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Johnhenre
Member
Username: Johnhenre
Post Number: 97
Registered: 1-2004
| | Posted on Saturday, September 01, 2007 - 3:43 am: | 
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ANYone have knowledge of swr using a mfj my wave is 1:5 all around reflect is all but perfect.but the audio when modulated is unacceptable by far.swr climbs to over 3; plus i've done all of the antenna adjusting,coaxial checks anyone that may have a knowledgeage answer i'd like help hear. thanks in advance john |
Dale
Senior Member
Username: Dale
Post Number: 1118
Registered: 12-2002
| | Posted on Saturday, September 01, 2007 - 10:51 am: |
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also are ya checking with just
1radio
2 swr meter
3antenna
dale/a.k.a.hotrod
cef426
cvc#64
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Marconi
Advanced Member
Username: Marconi
Post Number: 751
Registered: 11-2001
| | Posted on Saturday, September 01, 2007 - 12:54 pm: |
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With some meters it is not advisable to check SWR with input from the mic when you key up. Most meters cannot account for the changes in power due to modulation. In fact some meter instructions tell you to cut your mic gain down/off so this cannot happen. Just go by a small amout of dead key and check your SWR.
If you want to monitor your systems SWR under modulate power, you will have to get a meter that will do that.
If you insist on doing it that way, then try to set the meter in the forward position with a modulate signal and then switch to reflect and check the modulated signal. Then as you talk you will see SWR about as close as you can to what the correct SWR is under modulated power.
If you get the meter set right either way, right on the money, the SWR should be the same both ways. Within reason, the SWR from an antenna does not change with changes in RF power. |
Johnhenre
Member
Username: Johnhenre
Post Number: 98
Registered: 1-2004
| | Posted on Saturday, September 01, 2007 - 1:06 pm: |
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Tryed all of the above and below radio 3900's 44's 29's.213 cable. all is kinda new.also the mfj-259 is new. swr 1;1 can get it down flat, 3 watts.swing 20 to 40 watts this is were the the swr rise's to high.antenna is hot and adjustable.ohm's set at 47 ohm's,reflect 5% actaully perfect just keep the swr stable.? |
Johnhenre
Member
Username: Johnhenre
Post Number: 99
Registered: 1-2004
| | Posted on Saturday, September 01, 2007 - 8:51 pm: |
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Guys thanks for your replys.but i finial figuired it out.the old hands on way and a dosy,So much for (MFJ) costly little bugger that actually can at least tell you your resistance in ohm's which is generally is ok if the swr is right But it can't detect detect driven elements especally a back door element which was my problem,just a little insite on mobile antenna system's Mybe i did'nt real the instruction's that came with my 2nd mfj meter. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 3914
Registered: 7-2004
| | Posted on Sunday, September 02, 2007 - 9:10 pm: |
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Johnhenre, i think you may be under a bit of confusion as to how to read the 259, as well as an SWR meter. an antenna analyzer will, as you found out, tell you LOTS of things about your antenna-if it is resonant on the freq you intend to operate on, or where it actually is, and how efficiently it is tuned to the operating frequency, its impedance, or match to the transceiver and coax, and whether its reactance is inductive or capacitive. for ease of understanding, a bit of simplification here-the 259 analyzer is itself a tiny transmitter used to measure 'where' the antenna is, then YOU adjust the ANTENNA. generally, you adjust the overall LENGTH of the antenna for resonance, and finally adjust the feedpoint MATCH, or coil on say a maco v5/8 or gamma on a beam, til you get r=50 & x=0. or as close as you can get. with those #'s you'd see 1.0:1 on the mfj, and you'd be perfect, on 1 channel at least. obviously, you probably won't see those exact #'s with a 1/4 wave on a mobile-especially a non-tunable one such as 102" whip, but, like i said 'close' is what you're after. once you are 'resonant', you tune as close as possible. a 2nd antenna used as a reflector only and NOT hot just needs a mathematical difference in electrical length as compared to the hot antenna, and separation distance. anyway, the 259 can tell you that a 1.1:1 swr is on a harmonic freq & NOT resonant where you want to be, and vice versa.
as for SWR meter, like marconi says, SOME such as autek wm1 are designed to NOT see PEP wattage, just carrier. now, if you take a 'regular' meter, put 3 watts carrier into it & adjust the 'calibrate' control & read meter. now, put 40 watts CARRIER into it & you will see calibrate is WAY off. same thing is happening when you modulate the input signal-you threw the calibration out of whack. so, if your meter shows a # you are happy with, with a dead key, don't worry about what it shows while talking, put it in the 'power' setting. i have not noticed any strange swr readings on a meter with a reflector on a mobile, at roughly the correct spacing. an analyzer will show correct resonance & R, X may or may not be affected on the analyzer, to see how things are working there, you'd check with a field strength meter for F/B & S/S. |
Johnhenre
Intermediate Member
Username: Johnhenre
Post Number: 100
Registered: 1-2004
| | Posted on Thursday, September 06, 2007 - 7:30 pm: |
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THANK'S PAN'' BUT I'M FINE ON THE DRIVE ELEMENT.I'M ONLY USEING A 3 WATT DEAD SWR.1:1 R=50 OR I CAN CHANGE THIS X=.1 YOU MIGHT SAY PERFECT.BUT GO'ES TO HIGH WHEN AUDIOED INTO THIS IS NOT NORMAL AT A LOW DEAD KEY?? THE ONLY WAY TO KEEP IT DOWN IS A BACK DOOR WHICH IS'NT RECONIZE BY THE MFJ 259.NOT EVEN IN RESISTANCE.BUT IT GETS IT FROM RISING WHEN AUDIO IS SPOKEN.I'VE GOT SPACEING FULLING ADJUSTABLE AND HEIGHT AJUSTABLE.ALSO THE DERECTOR'S ALL ARE ABLE TO ADJUST EITHER WAY OR HEIGHT ALSO.SO WHY DO'NT THE MFJ DETECT ANY CHANGE'S MADE TO THE ANTENNA EXCEPT THE DRIVEN ELEMENT? THE ONLY WAY YOU CAN SEE THE CHANGES IS TO GET OUT APPROX. 100FT, OUT AND SEE IT ON A HAND HELD FEILD STRENGHT METER. JOHN |
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