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Author Topic: RF in the shack  (Read 1978 times)
KC9NRN
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Posts: 9




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« on: September 21, 2012, 11:29:44 AM »

While testing my Yaesu FT-1000MP Mark V on 10 meters it killed my Samsung 8000 (the power led was flashing and the screen all screwed up) TV forcing me to turn it off and back on to straighten it out and it also caused 2 of my computer monitors to blank out so they had to be shut down and turned back on.

I realize whats causing it but not sure what I can do about it. If I cut back power to 100 watts or elss there doesn't seem to be a problem but going above 100 there is. SWR is fine. The antenna is in the attic and the coax runs up the middle of the house to the attic for now until I can get the antenna outside.

I'm a newb as well, I got my ticket in 2008 but was not active between late 2008 through AUgust of 2012 due to family illness. I have to study the antenna book and get back in the saddle fully. I see people showing pictures of their shacks with mugh higher power and I have to ask myself if it's because the antenna being in the attic or the coax running through the house, or heck both.

My Icom 746Pro never had this issue but then it was 100 watts...
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WB2WIK
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Posts: 20545




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« Reply #1 on: September 21, 2012, 11:41:12 AM »

The antenna's too close. Tongue

The "threshold" for your RFI appears to be something just over 100W, so I think you just got lucky with the Icom.

There's all sorts of tricks you can do for both the television and the monitors, but if you have plans to relocate the antenna farther away, I'd just run 100W for the time being (there's very little difference between 100 and 200W), and then try it again with the antenna farther away.

That usually solves the problem.

It's possible the coax is the culprit if you have a lot of common mode coming back down the cable shield from the antenna, and an RF choke balun right at the antenna feedpoint might help with that: Depends on the antenna.  A conventional dipole with a current balun feed normally doesn't have this problem.  Some other antenna designs do.
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KC9NRN
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Posts: 9




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« Reply #2 on: September 21, 2012, 05:05:51 PM »

I did forget to mention this is also a different 20m dipole, I gave the Radiowavs 20m dipole with 1:1 Balun away with the Icom, this new dipole uses the same RG8X feedline but I'm now using a different 20meter dipole with 1:1 Balun. I am looking into getting an MFJ 269 analyzer as well to check things out.

I'm going to go for the General soon so I can get onto more bands and do some real testing of this rig and antenna set up.
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WX7G
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Posts: 5920




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« Reply #3 on: September 21, 2012, 05:21:05 PM »

A 20 meter dipole (about 33') presents an impedance of roughly 2000 ohms on 10 meters. The VSWR on your coax is 40:1 and that is not a good thing.

How is the RFI on 20 meters?
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AC5UP
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Posts: 3825




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« Reply #4 on: September 21, 2012, 05:49:28 PM »

The antenna's too close. Tongue

Ditto.

I have an SWL antenna outside my bedroom that just happens to resonate on 20 and would make a pretty darn good antenna if it was more than 12' off the ground. I didn't put it up for DX'ing, it's just a quick & dirty 66' of #18 wire fed a quarter wave from the end nearest the house.

It loads well enough that I can hear myself in the bedroom stereo through a large pair of three way speakers if I run more than ~50 watts. Did I mention the stereo does not need to be turned on? Tis' true. The speaker wires alone pick up enough RF to give me plenty of volume through both speakers with the left side being the loudest. That's what I call RF coupling, and yes, the left speaker is closest to the antenna. Like maybe 4' - 5' if I had an X-Ray tape measure. The antenna does have a 1:1 balun at the feed point and is a clean install by an experienced amateur with above average intelligence and exceptional good looks.

It's just too damned close to the speakers, and the answers I'm sure you'll get about ferrites on the power cords and such address the symptoms.............  Not the cause.

Either crank the power down or get the antenna away from the house where it belongs.  It's an outdoor toy.   Tongue
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KC9NRN
Member

Posts: 9




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« Reply #5 on: September 22, 2012, 11:23:48 AM »

A 20 meter dipole (about 33') presents an impedance of roughly 2000 ohms on 10 meters. The VSWR on your coax is 40:1 and that is not a good thing.

How is the RFI on 20 meters?

The 10 meter contact was using the built in tuner in the Icom 746Pro, this test was on 20m using the Yaesu, should have been fine but the SWR went up near 5, it was shut down after that. The person I had here was Extra class so he did the test on 20m (not giving out his id though).

With no tuner used it put out near nothing with full power applied, the red high swr led never turned on either. I realize I have a lot to learn since I have been out of the hobby a few years and I'm reading a lot so hopefully I get better at this.
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KC9NRN
Member

Posts: 9




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« Reply #6 on: September 22, 2012, 11:25:51 AM »

The antenna's too close. Tongue

Ditto.

I have an SWL antenna outside my bedroom that just happens to resonate on 20 and would make a pretty darn good antenna if it was more than 12' off the ground. I didn't put it up for DX'ing, it's just a quick & dirty 66' of #18 wire fed a quarter wave from the end nearest the house.

It loads well enough that I can hear myself in the bedroom stereo through a large pair of three way speakers if I run more than ~50 watts. Did I mention the stereo does not need to be turned on? Tis' true. The speaker wires alone pick up enough RF to give me plenty of volume through both speakers with the left side being the loudest. That's what I call RF coupling, and yes, the left speaker is closest to the antenna. Like maybe 4' - 5' if I had an X-Ray tape measure. The antenna does have a 1:1 balun at the feed point and is a clean install by an experienced amateur with above average intelligence and exceptional good looks.

It's just too damned close to the speakers, and the answers I'm sure you'll get about ferrites on the power cords and such address the symptoms.............  Not the cause.

Either crank the power down or get the antenna away from the house where it belongs.  It's an outdoor toy.   Tongue

Agreed, it's an out door toy, however my Icom had no problem getting out on both 10 and 20 meters using that 20m dipole and the built in tuner. SWR on 10m was a litle over 1.5, the Icom was a great radio and I wish I had it back! Smiley
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