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kattracker
| | Posted on Tuesday, July 15, 2003 - 11:47 am: | 
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Any one have any ideas why my swr is high ONLY when the amp is on?
I am running a Galaxy DX959, Firestick KW-6, Firesticks best coax, and a Palomar 250.
When the amp is off the swr could not be better. Turn on the amp and swr goes to 3 or higher.
I tried a ground from the amp to chassis and it made no difference either way. I can turn the rf power down on the radio to 1 watt input and it seems ok. Put 3 watts input to the amp and the swr is 3 or more.
Any ideas?
Thanks,
Kattracker |
Dx431
| | Posted on Tuesday, July 15, 2003 - 12:01 pm: |
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Deadkey 1.5-2w, you should be fine.
431 |
bruce
| | Posted on Tuesday, July 15, 2003 - 12:29 pm: |
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harmarnics from amp will show as SWR |
Danmandmc
| | Posted on Tuesday, July 15, 2003 - 1:07 pm: |
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The first thing I would do is change out the jumper cable between your amp and radio. I have a 2510 that finally accepted a six foot jumper with good SWRs. I was using a one foot then a two foot with same problem as you. I went to the six foot, made of high grade coax and good connectors soldered. Try this before going into the electronics of your equipment. It may work. |
Bigbob
| | Posted on Tuesday, July 15, 2003 - 4:14 pm: |
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Allow me to be stupid for a second,are you resetting the meter with the amp on or are you setting it with the radio and turning the amp on and taking a reading,all meters will do this with the latter.I made this mistake and did all sorts of nutso things to remedy it(I was in the dark,no forum then,or internet)then a local tech said I had to reset the meter with the amp,I was so embarassed,it's voltage sensitive,more watts means more volts,duh,boy was I dumb. |
Znut
| | Posted on Tuesday, July 15, 2003 - 6:40 pm: |
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Coil 6 feet of coax into a 4 inch diameter coil and tape or tie wrap tightly. Try this on either side of the meter until your readings compare to those 'barefoot'. This is my remedy for everything. A little choke to catch stray RF.
Okay, it probably won't work in your case but it's worth a try. |
Tech808
| | Posted on Tuesday, July 15, 2003 - 7:12 pm: |
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Kattracker,
Check COAX on ANTENNA and on JUMPERS and make sure ends are secure, soldered well and NO Shorts.
Reset Meter with Radio Only hooked to meter, check on Ch 1 ~ Ch 20 ~ Ch 40.
Then when AMP is in Line and ON reset meter and then check again on Ch 1 ~ Ch 20 ~ Ch 40.
Most of the SWR problems I have seen with putting an AMP in line are coax related.
Just my Thought's.
Lon
Tech808 |
ham_borg
| | Posted on Tuesday, July 15, 2003 - 9:47 pm: |
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Like Bruce said, harmonics.
http://www.wilsonantenna.com/swrg.htm
4. If the SWR is good until power is applied:
The antenna is not the problem. In this case, it is the amplifier. You have already established that the antenna is properly tuned and in good working order with low SWR, except when power is applied. Assume a ham operator is on 10 meters using a solid state amplifier. With the radio only, the SWR is 1.1:1; when the amplifier is turned on, the SWR jumps to 2.0:1. The amplifier is not only transmitting at 28 MHz, but is also transmitting on a second frequency of 56MHz. This is known as a "second harmonic" (2X the fundamental frequency of 28 MHz, transmitting at 56 MHz). Thus the SWR meter is reading both the reflected signal of the normal frequency and the rejected second harmonic signal. The antenna will not accept energy transmitted at 56 MHz, and returns it all back to the radio, which shows up on the meter as high SWR because the meter can not tell the difference between 28 MHz and 56 MHz. In fact, as much as 30% of the power is at 56 MHz. This is generally due to an amplifier that is not adequately filtered. Adding a Low-pass filter at the amplifier output is the only solution. For best results, connect the low pass filter directly to the amplifier using a barrel connector.
Resistance to the truth if futile.
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Kattracker
| | Posted on Tuesday, July 15, 2003 - 10:38 pm: |
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Bigbob,
Regarding your question about resetting the meter.
I am going by what the meter reads in the radio. The galaxy DX959 shows instant swr with no calibration needed. It also has a high swr warning light.
I am aware that relying on built-in meters can be unreliable, so I tested it with an external meter and readings were very close. I tried calibrating the external meter both ways and swr is high with amp on.
Bruce replied saying harmonics could be a problem. I am not sure, but I do know this, When keying up in my driveway with the amp on, it turns on both touch lamps in the house.
Thanks to all who replied to my initial posting. I will dig into it as soon as I can and hopefully remedy this annoying problem.
Thanks,
Kattracker |
Znut
| | Posted on Tuesday, July 15, 2003 - 10:39 pm: |
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Yeah, what he said. Turn the amp on 'low' and (preferably) turn down your dead key on your radio.
Also, get those 6' and 12' lengths of coax swapped around or something.
Also, try a coil of... Sorry, I couldn't help it.
Anyway, do you live close by? Since Bruce won't come over and show you maybe I can.
Do not overdrive that amp. You will get multiple harmonics if you do. You only need to drive that 250 with a deadkey of 2 or 3 watts! Those transistors have a 10db+ gain at 27 mhz. After 70 watts each (+ or -) output they are not kind anymore. So look at it as if it is a 140 watt amp. Then you will be more satisfied with the 170 watts you actually get out of it (up to 250pep.) |
Kattracker
| | Posted on Tuesday, July 15, 2003 - 11:15 pm: |
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Znut,
You ask if I live close by. I have no idea as I do not know where you live. I live in North Central Indiana.
Kattracker |
Tech671
| | Posted on Wednesday, July 16, 2003 - 5:38 am: |
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If you are reading swr on the radio's meter....first of all you said with radio set to 1w, the swr was fine. The radio *should* be set between 1 and 2w with that amp anyway.
Secondly you can experiment with different coax jumpers between the radio and amp such as 6' and 12'. A different coax length may present a "happier" input impedance between the radio and amp and the radio will read a lower swr.
Fooling the meter with coax length? Maybe so, but the radio will run cooler and perform better while it's being "fooled". |
Taz
| | Posted on Thursday, July 17, 2003 - 12:04 am: |
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Trial and Error, but usually with CB when there is a problem its only a possibillity for a few things. |
bruce
| | Posted on Thursday, July 17, 2003 - 10:38 am: |
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cut the input down to almost nothing and see if the swr measured at the output dosnt go down ill bet it does ... |
Bullet
| | Posted on Thursday, July 17, 2003 - 1:01 pm: |
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i believe ham-borg nailed it here!
you can try the lowpass filter and coax jumpers and look for improvement but if it was me id sell the amp and buy a higher quality ham amplifier.
ive had several palomar mobiles and ive not found one i really like yet. ive had ok luck with texas star amps and with TNT amps.
but if you want something good, go with a good name brand ham amplifier they cost abit more but thats because thier built rite and will provide you with good service |
frasiercrane
| | Posted on Thursday, July 17, 2003 - 4:06 pm: |
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I see CBers are still as superstitious as I remember them.. coil up some cable on both sides of the meter? Tuning SWRs with different cable lengths? I thought I'd taught you all better years ago.. anyway, my earlier post was the real deal, but I don't see it now.. must've offended someone's religion.. btw.. coax is the same impedance no matter how long it is.. you can all use trial and error and Harry Potter spells.. I'll stick to physics.. |
2600
| | Posted on Thursday, July 17, 2003 - 4:16 pm: |
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Hey, KatTracker,
Makes me wonder how come nobody has mentioned the nature of WHAT the radio's internal SWR-light/meter is actually READING when the amplifier is keyed and in line?
When the amplifier is on and keyed, the radio is no longer feeding power into the antenna. The amplifier is now doing that.
The radio is now feeding its transmitter power into the AMPLIFIER'S INPUT CIRCUIT, the part that feeds into the RF transistors (pills) in the linear. A good input circuit will 'fool' the radio into thinking that a proper antenna is attached. A rotten input circuit will present a high SWR to the radio's final stage.
An antenna will present the same SWR to the radio at all drive levels, from lowest to highest peaks, and in between. That input circuit in the linear can't really do that, exactly.
In the bad, old days linears would have an adjustment screw inside to optimize the "input match", and keep that 'input match' SWR down below the usual 2-to-1 dividing line. The conventional wisdom was, below 2:1, don't worry. Above 2:1, something might get hurt.
Amplifier design has come a long way in some respects, not so far in others. Adjustable components cost more, so you will find very few newer solid-state linears with those 'trimmer' screws inside them. Newer designs will have fixed parts in that circuit.
I'm pretty sure that amplifier has a "high/low" or such control on the front. If the radio's internal SWR meter reads better on "low", or "medium", that's a clue. And a really cheap fix. Don't sweat a few Watts' difference in the output. An honest comparison of the 'swing' reading on the other guy's S-meter at his end will reveal this if you try it both ways.
If the high/low switch doesn't do the trick by itself, 671's suggestion is the next cheapest, and most cost-effective strategy. The jumper length that delivers the lowest SWR reading on the radio's internal meter is hard to predict. If you have a variety of different length jumpers, just see which one shows the lowest reading on the radio's SWR meter. If one of them keeps it below 2-to-1, put a nail in it and get on with life. I suppose this may sound too good to be true, but I'll skip putting you to sleep with "why" and just second 671's motion that it ususally works.
For an amplifier that size, DON"T worry about how many Watts of carrier the radio is delivering to the amplifier. Worry about how many Watts of carrier are coming OUT of the amplifier. Much more than about 40 Watts of carrier will tend to reduce the audio level that they hear at the other end. Much less than that, and folks at the outer edge of your range will not hear you as well. The "dead key" DOES serve to quiet the noise level they hear between words, and when you stop to take a breath. Set the radio's carrier level so that the amplifier shows around 40 Watts, and don't worry whether that is 1-1/2 or 2-1/2 Watts. The carrier power coming OUT of the amplifier is the number that counts.
73 |
Bigbob
| | Posted on Thursday, July 17, 2003 - 8:53 pm: |
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I have a palomar 250,it has a trimmer on the output transformer but not on the input,you can fool the meter with diff. length coax between the rad. and amp 6' usually works(impedance inverter),also if the radio is putting out harmonics at a very reduced level so as not to cause problems barefoot the amp will amplify those also and run hotter than h***,so have a competent tech check the 54mHz trap in the radio,it's a grounded coil in the output chain with a slug in it,some "golden screwdrivers" adjust this mistakenly and throw it all out of wack,it can actually be tuned to 27mHz and completely kill the output,wild,huh!Just some thoughts. |
Superdxr
| | Posted on Thursday, July 31, 2003 - 10:29 am: |
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maybe your amps tuned input is out of wack, get it checked by a tech. |
bruce
| | Posted on Thursday, July 31, 2003 - 12:17 pm: |
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JUNK OUTPUT 2ND 3RD HAR. THATS WHAT IS CAUSING IT..... |
Taz
| | Posted on Thursday, July 31, 2003 - 6:02 pm: |
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Well, I know a longer jumper fixed my swr on my amp
Cause it was about a 2.0 between radio and amp, and since my radios going to be moved about 10FT from where it was then 18ft of coax did the trick.  |
228
| | Posted on Saturday, August 02, 2003 - 2:24 pm: |
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"Use only the minimum amount of power necessary to obtain a set meter reading"........
if the swr meter is connected between the output of the amp and the antenna this rule applies.
using more power than necessary to obtain a set meter reading will result in higher swr readings.
the easiest way to eliminate problems between the radio tx output and the amp input is to make sure that the jumper is either less than 1/20th of a wavelength at the operating frequency (approximately 16 inches or less) or if this length is not long enough to connect the two pieces of equipment then use a tuned halfwave line instead.
228
firecommunications.com |
Kattracker
| | Posted on Saturday, August 02, 2003 - 8:14 pm: |
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Well, I found the problem and it is fixed.
I took the bracket off where it mounts to my truck and cleaned off the dielectric grease I put on to minimize corrosion.
Now the swr barely registers, and when I go to my channels way below channel one it is 1.5 at the highest.
There is almost no difference in the swr with the amp on or off.
Kattracker |
bruce
| | Posted on Saturday, August 02, 2003 - 10:40 pm: |
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KATTRACKER you PROVED my points .... guess what is the best way to generate harmarnics? Well its cleaned up and working ! COOL |
Bigbob
| | Posted on Sunday, August 03, 2003 - 6:03 am: |
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How often many of us engineer our own problems is myriad. |
Kattracker
| | Posted on Friday, August 22, 2003 - 7:38 am: |
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Mark Brown,
Actually you are correct. However, having contacts with the FCC and local goverments I can truly say this. The FCC in not simply against 11 meters and amp usage. The problem they have is when people cause problems by using them.
If you use an amp as I do, which is out in the boonies where there is no one to interfere with other than the person I am talking to. There is not a real problem.
Again, technically is IS against the FCC codes to have an amp on 11 meter. Use it wisely and nothing will ever be said from the FCC. Unless of course someone complains...
Kattracker
Forum Master Note : Sadly Mark Browns message should never have been approved therefor it has been removed. To put Kattracker message in context Mark Browns post was about the legality of amps.
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