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考畢茲振盪器（英語：Colpitts oscillator），又稱考畢子振盪器，是由美國電機工程師艾德溫·考畢茲於1918年發明的一種LC振盪器（利用電容和電感結合決定振盪頻率的電子振蕩器）設計。 Colpitts振蕩器的特點是主動器件的回饋來自一個與電感串聯的，由兩個電容構成的分壓器。
像其他的LC振蕩器一樣，Colpitts電路由一個增益器件（如雙極接面型電晶體、場效應管、運算放大器或真空管）的輸出連在它的輸入上，回饋迴路包含一個LC並聯電路（調諧電路）作為一個帶通濾波器固定振蕩頻率。Colpitts振盪器可以看成是Hartley振盪器的對偶，在哈特萊振盪器中回饋訊號來自用兩個線圈串聯（或是一個抽頭線圈）組成的「感性」分壓器。圖1顯示了共基極Colpitts電路。L 和串聯組合的 C1 與 C2 構成的並聯諧振電路決定了振蕩器的頻率。在 C2 兩端的電壓作為回饋施加到電晶體的基極-射極接面，用以產生振蕩。圖2顯示了共集極版本。這裡 C1 兩端的電壓提供回饋。振蕩頻率約為LC電路（即兩個電容器與電感的串聯組合）的諧振頻率，{\displaystyle f_{0}={1 \over 2\pi {\sqrt {L\left({C_{1}C_{2} \over C_{1}+C_{2}}\right)}}}}https://wikimedia.org/api/rest_v1/media/math/render/svg/0ac3e744cf7779cf8206193d6d05e7853a7d2bcb由於結電容和電晶體的阻性負載，振蕩的實際頻率會略微降低。與任何振蕩器一樣，為了穩定工作，主動元件的放大率應略大於電容分壓器的衰減。因此，使用可變電感可變頻率振蕩器調諧時，相對於調整兩個電容的其中一個來說，可使Colpitts振蕩器達到最佳性能。若需採用可變電容器調諧，應該將第三個電容與電感並接（或者像在克拉普振盪器中那樣串聯）。
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NVIS Army FM 24-18Appendix M with GraphicsNEAR-VERTICAL INCIDENCE SKY-WAVE (NVIS) PROPAGATION CONCEPT M-1. Evaluation of Communications Techniques The standard communications techniques used in the past will not support the widely deployed and the fast-moving formations we intend to use to counter the modern threat. Coupling this with the problems that can be expected in deploying multichannel LOS systems with relays to keep up with present and future operation, high frequency (HF) radio and the near-vertical incidence sky-wave (NVIS) mode take on new importance. High frequency radio is quickly deployable, securable, and capable of data transmission. It will be the first, and frequently the only, means of communicating with fast-moving or widely separated units. It may also provide the first long-range system to recover from a nuclear attack. With this reliance on HF radio, communications planners, commanders, and operators must be familiar with NVIS techniques and their applications and shortcomings in order to provide more reliable communications.M-2. Problems Encountered in Propagation of Radio Waves Under ideal conditions, ground wave component of a radio wave becomes unusable at about 80 kilometers (50 mi) (fig 2-12). Under actual field conditions, this range can be much less, sometimes as little as 3 kilometers (2 mi). Sky waves, generated by standard antennas (for example, doublets) which efficiently launch the sky wave, will not return to earth at a range of less than 161 kilometers (100 mi). This can leave a skip zone of at least 80 to 113 kilometers (50 to 70 mi) where HF communications will not function. This means that units such as long-range patrols, armored cavalry deployed as advance or covering forces, air defense early warning teams, and many division-corps, division-brigade, division-DISCOM and division-DIVARTY stations are in the skip zone and thus unreachable by HF radio even though HF is a primary means of communication to these units.http://kv5r.com/wp-content/img/ham/tig/24180014.jpgM-3. Concept of Near-Vertical Incidence Sky-Wave Radiation Energy radiated in a near-vertical incidence direction is not reflected down to a pinpoint on the Earth’s surface. If it is radiated on too high a frequency, the energy penetrates the ionosphere and continues on out into space. Energy radiated on a low enough frequency is reflected back to earth at all angles (including the zenith), resulting in the energy striking the earth in an omnidirectional pattern without dead spots (that is, without a skip zone). Such a mode is called a near-vertical incidence sky wave (NVIS). The concept is illustrated in figure M-1. This effect is similar to taking a hose with a fog nozzle and pointing it straight up. The water falling back to earth covers a circular pattern continuously out to a given distance. A typical receive signal pattern for antenna AS-2259/GR is shown in figure M-2, and the path length and incident angle are shown in figure M-3. A typical elevation plane pattern is shown in figure M-4. The main difference between this short-range NVIS mode and the standard long-range sky-wave HF mode is the lower frequency required to avoid penetrating the ionosphere and the angle of incident signal upon the ionosphere. In order to attain a NVIS effect, the energy must be radiated strong enough at angles greater than about 75 or 80 degrees from the horizontal on a frequency that the ionosphere will reflect at that location and time. The ionospheric layers will reflect this energy in an umbrella-type pattern with no skip zone. Any ground wave present with the NVIS signal will result in undesirable wave interference effects (such as, fading) if the amplitudes are comparable. However, proper antenna selection will reduce ground-wave radiated energy to a minimum, and this will reduce the fading problems. Ranges for the NVIS mode are shown in figure M-3 for typical ionosphere height and take-off angles. Since NVIS paths are purely sky wave, the path losses are nearly constant at about 110 dB +10 dB. Relative gain performance of the AS-2259/GR NVIS antenna is shown in figure M-5. This is significant for the tactical communicator because all the energy arriving at the receiving antenna is coming from above at about the same strength over all of the communications ranges of interest. This means the effect of terrain and vegetation (when operating from defiladed positions such as valleys) are greatly reduced, and the receive signal strength will not vary greatly.
