Aerial is basic concept
Aerial is the ear of FM DX, faint electric wave enters receiver through line of make a present of from aerial, ability lets us hear the voice of distance broadcasting station. One receives systematic stand or fall, aerial took an in part. We hope aerial can have tall gain, become faint signal resonant, we hope aerial can have certain choice capacity, block strong stand of interference of stage of notify sb of a phone call and this locality outside, we hope system of day make a present of reduces loss as far as possible, send the front of receiver the signal of each small bend over.
The person that uses portable radio to listen to FM DX to great majority says, their antenna perhaps is the telescopic antenna on the radio only, although such antenna is simple convenient, but to FM DX, it is insufficient anyhow, although do obeisance to ionosphere bestow, such aerial system also is not to be impossible receive DX signal.
My general introduces a few antenna that abstain common and easily, these days line can use us the gets easily data in daily life is made. My meeting one by one makes these days line, take made course the picture, give out as far as possible detailed dimension data. Although I am in the process that make,can employing aerial analyzer is the equipment such as integrated instrument even, but I debug those who tell a reader not to use these costly instruments the method. At least, complete the material according to me, dimension always won't wrong.
Aerial electric wave
Before telling aerial, have to carry electric wave first.
The goal that we make antenna is to catch electric wave, accordingly, before the issue that considers aerial, be necessary to study the issue of electric wave first absolutely.
FM broadcast wave band, it is on frequency arrive from 87.5MHz 108MHz, corresponding wavelengh is 3.4 meters go to 2.7 meters, say to make 3 meters of wave band commonly, it is VHF (Very High Frequency) a paragraph. This wave band is the following, 54MHz arrives 87.5MHz is telecast wave band, above, 108MHz arrives 136MHz is aviation communication wave band. The electric wave of VHF wave band travels, basically have
3 kinds of ways:
please Click here to get our dipole antenna
Aerial ground wave
This is to point to arrive from emissive antenna between receving antenna, do not pass any launching, arrive directly, electric wave is just like a bundle of light same, so someone says it travels for the line of sight. The line of sight transmitted this name to also show the distance that way of this kind of transmission can transmit is not far. This has two reasons, it is electric wave sets out from emissive dot above all, its energy decreases successively with power series, and receiver should solve v can goodly broadcast, need particular signal strength. The place with place far aether, signal is too weak, can't demodulation. If be this reason only, so the gain that enhance emissive power desperately or adds receving antenna, perhaps can enlarge the limits that listen. But, still having a serious problem is, the earth is round, the electric wave that why gave out holds the post of on the earth, press the direction of linear advancement, will leave the earth finally to shoot to the sky. As a result of,basically be the 2nd reason, popularly is told, the linear wave that a launcher gives out, can transmit 70km far ground to receive only place. If bilateral height increases, so this distance still can increase, but always be finite. So, 70km, it is the limit that this locality listens to, actually, as a result of mountain range, upland, building hold back, reflection, this distance sells at a discount greatly even, the distance that can estimate commonly is 35km.
Ionosphere emissive wave
This is to point to what electric wave passes ionosphere to blast off achieve receive debit. The reason inside this is very much. Ionosphere itself has many arrangement, supportive shortwave (1.8MHz arrives 30MHz) catoptric ionosphere is F1 and F2 layer. F1 and F2 are not to reflex all radio wave readily, they can catoptric is highest frequency is finite, the electric wave that exceeds this frequency cannot get reflection completely, cross ionosphere to shoot however to aerospace. If do not have this character, so Telstar existed impossibly, telstar works outside ionosphere. This highest frequency calls MUF (Max Usable Frequency) . MUF and very much element are concerned, advocate if mix,brisk rate and season concern macula. Macula is active, MUF is tall, to be warm, MUF is tall also. How much can MUF go to high high most? Be in commonly macula is active period summer, MUF arrives in 20MHz between 40MHz, exceed 50MHz rarely. In low when meet even low arrive under 10MHz. But when macula is unusually active, MUF achieves 100MHz likely also accidentally. At that time, blast off likely through F layer receive DX FM. But the main form that this is not FM DX, FM DX basically is to pass layer of another ionosphere E. The occurrence of original E layer is to destroy F layer, so we might as well write down F layer to be Friend layer, e layer is Enemy layer. But the occurrence of Es layer, can form however short-term inside the reflector with extremely high density. The density of reflector is high, mean can reflex electric wave better. When Es layer is so enlightened, the signal of DX broadcasting station is met singularly is strong. The spare broadcasting station that works with 10 meters of spare wave band in 6 meters knows, when Es layer is enlightened, very little power, even 5W, make DX contact likely also. Of Es enlightened, basically be the transmission way that offerred electric wave of 800km less than. Because signal is very strong, actually a lot of moment do not need very good equipment to be able to be received, of need is patience and luck. Besides these two kinds of reflex, FM DX passes troposphere reflex and meteoric beyond mark likely still to arrive at your receiver.
Ground wave and atmosphere wave guide
Original for, theoretic VHF is nonexistent wave. But countless practice make clear, VHF also is existing somehow ground wave travels. So we receive 200km steadily to control the signal of broadcasting station. Jiangsu and Anhui the spare broadcasting station of two provinces, annual National Day when undertake saving experiment of VHF mobile communication completely, the distance that also proved VHF electric wave can be controlled in 200km receives transmission. Atmosphere wave guide is additionally one kind of method that transmits VHF electric wave possibly, nevertheless people studies not quite much still.
Since existing these likelihoods
please Click here to get our dipole antenna
Our other product:
