Coaxial cable - what should we know??

Coaxial cable is a cable type used to carry radio signals, video signals, measurement signals and data signals. Coaxial cables exists because we can't run a open-wire line near metallic objects or bury it. We trade signal loss for convenience and flexibility. Coaxial cable consists of an insulated center conductor which is covered with a shield. The signal is carried between the cable shield and the center conductor. This arrangement give quite good shielding against noise from outside cable, keeps the signal well inside the cable and keeps cable characteristics stable.

Coaxial cables and systems connected to them are not ideal. There is always some signal radiating from coaxial cable. More shield coverage means less radiation of energy.

Coaxial cables are typically characterized with the impedance and cable loss. The length has nothing to do with a coaxial cable impedance. Characteristic impedance is determined by the size and spacing of the conductors and the type of dielectric used between them. For ordinary coaxial cable used at reasonable frequency, the characteristic impedance depends on the dimensions of the inner and outer conductors. The characteristic impedance of a cable (Zo) is determined by the formula 138 log b/a, where b represents the inside diameter of the outer conductor i.e. shield or braid, and a represents the outside diameter of the inner conductor.

Most common coaxial cable impedances in use in various applications are 50 ohms and 75 ohms. 50 ohms cable is used in radio transmitter antenna connections, many measurement devices and in data communications (Ethernet). 75 ohms coaxial cable is used to carry video signals, TV antenna signals and digital audio signals. There are also other impedances in use in some special applications (for example 93 ohms). It is possible to build cables at other impedances, but those mentioned earlier are the standard ones that are easy to get. Here is a quick overview of common coaxial cable impedances and their main uses:

50 ohms:
50 ohms coaxial cable is very widely used with radio transmitter applications. It is used here because it matches nicely to many common transmitter antenna types, can quite easily handle high transmitter power and is traditionally used in this type of applications.

60 Ohms:
Europe chose 60 ohms for radio applications around 1950s. It was used in both transmitting applications and antenna networks. The use of this cable has been pretty much phased out, and nowadays RF system in Europe use either 50 ohms or 75 ohms cable depending on the application.

75 ohms:
The characteristic impedance 75 ohms is an international standard, based on optimizing the design of long distance coaxial cables. 75 ohms video cable is the coaxial cable type widely used in video, audio and telecommunications applications

93 Ohms:
This is not much used nowadays. 93 ohms was once used for short runs such as the connection between computers and their monitors because of low capacitance per foot which would reduce the loading on circuits and allow longer cable runs. In addition this was used in some digital communication systems (IBM 3270 terminal networks) and some.

Mostly that we use is the 50 ohms RG58, RG8 or RG213.

EXTRA LONG LIFE BATTERIES-some usable tips....

• Here is some tips to make yours batteries get the extra long life. Let's try it and feel the different...

Step1

Use rechargeable batteries. Use a nickel metal hydride battery if possible. These batteries have a larger capacity to store energy than single use batteries. Let them completely drain before recharging them to keep the integrity of their usage span. Batteries have an energetic memory. If you charge it when it is only half empty, it will start to feel as if that is the base or lowest amount of energy it can retain before stopping it's function.

Step 2

Turn off your electronics, completely. This is by far the best advice for extended life, as every battery is essentially good for a number of hours for use.

Step 3

Change usage. The next thing that drains a battery are the bells and whistles a piece of equipment may have. For instance,cellphone will last much longer on a "ring" setting versus a vibrate setting. The vibrate setting takes significantly more battery power to accomplish. Extrapolate this same idea to things like flashes on your camera. Only use the flash when you must. On your video camera avoid additional uses like "playback" until you can get to an outlet and use the electricity from the wall.

Step4

Store batteries next to the cool place. Alkaline batteries will last 5 percent longer by placing them in the freezer. But they must be warmed up before use to room temperature. It may be more effective to freeze NiMH and Nicad batteries often used for things like electronics or cameras. These batteries only keep their charge for a few days when resting at room temperature. But if you store them in the freezer they will retain 90 percent of their power.

note: I'm not responsible if anything happen to you or yours batteries when doing these. This is under your own responsibility!! I'm sorry........

standby for new member....

It's seem long time for me didn't update my blog. Honestly I did not have any idea to posting here... but maybe this picture ok... this is the 10m delta loop (credit to 9w2LLK, tq)

WinRadio-monitoring from your own PC

WinRadio is the alternative way for those interesting in monitoring hobby. A traditional table-top receiver still a good choice, but nowdays PC-controlled receiver also a choose . Compare to the price the PC-controlled receiver is more cheaper than traditional table-top receiver and give you more memory capacity is in practise unlimited. Each memory file can hold 1000 channels, and you can create as many memory files as you can fit in your computer.

For more information, 1
, 2

me; mostly still choose a traditional table-top receiver, nampak gempak sikit shack tu.... hhehehe
macam kat bawah ni...

icom R9500... mampu ke? heh....