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Here we discuss the most important steps. 240 </p> 241 <p class="text-muted"> 242 Below you will see the main screen with a set of reasonable 243 input values for a high-power broadcasting station with 244 transmissions to Southern Africa. 245 </p> 246 <p> 247 <img alt="" src="/2023/img/main-screen.png" /> 248 </p> 249 </div> 250 </div> 251 </section> 252 <!--Section: Content--> 253 254 <hr class="my-5" /> 255 256 <!--Section: Content--> 257 <section> 258 <div class="row"> 259 <div class="col-md-3 gx-5 mb-4"> 260 <h4>Basic parameters</h4> 261 </div> 262 <div class="col-md-9 gx-5 mb-4"> 263 These are the basic settings which you can initially set up as 264 follows: 265 266 <p></p> 267 <table border="0" cellpadding="2" cellspacing="2" width="600"> 268 <tr valign="top" align="left" bgcolor="#ffcc33"> 269 <th>Parameter</th> 270 <th>Recommendation</th> 271 </tr> 272 273 <tr valign="top"> 274 <td><b>Method</b></td> 275 <td> 276 Select Method Number 20 (Complete System Performance). If 277 you are running circuits over 7000 km, use Method 30 278 (Short/Long Path Smoothing). 279 </td> 280 </tr> 281 282 <tr valign="top" bgcolor="#ebeff2"> 283 <td><b>Year</b></td> 284 <td> 285 This is a user-specified value. It has no effect on 286 calculations. 287 </td> 288 </tr> 289 290 <tr valign="top"> 291 <td><b>Coefficients</b></td> 292 <td> 293 Select CCIR (Oslo). This is the default for using VOACAP in 294 long-term predictions. 295 <b>Do not use URSI88 (Australian)</b>. 296 </td> 297 </tr> 298 299 <tr valign="top" bgcolor="#ebeff2"> 300 <td><b>Time</b></td> 301 <td> 302 Select UT (Universal Coordinated Time). Local Mean Time does 303 not mean your local time but the local sun time at the 304 receiver. 305 </td> 306 </tr> 307 308 <tr valign="top"> 309 <td><b>Transmitter</b></td> 310 <td> 311 Select the transmitter location from the pre-defined lists, 312 sorted by city (worldwide), by nation (worldwide) and by 313 state (USA). You can also enter the coordinates manually. 314 </td> 315 </tr> 316 317 <tr valign="top" bgcolor="#ebeff2"> 318 <td><b>Receiver</b></td> 319 <td> 320 Select the receive location from the pre-defined lists, 321 sorted by city (worldwide), by nation (worldwide) and by 322 state (USA). You can also enter the coordinates manually. 323 </td> 324 </tr> 325 326 <tr valign="top"> 327 <td><b>Path</b></td> 328 <td>Select Short or Long Path. The default is Short Path.</td> 329 </tr> 330 331 <tr valign="top" bgcolor="#ebeff2"> 332 <td><b>Freq(MHz)</b></td> 333 <td> 334 Enter the frequencies to be used for calculation. Use the 335 zero (0) value to remove a frequency from the set. A set of 336 11 user-specified frequencies can be defined. Also three 337 pre-defined frequency sets are available which can be 338 modified if needed. 339 </td> 340 </tr> 341 342 <tr valign="top"> 343 <td><b>Fprob</b></td> 344 <td> 345 Do not use all default values. Set foE to 1, foF1 to 1, foF2 346 to 1 and foEs to 0 (zero, instead of 0.7). 347 </td> 348 </tr> 349 </table> 350 <p><h5>
350Note about Coefficients</h5> 351 352 As noted earlier, while using VOACAP or VOAAREA, 353 <b>be sure to select the CCIR coefficients</b>. George Lane 354 explains,<br/><br/> 355 "<b>Do the URSI coefficients provide more accurate predictions?</b> We 356 do not know. What we do know is that original IONCAP using the 357 CCIR data base, corrects the predicted values by using the 358 Transmission Loss tables and determines the variability of the 359 MUF values over the month using the F-tables. These are huge 360 corrections. They are based on taking the predicted ionospheric 361 calculations using the CCIR data and subtracting them from 362 actual system performance data taken over the 1958 to 1963 time 363 period. The differences are collected into the two sets of 364 tables I just mentioned. The corrections are applied to any path 365 prediction you make using IONCAP in order to predict signal 366 power, SNR, reliability and required power gain. If you change 367 the ionospheric maps for only the F-region and do not 368 recalibrate the predictions against measurement, you do not know 369 if you made an improvement or not. Chances are you have ruined 370 the correlation." 371 </p> 372 </div> 373 </div> 374 </section> 375 <!--Section: Content--> 376 377 <hr class="my-5" /> 378 379 <!--Section: Content--> 380 <section> 381 <div class="row"> 382 <div class="col-md-3 gx-5 mb-4"> 383 <h4>Critical parameters</h4> 384 </div> 385 <div class="col-md-9 gx-5 mb-4"> 386 <p>The following are critical user-specified parameters. 387 388 <h5>Groups</h5> 389 390 <img alt="" src="/2023/img/groups.png"> 391 392 <p><table border=0 cellpadding=2 cellspacing=2 width="600"> 393 394 <tr valign=top align=left bgcolor="#ffcc33"><th>Parameter</th><th>Recommendation</th></tr> 395 396 <tr valign=top><td><b>Months</b></td><td>Enter the number of the month (e.g. December = 12.00). You can specify a total of 10 months at a time. The format is MM.DD (month.day). VOACAP is not, however, suitable for daily predictions. Therefore, do not specify any day since if you do, the value of Coefficients will automatically be set to URSI88.</td></tr> 397 398 <tr valign=top bgcolor="#ebeff2"><td><b>SSNs</b></td><td>Enter the monthly smoothed sunspot number for the given month.</td></tr> 399 </table></p> 400 401 <hr class="my-5" /> 402 <p><h5>Choosing the correct sunspot number (SSNs)</h5></p> 403 404 <p>There are a number of sunspot resources available on the internet. However, be sure to use the values from the following resource: 405 <a href="http://sidc.oma.be/silso/FORECASTS/KFprediML.txt">Predicted Monthly Sunspot Numbers</a>, from SILSO, Royal Observatory of Belgium. 406 407 408 <hr class="my-5" /> 409 <p><h5>System</h3></p> 410 <img alt="" src="/2023/img/system.png"> 411 412 <p><table border=0 cellpadding=2 cellspacing=2 width="600"> 413 414 <tr valign=top align=left bgcolor="#ffcc33"><th>Parameter</th><th>Recommendation</th></tr> 415 416 <tr valign=top><td><b>Man-made noise</b></td><td><b>This is a critical setting</b>. You can accept the default value of 145 (residential environment). If your receive location is in a quiet environment, you can use 155 or higher. There are still other values available, see the input help.</td></tr> 417 418 <tr valign=top bgcolor="#ebeff2"><td><b>Min. take-off angle</b></td><td>If you are a radio amateur or SWL, enter the take-off value of 3. For better antenna installations, you can use the value of 1.</td></tr> 419 420 <tr valign=top><td><b>Req'd circuit reliability</b></td><td>Accept the default value of 90%.</td></tr> 421 422 <tr valign=top bgcolor="#ebeff2"><td><b>Req'd SNR</b></td><td><b>This is a critical setting</b>. For a reasonable BC listening quality, use 67. For a reasonable CW reception quality, use 24 (or 27) and for SSB, 45.</td></tr> 423 424 <tr valign=top><td><b>Multipath power tolerance</b></td><td>Accept the default value of 3 dB.</td></tr> 425 426 <tr valign=top bgcolor="#ebeff2"><td><b>Max. tolerable time delay</b></td><td>Accept the default value of 0.10 milliseconds.</td></tr> 427 428 </table></p> 429 430 <hr class="my-5" /> 431 <p><h5>Antennas</h5></p> 432 433 <p><b>Selecting the transmitter antenna</b></p> 434 435 <p><img alt="" src="/2023/img/tx-ant1.png"> 436 437 <p><table border=0 cellpadding=2 cellspacing=2 width="600"> 438 439 <tr valign=top align=left bgcolor="#ffcc33"><th>Parameter</th><th>Recommendation</th></tr> 440 441 <tr valign=top><td><b>TxAnt=</b></td><td>Select the transmitter antenna from the pre-defined lists. You must familiarize yourself with the available antenna patterns using the HFant program, included in the VOACAP softw
441are package. This window is the place where you can define different antennas for different frequency ranges. In the example above, we have defined one antenna for the frequency range of 2 MHz (Min) to 30 MHz (Max).</td></tr> 442 443 <tr valign=top bgcolor="#ebeff2"><td><b>MainBeam</b></td><td>Enter the main beam of the antenna (in degrees).</td></tr> 444 445 <tr valign=top><td><b>at Rx</b></td><td>Sets the main beam towards the receive location.</td></tr> 446 447 <tr valign=top bgcolor="#ebeff2"><td><b>TxPower</b></td><td>The transmitter power which is fed to the antenna. Usually, we need to assume some power losses in transmission lines, etc. so you may set this value, for instance, to 80% of the transmitter power.</td></tr> 448 449 </table> 450 <hr class="my-5" /> 451 <p><h5>Selecting the receive antenna</h5></p> 452 453 <p><img alt="" src="/2023/img/rx-ant1.png"></p> 454 455 <p><table border=0 cellpadding=2 cellspacing=2 width="600"> 456 457 <tr valign=top align=left bgcolor="#ffcc33"><th>Parameter</th><th>Recommendation</th></tr> 458 459 <tr valign=top><td><b>Receive Antenna=</b></td><td>Select the receive antenna from the pre-defined lists. You must familiarize yourself with the available antenna patterns using the HFant program, included in the VOACAP software package. The default antenna SWWHIP.VOA represents a typical shortwave whip antenna.</td></tr> 460 461 <tr valign=top bgcolor="#ebeff2"><td><b>Receiver bearing</b></td><td>If it is a directional antenna, enter the main beam in degrees. For non-directional antennas, enter the value of 0.</td></tr> 462 463 <tr valign=top><td><b>at Tx</b></td><td>Sets the main beam towards the transmitter location.</td></tr> 464 465 <tr valign=top bgcolor="#ebeff2"><td><b>Gain</b></td><td>This is valid only for isotropic antennas. The gain value is ignored if used with other antenna types.</td></tr> 466 467 </table></p> 468 </div> 469 </div> 470 </section> 471 <!--Section: Content--> 472 <!--hr class="my-5" /--> 473 </div> 474 </main> 475 <!--Main layout--> 476 477 <!--Footer--> 478 <footer class="bg-light text-lg-start"> 479 <hr class="m-0" /> 480 481 <div class="text-center py-4 align-items-center"> 482 <p>Follow OH6BG on social media</p> 483 <a 484 href="https://www.youtube.com/channel/UCVg16ZokJHYTA2HJqeS1npA" 485 class="btn btn-primary m-1" 486 role="button" 487 rel="nofollow" 488 target="_blank" 489 > 490 <i class="fab fa-youtube"></i> 491 </a> 492 <a 493 href="https://bsky.app/profile/voacap.bsky.social" 494 class="btn btn-primary m-1" 495 role="button" 496 rel="nofollow" 497 target="_blank" 498 > 499 <i class="fab fa-twitter"></i> 500 </a> 501 <a 502 href="https://github.com/OH6BG" 503 class="btn btn-primary m-1" 504 role="button" 505 rel="nofollow" 506 target="_blank" 507 > 508 <i class="fab fa-github"></i> 509 </a> 510 <a 511 href="https://airwaves.social/@oh6bg" 512 class="btn btn-primary m-1" 513 role="button" 514 rel="nofollow" 515 target="_blank" 516 > 517 <i class="fab fa-mastodon"></i> 518 </a> 519 </div> 520 521 <!-- Copyright --> 522 <div class="text-center p-3" style="background-color: rgba(0, 0, 0, 0.2)"> 523 © 2003-2025 Jari Perkiömäki 524 <a class="text-dark" href="mailto:[email protected]">OH6BG</a>. 525 <a href="voacap-disclaimer.html">Disclaimer</a> 526 </div> 527 <!-- Copyright --> 528 </footer> 529 </body> 530</html>
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