| Author |
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Taz
| | Posted on Thursday, June 13, 2002 - 9:53 pm: | 
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Hey guys,
I see this question all the time.
I cant get my swr between my radio and amp below a 2. I have tried a 2 foot jumper and a 5 foot. ( i know a 5 foot wont work
arrrr |
Insider
| | Posted on Friday, June 14, 2002 - 10:39 am: |
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Popular consensus is to use either 3ft or 9ft of coax.
Funny why that is, being that if everything is truely 50 ohms, then it shouldn't matter what the coax lenght is.
I personally use 2ft between my radio and KLV 200/V and the SWR is 1.3 between the radio and amp with the amp off. When the amp is switched in, the SWR between the radio and amp is 1.05ish to 1. |
Taz
| | Posted on Friday, June 14, 2002 - 5:36 pm: |
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ok. i will try 3 |
Bigbob
| | Posted on Friday, June 14, 2002 - 7:55 pm: |
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If you don't have a perfect match at antenna(practically impossible)and say have 100 feet of coax or 10 feet,you can get an infinite number of readings depending on where you tapp into it.I ran a 5ft. section to boomer400 then 1foot to my meter pickup,3ft.to low-pass fltr.,81ft. to antenna[1.13 swr on 27.685,2.3on 25.615,1.4 on 28.315]oh,and 1.2 on radio meter,hows them apples?It took 2 days and a soldering gun and side cutters and good ol' tial and error to accomplish this.So if you don't have patience for this,you can get a 2.5 kilowatt MFJtuner for about 5 bills,hows that? |
Taz
| | Posted on Friday, June 14, 2002 - 10:01 pm: |
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lol. haha. its only at a 2 with the amp on high between the radio and amp. with the amp off its flat. from amp to antenna its 1.1 |
Znut
| | Posted on Saturday, June 15, 2002 - 2:00 pm: |
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Taz,
Sounds like the amp could use a little more matching on the input. You could either get the golden screwdriver on the trimmer cap on the input transformer of the amp or put an antenna tuner between the radio and the amp. You should ask the techs their opinion. Maybe one will post a photo of the device you should adjust inside of the amp.
By the way ( should I yell?)- you guys make me crazy playing with coax lengths! The only way that can change anything is by making a bad SWR look better on a voltage bridge (CB SWR meter). Different coax lengths only move the potential relative to where that diode is in the meter. That standing wave is still there!
Good luck,
Randy(Znut) |
bruce
| | Posted on Saturday, June 15, 2002 - 3:23 pm: |
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ament znut |
ss8541
| | Posted on Saturday, June 15, 2002 - 10:48 pm: |
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well changing coax length here -is- good znut. yes, you are just changing the impedance that the radio is staring into while the amp is on. but, the radio is happy, it is putting out full power, so no harm.
and taz, a 2:1 swr is not bad so why change it? the radio is 'happy' with this. like the old saying, don't fix what isn't broke. |
Znut
| | Posted on Saturday, June 15, 2002 - 11:47 pm: |
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ss8541,
The SWR is still 2:1 at the amp, no matter what the SWR meter/voltage bridge says. Playing w/the coax won't do much.
Znut |
Taz
| | Posted on Sunday, June 16, 2002 - 1:49 am: |
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So a 2.0swr isnt bad? at a 2.0 there is some loss there in power. |
bruce
| | Posted on Sunday, June 16, 2002 - 8:16 am: |
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See thats my point it is like antenna tunners it just hids the problem. Cutting coax unless your making phasing lines only makes you feel good.
Fix the antenna and there will be lettle VSWR to worry about. By the way z-nut my new HF ant is up with the antenna tunner it goes 80-6 under 2/1
bruce |
Marconi
| | Posted on Sunday, June 16, 2002 - 11:41 am: |
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Well guys, I have to agree with 8541. True, this is not a broad band fix. In some cases playing with jumper lengths may be the only fix going, especially if you are having amp related problems and you don't have good control over all the matching points already mentioned. To this extent, I think this is more or less a load problem and is a frequency related issue that crops up when your RF stuff and the line are not in good harmony. Seems to me this type of problem is often just a simple distribution of power problem.
If the 2.0:1 SWR does not cause any obvious disharmony to the system then there will probably not be much if any noticable or measurable loss of power out in the distance either. In fact at times I see better close in field strength readings with some SWR present on the line. I believe this has to do with the amount of current you are able to get to the antenna, but can't tell you what is actually happening and why. I don't know exactly how to affect changes either, but I think it may have something to do with some existing phase relationship and the value of the re-radiated signal that you may see reflected on your meter. Do the same deal tommorrow or take it all down the road a bit and you may see a totally different result. Strange stuff RF.
Have you ever taken your stuff to the tech and he show you a good result, and when you get home it is no-way-no? What do you think?
Marconi |
Marconi
| | Posted on Sunday, June 16, 2002 - 11:49 am: |
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Taz, try a 6' - 7' - 9' jumper or anywhere inbetween and see if you can get the SWR down between the radio and the amp. How are you checking the SWR in this area?
Marconi |
Insider
| | Posted on Sunday, June 16, 2002 - 12:04 pm: |
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Doesn't that power that's reflected back to the transmitter get reflected back up the line again, minus losses in travel and phase cancelations along the way?
Yes, there is a loss, but you're sending that signal into an amplifier, so that slight loss is being compensated for by the amp. Now if you want to be a purist on this, one can probably successfully argue that the reflections are degrading the signal to noise ratio by a factor of X due to a mixing of the signals and some phase cancelations.
No question about it, high VSWR is bad, but 2:1 should be safe for modern devices--especially since no CBer I know of keeps their radio keyed up for hours on end.
I'm glad there are some folks who agree with me on the coax lenght issue. Besides, if you want to do conjugate matching, I think that's what it's called when you use coax as a transformer, it's frequency dependant, where as a properly set up broadband system should maintain its match over the coverage range.
Now here's something I need confirmation on. I'm 100% sure I'm right, but lets hear what the experts have. Someone told me that the more power you run, the higher the VSWR is between the amp and the antenna.
I tried to convince them that there must be a mismatch in either their amp (not tuned properly) or the antenna because VSWR is a ratio and ratios don't change as long as the quantities measured change proportionally.
I argued, assuming everything is working correctly, but slightly mistuned, the higher VSWR is always there, but the added power is revealing it as you are now making up for any line loss or poor sensativity on your VSWR bridge. They were concerned as their VSWR went from being flat with no power up to 1.2:1 with power. |
Taz
| | Posted on Sunday, June 16, 2002 - 7:29 pm: |
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I am using the swr meter in the radio for between the radio and amp. I will try a different meter and see what I come up with. |
Galileo
| | Posted on Sunday, June 16, 2002 - 8:08 pm: |
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5 foot of coax is 50 ohms, 50 foot of coax is 50 ohms..If all inputs and outputs are 50 ohms, the length of coax will make little or no difference... |
Taz
| | Posted on Sunday, June 16, 2002 - 8:20 pm: |
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Same. |
Bigbob
| | Posted on Sunday, June 16, 2002 - 10:31 pm: |
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TAZ,put a cb match box between radio and 550,now u have infinite adjustment with any coax length. |
Znut
| | Posted on Sunday, June 16, 2002 - 10:55 pm: |
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Taz,
I think you what the situation is by now.
Did you ask the tech's yet about how to trim that amp out? You may be able to do it. You will need to leave that SWR meter between the radio and the amp. If you can, put a power meter between the amp and the antenna. When you begin to turn the screw on the cap, your SWR should change. You should see a change in power out of the amp(even on low, hint) at the same time.
Until you fix it, just don't key more than a couple of watts into the amp and you don't have to worry about the radio. You should still get plenty out of the amp on the highest setting. If you're not long winded, your rig may be fine like it is.
Take care,
Randy(Znut) |
Taz
| | Posted on Sunday, June 16, 2002 - 11:37 pm: |
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ok, thanks znut. |
ss8541
| | Posted on Monday, June 17, 2002 - 12:38 am: |
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insider, there are atleast 3 answers to your higher power, higher swr question.
1) is that as the current through the rf trans increases, the rf impedance of the rf trans collector is decreasing. after it is 'transformed' by the ferrite transformers, it is probably getting further away from 50ohms with the higher power than with the lower power.
2) is that with higher power, the harmonic and spurious signal content is higher. so with an antenna that is tuned for 27mhz, all that other trash is being sent right back down the coax, since the antenna isn't accepting it.(this is the reason swr's will normally go down when a low pass filter is added to an amp). when using a dummy load, this is not as noticeable since it absorbs the harmonics and other trash.
3) and this is something that was just recently brought to my attention by an am broadcast band engineer. the more power you put into an antenna, the more it 'couples' into surrounding objects. and those objects in turn 'couple' more of that power back into the antenna.
and marconi is right, some systems you can't get below a 2:1. the new fiberglass trucks are a fine example. if i can get them that low(which is fine), and the customer is not an 'swr freak', i leave them there. if i can't or the customer wants to see that perfect 1.5:1 or lower swr, then i use the conjugate match method. usually a 6-9ft section(since these lenghts are impedance inverters or close to the inverting point) will drop a high swr down to a nice match at the radio or amp. now the radio or amp is happy and so is the customer. i just made an over the road driver happy sat like this. he was going to be in town for a while, and had called the motorola dealer because he was tired of dealing with cb shops. i gave him 'my' business # told him to call and leave a msg, and i would get up with him after my fulltime job. he had been through 3 sets of antennas from 3 different shops who all had supposedly tuned the system down as low as it would go. well they hadn't even done that. and -all- had used the same coax so all antennas tuned out about the same. his true swr was about a 2.8:1. i got them down to a 2.2:1 b4 they started to climb again. i added a 9ft section to the existing coax and boom less than 1.4:1 across the 40ch band. did i fix his true swr problem. no but now his radio is happy with what it is 'seeing' and so was the customer. i explained this all to him, but he could care less as long as when he checked swr the needle barely moved.
taz, you can 'trim' that amp out, but there really is no need to do that. the 2:1 is the swr that the amp is showing the radio. it is now the radios load/antenna. like i said, a 2:1 is fine. it will not hurt the radio, and no one on the rxing end will ever know, since this will not make a noticeable difference in how it drives the amp. |
Insider
| | Posted on Monday, June 17, 2002 - 9:06 am: |
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Fascinating stuff. I must not have had my coffee: I completely forgot about the harmonic content of the signal. I hear many say they don't want to use lowpass filters for the reason, you guessed it, SWR may increase slightly with some of them.
Point 3 is an excellent tidbit and makes sense when you think about it: AM radio station antennas are often out in open fields. Next time I check the tower lights at night I'll ponder that one.
Taz, let us know what happens |
Kirk
| | Posted on Monday, June 17, 2002 - 12:22 pm: |
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just my 2 cents here.....an swr of 2.0 (if your meter is correct....Bird equiv??) is still totally acceptable on 10 and 11 meters. As you go higher in frequency, that's where loss plays a major role, but your really not loosing much at 27 Mhz. I can totally understand the concern however...been there and done that. Good luck |
CATMANKZZA1806
| | Posted on Monday, June 17, 2002 - 1:00 pm: |
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I have more luck with a steel antenna...
If i can't get my swr down with the stinger then i run a ground cable to the antenna itself more grounds better the swr That is my saying..
But i have a wilson 5000 magnet mount on my mobile radio. I have a Galaxy77 with a messenger500 my swr is a 1.1. Swr varies the spot where you are also. You might have a real good one at one place a higher one elsewhere. Wheather has alot to do with it also...
You keep working with it you'll get your swr down at that average point from one frequency to the other...
CATMANKZZA1806 |
Bigbob
| | Posted on Monday, June 17, 2002 - 6:05 pm: |
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God,ZNUT,you make sure you stress low low input when he tunes that amp RF burns are not fun. |
Biged
| | Posted on Monday, June 17, 2002 - 8:14 pm: |
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Speaking of RF burns. Heres one you will laugh at. We were staying at my father-in-laws while our house was being built. I quickly got tired of not having a radio so I broke my Turbo out of its box and hooked it up to a wilson 5000 that I stuck to the I-beam in the basement. It was horizontal. It didnt get out or hear real well but my SWRS were fair so I mostly just listened. Well, when I was checking my SWR's when I first hooked it up, I felt a little "zap" on my lip from the wire mesh on the RK-56. At that point, I had never heard of RF burns. I thought I was going crazy. So I did it again, only at high power. WOW!!! It put a red mark on my lip and a small blister shortly followed. I found out later from one of my ham buddies that thats what they called an RF burn. By the way, my radio was only about 6' away from the very tip of the antenna. ROOKIES! |
Taz
| | Posted on Tuesday, June 18, 2002 - 2:45 am: |
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you got to learn somwhere.
I have one more question.
I am putting a 6 watt deadkey into a klv-550 from my melaka and only 40 out on high. uhh is that from the 2.0 swr im getting? |
Marconi
| | Posted on Tuesday, June 18, 2002 - 12:15 pm: |
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Hey Taz, you could have told us this 5 days ago. You have a problem with your amp. Sounds like to me that the melaka is just going right through the amp and the amp is not doing a thing. What do you think?
My answer to your question is no!
Marconi |
ss8541
| | Posted on Tuesday, June 18, 2002 - 5:20 pm: |
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taz, marconi is right. this is the most important piece of information you should have gave with your question. -NO- the 2:1 swr has nothing to do with that low of an output with the input you have. even with a 3:1 you should have more than this out of the amp with a 6w carrier.
b4 i go any further with this, since there are a few scenarios here that could cause you problems and swr reading, let me ask this; is the swr deal and the low power something that just happened or is this something that you have had since every since you owned the amp? also are you the 1st owner?
and you also said something about changing finals in an amp one time. is this after doing that?? |
Bigbob
| | Posted on Tuesday, June 18, 2002 - 7:55 pm: |
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HAY TAZ you forget to hook up coax on output of 550? Mine kicks out 200 on hi. with 6 in and thats to much drive 2.5 will do the same thing,god TAZ, I hope you didn't try to tune more poop out of it because of the smaller pills.Really those pills will put out at least 125 watts a piece.Check the contacts on the manual switch and on the relay,a bit of grease on the contact will act as a resistor to RF and cause exactally that. |
Taz
| | Posted on Tuesday, June 18, 2002 - 11:10 pm: |
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I sent it to 307 for repairs cause I blew out the front end on it several months back |
Taz
| | Posted on Wednesday, June 19, 2002 - 2:01 am: |
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Sorry guys, i had the switchbox on the flatside and it read 40 with a 5 watt deadkey.
Put it on the verticle and I get 80w out with 6 in.
dont shoot me |
Bigbob
| | Posted on Wednesday, June 19, 2002 - 9:17 pm: |
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Are you just jerking us around taz because the dates on your posts with all you been stating just don't add up.Everything and I mean everything I've bought from Coppers has worked perfectly,UNTIL I GOT OUT MY SCREW DRIVER AND TOTALLY SCREWED UP EVERYTHING,NEVER AGAIN THE SEAL STAYS SEALED,I'M NOT BLOWING $875 THIS TIME.It's still anemic,what the heck did you do to it,I'm sorry I presume to much,that question should come from your parent. |
Taz
| | Posted on Wednesday, June 19, 2002 - 10:10 pm: |
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No bigbob ask 307, i blew the from end out of it from over drive months back sent it to 307 got it back and its worked like this ever since. I havent checked it on a dummy load. Of corse my older readings were taken on an imax and not a beam. I know the antenna isnt going to give me proper wattage readings. |
Insider
| | Posted on Wednesday, June 19, 2002 - 10:14 pm: |
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Taz, are you sure that meter and or switch box are in good order, likewise for coax and connectors?
Unless I'm ignorant of something, and I'll admit defeat when I am, I don't see how the antenna polarity should be affecting the wattage readings that much.
Do you have a dummy load to test that amp into to rule out any antenna, meter, and switchbox issues? |
Taz
| | Posted on Thursday, June 20, 2002 - 12:35 am: |
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the meter is before the switchbox
no dummyload |
Bigbob
| | Posted on Thursday, June 20, 2002 - 6:22 pm: |
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Somethings hinkey here I haven't figured out what yet ,but I'm workin' on it.What do you mean by front end exactly,that is what parts blew out? |
Bigbob
| | Posted on Thursday, June 20, 2002 - 6:26 pm: |
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I said before those sd1407s won't take dual final input unless you keep the dial at a low setting or keep your dead key and swing at normal cb output. |
Taz
| | Posted on Thursday, June 20, 2002 - 9:03 pm: |
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I drove it to hard.
he said i blew out the front end out from overdrive. |
Bigbob
| | Posted on Thursday, June 20, 2002 - 11:24 pm: |
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I'm sorry TAZ,I am stupid,what exactly is the front end?Don't get me wrong,I'm not being rude. |
ss8541
| | Posted on Friday, June 21, 2002 - 12:18 am: |
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'front end' is usually related to the rx rf amp and mixer of a rxer. i take it that the front end here is the swamping network of the amp, bigbob.
i really don't see why taz doesn't personally talk to 307 about this. why bring this on the forum? if 307 worked on it last, shouldn't he be the one to ask(off the forum i might add)?
all techs make mistakes(and in some cases it is the know-it-all customers). i have a radio back to me now from a forum member here. if it is my fault it will be a free repair, reimbursement for shipping to me, and free shipping back. with the free repairs i have seen 307 give here, i'm sure he would do the same for taz. it only takes an email.... |
PSYCHORADIO
| | Posted on Friday, June 21, 2002 - 6:17 am: |
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I think that desert heat down there in Phoenix is getting to poor TAZ. |
PSYCHORADIO
| | Posted on Friday, June 21, 2002 - 6:20 am: |
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somethin else Taz, put the srewdriver down and back away from it. |
Taz
| | Posted on Friday, June 21, 2002 - 7:06 am: |
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ok guys, is this better?
125 watt deadkey, 6 watt carrier, 410 watts swing and 1.7 swr?
thats as good as I have gotten it so far. |
Taz
| | Posted on Friday, June 21, 2002 - 10:51 pm: |
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(1.7 between radio and amp) |
Bigbob
| | Posted on Friday, June 21, 2002 - 11:55 pm: |
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What the hell is goin' on around here,am I goin' insane.One minute he's havin' trouble and asking questions,the next minute it's all fixed with no explanation like it was never really broke,huh?Were we just wastin' time here,1.7 is great. |
Marconi
| | Posted on Thursday, June 27, 2002 - 8:32 am: |
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Taz, I have gone back and read this entire thing over and I think you are playing games. Your first post noted, "I see this question all the time.", then you begin to respond as though you were the one having the problem and not just simply raising a question of another. By itself that approach is not too bad, but then you start coming out of left field with your responses.
I am like BigBob, I don't get it! Can you explain to us what you did to get your SWR below 2, which all of a sudden made your station seem to come alive? To be specific, maybe you can explain how you now are getting "...125 watt deadkey, 6 watt carrier, 410 watts swing and 1.7 swr.", in light of the fact you told us earlier that "I am putting a 6 watt deadkey into a klv-550 from my melaka and only 40 out on high. uhh is that from the 2.0 swr im getting?", and other such stuff noted below.
Some of your prior statements,
"...Sorry guys, i had the switchbox on the flatside and it read 40 with a 5 watt deadkey.
Put it on the verticle and I get 80w out with 6 in."
"Of corse my older readings were taken on an imax and not a beam. I know the antenna isnt going to give me proper wattage readings."
"...I drove it to hard and blew out the front end out from overdrive"
"No bigbob ask 307, i blew the from end out of it from over drive months back sent it to 307 got it back and its worked like this ever since."
Your comments just don't fly.
Marconi |
Insider
| | Posted on Thursday, June 27, 2002 - 11:13 pm: |
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Taz,
You're currently putting a 6 watt carrier into your KLV 550, correct? In a forum post (Ask The Tech/Amplifiers/KLV 550 Question) you mentioned that the amp requires only a 2 watt carrier, 2 1/2 at most. Was that previous post incorrect?
I'm asking because I don't own a KLV 550 and am a bit confused by the sudden jump in input power requirements from that post to now.
As written expression often doesn't show the whole story, don't take the above the wrong way. I want to help trouble shoot your problem as best as possible, though from your last post, it seems as though you fixed it. If that's the case than let us know what was wrong--it just might be useful to someone later on. |
Taz
| | Posted on Friday, June 28, 2002 - 3:06 am: |
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well, i can asure you that i am NOT playing games. I said i see it over and over but never remembered the answer. everyone says the amp is working ok so i will leave it at that.
Noe the 2 1/2 watt thing was what i have heard from everyone else. I drive it with 6 to get what everyone else gets with 2 1/2.
My amp seems to be doing the wattage its supposed to do after i changed the jumper. |
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