The Stuff Of Radio
I N S T R U C T IO N S
Master Mobile DELUXE ULTRA-HI “Q” & ULTRA HI “Q” COILS
The Master Mobile Ultra-Hi “Q” and Deluxe Ultra-Hi ‘Y2″ series coils are designed to be used with a three foot base section (Master Mobile Models 88 or 88S) and a five foot whip (Master Mobile Model 100-60S). Either a bumper or body mount may be used. However, a heavy duty spring is recommended (Master Mobile Models 444, 446 and the 232 series, X, XC, XSSC, XSS,XX, XX or XXSSC). The 232 series mounts are to be preferred; the higher the antenna is raised, the more efficient it becomes. It is not necessary to add external bracing to support the antenna.
These coils are designed for single band operation and are made so as to resonate below the low end of the phone portion of each respective band. -The coil must be resonated to your operating frequency or the center frequency of the range of frequencies you normally use. It will,no doubt, be necessary to remove a part of a turn or possibly even several turns depending on your choice of frequency.
The antenna can also be out to the highest frequency normally used and then used in conjunction with the Master Mobile ‘Master Matcher” unit which was designed for this purpose. The Master Matcher” can be mounted in the trunk and turns added as needed to bring the antenna into resonance as the operating frequency becomes lower. A field-strength meter is provided to be mounted under the dash and the roller coil is motor driven so that the antenna may be resonated from the front seat of your vehicle. You will notice that the tuning is quite sharp when using the “Master Matcher” with the UHQ and Deluxe UHQ coils. It may be difficult to properly load the transmitter unless the antenna is properly tuned, this is due to the extremely high “Q” of the coil itself, thereby providing the highest possible efficiency.
The procedure for removing turns from the coils is as follows: Disconnect the feedline from the base of the antenna. (This must be done) Insert a one or two turn wire loop between the antenna base and ground. Keep the leads as short as possible and be sure they are properly secured. With a grid-dip oscillator coil inserted into the one or two turn loop, carefully tune grid dip oscillator until a share did is noticed indicating resonant frequency of the antenna. By using the GDO as a guide, redip the antenna each time a portion of a turn is removed from the coil until the antenna has been resonated to the desired frequency.
Do not remove more turns than are necessary, as the more turns you have operating outside the car, the more efficient your antenna system becomes.
After you have properly tuned the antenna to resonance with the GDO, remove the wire loop from the antenna base and reconnect the feedline from the transmitter. When the transmitter has been retuned, you will find the antenna will load properly on the resonant frequency. When you QSY to a different frequency, you merely repeak the antenna using the roller coil and you are ready to operate efficiently again on the new frequency.
Make sure the coil ends and the nuts holding the plastic caps on the coil are properly secured.
To facilitate quick changing of the loa^tling coils, try the E-Z-295 Quick Disconnect also manufactured by Master Mobile. They are available from your Master Mobile Distributor.
It is normally convenient to feed a mobile antenna with 52 ohm coax such as RG-8/U or RG-58/U. Either of these cables has a characteristic impedance of 52 ohms. It is common knowledge that the maximum transfer of energy can only be accomplished when impedances are properly matched.
The bottom impedance of a quarter wave radiator installed on a vehicle is, approximately, 45 ohms. The normal base loaded or center loaded mobile antenna will have a feedpoint impedance between 20 and 35 ohms.
Since the length of the transmission line seldom exceeds 15 ft., the losses involved are negligible, even at 2g Mos., with a fairly high SWR. However, unless a line of this length is made reasonably flat, difficulty may be encountered in obtaining sufficient transmitter loading.
The Master Mobile Micro-Z-Match Model 925 has been designed to facilitate proper matching at the base of the antenna. It may be used either with or without the Master Matcher unit.
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