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XLAXX
| | Posted on Wednesday, October 23, 2002 - 12:21 pm: | 
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Here's my dumb situation:
I have a Ameritron Dummy Load that I bought from HRO. It was about $80.
I filled it up with the trans. oil to the exact level it states in the directions.
COAX jumper to the load is 6 ft.via antenna switch.
OK, when I test my radios for wattage readings and such, I get a reading of about 10-20 watts lower into the dummy load than going to the antenna on the air. SWR to the dummy load was basically flat at 1:1-2. Antenna SWR is 1:2-3.
My current set-up is :
RADIO - MULTIPLE RADIO SWITCH BOX - METER - LOW PASS FILTER (Bencher Gold from HRO) - ANTENNA/DUMMY LOAD SWITCH BOX - out the door to antenna.
Sometimes I'll run an amp immediately after the radio.
I didn't think that a Dummy Load would suppress wattage and harmonics that much...???, especailly back to my meter??? Need help....
What should I do??? Any recommendations????
Thanks
XLAXX |
bruce
| | Posted on Wednesday, October 23, 2002 - 1:12 pm: |
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if i get this right the dummy load is FLAT 50 ohms on your 2nd and 3 Rd harmarics but your antenna would be a very high SWR. now watt meters will read HIGHER if they are looking into a HIGH resistance load so your readings are effected by the fact that the beam and cantenna have diffrent responces. That would be my guess
Bruce |
409
| | Posted on Wednesday, October 23, 2002 - 1:29 pm: |
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If your SWR is a little high to the antenna, then your wattmeter will show more apparent output due to the reflected power. The dummy-load with a lower SWR shows mostly true output. The reading will be lower. |
XLAXX
| | Posted on Wednesday, October 23, 2002 - 2:40 pm: |
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Bruce/409-
Are you saying that my SWR to my antenna is too high? Antenna SWR is really not that bad at 1:2-1:3 for a MACO V 5/8. The Dummy Load is a 50 ohmer yes, the Dummy Load SWR was about 1:1 - 1:2. I have a PDC 7000 meter that has readings for 10, 100, 5000. Maybe it's the meter??
Bruce- explain your response on a 6th grade level to me, wasn't sure what you meant by 2nd/3rd Rd harmonics.
Is there actual "backflow" of the signal that could cause suppression, or does the oil disperse the signal adequately into the dummy load??
Maybe I need to lower or elevate my Maco???????
XLAXX |
bruce
| | Posted on Wednesday, October 23, 2002 - 8:02 pm: |
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Xlaxx
A antenna only LOOKS like 50 ohms at CB but your RADIO puts out 27, 54 and 72 mhz power Now the 54 ia down in MILLAWATTS as is 72 IN A STOCK radio however as you tweek and peak a set they tend to go up fast THAT power STILL goes through your watt meter but its NOT looking at 50 ohms but what ever the antenna looks like at 54 or 72 and you will get VERY high readings to prove my point if you can turn down your radio power to say 1/2 watt then didconect your load ill bet the watt meters will go very high. and THATS what your seeing nothing wrong with your radio just a fact of radio life! |
Marconi
| | Posted on Wednesday, October 23, 2002 - 8:30 pm: |
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XLAXX, you have tripped onto a mystery and a good learning experience. I do not have all the answers, but I will bet that your lines and the devices are playing tricks on your results. It is like changing jumpers and getting different SWR from your antenna.
How did you hook up the dummy load?
You state; COAX jumper to the load is 6 ft.via antenna switch. Then you describe your setup as; RADIO - MULTIPLE RADIO SWITCH BOX - METER - LOW PASS FILTER (Bencher Gold from HRO) - ANTENNA/DUMMY LOAD SWITCH BOX - out the door to antenna.
Did you mean SWITCH BOX ANTENNA/DUMMY LOAD...?
Considering the test you wish to do, you may have too much stuff in line up to the antenna if it is not right on the money and maybe to the dummy load as well since it is at the end of everything also. I may be wrong about the setup so consider that in my remarks. All that stuff can add to the reactive condition in the jumpers and feed line.
Do you happen to have an SWR meter in the radio?
I hear the arguments already. The only thing we are looking for here is consistency to base some conclusions on. We already have inconsistency, right! That was not what you expected. Relative readings are all we need to show us this much. A meter in the rig will help eliminate another line and device and the variables they present. Of course this is assuming the meter is responsive. It would be nice if you had an analyzer here, it is much more informative or confusing. Not sure which yet.
Boy where to start. I believe I will leave it at that and you play around with it a little more and let us know. Maybe answer the questions I posed and let's get started.
Marconi |
XLAXX
| | Posted on Thursday, October 24, 2002 - 12:52 pm: |
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Marconi-
Thanks for the reply.
My setup goes like this and I will detail it:
Radio- 3ft coax jumper- PDC multiple radio switch box- 3ft coax jumper- PDC 7000 meter- 3ft coax jumper- Bencher Low pass filter- 3ft coax jumper 3 position switch box (going to a ground, antenna, dummy load)
Out of one of the connections for the switch box is 6ft coax jumper to dummy load, the other is to the antenna. The dummy load is an Ameritron 50 ohm bucket with trans. oil in it filled to 3/4" from top as per instructions. Vent cap open.
Sometimes I will run an amp between the radio and multiple radio switch box. separated by 3 ft coax jumpers. All cables are new. Coax to antenna is the 95% shield from Copper.
The dummy load sits in a cardboard box to protect carpet from spillage under my bench.
My PDC meter has an SWR meter on it. I have several radios with SWR meters on them and they have only bars as a reading. Sometimes my SWR readings on the radios are only 1 bar or non-existent. SWR on the PDC meter is 1:2 on Dummy Load, 1:2-3 on antenna.
OK, where do I start??????
Thanks for the replies!
XLAXX |
Bigbob
| | Posted on Thursday, October 24, 2002 - 9:53 pm: |
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If at all possible attach a swr meter as close to the antenna as you can for a more precise reading.You see if you have a reactive antenna and an odd length of coax by adding jumpers you can get different readings of swr,your load is 50 or 52 ohms a 6ft jumper is an impedence transformer,hence not a perfect match.Of course inaccurasies in your meter could come in to play here,for a more accurate antenna reading if it is reactive make sure your coax(if it is solid polyethylene dielectric)is measured in multiples of 12ft,if nesessary cut a jumper of like material to bring this about.If your coax is polyethelene foam dielectric the multiples are 13.5ft,the same procedure with foam jumper,now you should get a good relative reading you can use as your baseline.Now compare this to your dummy load.Make an rg8x or mini-8 jumper 13.5 ft long for your load then you'll be able to compare apples to apples.Try testing with just the radio and amp and meter,to load then to ant.by direct connection.I have a maco rec.preamp that kills 1/3 of the power from radio so I don't use it.Hook all your gadgets up to the ant. side of the meter one at a time,radio,meter,gadget in that order using the 13.5ft jumper on gadget end to dummy load,I think you'll be surprised.Bigbob |
Marconi
| | Posted on Friday, October 25, 2002 - 5:50 am: |
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I will be contesting this weekend and don't have time, but BigBob brings up similar points I was making the other day. Keep it simple when making comparisons of this type.
BTW, I find my three foot jumpers to be among the most reactive jumpers of just about any length. They tend to show more reactance when measured between a good non-reactive dummy load and a good antenna analyzer, that can display reactance as a value, than all other lengths. That does not mean these jumpers will not work in a setup. It just means they tend to exhibit some additional reactance that will likely be added to any reactance in your antenna.
If you cut some jumpers as BigBob notes, try and cut them for the exact frequency that you are testing for. I guess BB's figures are for middle of band. It probably won't make a huge difference, since these things are a bit forgiving, but if you are going to make a jumper, make it for a frequency you like to work. Basically you can use the same formula and VF's as noted for making 1/2 and 1/4 wave jumpers, just divide the 1/2 wave in half.
See you in a couple of days.
BB is on track here. Bruce has a point here that is valid, but if you understand the harmonics stuff, then you are a better man than me.
Marconi |
Marconi
| | Posted on Monday, October 28, 2002 - 6:55 am: |
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XLAXX, how are you coming with your checking with the dummy load.
Marconi |
XLAXX
| | Posted on Monday, October 28, 2002 - 11:54 am: |
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Still the same. I removed everything and just ran the radio to the wattmeter to the dummy load 25-35W swing....
LOWER WATTAGE READINGS!!!
Ran radio to wattmeter to antenna and get 50+ swing on radio. SWR to antenna is 1.2-1.3 only. The coax jumpers are the ARIES type mini 8 with amphenol pl 259's. Brand new. I don't get it??? Coax to antenna is the 95% shield RG8 from copper, total length was cut to be divisible by 3 from antenna to antenna switch box.
I was telling Bruce that sometimes I run a 23' RG8 95% coiled choke that is an old trick that keeps SWR down. Even with this out of line it still does the same thing. NEED HELP! |
Ironmask
| | Posted on Monday, October 28, 2002 - 7:46 pm: |
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This may not be in line with the discussion but, I ran into a situation where the SWRs seem to climb with out an explanation.
I changed jumpers, checked coax for ground and continuety etc. After banging my head against the wall for some time I rechecked the coax and found that one end had the center conductor too long for the fitting it was to connect to, thus prohibiting the shield side from making good contact.
My question is: Are all connectors correct and tight enough? This would also pertain to the fittings on each appliance used. Just a thought. |
Marconi
| | Posted on Tuesday, October 29, 2002 - 6:39 pm: |
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XLAXX, what do you think your radio is supposed to do 35 or 50 watts?
What kind of radio do you have?
Do you have variable output?
Marconi |
XLAXX
| | Posted on Wednesday, October 30, 2002 - 11:27 am: |
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M-
I have a VR9000, Gen. Lee both have low dk about .6-.8 The 9000 has adjustable rf, the Gen Lee has the lo/hi switch. I have seen the VR swing up to about 40-42W, the Gen. Lee swings to low 50's.
Like I said earlier, I have changed everything out with new cable.
What do I do next?
Thanks
XLAXX |
Scrapiron63
| | Posted on Wednesday, October 30, 2002 - 2:54 pm: |
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XLAXX, let me add to the confusion, and thats what it amounts to when talking about swing and antennas. It sounds like you have a good set-up on your antenna, and I doubt if anyone could tell on the other end if the swing is 25 or 40 watts. At my shop I have a 1000 watt dummyload, a beam antenna and groundplane(Imax-2000), the match at the frequency I mostly use, is flat on all three. The beam and dummyload will show the same key and swing, the I-max shows quite a bit more. Maybe its got to do with coax length, I use a dosy meter with the build in antenna switch, going out from it I have a 12 ft. jumper to the dummyload, about 40 ft to the I-max, and about 100 feet to the beam. I like the dosy meter with the antenna switch for this purpose, as it eliminates another jumper and switch box. I use a 9 ft jumper going back from the dosy to whatever Amp I happen to have in line. Going back from the Amp is a 3 ft jumper to a reversed 6 position switchbox, from which I can have up to 6 radios inline for testing, admiring, ha, or whatever. From that switch box, I use whatever length jumper I need to reach the radio, most are 9 ft. but one is 150 ft. to the radio inside my home. With this configuration, I never show any backup SWR on the radio meters, with the exception of a few transistor amps I have tried. I've seen some of those that raises the SWR going both ways, go figure that one, so dirty running I guess.
scrapiron |
XLAXX
| | Posted on Wednesday, October 30, 2002 - 4:02 pm: |
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Scrap-
You seem to be hitting this issue on the head because Marconi mentioned in his thread about the length of the jumper cable. I have several 3ft jumpers in line and a 6ft to the dummy load everything goes through a three position antenna switch (1 ground, 2 antenna, 3 dummy). Maybe it's the reversed PDC 6 position switch box I have in line??
Ok I'm going to list my set-up again to see if any adjustments can be made here by you or anybody else:
Radio
Reversed 6 position switch box
Amp (sometimes)
Meter
Low pass Filter
3 position Antenna switch box (1 goes to antenna,
2 goes to ground, 3 goes to 1500W 50ohm dummy load)
Antenna is 5/8 Maco w/ gpk about 78ft of coax 95% shield, from switch box to antenna.
All coax cables are 3ft Aries brand with Amphenol connectors.
Maybe I have a bad dummy load?? Oh well, my head hurts.
Thanks
XLAXX |
Bigbob
| | Posted on Wednesday, October 30, 2002 - 9:21 pm: |
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I agree with bruce,your problem has less to do with dummy load and coax and more to do with resonant freq. of ant. and excess harmonics from radios.Most dummy loads are extremely broadbanded,antennas are not by contrast,use a 13'6" jumper from meter to load and 13'6"jumper from radio to meter,please,humor me.A 6'9"jumper is an impedence transformer,13'6" is an impedence repeater in foam coax,6' is very close to6'9",so just try what I suggest or not and retune the output impedence of the radios,alot of rigs have a coil that's ajustable after the final,it's purpose is to supress 1st harmonics.Your meter is probably good for 2thru30 megs.HF,harmonics are VHF, your meter may be totally off the wall,have your rigs checked with a spectrum analyser or a competant tech. |
Marconi
| | Posted on Thursday, October 31, 2002 - 1:10 pm: |
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Hey BigBob, I agree with the 12' jumper using PE coax, but how do you come up with 13' 6" using foam? The difference I get probably won't make a big difference here, but I am curious. I get the following for foam coax for center of 11 meters at about 15' and about 7.5" for the 1/4 wave.
My antennas are like Scrapiron notes, they all are resonant at about the same place. They all act very similar to the dummy load. I believe that XLAXX has reactance in his antenna and it is showing him more watts than it should. But he tells us that his radio's put out about a true 50 watts to the antenna with a 1.1:1 SWR, and only about 25-35 into the dummy load. I can only guess then that you might be right about his rigs being all tweaked up and probably causing these indications. I am not a tech, for sure, but I have heard of some techs that do fix the radios to show more watts by messing with the harmonics as you note. Do you think that is what is happeing with XLAXX?
If so, then why does the dummy load act different, if the problem is with the radio? Broadbanded or not, doesn't the dummy load look just like a resistor to the line, just like the antenna should?
Marconi |
Bigbob
| | Posted on Thursday, October 31, 2002 - 6:04 pm: |
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I give up ,I concede,please forgive me. |
Bigbob
| | Posted on Thursday, October 31, 2002 - 7:39 pm: |
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THE dummy load is a 50ohm load regardless of freq.thus no standing waves.13.5 ft. foam pe 78% velocity factor as compared to 66% factor for 12ft. solid pe,if you have a reactive load then you need coax in 1/2 wavelenths(an impedence repeater) so you can "see" the antenna swr at your rig;the lengths are based on 27.205.You can use a 1/4 wave section of coax to effectively "change" high swr to a more reasonable level "at the radio".I can use a 1/4 wave of coax to change 3:1 to 1.3:1 at the radio. |
Marconi
| | Posted on Friday, November 01, 2002 - 12:00 pm: |
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BigBob, maybe we may only agree to disagree, but you might be right. I have been made to see a different viewpoint before, and I often get a better understanding in doing so.
I was just asking why you used 13.5' as the length for a resonant 1/2 wave line when using Mini 8, for the middle of 11, meters with whatever VF it has. Mini 8, usually has PE foam as a dielectric, and my chart shows 80%-84% velocity factor for most of this particular coax. The length you noted and VF you mentioned were just different from my understanding. I believe we can get thru all this anyway. I‘m sure not looking to come to blows here. I don’t believe they call you BigBob for nothing.J
Here is the way I see the calculations issue that has come up and the reason for my question. Again, the difference is not a real big deal, but it can detract somewhat from the real discussion about XLAXX’s issue when using his dummy load. I figure this business this way:
492 x VF/freq = resonant 1/2 wave line multiple
492 x .82 = 403.44 / 27.205 = 14.8'
Now, there is a way to figure the VF using math, but whatever the VF really is cannot be resolved by discussion. Generally, we use the best info we can get, generally that has to do. I just don’t trust the coax producer's specs, so I check them out. The math I use to check the VF from the results of trimming coax to length or from simply cutting the coax, to length, using the formula:
492 / 27.205 = 18' so 14.8' / 18’ = 82% VF
I rounded off here, but if my new length passes this test then I believe the VF noted by the manufacture. Does this prove my length and the VF?
You may use a different value in your math, like 468, instead if 492, but if we use your VF and use my math, we get the following:
492 x .78 = 383.76 / 27.205 = 14.1’
You get 13.5’ which would happen only when using a 75% VF or when using 468, in you formula. I would have know what you were doing, and I would said nothing in disagreement, if you had told us your 1/2 wave jumper was about 11.4’, instead of 12’. It just looked like you were using 492, for the .66, VF coax, and 468, when using the Mini 8.
So, you see my dilemma? How say you?
Marconi |
Bigbob
| | Posted on Friday, November 01, 2002 - 6:03 pm: |
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My thursday 10-31 6:04 post was because I felt overwhelmed and I was feeling ill,but after supper as you can see I felt much better,thank you. |
Marconi
| | Posted on Sunday, November 03, 2002 - 11:44 am: |
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Hey XLAXX, how is your checking with your dummy load coming along?
Marconi |
XLAXX
| | Posted on Monday, November 04, 2002 - 5:24 pm: |
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OK-
I found the problem!!!
I have a Maco v5/8 antenna. I got up on the roof this weekend and took the sucker down and remeasured it. The instructions say to measure the length of the antenna from its base which in the instructions are a little confusing. The base of the antenna is NOT the black collar but the actual BOTTOM of the entire unit! OH MY! I was off on my measurement by 10". So basically the length was 250" instead of 240" at 27mhz! WAY OUTTA BAND! My gamma match was just a tad off too,... maybe a bird crapped on it or sat on it or something. Now my SWR's are completely flat according to my PDC 7000 and the vectronics meter we used. I got really good ears too! But you guys were right,... my watt readings are a little lower,... BUT they are now the same into the antenna and to the dummy load. My antenna was definitely reactive and probably reflected a lot of power back into one or two of my rigs. Probably would have blown up an amp too! By the way my neighbor was taking pictures of me on my roof while doing this. He doesn't like me too much. He says that he can hear me through everything but the toaster. Should I be worried about a lawsuit???
Thanks |
Bigbob
| | Posted on Monday, November 04, 2002 - 8:14 pm: |
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Nothing like engineering your own problems,and ahem,marconi you'll kick me for this,but I got my specs.from a 1998 rad.shack catalog;their product so I used their specs,my face is red. |
bruce
| | Posted on Monday, November 04, 2002 - 8:16 pm: |
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Funny but back in the 60's when i was in the army a lady called my dad and b**** that ever since i put up that ham antenna their toaster doesnt work.
Maby we could get them together.... O as for the lawsuit check and find out has your town passed a CB radio interferance law thats complys with the FCC local preemption. If not find out what you are interfering with and get a copy of part 15 and the FCC web site has usefull info on what you must do and HE must do ...... e-mail me if you need to.... by the way good job! you worked the problem out and ill bet next time you know this one Heck this is how WE all learned! |
Marconi
| | Posted on Tuesday, November 05, 2002 - 7:11 am: |
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Yes XLAXX, I agree that Maco made a mess of the words explaining the bottom of their antenna. They didn't even put a little arrow in the picture like they did at several other points that called attention to some important facts. This is probably a worst case of misdirection and there are plenty out there likely sitting on a pole or tower right now working, but working badly.
Well BigBob, don't worry. At my age I have learned a few things over time. One is, don't believe everything you read. The other is, don't believe hardly anything you hear on the CB radio. Oh! BTW, don't worry about my kicking you. I'm still kicking, but not too high.
Radio Shack you say????
Hang loose,
Marconi |
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