Even with a similar transmitter and antenna, the report received and the contact experience need not exactly be the same especially when contacting Dx stations. It was already told that not only the peculiarities of the atmosphere but also the height of the antenna are determining. Directional qualities of low level antennas will be low and the radiation angle will be high. Only low radiation angle signals go to more distance. But at low angle radiation the dead zone effect will be higher. Away from line of sight of antennas the next point of the same signal will be where the nearest reflected wave reaches the ground. Th area in between these two points where no signals from that particular antenna is available is called the dead zone. See fig: C-29/1
The effect of sunspots on propagation also are relevant. The study on the effects of sunspots are still continuing. Those black spots on the face of the sun which keeps changing in size and number, keeps changing the magnetic activity of the sun - thus invariably influencing radio propagation in the earth's atmosphere. Simply because it repeats its activities at an eleven year pattern, this sun spot activity also is called 'eleven year cycle'.
There had been seasons in which there were no sunspots. During sunspots those ultra violet radiations from the sun create strong magnetic hurricanes on the earths atmosphere. Black outs where no radio transmission is practically done are the result of these magnetic bursts.
Anything in the vicinity of the transmission field is subjected to change as if a thing in a microwave oven. For human beings close to the feed point, continuous interaction results in heating of internal organs. if he heat crosses 2 degrees Celsius experiments have proved that it could end up in physical disabilities. If a man remains close to a 400W power 7 MHz transmitter antenna continuously for a hour, the level of heat it causes in the body can be calculated to be 1 degree Celsius. This is enough for partial blindness or deafness. The more the frequency the more will be the magnetic energy the body absorbs. Even if the VHF transceivers are very low in power, continuous usage keeping it close to the body might cause to generate enough body heat that could be badly damaging our body functions.
Whatever be the type of antenna used, the length of the feeder cable could make transmission losses and it is always advised to keep the length as low as possible. Antennas are designed at a style in which the antenna feed point comes directly above the transmitter. The easiest of antennas is the single wire antenna, except that a matching circuit and trans-matching arrangement is necessary for it. One big problem here is the 'hot chassis', the problem created by RF energy that are found at various points on the chassis. Unless the chassis is strongly earthed using appropriate accessories, it may end up in damage of various components. Still single wire antennas have the quality of adaptability to different bands.
It is not simply space availability or limitation based issues that compels for inverted 'V' and sloper dipole antennas. Both are vertically polarised and are better in ground waves and long distance contacts, compared to horizontally polarizsed antennas.
If the impedance of Sloper antenna is 75 Ohms the impedance of the inverted V is 50 Ohms. Always a 90 to 120 degree feed point angle is recommended. In either cases the formula to find the length of a dipole arm is = 468/F (MHz)=L (feet). When an antenna is tuned to other meter bands through trans-match, efficiency will be low at all higher frequencies than the one to which the antenna is tuned.
Any wire is usable for an antenna, provided it should not be subject to chemical and physical changes in the due course. Normally copper wires of 12,14 and 16 SWGs are ideal. If it can be mounted without breaks and damages and protected against natural obstacles, 26 SWG is enough for a low power transmitter. Stranded type or single wire type also make no much difference in its gain. If the available space is very limited there are certain modification possibilities - antenna arms can be bent. Inductors and capacitors connected in series to antenna arms also leads to frequency resonation and a trans-matching circuit to bring impedance match too together makes it complete.
There is also the tradition of fitting loading coils in the centre of both the arms to bring the antenna into an impedance matching situation. All these short cuts but increases the 'Q' of the antenna and reduces the bandwidth. Make 60 turns at one and half inch dia. with 16 SWG wire leaving one foot at one end and eight feet at the other end. Connect the feeder cable at the one foot side keeping terminals at half inch distance (just like we do in horizontal dipole. Fix the other ends of the arms (eight feet long part) as shown in C-29/3. This is the details of a 40 M antenna. With any ATU illustrated already, this will also give good results, with slight decrease in gain.
Study of antennas is quite interesting. Basically it was mere enthusiasm that led Louis Varney (G5RV) to the invention of the very popular multi band G5RV antenna in 1946. This antenna is very popular in the United States and is found best for 20 meters. It should be noted that this antenna can be erected as horizontal dipole, as sloper, or an inverted-V and with a trans-match, it can be operated on all HF amateur radio bands (3.5–30 MHz).
In effect this is a dipole only with each arm measuring 51 feet each. If that much open space is not available, each arm can be bent in 90 degree at 31 feet to hang the remaining 20 feet vertically down. Height is vvery critical for G5RV Antennas. Even if this works in 25 feet too, 3o feet is the ideal recommended height. it is 300 ohms TV ribbon cable that is used for feeder cable. The length of the feeder cable is fixed at 29 feet 6 inches. If the height is low the lower part of the feeder cable can be bent slightly. Because the length of this cable is critical in impedance matching at different bands, this part of G5RV antenna is called matching stub. This antenna can be erected in inverted 'V' pattern with a 30 feet high pole in the centre. If it is open wire that is used as matching stub the suggested length is 34 feet. This matching stub is connected to a trans-matching arrangement. After trans-matching antenna is connected to the transmitter through an SWR meter. That portions that is not matching stub can be 75 ohms coax cable, ribbon wire or open wire. Compared to a dipole a 3 db more gain is marked for G5RV Antenna.
Low angle radiation that is very much required for bands above 7 MHz is the speciality of G5RV Antennas. Another version of G5RV is available at half the size of the measurements given here. Here, the length of the matching stub also will be half. For better G5RV, the ribbon wire matching stub is soldered to the arms at the centre with each wire end coiled at 9" length.
There is also the tradition of fitting loading coils in the centre of both the arms to bring the antenna into an impedance matching situation. All these short cuts but increases the 'Q' of the antenna and reduces the bandwidth. Make 60 turns at one and half inch dia. with 16 SWG wire leaving one foot at one end and eight feet at the other end. Connect the feeder cable at the one foot side keeping terminals at half inch distance (just like we do in horizontal dipole. Fix the other ends of the arms (eight feet long part) as shown in C-29/3. This is the details of a 40 M antenna. With any ATU illustrated already, this will also give good results, with slight decrease in gain.
In effect this is a dipole only with each arm measuring 51 feet each. If that much open space is not available, each arm can be bent in 90 degree at 31 feet to hang the remaining 20 feet vertically down. Height is vvery critical for G5RV Antennas. Even if this works in 25 feet too, 3o feet is the ideal recommended height. it is 300 ohms TV ribbon cable that is used for feeder cable. The length of the feeder cable is fixed at 29 feet 6 inches. If the height is low the lower part of the feeder cable can be bent slightly. Because the length of this cable is critical in impedance matching at different bands, this part of G5RV antenna is called matching stub. This antenna can be erected in inverted 'V' pattern with a 30 feet high pole in the centre. If it is open wire that is used as matching stub the suggested length is 34 feet. This matching stub is connected to a trans-matching arrangement. After trans-matching antenna is connected to the transmitter through an SWR meter. That portions that is not matching stub can be 75 ohms coax cable, ribbon wire or open wire. Compared to a dipole a 3 db more gain is marked for G5RV Antenna.
The impedance-matching symmetric feed line (ladder-line or twin-lead) can be either 300 Ohm (8.84 metres or 29.0 feet) or 450 Ohm (10.36 metres or 34.0 feet). As is in general the case for all electric antennas, the height of the G5RV above the ground should be at least half of the longest wavelength to be used. There are many variants of the G5RV antenna.
Low angle radiation that is very much required for bands above 7 MHz is the speciality of G5RV Antennas. Another version of G5RV is available at half the size of the measurements given here. Here, the length of the matching stub also will be half. For better G5RV, the ribbon wire matching stub is soldered to the arms at the centre with each wire end coiled at 9" length. 
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