  (- (+ (* 20 (log10 f)) (* 20 (log10 d)) 32.45)))\n\n;\n; execute\n;\n(let* (\n       [ptx_watts (get_user_input \"Transmit power (W)?\")]\n       [f         (get_user_input \"Frequency (MHz)?\")]\n       [e_degrees (get_user_input \"Elevation (\u00b0)?\")]\n       [h 403]               ; satellite height in kms\n       [cable_loss -3.55]    ; measured dB\n       [tx_gain 6.0]         ; Cebik Moxon modelled gain in dB\n       [roof_loss -6.0]      ; assumed loss of signal going through the roof in dB\n       [rx_gain 2.0]         ; assumed receive gain at satellite in dB\n       [sat_max_sens 124.0]  ; assumed satellite maximum sensitivity in dBm\n       [distance_to_satellite (satellite_distance e_degrees h)]\n       [ptx (watts2dbm ptx_watts)]\n       )\n  (begin\n    (printf \"Transmit power:   ~a W (~a dBm)\\n\" ptx_watts (~r ptx #:min-width 1 #:precision 2))\n    (printf \"Frequency:        ~a MHz\\n\" f)\n    (printf \"Satellite height: ~a km\\n\" (~r h #:min-width 1 #:precision 0))\n    (printf \"Elevation angle:  ~a\u00b0\\n\" e_degrees)\n    (printf \"\\nSatellite is ~a km away\\n\" (~r distance_to_satellite #:min-width 1 #:precision 0))\n    (printf \"Signal at satellite is ~a dB above noise\\n\"\n            (~r  (+ ptx cable_loss tx_gain roof_loss (fspl f distance_to_satellite) rx_gain sat_max_sens) #:min-width 1 #:precision 0))))\n\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"<p>I\u2019ve had a little luck transmitting to a satellite. I\u2019m using packet as I can use the 2m Cebik Moxon aerial for both transmit and receive. To see if the ISS should be able to hear my signals I wrote a link budget program in Racket. There\u2019s a few assumptions in it but it seems &hellip; <\/p>\n<p class=\"link-more\"><a href=\"https:\/\/fletch.scot\/wp\/?p=46\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;Satellite Aerial Link Budget&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[13,26],"tags":[6,18,7,30,31,32],"class_list":["post-46","post","type-post","status-publish","format-standard","hentry","category-aerial","category-space","tag-aerial","tag-antenna","tag-cebik","tag-code","tag-racket","tag-satellite"],"_links":{"self":[{"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=\/wp\/v2\/posts\/46","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=46"}],"version-history":[{"count":1,"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=\/wp\/v2\/posts\/46\/revisions"}],"predecessor-version":[{"id":47,"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=\/wp\/v2\/posts\/46\/revisions\/47"}],"wp:attachment":[{"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=46"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=46"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fletch.scot\/wp\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=46"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}