HFU HF Underground
General Category => General Radio Discussion => Topic started by: Jason on June 09, 2018, 1906 UTC
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I'm running my ICOM7200 in the bedroom, I'm needing a better antenna for greater RX, in hopes of rigging antenna in room for RX ONLY ?
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Run a few loops of wire around the window frame. If fed at a corner you get vertical polarisation, if fed at a middle of top or bottom section you get horizontal. I used a IC703 (10w qrp rig) to make stateside ssb contacts using the window loop antenna on 40m often. Worked fine for wideband hf rx but a preselector/antenna tuner would help wring more rf out of the antenna.
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I would try a tabletop magnetic loop, I ran a setup like this in southern california for several years. The BIG advantage of RX only is that you can use high Q, components without needing to worry about heating or loss too much, the big disadvantage is that a magnetic loop that works well for, say,10 to 30 Mhz, wont do well below that. If having 2 loops is an acceptable solution, go for it.
Some people build tabletop loop tuner boxes that do this, with quick change loops and ferrite loopsticks.
https://www.youtube.com/watch?v=q7PZpjEUKEk
unfortunately, I do not speak german, but even the demo itself shows this tabletop antenna. Building something like this is a good path to acceptable indoor reception. Of course, companies like AOR and Wellbrook make commercial antennas like this if one is willing to spend the money.
PS. Joshs suggestion of wire around the window also works quite well, and is far easier to implement, I have done this as well, but I found I prefered the selectivity of a tuned device.
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If you have $400 burning a hole in your pocket get a Wellbrook loop. I had great results way back with my R8 just running a chunk of very thin wire up the wall and around 3/4 of the ceiling corners. It always was quite good as long as you had some chunk of wire at least 20 feet long even on the first floor ceiling.
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"PS. Joshs suggestion of wire around the window also works quite well, and is far easier to implement, I have done this as well, but I found I prefered the selectivity of a tuned device."
The loop I used was a coax fed true loop, and a transmatch was always used, either an external one for higher powered rigs or the internal one in the IC703 qrp rig. The transmatch greatly increases selectivity at the antenna port. I had a lot of ferrite beads on that coax to keep rf off the coax.
For tx use, such a loop is fine on ssb voice mode as the average power is low, keeping the wire from heating up due to the losses from amps of rf flowing in it, for rx use you can use a string wetted with salt water as the loop. If you do digimodes like jt and so on, you have to reduce power to 5w or so to keep the wire loop from heating up. I used silver wire with a teflon coating for the loop. A copper tube or pipe would have been better for tx as the losses are reduced the thicker the conductor.
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A decade ago, in my last APT, I put up an 11M dipole in a "V" with an LDG 100Pro tuner. That's actually worked well on CB, then on 10M SSB and 29.600MHz Simplex. It heard fairly well down to 20M. It did fair to listen to the strong 75M and 40M stations, but not great, as expected.
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it would work really well if you can feed some wire through a window, so antenna is outside.
You can use a simple piece of wire.