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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, 5:14 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, 11:25 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, 7:52 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, 9:03 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, 7:13 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, 9:43 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, 1:13 PM
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This complicates things...
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Old 07-21-2014, 7:45 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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Old 10-23-2014, 6:01 PM
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Quote:
Originally Posted by Boombox View Post
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.
Thanks to everyone on this. I went ahead and run a slinky antenna from a tree. I have paracord on the one end slung over a high branch & tied to a lower branch. The other end is secured to the house. I can let it loose & stake it into the lawn so its vertical or just keep it tied to a hook & keep it out of the way. Even at the tied up / angled position it works great. I have a 30 foot lead wire coiled along the paracord run to the house when its tied up & I just undo the twist along the paracord when its staked down vertical. Its a good system so far.

Still need to do a ground, how far down should I drive my ground stake/pole/etc? I've called the locate people & there is nothing in the way of utilities underground at the location I plan to drive my grounding rod down...
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Old 10-23-2014, 6:26 PM
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Whats doin Joe-glad you have the antenna ready. Your ground rod should be 8'. Also, if there is a cold water supply pipe nearby your feedline, or an electrical service conduit nearby that goes underground to the service, those make good grounds too. Depending upon the conductive characteristics of the earth into which your ground will go, sometimes one rod is inadequate, in which case guys will drive two or three every 8'. If RF is all you're after, it will be ok though.
BTW have ya tried the setup on SW yet to at least see how much pull it has? And how many feet is the slinky?

For reads http://www.arrl.org/grounding
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Old 10-23-2014, 7:49 PM
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I second the simplicity of the inverted-L, despite what appears below!

When using one, I recommend putting an inline 1:1 RF choke (Like an MFJ 915) AWAY from the feedpoint, so that you can take advantage of the both modes of the coax (common and transmission) serving double duty as both a transmission line, and a "counterpoise" of only one wire. This assumes that your coax is on the ground and not in the air. A 12-20 foot jumper (not critical) or so will do - as the ground is going to detune the common mode anyway - and of course another coax run from the other side of the choke to the shack.

Note: In my case, I use a short one designed mainly for 25 meters and higher in freq, with an LDG 4:1 UNUN at the feedpoint near the ground. The counterpoise is a 12-foot (not critical) lmr-400 jumper before it sees the 1:1 choke. From there, about a 20 foot run to the shack which keeps additional swr losses somewhat low. The system is purposely non-resonant, and the losses are low enough that a shack tuner is not really necessary.

It is only 18 feet total - 8 feet vertical, and 10 feet horizontal making it stealthy. At night, there is so much signal on the low bands anyway, that this still works ok on rx down to about 5 mhz. If I wanted better low-end, a total of 31 or 43 feet works well. Just saying that under certain circumstances, having a very long inverted L is actually not good on the high bands due to the reception pattern, which is already a tad high anyway.

If the coax is also the *one and only* counterpoise, then for the best general directional pattern, run it underneath the horizontal wire. Otherwise, your pattern may have a really funky skew to it. More counterpoise wires spaced around the feedpoint (also not critical in length when on the ground - more short is better than a few long) alleviate this issue.

Any version of bending will do, like half horizontal and half vertical, but any combination not exceeding about a 1/3 ratio either way kind of classifies what an inverted L is. My preference is to run as much vertical as I can before exceeding 2/3 of the length, otherwise I'm making a true vertical and losing some stealth.

There is more to it like additional swr loss, and reception lobes vs length of wire, but I'll leave it there for now.

The 1:1 choke away from the feedpoint accomplishes 3 things:
1) Coax still acts like a normal transmission line
2) Purposely using part of the coax common-mode as a *limited* choked counterpoise.
3) Helps prevent shack noise from traveling back UP the coax to your feedpoint and back to the shack again.

Ideally run more counterpoise wires. Still, without anything but the coax, the antenna is going to use the shield as the counterpoise anyway, so you might as well put a choke on it to accomplish the above - but to do so you choke it away from the feedpoint, not near it. If you choke it in the shack at the rig, you kind of defeat the purpose. You could choke at the feedpoint if you have multiple wires, but why not make use of the nature of the beast?

Last edited by hertzian; 10-23-2014 at 9:07 PM..
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Old 10-23-2014, 9:46 PM
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Quote:
Originally Posted by ridgescan View Post
Whats doin Joe-glad you have the antenna ready. Your ground rod should be 8'. Also, if there is a cold water supply pipe nearby your feedline, or an electrical service conduit nearby that goes underground to the service, those make good grounds too. Depending upon the conductive characteristics of the earth into which your ground will go, sometimes one rod is inadequate, in which case guys will drive two or three every 8'. If RF is all you're after, it will be ok though.
BTW have ya tried the setup on SW yet to at least see how much pull it has? And how many feet is the slinky?

For reads http://www.arrl.org/grounding


According to Google a slinky is typically 70-80 feet, Max 87 feet. I bought an original, with 30 ft of feedline that's 100 -110 feet-ish. It about 30 feet up and hangs (under the weight & stuff) about 20 feet. Nice thing is you can barely see it. Its a heck of a lot better than the stock whip and while the powered Kaito SW amplified diamond contraption I bought & hung in a window, beat the whip. The slinky puts them both to shame. Thanks to much input & help here, running a wire anywhere near my gutters would be a waste so this will have to do. Thanks for the grounding info... I got a lot of sledgehammer time coming up!
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Old 10-23-2014, 9:49 PM
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Quote:
Originally Posted by hertzian View Post
I second the simplicity of the inverted-L, despite what appears below!





When using one, I recommend putting an inline 1:1 RF choke (Like an MFJ 915) AWAY from the feedpoint, so that you can take advantage of the both modes of the coax (common and transmission) serving double duty as both a transmission line, and a "counterpoise" of only one wire. This assumes that your coax is on the ground and not in the air. A 12-20 foot jumper (not critical) or so will do - as the ground is going to detune the common mode anyway - and of course another coax run from the other side of the choke to the shack.





Note: In my case, I use a short one designed mainly for 25 meters and higher in freq, with an LDG 4:1 UNUN at the feedpoint near the ground. The counterpoise is a 12-foot (not critical) lmr-400 jumper before it sees the 1:1 choke. From there, about a 20 foot run to the shack which keeps additional swr losses somewhat low. The system is purposely non-resonant, and the losses are low enough that a shack tuner is not really necessary.





It is only 18 feet total - 8 feet vertical, and 10 feet horizontal making it stealthy. At night, there is so much signal on the low bands anyway, that this still works ok on rx down to about 5 mhz. If I wanted better low-end, a total of 31 or 43 feet works well. Just saying that under certain circumstances, having a very long inverted L is actually not good on the high bands due to the reception pattern, which is already a tad high anyway.





If the coax is also the *one and only* counterpoise, then for the best general directional pattern, run it underneath the horizontal wire. Otherwise, your pattern may have a really funky skew to it. More counterpoise wires spaced around the feedpoint (also not critical in length when on the ground - more short is better than a few long) alleviate this issue.





Any version of bending will do, like half horizontal and half vertical, but any combination not exceeding about a 1/3 ratio either way kind of classifies what an inverted L is. My preference is to run as much vertical as I can before exceeding 2/3 of the length, otherwise I'm making a true vertical and losing some stealth.





There is more to it like additional swr loss, and reception lobes vs length of wire, but I'll leave it there for now.





The 1:1 choke away from the feedpoint accomplishes 3 things:


1) Coax still acts like a normal transmission line


2) Purposely using part of the coax common-mode as a *limited* choked counterpoise.


3) Helps prevent shack noise from traveling back UP the coax to your feedpoint and back to the shack again.





Ideally run more counterpoise wires. Still, without anything but the coax, the antenna is going to use the shield as the counterpoise anyway, so you might as well put a choke on it to accomplish the above - but to do so you choke it away from the feedpoint, not near it. If you choke it in the shack at the rig, you kind of defeat the purpose. You could choke at the feedpoint if you have multiple wires, but why not make use of the nature of the beast?
Great info, thanks. For now, I'm limited but I may attempt something like this in the future. I just don't have the ideal environment to run the L...
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Old 10-24-2014, 8:04 PM
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I would highly recommend this little box to help protect the front end of that oldie-but-goodie - it would be very difficult, if not outright impossible, to get that radio fixed if you take a static strike....

A great first timer project

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Old 10-26-2014, 2:27 PM
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Quote:
Originally Posted by ka3jjz View Post
I would highly recommend this little box to help protect the front end of that oldie-but-goodie - it would be very difficult, if not outright impossible, to get that radio fixed if you take a static strike....





A great first timer project





Mike


Great, thanks. I think I had been referred to that post before but its confirmation that I need to deal with it.



I have a question, I just drove my ground rod down & it occurred to me... Where do I hook the ground wire to on my slinky antenna? The ends of the slinky are run through some short pieces of PVC piping. I then have the lead wire soldered on and running down & along the paracord anchor line then it comes off & into my house through a window.



Would I run a separate ground line off the end of the slinky like I have done with the lead wire or splice off the lead line & into the ground? Or... something else?
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Old 10-27-2014, 10:24 AM
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Or... It doesn't matter, just do whatever is easiest?
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Old 10-27-2014, 6:55 PM
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I say get some 50 0r 75 ohm coax from your radio out the window, then connect that coax's braid to the rod, then coax center conductor to the slinky lead. Then you'll have proper poise/counterpoise antenna system. This will likely knock out some RFI and give cleaner signals.
EDIT-so from what i have seen looking at your 440 there's an "RCA" jack for external antenna right? So for the radio side of that 50 ohm coax run, I would just leave a 3 inch lead off an RCA jack-the RCA negative wire (or shield) goes to the coax braid at that end, then the RCA positive wire goes to coax center conductor (keep the leads short at the RCA jack so the coax is the main feed to the slinky) This way the coax will protect good signal and you'll pick up less crap.
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Last edited by ridgescan; 10-27-2014 at 7:08 PM..
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Old 10-27-2014, 8:46 PM
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Quote:
Originally Posted by ridgescan View Post
I say get some 50 0r 75 ohm coax from your radio out the window, then connect that coax's braid to the rod, then coax center conductor to the slinky lead. Then you'll have proper poise/counterpoise antenna system. This will likely knock out some RFI and give cleaner signals.
EDIT-so from what i have seen looking at your 440 there's an "RCA" jack for external antenna right? So for the radio side of that 50 ohm coax run, I would just leave a 3 inch lead off an RCA jack-the RCA negative wire (or shield) goes to the coax braid at that end, then the RCA positive wire goes to coax center conductor (keep the leads short at the RCA jack so the coax is the main feed to the slinky) This way the coax will protect good signal and you'll pick up less crap.
A redesign! I hasn't considered using coax for my lead! At the slinky end would it matter if I loosely wrapped the ground wire (attached to the coax shield/weave) down the lead coax to the ground rod. It'd be like 20-25 feet then drop right down to the rod. The rest of the lead coax just would go thru the window to the radio. I'd rather not attach the ground line & just have it drop off & run along the ground to the rod...
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Old 10-28-2014, 12:51 PM
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Quote:
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At the slinky end would it matter if I loosely wrapped the ground wire (attached to the coax shield/weave) down the lead coax to the ground rod. It'd be like 20-25 feet then drop right down to the rod. The rest of the lead coax just would go thru the window to the radio. I'd rather not attach the ground line & just have it drop off & run along the ground to the rod...
If that is your preference joe, but what I would do is run the coax from the slinky, down to very close to the ground rod (within say 3-4'), tap the braid there at rod and make a connection to rod, then weaterproof that connection with some tight electrical tape wrap (also weatherproof your slinky lead solder point the same way) then run the lead to radio. The problem is that the lead to radio remains unshielded and will likely be noisy. When you run the coax all the way to the radio you shield the feedline all the way to the antenna.
If I had a crack at your antenna, I would run 50 ohm coax from radio to outside, then I would have the slinky feed end very near the ground point then run out from there to a tree or whatever. You can run that slinky in an upward slope from near the ground you know. This way the feedline can be continuous from radio straight to slinky/ground-both connections within a few feet, preventing RFI pickup.
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Old 10-28-2014, 1:19 PM
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Originally Posted by ridgescan View Post
If that is your preference joe, but what I would do is run the coax from the slinky, down to very close to the ground rod (within say 3-4'), tap the braid there at rod and make a connection to rod, then weaterproof that connection with some tight electrical tape wrap (also weatherproof your slinky lead solder point the same way) then run the lead to radio. The problem is that the lead to radio remains unshielded and will likely be noisy. When you run the coax all the way to the radio you shield the feedline all the way to the antenna.
If I had a crack at your antenna, I would run 50 ohm coax from radio to outside, then I would have the slinky feed end very near the ground point then run out from there to a tree or whatever. You can run that slinky in an upward slope from near the ground you know. This way the feedline can be continuous from radio straight to slinky/ground-both connections within a few feet, preventing RFI pickup.
Thanks, that tells me what I need to do! I really appreciate your input.
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