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Antenna Tuning Unit ATU For 27 MHz CB Radios - This reception apparatus tuning unit (ATU) empowers half-wavelength or more wire reception apparatuses to be coordinated to the 50-? reception apparatus data of 27-MHz Citizens' Band (CB) rigs. The ATU is valuable in those situations where a wire recieving wire is less prominent than a rooftop mounted "vertical" or ground-plane. It is likewise incredible for "extemporized" reception apparatuses utilized by dynamic CB clients on campgrounds and the like on the grounds that it permits a length of wire to be utilized as a decently powerful recieving wire hung between, say, a tree limb at one side and a tent post, at the other. Clearly, the wire closes then must be confined utilizing, for instance, short lengths of nylon wire. It is even conceivable to utilize the ATU to tune a length of security fencing to 27 MHz. 

The loop in the circuit comprises of 11 turns of silver-plated copper wire with a distance across of around 1 mm (SWG20). The interior breadth of the loop is 15 mm, and it is extended to a length of around 4 cm. The tap for the recieving wire link to the CB radio is made at around 2 turns from the cool (ground) side. Two trimmer capacitors are accessible for tuning the ATU.

The littler one, C1, for calibrating, and the bigger one, C2, for coarse tuning. The trimmers are balanced with the guide of an in-line SWR (standing-wave proportion) meter which most CB fans will have, or ought to have the capacity to acquire on credit. Select channel 20 on the CB apparatus and set C1 and C3 to mid-travel. Press the PTT catch and modify C2 generally advantageous (that is, most minimal) SWR perusing. Next, then again modify C3 and C2 until you get as close as would be prudent to a 1:1 SWR perusing.

may then be changed for a surprisingly better esteem. No compelling reason to re-conform the ATU until another radio wire is utilized. On the off chance that the length of the wire radio wire is precisely 5.5 meters, then C3 is set to greatest capacitance. In spite of the fact that the ATU is intended for half-wavelength or more reception apparatuses, it may likewise be utilized for physically shorter radio wires. For instance, if reception apparatus has a physical length of just 3 meters, then the staying 2.5 meters must be twisted on a length of PVC tubing. This makes a purported BLC (base-stacked curl) electrically abbreviated radio wire. In rehearse, the included curl can be made to some degree shorter than the hypothetical quality, so the genuine length is best controlled by trial and mistake. At long last, the ATU must be implicit an all-metal case to avert undesirable radiation. The trimmers are than gotten to through little gaps. The association with the CB radio is best made utilizing a SO239 ('UHF') or BNC style attachment on the ATU box and a short 50-W persuade link with coordinating fittings.