i have tried everything and i just cant get my reflect down. 1.6 lowest swr on all antennas i try. even when i put the back one on (bounceback system). im almost fed up already. its driving me nuts and my amps. i have 2 predator 10k 17" shaft antennas and 2 55 r4 antennas as well. they both tune the same, 1.6, i gotta get 1.3 swr or better. my reflect is waaaay to high and im gonna burn up my amps. not good. how did you? and the other guys do it at 5kw plus? i have puck mounts, lmr400uf coax, jumpers are 6ft,antenna coax is electrical (resonant) 1/2 wave from the line section to the antenna. 1" ground strap bonded doors, hood, body frame, etc. im out of ideas. when i run the bounceback setup its still to high as well. also the fact that two different antennas are tuning exactly the same at 1.6 is making me think something else is going on. not the location of the antenna on the roof. i posted elsewhere and of course the answers where all over the place.the main two answers where the antenna shaft length is too short. but if thats the case how do other guys get 1.1 swr with short shaft antennas (r55 etc). next was location on the roof, its all measured out. next main answer was coax is wrong length. people were saying resonant half wave (which i have now), resonant half wave WITH line section included, 11ft, 11 1/2ft, 12ft, 15ft, 18ft were the main lengths given. wow.i hate making coax over and over and over, plus going thru all those connectors aint cheap. what do you guys think? ps: im concentrating on getting just the one antenna to tune up ( the one in the front) then i will deal with the bounceback setup, that parts easy
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Mobile anybody on here run a high power (5kw+) suburban? i need some advice
- Thread starter groundwire
- Start date
5
579Pete
Guest
Recommend you edit the original post. (Paragraphs exist for a reason).
It’s hard to read.
Space it & add numbers/letters like an outline (is even better).
There may be assumptions you want to address.
(An earlier thread for readers to consult?).
Ex:
— How is 1.6-SWR bad?
Me? I have to check the TV is plugged in several times.
P.S. FWIW, some of my posts — specifically about Radio — take much more than an hour to tap out on this old telephone. Length isn’t always the reason. Clarity, is.
.
It’s hard to read.
Space it & add numbers/letters like an outline (is even better).
There may be assumptions you want to address.
(An earlier thread for readers to consult?).
Ex:
— How is 1.6-SWR bad?
Me? I have to check the TV is plugged in several times.
P.S. FWIW, some of my posts — specifically about Radio — take much more than an hour to tap out on this old telephone. Length isn’t always the reason. Clarity, is.
.
If your front antenna is the hot it's mounted to close to the center of the roof. On a Suburban roof the hot needs to be 2 feet or less (preferably less) from the windshield or the back. There is too much flat ground plane around the antenna.
even if im just running that one antenna? looking at pics of most of the two antenna suburbans that run high power, it's in the exact same spot. the angle of the picture of mine makes it look like its over the middle of the back seat but its actually right behind the front seats, just over head
Attachments
i just ordered some lmr-600 to replace the 400. the 400 may be too small for my application which could explain the rising reflect during transmission due to heating. and also so i can rule that out.
Maybe you are experiencing something completely different like harmonics that are rampant this would make it impossible. Are testing with just the radio or at high power Try? Try running coax direct from the radio to the antenna or use an analyzer and short length of coax and maybe you will see a change.
Sounds like common mode current on the coax braid? Some of those Palomar Engineering clip on ferrite on the coax as close to the antenna as you can get it and some at the amplifier output too. I use these in my shack and they helped to bring the SWR down after I got it down as far as I could with the gamma match. I get 1.1 with my 4 pill but I also doubled up on the feed back resistors inside my amp to reduce the oscillations because the SWR was crazy high after I replaced the DEI with HG.
good thought, my common mode current readings are less than 30ma as measured with my MFJ-854. so they are very low and should not be a factor
Firstly, LMR-400 won’t handle the power you intend, so, heating, like you say, may rise the SWR, like other guy told you, did you test SWR on low power, how much is it ? The most LMR-400 will handle is 3kw. LMR-600 will do handle 5kw without problem. Beyond 5kw, helix cable is used.
By the way, just enough coax cable length is needed to reach the antenna.
By the way, just enough coax cable length is needed to reach the antenna.
groundwire, while i don't really have much personal experience with this level of power, it might be a good idea to take things step by step.
sounds to me like you've tried a lot of stuff, and checked and re-checked things. usually when that does not yield a solution it's because of two things:
1. that thing that seems unchangeable and seems like it just HAS to stay the way it is.
2. that thing that you are SURE it can't be, and by now your brain is passing it over within a second of thinking about it.
Troubleshooting is a universal art and isn't confined to RF, although i've never encountered any other kind of troubleshooting so fraught with anomalies.
first, if you have access to an antenna analyzer that would be a great tool to get some initial data from. maybe see if you can borrow one from someone for a day or two?
how about listing out your equipment chain here?
radio (please list all mods done)- length and type of coax-amplifier (driver?)-length and type of coax- (2nd amp?)- length and type of coax- antenna.
better to start with just the one antenna and get that right before moving on the the directional setup.
set things up so that you are using just the radio, the actual coax that goes to the antenna, and a less than 1 foot jumper placed right at the feedpoint of the antenna.
put an SWR meter in line with that coax, right at the antenna, and read your SWR on channels 1, 20, and 40.
post those numbers here.
if you can't get the SWR below 1.6 here, then stop.
do not add anything else into the equation and fix this issue.
try putting ferrite snap on chokes of the proper mix, (31, 43, etc.) on that 1 foot jumper. like, the whole foot of it.
did that change the SWR?
if yes, you have common mode currents and need to run a good 12" of chokes at the feedpoint of your antenna.
next, does moving the coax around as you are checking the SWR cause the reading to fluctuate? that's a telltale sign of common mode currents.
again, ferrite is your friend.
dont forget to try a different SWR meter to corroborate your readings.
If you are able to get the antenna SWR down to 1.3 or below doing things this way, then add the amp (only the driver if you are using multiple amps) again using the actual coax you intend to be there all the time.
put the SWR meter in between the radio and the amp, using the actual coax that would go to that amp, and again, with a short 1 foot or less jumper at the back of the amp.
check the SWR going in to your amp. what is that SWR?
is it 1.3 or lower?
remember that whatever power gets reflected back to the radio doesn't just stop there, it bounces back and forth down the coax, and will affect the purity of the signal coming out of that amp.
if that SWR is too high, then this is the place to start and you need to make sure that your radio is actually putting out 50 ohms and without a bunch of harmonic content.
that's why i asked about the mods done.
if the radio is ok, then you need to tune the input of your amp to get that reflect down.
if all that is ok, then put the SWR meter back at the feedpoint of your antenna, but this time after the amplifier, again using the actual piece of coax that will be going to the antenna.
did that SWR go up from your initial reading using only the radio?
that most likely means that your antenna has some unwanted reactance or the output tuning of your amp needs adjusting.
the more links in the chain, the more complicated this all becomes but im sure you can see from what i laid out that you need to add things in one at a time to find the source (or sources!) of your problems.
most of us would be fine with an SWR of 1.5 or below, but i understand that at high power levels, you need to be much more critical of your tunings.
please post your results here if you want help determining which piece of equipment is the problem and why.
LC
sounds to me like you've tried a lot of stuff, and checked and re-checked things. usually when that does not yield a solution it's because of two things:
1. that thing that seems unchangeable and seems like it just HAS to stay the way it is.
2. that thing that you are SURE it can't be, and by now your brain is passing it over within a second of thinking about it.
Troubleshooting is a universal art and isn't confined to RF, although i've never encountered any other kind of troubleshooting so fraught with anomalies.
first, if you have access to an antenna analyzer that would be a great tool to get some initial data from. maybe see if you can borrow one from someone for a day or two?
how about listing out your equipment chain here?
radio (please list all mods done)- length and type of coax-amplifier (driver?)-length and type of coax- (2nd amp?)- length and type of coax- antenna.
better to start with just the one antenna and get that right before moving on the the directional setup.
set things up so that you are using just the radio, the actual coax that goes to the antenna, and a less than 1 foot jumper placed right at the feedpoint of the antenna.
put an SWR meter in line with that coax, right at the antenna, and read your SWR on channels 1, 20, and 40.
post those numbers here.
if you can't get the SWR below 1.6 here, then stop.
do not add anything else into the equation and fix this issue.
try putting ferrite snap on chokes of the proper mix, (31, 43, etc.) on that 1 foot jumper. like, the whole foot of it.
did that change the SWR?
if yes, you have common mode currents and need to run a good 12" of chokes at the feedpoint of your antenna.
next, does moving the coax around as you are checking the SWR cause the reading to fluctuate? that's a telltale sign of common mode currents.
again, ferrite is your friend.
dont forget to try a different SWR meter to corroborate your readings.
If you are able to get the antenna SWR down to 1.3 or below doing things this way, then add the amp (only the driver if you are using multiple amps) again using the actual coax you intend to be there all the time.
put the SWR meter in between the radio and the amp, using the actual coax that would go to that amp, and again, with a short 1 foot or less jumper at the back of the amp.
check the SWR going in to your amp. what is that SWR?
is it 1.3 or lower?
remember that whatever power gets reflected back to the radio doesn't just stop there, it bounces back and forth down the coax, and will affect the purity of the signal coming out of that amp.
if that SWR is too high, then this is the place to start and you need to make sure that your radio is actually putting out 50 ohms and without a bunch of harmonic content.
that's why i asked about the mods done.
if the radio is ok, then you need to tune the input of your amp to get that reflect down.
if all that is ok, then put the SWR meter back at the feedpoint of your antenna, but this time after the amplifier, again using the actual piece of coax that will be going to the antenna.
did that SWR go up from your initial reading using only the radio?
that most likely means that your antenna has some unwanted reactance or the output tuning of your amp needs adjusting.
the more links in the chain, the more complicated this all becomes but im sure you can see from what i laid out that you need to add things in one at a time to find the source (or sources!) of your problems.
most of us would be fine with an SWR of 1.5 or below, but i understand that at high power levels, you need to be much more critical of your tunings.
please post your results here if you want help determining which piece of equipment is the problem and why.
LC
i
i was using the 400 with my 8 pill, the 600 is on the way for the 16 pill. low power swr 1.6, high power swr 1.6, the only thing that rises with power increase is the reflected power.
well that would make sense since the reflected power is a percentage based on the SWR.
if you can't get the SWR down below 1.6 with your radio, try a stock radio.
there are many mods that get done to radios in order to make more power, and they change the output of the radio to where it's not really 50 ohms anymore.
If your radio is stock, then the only place to look for improvement is at the antenna itself.
good luck.
LC
radio is stock, yaesu ft-891. the whole system runs perfectly on a dummy load. once the antenna is connected back up high swr, so its an antenna issue. either the shaft height, mounting location, roof rack cross bars causing it (which i just thought of last night. im gonna take them off.
yeah if that's the radio, that's about as clean as you're going to get.
I think your best bet is to find an MFJ 259 antenna analyzer and use that to find out what is up with the antennas.
too bad no one who actually runs one of those antennas is responding with their experiences, as that would be the most helpful.
good luck with it.
LC
I think your best bet is to find an MFJ 259 antenna analyzer and use that to find out what is up with the antennas.
too bad no one who actually runs one of those antennas is responding with their experiences, as that would be the most helpful.
good luck with it.
LC