| Author |
Message |
    
Capt205
Intermediate Member
Username: Capt205
Post Number: 138
Registered: 5-2005
| | Posted on Friday, September 22, 2006 - 9:09 pm: | 
|
OK....this is a long one.
I finally got everything installed, radio into 2x2290's into 8x2879's, and this thing is sounding good according to the locals. Power in the vehicle is not an issue. Antenna is a Wilson 5000 roof mount.
Now, here is what is bothering me. SWR radio only is < 1.2:1, radio and 2 pill is the same, radio and both the 2 pill and the 8 pill shows a high (3:1) on the dead key...but with modulation it swings backwards to about 1.4:1. Radio and 8 pill only is 3:1 with a backwards swing to about 2.7:1.
I have been told that this is reflect. What causes that, and how do I fix it? Is it bad? Any help will be appreciated. |
Im4jc
Intermediate Member
Username: Im4jc
Post Number: 184
Registered: 11-2005
| | Posted on Saturday, September 23, 2006 - 11:38 am: |
|
Yeah, Capt205, it's bad. So bad, in fact, that you'll have to send me that 8 pill. I promise that I'll take good care of it. Of course, you may never see it again... |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1793
Registered: 1-2005
| | Posted on Monday, September 25, 2006 - 1:43 pm: |
|
Capt205, Oh man what a headache. I know how you feel. I have been there so let me see if I can help get rid of some of your worries.
First off, I think that the Wilson 5000 is rated at 5000 watts. You only want to put half of that power into the antenna. I suggest the Predator 10K with the amount of power your running. The 102 inch SS whip is the only other antenna I would use. I also suggest rg213 or 9913 type coax. Make sure everything is well grounded to the vehicle. Each piece of gear and the antenna also the trunk lid, hood and doors. Heavy gauge power wire from the amps to baterry and heavy ground strap from the amps to vehicle chassis.
Second make sure that your antenna is perfectly resonant to the freqs you operate on. What I do is just run the radio to the swr meter to the antenna and get the best match possible. Try more than one swr meter if available. Once you have determined your 50ohm antenna is tuned to resonate perfectly to your desired freq then nothing else you put inline is going to change that.
So you have all your amps inline and on and you check swr. You never check swr by modulating. Only deadkey. You already know your antenna is tuned so your getting bad readings when the amp is on. The amp is not only transmitting on 27 mhz but on a second freq of 54mhz. Its the second harmonic ( 2X the fundamental freq of 27mhz )being transmitted.
So, the swr meter is reading the reflected signal of the normal freq 27mhz ( which is low ) and the REJECTED 2nd harmonic freq together! The antenna will not except energy transmitted at 54 mhz and sends it back down into the radio which shows up on the meter as high swr because the meter cannot tell the difference between 27 and 54 mhz.
As much as 30percent of your power could be in the 54mhz signal! This problem is caused by amps that are not filtered well.The only solution is to add a low pass filter to the output of the amp housing with a barrel connector.
It sounds like you have done everything right and your real swr is low. Just remember that when checking swr that modulating shows nothing and is innacrate. You only are concerned with checking swr with deadkey.
Hope I could help. Anything else I could help you with just post and I'm sure others are gonna jump in too!
Good luck!
Kenny
CEF491
Indiana |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1795
Registered: 1-2005
| | Posted on Monday, September 25, 2006 - 4:07 pm: |
|
One more thing. To simply answer your question what reflected power is and what causes it and how do you fix it.
When your checking your swr thats what you are measuring. It is caused when your antenna is not properly tuned or resonant to the frequency of operation just right. You get more or less depending on how far off or close your are to resonance = 1.1:1 voltage standing wave ratio.
In your case though I feel you already know your antenna VSWR is low. You have the infamous amp problems we have all encountered once or twice. |
Capt205
Intermediate Member
Username: Capt205
Post Number: 139
Registered: 5-2005
| | Posted on Tuesday, September 26, 2006 - 10:21 am: |
|
Thanks....Like I said, with everything inline but turned off, swr is great. Turn the little 2 pill on and swr is still great. But turn on the 8 pill with or with out the 2 pill on, and the swr is not so good, swing backwards as described above.
Power to 2 pill is 4ga to battery, power for TS1600 is 2ga to the other battery. 200amp alternator and 2 1100amp cca batteries.
Grounds are tinned braid at all 4 corners of the bed and all 4 corners of the cab, all to the frame. Also front fender to hood at the hinges, and battery grounds to front fender on both drivers and passengers sides. This is in addition to the factory grounds on a 2003 F350 7.3 Superduty.
I have tried different length jumpers, but to no significant resolve, and am kinda stuck. |
Therealporkchop
Advanced Member
Username: Therealporkchop
Post Number: 871
Registered: 11-2002
| | Posted on Tuesday, September 26, 2006 - 12:09 pm: |
|
Coax length has no effect on actual SWR. The only issue with length is impedance repeating such as a mismatch which can give a false reading. 3:1 can be actually higher or lower.
You could have a mismatch in that 1600 causing the high 3:1 reading. Even with only it and the radio you know the drive isn't there and you are checking SWR with a deadkey only.
Check your reflected power with a reflected power meter and drop kick that SWR meter into the next county. They are usually grossly inaccurate as most wattmeters are too. Get a good one or borrow someones antenna tuner such as an MFJ piece.
What's the actual RF power output measured as average power and not PEP power? The 5000 roof mount may work but I also preach the Predator way. It's an investment you won't regret.
Times MicroWave LMR coax. Ultra-flex if you need something a little more flexible. This coax will cure any coax related issues, this I know from experience. Or Andrews coax is nice stuff also and why skimp now with what you've already invested?
Pat can offer more insight into coax jumper length if he has time and he can offer you very useful and CORRECT information on coax length period.
Chop |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1799
Registered: 1-2005
| | Posted on Tuesday, September 26, 2006 - 11:50 am: |
|
Yeah I was gonna mention the jumper lenghts but since you said the swr was low with all the amps inline and off then the jumpers are no use.
Trust me Brian! I have heard your station before and no doubt I believe you know what your are doing. Reading how you installed everything and all.
I am confident that the way it is now you are safe to run your gear. As long as the radio is low enough into the 2 pill. Do not worry about the SWR reading swinging backwards when you talk! If you deadkeying lets say 50 watts and the swr reading is 1.1:1 thats good. Now talking into the mic causing the meter to move you are increasing the power which UN calibrates the meter. Anytime you increase or decrease the wattage you have to recalibrate. So the worry your having about the SWR meter swinging backwards.......forget about it! Its unneccasary worry! Take any info you hear on air with a grain of salt! Most of what we hear is myth! The info I am giving you is coming out of a personal binder of mine that is 3 inches thick! All this info I have collected is from a period of over 3 years plus from reputable techs and forums. Which my favorite tech and most respected is Lou Franklin. I have most of his books.
I do my best to give out the best info I can, NO MYTH!
So Brian, what brand name of amps are you running? Also what radio are you using and how hard are you driving the 2 pill? 2 pill needs less than a dual final radio to perform 100%
I feel that the trouble you are having is with that 8 pill emmitting the 2nd harmonic.Or the 2 pill emitting the harmonic and really getting amplified by the 8 pill! If you just give it a try and put a low pass filter on I bet you will be suprised. Sometimes it works and sometimes no.
Bottom line just have fun man! You sound like you have one rockin setup and I really hope to make a contact with ya soon with it. I'll check for your local roundtable this week. 37 LSB around 7 to 8 pm right? Listen for me. With all that power though don't be puttin my radio on lockdown ok? Hope I could help. |
Capt205
Intermediate Member
Username: Capt205
Post Number: 140
Registered: 5-2005
| | Posted on Tuesday, September 26, 2006 - 5:24 pm: |
|
Hotwire....we had to move up to 27.5450 due to a couple of bad locals, but we are in there every morning and evening.
Thanks for the replies. |
Hotwire
Senior Member
Username: Hotwire
Post Number: 1803
Registered: 1-2005
| | Posted on Wednesday, September 27, 2006 - 11:56 am: |
|
Capt205, Well heck! Thats even better! I'll be right at home then. I'm going to go ahead and assume your using LSB like before. May be rough at first. The band has been opening up in the evenings and I have been able to work a lot of West Indies DX on that freq here lately lsb and usb. Lets see if mother nature can push the DX a bit further north for us. Be on the lookout for
491 in the Hotwire mobile straight out of the cornfield! 73 my friend |
