HF transmitting shutting computer off

[KC9FSH]

Today I changed around my antenna set-up slightly and since the changes I haven't been able to transmit on 20 or 40 meters for more than couple of seconds without my computer shutting off.

I'm restricted on antennas so I have to use the aluminum rain gutters as the antenna. It's basically a dipole but made out of the gutters.
Before I just had the coax connected to the gutters. Now I have a 10 foot run of rg-8 from the tuner to the 4:1 balun that I have outside. From the balun I have a 10 or 15 foot run of 300 ohm twinlead that is connected to gutters.

Does anyone have any ideas on things that I could do to help prevent this from happening? I do all my logging on the computer and my primary operating mode is PSK31.

Thanks,
Tim
KC9FSH

[W9GB]

Tim -

You have stray RF in your shack, which is most likely shutting down your computer's switch-mode power supply.

Find the source of your stray RF (mismatches, etc.). A choke balun is used to prevent some problems (along coax shield, etc.)

gb

[AG3Y]

Did you bring the twinlead off at a 90 degree angle from the gutters, or is it running in parallel to them ? Same question about the coax ? If your feedline is running parallel to the gutters, you are probably inducing a lot of RF back onto the feedline as Greg is suggesting.

You might want to try MFJ's "artificial ground" which is essentially a radial wire with a series tuning circuit to make the radial resonant on the bothersome frequencies. This puts the voltage at the far end of the wire, and removes the voltage from the immediate vicinity of the rig and computer.

Your best bet is making sure your feedline is not unbalanced or picking up any induced RF voltage from the antenna, itself! Good luck. Low profile antennas are often bothersome!

73, Jim

[K0RGR]

I wonder how likely it really is that your antenna is 'balanced' - that means both sides are completely equal. If one side of the gutter is closer to something conductive than the other, you likely have substantial imbalance on the feedline. 'Balanced feeders" only work when they are balanced. Otherwise, they radiate RF like haywire.

I think losing the balanced feeder in favor of coax might work better.

[KC7YPJ]

move the balun inside with as short of coax jumper between it and your radio as you can manage (1-3&#39, cut a 27' length of the 300ohm twinlead, run it through the hole you had the rg-8 ran through then hook it up, using coax to feed an antenna (whatever it's made of) that is being used on multiple bands with a tuner is wasting your valuable signal, and coax in that situation makes just as good if not a better rf radiator than balanced line with the kind of swr your gutter likely presents at the feedpoint.

probably the best option for feeding your gutters (just a guess since I have no idea how they are configured) is to feed it as a longwire rather than balanced feed with the balun, you can use your rg-8 to feed it, conect the center conductor to the gutter system and leave the shield disconnected on the outside.

[AG3Y]

NO ! You should NOT leave the shield disconnected on the outside !

You have to balance the RF current somehow, and if you do not have a counter-poise on the far end of the shield , you are absolutely Going to see RF inside the shack, making all kinds of havoc !

If you insist on end feeding the gutters, please install a good RF ground system below them. I am talking about radials extending out from the feedpoint in as many directions as you can put them, and using as many as you can install.

Take it from me, you do NOT want to use a coax feed in the way that is suggested in the previous post !

Get a copy of the Radio Handbook, or HF Antenna Manual, and read the chapters on antenna feedlines and RF grounding !

73, Jim

[KC9FSH]

Thanks for the replies everybody. First thing I will try to do is is reroute the feed line. I have a feeling that this is probably the cause of the issue. If that doesn't work I may try to make choke balun. Worst part is I had one made up but I just took it apart for another project. But oh well, they are pretty easy to make.

Thanks again for all the advice, I'll post again with my results after I try a couple of changes.
73,
Tim KC9FSH

[KC7YPJ]

would be nice if people payed attention and thought about how something is suggested rather than taking bits and pieces and going off the deep end, using coax to feed longwire as I described is in no way a bad thing, center conductor attatches to longwire port on tuner, then ground the shield to your earth/rf ground, the shield dead ends without connecting to anything else once you have cleared the house, it simply cuts the radiation of the longwire while it is in the shack, pretty interesting concept, and one that has been practiced for decades...

[AG3Y]

May work for receiving, but NOT recommended for transmission work. You are not matching the impedances of the coax to the antenna, etc. etc.

However, do what you want to do. I only know from about 42 years of experience in the Electroncs and Broadcasting business what GOOD ENGINEERING PRACTICE is, and running a coax and not doing something with the far end of the shield is NOT IT ! ! !

Best luck ! Jim

[K4EEZ]

I agree with Jim, AG3Y post
you could also use a field meter to see howmuch RF is in and around your shack
remember the roof is not just made of wood, there are all sorts of metals in and around the roof that can be in the radiated near field....

how much rf are u running into the antenna?
what is the swr like?
do u have a ground? is the rig have a GND?
are u on a 2nd floor or on the ground floor?
put an mfj antenna annalyzer on there and see what u get

so many questions unanswered...
good luck 7 3