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Receive Antennas (below 30MHz) For all topics related to receive antennas used on HF, MW, LW, etc. For transmit antennas use the Amateur Radio Antennas forum.

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Old 07-10-2014, 4:14 PM
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KA3JJX / Boombox - could I trouble you for input on a U shape as described above?



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Old 07-10-2014, 10:25 PM
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err..the call is KA3JJZ, not JJX....anyhow I would recommend against a U shape if at all possible. There is a chance that the 2 legs will, on some frequencies, interact with one another - and it's difficult to say if it would be an improvement or not.

A traditional L (known as an 'inverted L') will work just fine. And while the statement 'longer is better' is true when you are working with a base unit, like an Icom R75 (to a point), it's generally not advisable to go too long when feeding a portable. Fortunately you do have a RF gain control on that portable (if memory serves), so if you start noticing stations showing up where they don't belong, or a band is a garbled mess of signals, you can back off the gain. It's a sign of overloading. It won't generally damage the radio, but it will most certainly jangle your nerves a bit :.>>

However being in the Plains, you could probably get away with a 75 or 80 foot antenna (keep in mind that in the case of an inverted L, the flat top and feed line count as part of the antenna) which would give pretty decent performance right down to 4 Mhz or so (it should even work on 3 Mhz with reasonable efficiency). If you were on the East Coast that might be pushing it a bit, but where you are, it should work pretty well.

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Old 07-11-2014, 6:52 PM
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Outstanding, that's what I needed. I sincerely apologize for the typo, no disrespect intended. Thank you very much for your help & the others also.





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Old 07-11-2014, 8:03 PM
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May as well add in mine too. You mentioned an "L" wire earlier-I ran a 100' wire configured as a horizontal "L" here for a long time and it did pretty well. Since it was endfed, of course RF didn't see it as an L but it did certainly behave like a 100' wire. I did the L because of space constraints, but it was fun DXing with that setup. Hope that adds to your possibilities.
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Old 07-19-2014, 6:13 AM
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Mike, I take exception to your statement on disconnecting an antenna during a thunderstorm. If you hear thunder it is WAY to late to disconnect safely! A well grounded system following NEC rules you should not have to disconnect. However, if you do disconnect put the end of the coax outside the shack! If lightning strikes an antenna it will cause a very large bolt/discharge into the room.
If you are going to bring up safety do it right. All ground must be to a central ground as in you electric panels ground rod. If your shack is more then 16 feet from the ground then drive another rod and lead it to the main ground rod. It all has to be connected.
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Quote:
Originally Posted by ka3jjz View Post
Re grounding - if that radio has a jack or one of those push in jacks for a ground, by all means, a good ground may help. I should warn you, though that making a good ground is a fair amount of work - it is NOT just an 8 foot rod driven into the ground. If you're unfamiliar with NEC codes and properly grounding your home, be safe and get a good electrician.

We've had numerous discussions on good grounding in the various forums - a well structured search will do the job.

Don't ground a portable that doesn't have some sort of dedicated ground jack (unless the owner's manual says you can). In at least some cases, this can introduce a shock hazard.

By all means, though if a TStorm is in the area, do disconnect the antenna (and if possible ground it) and put some distance between it and the radio. Mike
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Old 07-19-2014, 8:43 AM
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While I agree with most of that, I still maintain that disconnecting an antenna (and the power supply too) from the radio (and yes, get the cable outside the shack) is the safest course. NEC rules aside (it should protect you, but as we all know, lightning has its own rules), they're no guarantee.

Case in point - a few years ago we had a derecho blow through this area with a lot of lightning. I had disconnected all my electronics, but had left a few power strips connected. I took a near-strike, and lost at least 2 strips and one box in the wall. Had I had any outdoor antennas, I would have done as you had suggested, but as my experience proves, depending on NEC rules to protect you can be foolish. Had I had any electronics connected to those plugs (or any outdoor antennas connected to a radio) I would have very likely lost them too

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Old 07-19-2014, 12:13 PM
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This complicates things...
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Old 07-21-2014, 6:45 AM
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It doesn't have to be that complicated.

Just don't listen to the DX-440 on an external antenna, or have it connected to an external antenna, when there is a chance of thunderstorm activity. Living in Kansas, you are probably well aware of local weather conditions, enough to know when there may be t-storms happening (as opposed to here in W. Washington where t-storms are rare). Just err on the side of safety, not just for the radio, but for you also.

Ground the antenna when not in use. Have a thick wire (aluminum wire is very good for this, but any thick wire will do) that goes from your outer windowsill (or your outside antenna connection) to a ground post hammered into the ground, or even a cyclone fence post will work. When you're not listening, clip the antenna lead to the ground wire.

You may want to stick with a good indoor antenna if this talk of grounding seems complicated. Even 20 feet of wire connected to a DX-440 will bring in plenty of signals. That's all I presently use with mine, and it picks up plenty of SW broadcast and ham signals.

When I first got my DX-440, all I used was the 15-20 ft speaker / zip cord 'dipole' I mentioned earlier, and it worked well. I heard SAC, USGHFS air comms, ships at sea, SW broadcasters from all over the world, and it was just on that antenna.

Hope this helps.
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