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Author Topic: Reported RF.......What to do?  (Read 922 times)
NZ4Z
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« on: February 18, 2008, 11:06:54 PM »

I have a Yaesu FT-2000, Heil PR-781 (using Heils recommenced settings for the FT-2000), Heathkit SA-2060A Tuner, Ameritron AL-572, out to a 260 ft Windom......... The people I have been in QSO with the last little bit says I have bad RF.... Any suggestions where to start?.....I put a big snap on ferrite on the mic cable.....nothing elsewere.

Thanks in Advance

73

Steve
NZ4Z
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WA2HMM
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« Reply #1 on: February 19, 2008, 02:31:55 AM »

"says I have bad RF.... ", is that anything like bad breath??  I know my RF bites me occassionaly.

In all seriousness Steve, I think you probaly mean the audio sounds ratty. That might be caused by a few things.
Is the Mike Gain set to high???
Are you OVER-driving the amplifier, causing flat-topping???
How is your ground system???
As you say, "Bad RF", RF getting back into the audio???
Get into a QSO with someone, who can copy you good enough to give to a audio report.
Then try to crank the mike gain lower, see if that fixes the problem.
Try to low the drive to the amplifier, either manually  by turning the drive control down, of connecting up the ALC to the amplifier, and adjusting that.Is it only on one band??? Check your ground system, try shortening the ground bus, or lenthening it, see if the problem goes away. Make sure the connections are good both mechanicaly as well as electricaly. Keep in mind, you are working with RF not DC. If you are checking your grounding with an ohm-meter; zero ohms DC is not zero ohms at say 20 meters...The ground bus should be the bigest wireS you can find, copper braiding . Yes wireS, keep in mind certain lengths will be resonant at some frequency, so multiple wires work best.

Good Luck Steve, Hope this helps, 73 Charlie, WA2HMM
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WD8PTB
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« Reply #2 on: February 19, 2008, 03:01:26 AM »

Good advise; I would add make sure you get min swr with tuner.  Even 2:1 could cause rf in shack especialy if the swr without tuner is high. 73 WD8PTB
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AC5E
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« Reply #3 on: February 19, 2008, 04:00:40 AM »

Hi Steve: Your OCF dipole will inherently have RF on the shield, and the balun at the feedpoint may or may not knock it down enough to keep it out of your shack. From your description I suspect it is not - or your transmission line is picking up enough RF from the antenna to cause the problem.

I find a solidly grounded lightning arrestor at the point the coax enters the shack, with a second current balun between the arrestor and the jumper to the shack almost invariably takes care of that problem; and gives you a great deal of lightning protection as well.

Since you will operate down to 160 the usual coiled coax choke balun will not do. If you have enough turns to be effective on 160 and 75 you lose impedance on 40 and up. You can go with a 6-8 turn coil, with a 15-20 turn coil at right angles, but that takes a lot of coax. I cheat and use a pair of Radio Works "line isolators," one at the arrestor and the other at the tuner, and have had no RF trouble since I went that route in 1989.

That's with an Alpha 87A, and an Alpha Delta DX-CC at 20 feet directly over the shack. So it seems to work for me.

73  Pete Allen  AC5E
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AD5VM
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« Reply #4 on: February 19, 2008, 04:14:08 AM »

I have the same radio and the Heil PR20 mic (very similar element) If you have the processor turned on, turn it off or at least keep it down below 9:00.

Ensure you have a good station earth ground.

Use a choke balun at the antenna feedpoint.

Use a second receiver to listen to your signal and connect a dummy load at the antenna feedpoint to eliminate the antenna, then at the output of your tuner to eliminate your feedline, then at the output of your amp to eliminate the tuner, then at the rig to eliminate the amp!
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WA3SKN
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« Reply #5 on: February 19, 2008, 05:16:36 AM »

"Any suggestions where to start"...
A dummy load!  Place another receiver accross the room with a dummy load on the transmitter and listen with headphones to your transmit audio.  Does is sound clean?  If not, drop the amp, etc and start with the load on your set... adjust audio controls for a clean sound.  Then add the amp with the dummy load and make sure the audio is clean.
Then back to the antenna and check for RF getting into your setup.
Don't try and shoot an RF tbl without first verifying you sound good on the dummy load, there are too many variables!
Good Luck!
73s

-Mike.
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N8BMB
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« Reply #6 on: February 19, 2008, 05:22:24 AM »

I had a similar problem.  Check your power supply.  If it is not doing the job or is not a switching power supply, it may also sound like an RF problem.

Good Luck!

Dennis - N8BMB
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KG8JF
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« Reply #7 on: February 19, 2008, 06:01:36 AM »

I am running the mic gain on my Tentec Orion at 11, yes that is one, one.  The default is 50.  Tentec mics must be a lot different from Heil HC-4 and 5.  Any lower and the rig will not key.

I am driving an ALS-600 with 90 watts and get about 500 watts out and the audio seems to be OK.  That means no negative comments.
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AC5E
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« Reply #8 on: February 19, 2008, 09:10:19 AM »

Well, I use the Ten Tec 705 and 709 with my Orion and 11 or so is par for the course with my Ten Tec mikes as well. As long as the ALC light blinks on voice peaks you are OK.

Now, there have been some gripes that Ten Tec's are "sensitive" to RF. I have not found them so, but I went to the extra trouble as described in my first post to keep RF out.

73 Pete Allen  AC5E
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N6AJR
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« Reply #9 on: February 19, 2008, 11:26:47 AM »

I use a pegasus with my als 600 and I think I only drive it with about 55 or 60 watts, it sounds like you are driving the amp into non linear area of operation.

on ssb you will only see some peaks oon the poser meter, but if you do helloooooooo you will see something approaching true output.  no carrier on ssb so it reads low.  what does it do on fm or cw.  set power there.  

I use an alpha 87 a with my orion and it ne=ver need more than 50 watts for full power out.
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N2CMD
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« Reply #10 on: February 20, 2008, 04:51:52 AM »

Steve,  Turns out I was listening around yesterday and I heard you testing this with some guys. I'm not sure I would really call it RF.  It just sounded like bad audio to me. That radio has so many adjustments in it that could trash your audio, I would start there. Also as someone said above, start with just the radio in line and see if it's clean alone. Then you can start adding all the extra's back in.

Brian - N2CMD - Concord NC
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NZ4Z
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« Reply #11 on: February 20, 2008, 07:51:25 AM »

Well.....N4BY sent me a menu setting List for the FT-2000.....we changed em.....and barefoot they said it was awesome audio, perfect. But when I put the amp back inline, it had some noise....they were'nt sure if it was actual RF, but something for sure. So...I dunno.

Steve
NZ4Z
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WA2HMM
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« Reply #12 on: February 21, 2008, 12:07:42 PM »

reduce the drive to the amplifer, you might be over driving it and flat topping
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