SWR instellen van antenne

SWR instellen van antenne

Auteur Marcel Publicatiedatum 07-02-2013 Opmerkingen: 0

27 Mc CB radio SWR (staande golf) op antenne instellen.

In het Engels hebben wij een uitgebreid artikel op onze website staan.

Maar omdat het hebben van een juiste SWR heel belangrijk is, hierbij de verkorte CBShop tekst in het Nederlands.
 
Tegenwoordig verkopen wij veel 27 Mc antennes die trim vrij zijn. Als je deze antennes massa geef, en je kort de kabel niet in ben je al vaak helemaal klaar. De moderne cb antennes zijn zo breedbandig en kunnen zoveel vermogen aan, dat het afstellen eigenlijk niet nodig is.
 
Maar het nakijken van de SWR is altijd aan te bevelen. Je zou de plug niet goed op kabel gesoldeerd kunnen hebben. Of slechte massa hebben. Of een breuk in de kabel hebben. Dan is zelfs de beste antenne niet goed te gebruiken.
 
Gevolgen van een slechte SWR kan zijn dat je eindtrap van je cb bakkie kapot gaat van het vermogen dat weer de radio in gaat. Want dat is wat je meet met een swr meter. Wat komt er terug van het vermogen wat je uitzend. En op een eindtrap wordt geen garantie gegeven. Als deze kapot gaat is het immers geen fabrieksfout maar een gebruikers fout. En daarom is het belangrijk dat je een swr meter gebruikt bij de montage van een cbradio en antenne. Of dat nu thuis of in een vrachtauto is.
 
SWR ( staande golf verhouding ) , is een meting van hoe efficiënt uw antennesysteem het beschikbare vermogen van jouw radio zal uitstralen . In eenvoudige termen, zou je radio graag al zijn kracht uitstralen , maar kan dat alleen doen als de andere componenten samenwerken . Slechte coax en mounts, of inefficiënte antennes en grondvlak (massa) kan het systeem problemen veroorzaken. De eenvoudigste manier om het concept te begrijpen is om te denken in termen van waterstroom . Dat wil zeggen, als je een cm dikke kraan op een 2 cm dikke pijp zet, zal jouw potentiële vermogen worden beperkt door de een cm dikke kraan . Het instellen van jouw antennes SWR, zal de beperking van het uitgestraalde vermogen te verminderen
 
Als alle radio alleen zonden op maar een kanaal , zou het veel eenvoudiger zijn antennes te ontwerpen . Zoals het is, op CB alleen al zijn er 40 kanalen. Mobiele antennes kunnen alleen worden gemaakt om te werken op een bepaalde frequentie ( kanaal ) . Het doel van antenne fabrikanten is om antennes te bouwen die werken bij een frequentie in het midden van de beschikbare band (kanaal 19 op CB ) en het breed- bandig genoeg  zijn om de off - frequentie gerelateerde SWR op de twee uiterste einden van bewaren de band onder 2,0:1 . Opgemerkt moet worden dat als je communiceert op een specifiek kanaal, je natuurlijk daarop jouw antenne kunt afstemmen om optimale prestaties op deze kanalen te krijgen. De meeste mensen , echter geven de voorkeur aan de gehele bandbreedte te gebruiken bij het aftrimmen.
 
SWR power meter
 
Setting the SWR of Your Antenna
 
from Firestik®; Antenna Co. Technical Support
 
SWR (standing wave ratio), is a measurement of how efficiently your antenna system will radiate the power available from your radio. In simple terms, your radio would like to radiate all of its power, but can only do so if the other components cooperate. Bad coax and mounts, or inefficient antennas and ground plane can cause system bottlenecks. The easiest way to understand the concept is to think of it in terms of water flow. That is, if you put a one inch faucet on a two inch pipe, your potential output will be restricted by the one inch outlet. So goes antenna systems. Setting your antennas SWR will reduce the restriction of radiated power
 
If all radios only transmitted on one channel, it would be a much easier task to design antennas. As it is, on CB alone, there are 40 channels to contend with. Mobile antennas can only be made to resonate at one specific frequency (channel). The goal of the antenna manufacturers is to build the antenna to resonate at a frequency in the middle of the available band (channel 19 on CB) and make it broad- banded enough to keep the off-frequency related SWR at the two extreme ends of the band below 2.0:1. It should be noted that if you communicate on one or two adjacent channels anywhere within the band, you can tune your antenna to achieve optimum performance on those channels. Most people, however, prefer to use the entire bandwidth when tuning. 
 
THINGS YOU WILL NEED
1.Knowledge of what not to do .... read previous sections. 
2.Properly installed antenna system (mount, coax and antenna) that was made for the type of radio you will be using and has been tested for shorts and opens in continuity. (See "Testing Continuity") 
3.Functional radio. 
4.SWR meter. (See "SWR Meter Hook-Up") 
5.Short piece of coaxial cable (jumper) with PL-259 connectors on both end. 
 
SWR METER HOOK-UP
 
The SWR of the antenna, without feedline, can be measured by placing the SWR meter in-line at the antenna instead of at the radio. However, the coax can help or hinder performance. In the end, your SWR should be checked at the radio end because all components will be a part of the final operational system being used. 
1.Remember to check for continuity, shorts and opens in your coax and mount installation first. 
2.Take measurements in an open area with the vehicle's doors and hatches closed. 
3.All measurements should be taken with antenna tip on, unless you do not plan to use the tip in normal use.
 
swr instellen
 
THE SET UP
If already connected, disconnect the coaxial cable from the radio. Connect the coax cable that normally connects to the back of the radio to the SWR meter connector marked "Antenna" or "Ant". Now, connect one end of the jumper cable to the back of the radio and the other end to the SWR meter connection marked "Transmitter" or "Xmit". Your SWR meter is now in series (in-line) with your radio and antenna. Since you've already read the previous parts of this pamphlet, you should now have your vehicle in an open area, with all doors closed. Turn your radio on and tune to channel one or the lowest channel on your radio. If your radio has side band operation, make sure you are in AM mode before doing SWR tests. 
The following assumes that your SWR meter has a standard set of switches, knobs and meters. That is, there will be at least one switch with the marking Forward (FWD) in one position and Reference (REF or SWR) in the other. There will also be a knob or sliding controller marked "Set" or "Adjust". Most meters come with full instructions. If the common configuration does not match your meter you will need to rely on the meters manual for assistance. 
 
With the radio on the lowest channel (1 on CB) and the SWR meters switch in the Forward (FWD) position, depress the transmit switch (key up) located on the microphone. While holding the unit in this transmit mode, adjust the meter needle to the set position using the Set or Adjust knob on the meter. As soon as the needle is in alignment with the corresponding mark on the meter face, flip the switch to the Reference (REF) position. The meter is now showing your SWR on channel one. Note the value and quickly release the microphone switch. Record this reading on your paper to the nearest 1/10th. i.e. 1.8, 2.3, 2.7, 1.4, etc. 
 
Now, switch your radio to the middle channel (19 on CB). Place the meter switch in the Forward (FWD) position, depress the microphone switch and adjust the meter to place the needle on the Set position of the meter face. Once in the set position, place the meter switch in the Reference (REF) position and note the reading. Release the microphone switch and write this value down to the nearest tenth of a point. Note: If your antenna system is closely matched to the radio you may get little or no movement from the meter needle on this channel. This is normal. 
 
Finally, place your radio on the highest number channel (40 on CB). Place the meter switch in the Forward (FWD) position, depress the microphone switch and adjust the meter to place the needle on the Set position of the meter face. Once in the set position, place the meter switch in the Reference (REF) position and note the reading. Release the microphone switch and write this value down to the nearest tenth of a point. 
 
With these three readings, you can determine many things about your system. For instance ... 
Bullet If SWR on channels 1, 19 & 40 is below 2.0, your radio can be safely operated on any channel without causing damage to the radio's circuitry. 
Bullet If SWR on all channels is above 2.0 but not in the "red zone" (normally over 3.0), you may be experiencing coaxial cable reaction (bad quality, wrong length, etc.), insufficient ground plane, or have an ungrounded antenna mount. 
Bullet If SWR is in the "red zone" on all channels, you probably have an electrical short in your coax connectors, or your mounting stud was installed incorrectly and is shorted. DO NOT USE YOUR RADIO UNTIL YOU HAVE FOUND THE PROBLEM. 
Bullet If SWR on the lowest channel is higher than it is on the highest channel, your antenna system appears to be electrically short. See the following section title "Adjusting Short Antennas". 
 
 
ADJUSTING LONG ANTENNAS
 
If the SWR on channel 40 is greater than that on channel 1, your antenna is considered to be "LONG" and reduction of physical height and/or conductor length will correct this situation. Depending upon antenna model, this entails screwing down the tunable tip (Illustration #1: Firestik II, Firefly), or, removing the tip, making short slits in the plastic covering and unwinding and clipping off wire (Illustration #2: Firestik, Road Pal). Firestik Designer Series antennas require loosening the allen screws and lowering the metal whip (Illustration #3).
 
ADJUSTING SHORT ANTENNAS
 
If SWR on channel 1 is greater than that on channel 40, your antenna is considered to be "SHORT" and increasing the physical and/or electrical length of the antenna is required to correct this situation. Because we make our antennas extra long, readings which indicate "Short" normally stem from ground plane deficiency (lack of vehicle metal surface for the antenna to reflect its signal rom). This condition is often corrected by adding a spring and/or quick disconnect to increase the physical height. Ground plane deficiencies can also be compensated for by using dual (co-phased) antennas or special no-ground-plane antenna kits. 
 
Lengthening of the Firestik II and Firefly is accomplished by turning the tuning screw further out (Illustration #1). On Firestik and Road Pal models, it requires tip removal, short slits in the plastic covering and, the separation and upward repositioning of three or more wire turns (Illustration #4). Firestik Designer Series antennas require loosening the allen screws and raising the metal whip (Illustration #3).
 
NOTE: The shorter the antenna, the more sensitive it is to adjustments. For example, removing two wire turns on a 4 foot antenna might move the SWR by 0.3; the same amount removed from a 2 foot antenna may move the SWR by 1.0. Make smaller adjustments on shorter antennas.
 
DUAL ANTENNAS
 
Measurements and determination of short or long conditions are the same as the single antenna procedure. However, when tuning co-phased antennas, if you adjust one antenna, it is advisable to adjust the other in equal amounts to keep them in perfect balance.
 

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