The 11-Year Solar Cycle

The density of ionospheric layers depends on the amount of solar radiation
reaching the Earth, but solar radiation is not constant. Variations result from daily
and seasonal motions of the Earth, the sun’s own 27-day rotation and the 11-year
cycle of solar activity. One visual indicator of both the sun’s rotation and the solar cycle is the periodic appearance of dark spots on the sun, which have been observed continuously since the mid-18th century. On average, the number of sunspots
reaches a maximum every 10.7 years, but the period has varied between 7 and 17 years. Cycle 19 peaked in 1958,with an average sunspot number of over 200, the highest recorded to date.

Sunspots are cooler areas on the sun’s surface associated with high magnetic activity.Active regions adjacent to sunspot groups, called plages, are capable of producinggreat flares and sustained bursts of radiation in the radio through X-ray spectrum.During the peak of the 11-year solar cycle, average solar radiation increasesalong with the number of flares and sunspots.The ionosphere becomes more intensely ionized as a consequence, resulting in higher critical frequencies, particularly in the F2 layer. The possibilities for longdistance communications are considerably improved during solar maxima, especially in the higher-frequency bands.
One key to forecasting F-layer critical frequencies, and thus long-distance propagation,is the intensity of ionizing UV and X-ray radiation. Until the advent of satellites,UV and X-ray radiation could not be measured directly, because they were almost entirely absorbed in the upper atmosphere.The sunspot number provided the
most convenient approximation of general solar activity. The sunspot number is not a
simple count of the number of visual spots,but rather the result of a complicated formula that takes into consideration size,number and grouping. The sunspot number
varies from near zero during the solarcycle minimum to over 200.

Another method of gauging solar activity is the solar flux, which is a measure of the intensity of 2800-MHz (10.7-cm) radio noise coming from the sun. The 2800-MHz radio flux correlates well with the intensity of ionizing UV and X-ray radiation and provides a convenient alternative to sunspot numbers. It commonly varies on a scale of 60-300 and can be related to sunspot numbers, as shown in Fig 20.11. The Dominion Radio Astrophysical Observatory,Penticton, British Columbia, measures the 2800-MHz solar flux daily at local noon. (Prior to June 1991,the Algonquin Radio Observatory, Ontario,made the measurements.) Radio station WWV broadcasts the latest solar-flux index at 18 minutes after each hour; WWVH does the same at 45 minutes after the hour.

The Penticton solar flux is employed in a wide variety of other applications. Daily,
weekly, monthly and even 13-month smoothed average solar flux readings are commonly used in propagation predictions.High flux values generally result in higher MUFs, but the actual procedures for predicting the MUF at any given hour and path are quite complicated. Solar flux is not the sole determinant, as the angle of the sun to the Earth, season, time of day,exact location of the radio path and other factors must all be taken into account.MUF forecasting a few days or months ahead involves additional variables and even more uncertainties.

Adakah saat berikut sesuai untuk QRT?

Berikut adalah beberapa situasi yang sering menjadi pilihan bagi anda dan rakan untuk tidak meneruskan QSO di simpleks atau pun di repeater.

1.Apabila kualiti pemancaran anda menurun ini,ini dapat anda amati apabila mutu penerimaan merosot,bar meter hanya menunjukkan 1-2 bar sahaja.Jika kualiti audio anda diterima dalam keadaan putus-putus, rakan anda sukar memahami apa yang anda katakan,nyatakan QRX sehingga anda melepasi zon sukar,jika laluan bekenaan hanya beberapa minit sahaja jika agak lama QRT adalah jalan terbaik.


2.Apabila keadaan trafik jalan raya sibuk (bumper to bumper)keadaan ini memerlukan kita lebih berhati-hati jika tidak, mungkin kita dilanggar kenderaan daripada belakang atau kita melanggar kenderaan di hadapan kita.Maka oleh itu lebih selamat jika kita QRT daripada membuat pemancaran.

3.Apabila dalam kumpulan terlalu ramai dan anda agak keliru untuk putaran mikropon berikutnya lebih baik anda QRT dan mendengar rakan-rakan QSO,daripada pas sana kemudian pas sini,silap haribulan ada rakan yang kesejukan (istilah bagi mereka yang masih tertunggu-tunggu)putaran mereka tak diberikan..

4.Bagi sesetengah rig yang tidak punyai exhaust fan,QSO yang berpanjangan menyebabkan rig menjadi agak panas,bagi merehatkan rig berkenaan QRT daripada QSO adalah yang terbaik.

5.Apabila rakan anda berbicara dalam berkumpulan mengenai satu tajuk yang agak janggal buat anda elok QRT daripada QSO supaya anda tidak menggangu QSO mereka dengan penukaran tajuk QSO yang sedang rancak dibahaskan.

6.Apabila kenderaan anda hampir memasuki ke dalam feri,ingat anda tidak dibenarkan membuat pemancaran ketika berada di dalam feri.

7.Harmonic berada dihadapan dan cuba menekan-nekan button rig atau cuba mencapai ptt anda,saat ini ternyata lebih baik anda QRT jika tidak,ianya boleh mengundang bahaya apabila keadaan menjadi tidak terkawal,anda dalam keadaan memandu hendak memberikan fokus kepada pemanduan.

Sama-sama kita fikirkan apakah perlu kita teruskan QSO bila keadaan demikian boleh mengundang kecelakaan.