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Vanillagorilla
Intermediate Member
Username: Vanillagorilla
Post Number: 360
Registered: 4-2005
| | Posted on Monday, December 05, 2005 - 5:18 pm: | 
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Why would I check this? Haven't I tortured myself enough? Apparently not!
After always having quirky SWR issues and reading a few responses to questions here I decided to kill a 1/2 hr by pulling my hair out. 
I'll make it as simple as possible:
Station: Jeep mobile
Radio: Galaxy Pluto
Amp: TNT400
Coax: Double shield RG8X (main length being 21' from antenna)
Antenna: 17" single coil 10K
SWR/PWR meter: Rat shack (new)
SWR w/ meter between ant and amp (amp off) 1:1
SWR w/ amp out of circut (bypass amp) same 1:1
SWR between radio and amp...1:5..what gives?
OK..pull hair..lets break this down. SWR great with or without amp as long as meter is last in line before antenna BUT between amp and radio its 1:5? Nope..don't get it!
SWR between amp and ant w/ amp "on" can be dialed via var pwr to achieve best results usually between 1:2 and 1:7 although with HAIR TRIGGER reactions..just breath on that VR pwr once set and its goes in another direction. (another thing I can't understand but we won't go there right now...it works and I'll have no hair left!)
BUT....why SWRS fine except for between radio and amp? Yes...tried lengths of coax from 18inches to 12 feet...same....hmmmmm?
Who wants to take this one? And why your at it tell me again why it was important for me to see this?  |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2029
Registered: 7-2004
| | Posted on Monday, December 05, 2005 - 7:39 pm: |
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that's why i keep reflect meter AFTER amp only! i don't need to see too much info!!! not exactly accurate, but SWR's probably swing DOWN when you talk with amp on...close enough for government work, as they say!
actually, what that is saying, is there is a slight mismatch when the amp goes in line. PROBABLY the amp. if you say at one time it was 1.1:1 in that place...well, an OUTSIDE possibility is one of the matching transformers heated up & melted some insulation & made itself shorter. farfetched-yeah, but a possible explanation for the change.
if wattmeter AFTER amp is showing what it should be, SWR's are where they should be, & you're getting out-i'd leave it.
mine'll do the hair trigger thing, too, but right at where it is too much dead key for amp to be doing-so not a problem
just wait til the day you have a 150 watt radio driving a 500 watt box driving a 2000 watt box with 2 hot antennas, 3 wattmeters, 3/4 of a mile of coax.... |
Wildrat
Intermediate Member
Username: Wildrat
Post Number: 494
Registered: 12-2003
| | Posted on Friday, December 16, 2005 - 1:55 am: |
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That'll be the day!
Wildrat |
Rldrake
Junior Member
Username: Rldrake
Post Number: 21
Registered: 1-2006
| | Posted on Monday, January 16, 2006 - 4:24 am: |
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First, there is no such thing as "swr's". It is "standing wave ratio", not "ratios". Secondly, the difference between a 1.1:1 versus a 1.5:1 swr is totally of no significence. You are dealing with 27 megahertz here, not 27 gigahertz (where the heating would actually be measureable). Thirdly, these meters being used are not precision test instruments...the error margin in the meter would much greater than the 4/10ths "swr" difference that would be seen on the tiny scales of such meters. Such little variation would not even be of concern if seen on a meter such as the Bird 43 (the standard of quality/accuratcy the amateur radio community). The ever so slight difference between your transmitter's output and the amplifiers input (ohms resistive) should be of no concern. If your "swr" is below 2.0:1, just go at it and enjoy. 73 en gl |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2275
Registered: 7-2004
| | Posted on Monday, January 16, 2006 - 7:11 pm: |
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and "SOB's" should be "S'sOB", & "POS's" should be "P'sOS". and 2:1 is an 11% loss-correct, not a noticeable difference. in RECEPTION. my YAESU owners manual says not to use with an SWR of over 1.3:1. my ICOM owners manual says not to use with an SWR of over 1.3:1. my IC2KL manual says not to use at full power with reflected power of more then 3%. that's the 'legal' ones. all of the illegal ones recommend & 'will not warranty' with use when reflected power exceeds 3%.
4/10ths swr difference from 1.0:1 to 1.4:1, while maybe not being noticeable efficiency-wise, is still a 40% error on the meter's part-a very big error margin, in the meter, not the swr. if my bird meter was off 40% with the lowest useable slug installed, there would be lots of smoke in the air.
when an swr of 1.1:1 or less, measured by way of an analyzer is obtainable, why settle for 1.5:1? compound that bit of loss with lossy cable, and any other inefficiencies you can think of, and, 50%, 60% or even more of LOST power is quite possible. the installation being spoken of is MOBILE. already lacking compared to BASE. don't settle for 'acceptable', do the job completely, do it right, & work for 'the best'. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1041
Registered: 9-2004
| | Posted on Tuesday, January 17, 2006 - 12:55 am: |
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rldrake, it is obviously important to the person who started the thread. isnt that all that counts?
im curious why you felt the need to bring this old post back to the top?
i dont see any questions or opinions left unanswered.
matt |
Rldrake
Junior Member
Username: Rldrake
Post Number: 23
Registered: 1-2006
| | Posted on Tuesday, January 17, 2006 - 8:17 am: |
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Kid V, I "brought this post to the top" for no particular reason other than it just being typical of some people just being overly concerned about seeing ever so slight readings of reflected power at the points that they are measuring at. As for "any questions or opinions left unanswered"...the stuff written on this website does not even begin to cover the subject of reflected power on feedlines. The only thing I was even attempting to address was of the most basic and fundamental level. There are literally thousands of articles written in hundreds of publications covering this subject from the very basics to the most advanced theories and observations on this. I am only attempting to bring attention to how this subject really has people really wasting what could be good operating time fooling around with something so trivial. Like I tried to tell the original poster...he is just fine...get on the air,make contacts...have fun with it. That is what "counts". Since no antenna, amplifier input, or matching scheme is perfect (100% effecient), one should expect to see some reflected power...1.5:1 swr being very good. Seeing vertually no reflected rf power should actually be of more concern. Again, there is no such thing as 100% effeciency. The rf must go somehere...it must be either disipated as heat or as unwanted radiation (feedline loss typically). Posting some of these basic fundamentals to answer such questions is a way to help others that are interested in the art and science of radio. This is a large part of what all of our studies is all about. Thanks for asking. 73 en have a good day. |
Rldrake
Junior Member
Username: Rldrake
Post Number: 24
Registered: 1-2006
| | Posted on Tuesday, January 17, 2006 - 11:51 am: |
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Patzero, All of that is very interesting. I looked through some of my manuals...Manuals for the little Yaesu FT-817, FT-8900R, and the FT-2800M make no reference to swr at all, only to feed to standard 50 ohms (rf resistive). Icom 756 Pro2, 746, 718, and the 2100 suggest swr of 2 to 1 or lower. My Pro2's and 746's foldback circuits start reducing power output at about 2.5:1 and the 718 starts folding back at just a hair over 2.0:1. I don't recall at what point the little 2100 begins folding back at...but it seems like, if my memory serves me correctly, that it was at just a tad below 2.0:1 swr. I do not recall at all at what point the little Yaesu FT-817 foldedback at...and on the Ft-8900 and FT-2800, I have never even checked to see where at what point that foldback is set at. I do know that, without even digging out the manuals, that my Kenwood TS-520S and my Gonset G-50 did mention that they should be fed into an antenna with about an swr of about 2.0:1, or lower, which is really a bit odd as everyone knows that such rigs with very good tube finals are virtually "bulletproof" with a swr of up to 10:1 or so...and that they employ no foldback circuitry at all (of course 30 years ago foldback circuitry was usually, and just beginning to appear, on only the real top-of-the-line land mobile service equipment). Seems to me that today's TenTec top of the line Orion, with modern solid state finals, is also quite "beefy" and not too concerned with a swr of up to about 3.0:1...They don't even bother with foldback circuitry in them at all...pretty unique, nowadays, outside of some of the qrp rigs on the market (where there isn't enough rf power output to damage much of anything regardless of how much of the power is being reflected) I wonder if you are running one of the Yaesu 857 or 897 series rigs. I do know that one of the very few complaints that operators running those new models is the power foldback protection circuits kicking in at very low levels of reflected rf. Such would be quite a problem at most installations and would really limit the bandwidths at which they could easily cover at full power. If one were to move up or down much at all, if using a manual tuner, one would have to be constantly fiddling with it...and using an auto coupler wouldn't be very practical either as they usually try to hit a sweet spot of about 1.5:1 to 2.0:1 swr...above the point where the foldback kicks in. I'll have to have a look at a manual for your near legal limit Icom solid state amplifier. I don't understand why it would tell you not to run it at full power with a relatively slight mismatch when it's own internal auto coupler and foldback circuitry would never allow full output into such a mismatched load anyway. Seems like such an amplifier would only be well able to provide full, high power coverage of narrow bands like 30 or 17 meters...or 40 meters and up using a Steppir antenna...or some type of highly ineffecient terminated antenna. Such an amplifier makes using balanced, open wire feedlines pretty much out of question. Correct? I was under the impression that the very expensive Icom amplifiers, like yours, had provision for both unbalnced 50 ohm and balanced, open wire feedlines. Apparently, I am wrong on this impression? Thank heavens we still have the the good ol' tube type amplifiers and their matching networks that can easily handle up to about 20.0:1 swr quite easily. Do you happen to know if the near legal limit, solid state amplifiers made by Yaesu and Kenwood are also so limited? Also, I am curious as to what Icom rates the duty cycle on your amplifier at? Do they list the spec in your manual? I've never been around any solid state amplifiers...and as far as I know the only station that I've ever worked using one was W1AW (arrl at Newington)...so I am finding all of this most interesting. Oh, and one final comment...50% or 60% loss on the feedline thing...Yes, you are correct on that and about no real loss on receiving...although that 50% loss on the typical, relatively high loss,unbalanced feedlines occurs at more like around a swr of about 3.0:1...is not really, as I see it, as much of an issue. What I mean by this, say with a typical 100w transceiver...is anyone really going to know (hear) any difference between 100 watts and 50 watts? Not even quite 1 s-meter difference? Certainly not using FM mode. Would be even quite rare working a station on a weak signal mode. 73
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Marconi
Advanced Member
Username: Marconi
Post Number: 526
Registered: 11-2001
| | Posted on Tuesday, January 17, 2006 - 11:55 am: |
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VG said he was pulling his hair out trying to do something. I agree with Rldrake, too much is made of this SWR thing. That was his point and guys need to get on with the program and beyond this meter business. These meters are for reference only. I might admit that it is a challenge trying to get something perfect, but in this stuff the fact of adding losses to get things perfect has just about consumed us.
JMHO |
Rldrake
Junior Member
Username: Rldrake
Post Number: 27
Registered: 1-2006
| | Posted on Tuesday, January 17, 2006 - 7:01 pm: |
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Marconi: "....adding losses to get things perfect has just about consumed us.". I say: "Well said that, man!". Good to see someone else that understands something of the basic laws of physics, and the realization of "perfect", 100% effecient devices. I bet you don't even believe the nutty myth about the 400 mile per gallon "miracle carbuerators" out there. You no doubt have no problem grasping the idea of Ohm's Law either. 73 en gud eve to u, sir. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1049
Registered: 9-2004
| | Posted on Tuesday, January 17, 2006 - 8:06 pm: |
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while i understand the need for posting information for anyone that might be reading the thread; just remember that it is a very courtious thing to do to spend some time reading posts and getting to know people before trying to let everyone know that you know what you are talking about.
obviously you do, but bringing up old posts for the sole purpose of adding your two cents worth isnt the way to ingratiate yourself to people.
trust me, you'll have plenty of opportunities to convey some knowledge. just be patient and let the people on here get to know you a bit.
we all prefer taking the advice of friends over strangers.
welcome to the forum, im sure we'll get to know eachother quite well,
matt |
Rldrake
Junior Member
Username: Rldrake
Post Number: 29
Registered: 1-2006
| | Posted on Wednesday, January 18, 2006 - 2:20 am: |
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Thank you, Matt, I appreciate your comments. Indeed, I am new to this forum and probably do get really gung ho on this stuff. I do try not to come off as some sort of know-it-all, as I certainly do not know it all. I am by no means any sort of Electrical and/or RF Engineer. My friend and elmer, Bob K2DRH, is an engineer. A Nuclear Engineer at Commonwealth Edison's Quad Cities Nuclear generating facility. Besides being the top VHF to laser contestor in North America, he is also quite sucessful with 160 meter DX. Now there is a guy that really does, although he certainly would never claim to, know-it-all. You are quite right about me probably being much to eager to do a little Elmering here. It is just that when I see people's understanding of radio theory based on "CB myth", rather than true fact, basic theory, and fundamentals...that I want to nip-it-in-the-bud. I really do try to keep my comments simplistic and written in a non-technical manner. You won't find me ever trying to dazzle anyone with complex math formulas to try to get across any of the basic fundamentals that I try to address. I certainly do not know those complex formulas off the top of my head and I figure that if someone actually wants them, that they can look them up just as easily as I can. :-) I really do try to keep it simple...Kind of like Steve, WB2WIK/6, does on QRZ dot com's forums. Steve is another one who really does about know-it-all. They don't come much sharper than him. Anyway, thank you again for your comment. I better quit now. I do tend to get to long winded and ramble on and on. 73 en good evening. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1062
Registered: 9-2004
| | Posted on Wednesday, January 18, 2006 - 10:04 pm: |
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if you were to do a search on this forum for my past posts; you would see a number of suggestions predicated on a combination of myth and fact.
thank goodness the moderators have not allowed some of my more "colorful" posts.
because of reading "elmer" posts by people like you, hopefully there are a lot fewer now.
i, and many others here appreciate this kind of free knowledge, and are glad it is out here.
when you are reading through the posts, and you find something that keeps getting perpetuated, yet is false; by all means; start a thread on it.
i know i will read them thoroughly.
if you're interested, check out the thread titled. "tech833 or anyone else, question about .64 wave antennas", in the Antennas section.
id like to get your input so i can learn more about the feeding systems.
later,
matt |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2290
Registered: 7-2004
| | Posted on Saturday, January 21, 2006 - 10:29 am: |
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icom ic735 instruction manual...'a well matched 50 ohm antenna and feedline will provide the desired performance. obtain a quality antenna, preferably one with high gain, which operates on the bands of interest and install it as high as possible. be especially careful when installing the connectors since poor or loose connections greatly reduce the overall efficiency of the system...avoid connecting the antenna connector to open feedlines, and do not transmit under mismatched conditions. a match of not greater then 1.3 is recommended for full transmitter output. the transmitter will gradually reduce output as mismatch increases. operating the transmitter under less then optimal conditions could result in damage to the ic735.'
icom ic2kl instruction manual....'if you are uncertain, you should not operate with a power reflect shown to be greater then 3%....many references and resources are available on the subject....'
i have had the pleasure to speak with bob, K2DRH on 6 meter Es on several occasions, as well as his friend AA2DR, locally. i as well have learned several things regarding antennas, feedlines, matching, etc which were applicable to both 11 meters and my very bare bones, basic & simple 6 meter station.
as for adding losses to get things perfect, what was added? obtaining efficiency through 'using the best, doing the best, no shortcuts, no skimping' is (hopefully) eliminating the compunding effects of losses through inefficiencies. as we discussed elsewhere, why use a 200 watt amp on a 70cm radio with a mag mount antenna & corroded, damaged pl259's on waterlogged, kinked, spliced, damaged, too long rg58 coax? the stock 25 watt radio will probably be just as effective, if not moreso, with the correct connectors, on low loss feedline, properly attatched to a well mounted antenna. but, we are responding to 2 different questions, with completely different situations. while i appreciate you responding to both with the same answer, one is looking for the most efficiency, the other just needs to hit a repeater a few miles away.
a 'myth' is that an antenna tuner is assisting in getting your signal out. the 1.1:1 swr you just saw is allowing your transistors to feel happy as you try to get an oak tree to load up. it still won't radiate an efficient signal. cut down the oak tree & put up a real antenna, you can then sell the amplifier & take the wife out to dinner.  |
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