Indoor Antenna Construction Tips

Safety tips and troubleshooting ideas.

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If you have seen my indoor HF antenna page, you’ll notice that the SG-230 sits flat on a speaker cabinet that’s at table top height. I have a cat that thinks this is a great place to sit and observe life from. There have been times that when tuning up for CW operating, I’ve heard the thud of little cat feet hitting the floor. With that in mind my first tip is…

Safety First!

Note: RF Voltages can be extremely high so make sure you protect yourself and others in your home! Feed point voltages can sometimes be thousands of volts so make sure your antenna feed point is protected or in a place where nobody in your household can come in contact with your terminations.

With the terminals being exposed I’m sure that she has gotten a sizable jolt and decided that perhaps that isn’t a good place to sit. If you have pets or children in the home, care should be taken to limit the possibility of contact with any RF terminations.

I have read posts in many forums where people have asked about placement of counterpoise wires when trying to fabricate and indoor antenna. I have seen suggestions to “just run the wire around the room and put it under a rug”. Because of the possibility of high RF voltage at the ends of these wires care should be taken to prevent fire hazards and possibility of contact with members of the household.

Tune at the antenna not at the radio

Loops work better

I have found that loop antennas work better. With a closed loop there is no need for counterpoise wires.

With the SG-230, 80 feet of 14 awg wire is recommended and can be used in multiple loops to reduce the size.

I can’t stress enough to tune at the antenna and not at the radio. The point is to keep standing wave off of the feed line and not back at the radio. If you try using a wire antenna that isn’t resonant and tune the SWR out with the radios internal antenna tuner, you will find that RF will get into everything.

In my case, I have the loop antenna in a spare room with the automatic antenna coupler at the base of the loop. This method helps to prevent standing waves on the coax from getting into my equipment. This also helps put the most power into the antenna and not loosing any in the feed line.

Now that we are in the rise of a solar cycle the upper bands have become quite active. It’s not that hard to make a tuned resonant antenna for 10 or 12 meters that would fit in a room or attic. You should be able to fit a full wave loop and tune it with components available at any hamfest flea market. Having a tuned antenna puts more of your power into radiated signal as well as reducing the amount of SWR on the feed line. There’s a LOT of good DX on the upper bands so give it a shot, you may be surprised.

You don’t need to use an automatic antenna coupler, I use one just for convenience. When I first started experimenting it was with a simple MFJ tuner. I had a coaxial switch at the tuner and switched in my antenna analyzer so that I could pre-tune the antenna. The problem with that was all the back and forth when went outside the tuned range. If you only work one band this isn’t such a bad thing and could always build your own tuned circuit.

Man made noise and interference

Isolate your noise problem

The first step in isolating noise from your HF station is finding the source.

Start by un-plugging everything in your living space. Find a weak station and start restoring power to the various appliances in your home and check for increased noise.

The biggest disadvantages to using an antenna indoors is the close proximity to sources of man made noise. Generally, if I can hear someone I can work them. That being said, I have taken great care to reduce the noise being generated by devices in my apartment like wall warts (those plug in transformer style power supplies and chargers), CFL lights, computer monitors and LCD TV’s. The lower bands like 80, 75, and 40 meters seem to be most affected by noise.

Several years ago, I purchased some CFL lights and slowly replaced incandescent bulbs with them as they blew. As I added more CFL’s I found that the noise floor on 80 meters rose to a point where it was 20db over S9. It took me a while to put 2 and 2 together and when I switched back it incandescent I lowered my noise floor back down to at least an S7- or S8.

If your like me, you probably have many power strips full of wall wart style power supplies for your computer equipment and various chargers. If you find you have a LOT of noise you should try unplugging everything in your living space and then check for noise. Then you can slowly ad in necessary devices and determine what is generating the bulk of your noise. If it can’t be replaced with common power source you can at least unplug it when you want to get on the air.

Try to avoid putting your antenna near anything that may be a source of man made noise. In my situation I have my antenna near the ceiling and due to the construction of my building I know there is little or no electrical wiring near the antenna.

Next, look at some of my DX’ing and contesting tips if you use indoor antennas

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About the Author

k2zs_avatar

I’ve been licensed since 1982 when I passed my Novice exam and was given the call KA2QOZ.

My interests lean towards chasing DX and operating CW. I operate mobile HF with my Yaesu FT-100 when I can. Take a moment to browse through my site.

73 from Scott, K2ZS

Contact

If you're in Rochester, NY I can usually be found on:

 - 144.220Mhz USB
 - 145.11/144.51 WR2AHL Repeater

Otherwise, I can be found in the lower portions of the CW bands on HF.