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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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  #121 (permalink)  
Old 11-04-2018, 2:20 PM
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That 50x25 rectangle, according to my modeling, should work nearly as well as a perfect square, so don't sweat it. I wouldn't go any narrower than the 2:1 ratio for the rectangle, so I'm glad it fits!

Being on ground is important to get the lower angles, and just laying down is fine enough within a few inches or so. It was just when I saw some wire higher up in the shrubs and over the brickwork that caught my attention.

Contests are also a good time to play with the bands that are larger than 1 wavelength with their non-optimal patterns - reception is still there. For instance, my 60 foot loop, which is designed to go no higher than about 15 mhz, is doing "ok" up at 15 meters, where the contesters are active on cw. Hawaii, KH7B is blowing my doors down on 21 mhz even though my pattern is a skewed high-angle blob pointed away from the islands

Chokes are still important. Starting with an isolated transformer is still the best bet, followed by a good choke. What usually turns up is the ever-popular "ugly balun" choke, which is very limited in effectiveness. If one is going to use that, then by all means see this reference from G3TXQ:

http://www.karinya.net/g3txq/chokes/

Perfect for whipping something out to catch the second day of the contest while waiting for ferrites or an off-shelf commercial solution.

If one is running cable-tv 75 ohm coax, just be careful not to exceed the bend radius so as not to break it, or make the center conductor migrate into the insulator. Best to use an inline solution, or perhaps a jumper for this purpose.

Or, as long as one keeps these things in mind, just lay down what ya' got and try it and improve as you go. Gotta' run - I've got a Canadian VY station blasting me on 21 mhz...

Last edited by hertzian; 11-04-2018 at 2:45 PM..
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  #122 (permalink)  
Old 11-04-2018, 2:43 PM
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Quote:
Originally Posted by hertzian View Post
That 50x25 rectangle, according to my modeling, should work nearly as well as a perfect square, so don't sweat it. I wouldn't go any narrower than the 2:1 ratio for the rectangle, so I'm glad it fits!

Being on ground is important to get the lower angles, and just laying down is fine enough within a few inches or so. It was just when I saw some wire higher up in the shrubs and over the brickwork that caught my attention.

Contests are also a good time to play with the bands that are larger than 1 wavelength with their non-optimal patterns - reception is still there. For instance, my 60 foot loop, which is designed to go no higher than about 15 mhz, is doing "ok" up at 15 meters, where the contesters are active on cw. Hawaii, KH7B is blowing my doors down on 21 mhz even though my pattern is a skewed high-angle blob pointed away from the islands

Chokes are still important. Starting with an isolated transformer is still the best bet, followed by a good choke. What usually turns up is the ever-popular "ugly balun" choke, which is very limited in effectiveness. If one is going to use that, then by all means see this reference from G3TXQ:

Common-mode chokes

Perfect for whipping something out to catch the second day of the contest while waiting for ferrites or an off-shelf commercial solution.
Thanks for that, have finished testing now and added a choke as per G3TXQ one thing i noticed, moving from 15x15ft to 50x25 did bring the signals up but brought the noise level up too, not as much as before, I wonder as ive been using 50ohm rather than 75ohm coax it thats one of the issues or whether the ala-100 is just amplifying the noise too.

I will be building a second one following the design of KK5JY more strictly, using 75ohm cable and binocular ferrites and starting at 15x15ft I will also build the box similar and waterproof, The Loop on Ground Antenna - the "LoG"
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  #123 (permalink)  
Old 11-04-2018, 5:23 PM
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Thanks for the facebook link Les.

Possibly I havenít taken the potential common mode issues seriously enough, after the huge improvement from earthing the cable shield at the entry point I just assume all is well. There are large nulls to the south but that is probably explained close proximity to the house in that direction.

Next time I order parts Ill get some ferrite suitable for choking and see how that goes, also some extra BN73-202's to glue together as per K9AY's EWE transformer, I have a feeling it will do well in this application
https://www.w8ji.com/k9ay_flag_pennant_ewe.htm

Ian
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  #124 (permalink)  
Old 11-05-2018, 2:54 AM
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Building that like the KK5JY project details will be a good way to establish a baseline for sure.

If I had a preamp out at the feedpoint, like the Wellbrook, W4OP, W6LVP etc, I would probably not want to run two amps - that is I'd have the preamp in the rig turned off if possible. Ie, the Yaesu "IPO" turned ON (preamp off) or similar for other radios.

Or just rely on the preamp if necessary in the rig, and optimize the transformer, cabling and so forth.

The thing to remember is that results may differ somewhat depending on soil conditions too. I'm basically over dead sandy / rocky soil, and I'm floating the whole thing, so there's no real ground to speak of.

Whether it's my Kenwood TS590, or the Nasa/Target HF3 ssb receiver, they all run off batteries too, like a big Optima yellow-top. Part of the hobby for me.

I'd suggest that if you have an antenna farm going, and are putting the LOG through an antenna switch, disconnect ALL of that, even the switch, and run the LOG directly into the radio for initial evaluations. Perhaps even run rx-only on batteries for awhile.

THEN, put all your infrastructure back, and see if you are still close-coupling to something, or common-mode swamping from the other antennas is now part of the system.

In the end I have to resist the temptation to over-engineer it. I've heard stuff I've *never* heard before, without ears bleeding, but I have no illusion with the basic hemispherical pattern, no overhead null, etc, that this is a dx-killer.

Well, it IS for me, because I'm spending more quality time behind the dial. Summer static / thunderstorms on the low bands? What's that? Never heard that before. Now I do! Progress .....
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  #125 (permalink)  
Old 11-05-2018, 7:36 PM
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SKINNY loop?

Just tested the ultimate in skinny loops - to the point where it is really a folded-dipole. 36 feet long, 3 inches wide. Fed in the center of one of the long sides.

Used what's left of my 300 ohm windowed ladder line. Looked like a dragon on the grass and was a pain to keep down with stakes.

No surprise that it seemed a more efficient match to a 9:1 isolated transformer than the straight dipole-on-ground scenario. Especially 60-40 meters. Same basic directionality.

So yeah, a loop that really belongs to the DOG family. Thought I'd sneak that in here, but I'll mention it in the other thread about DOGS.
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  #126 (permalink)  
Old 11-09-2018, 5:18 AM
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Default Let's get a grip on reality folks

Just a note about the "dx capabilities" of the LOG, and to take any other "reviews" with a grain of salt.

NOBODY claims that this is a dx-killer / hunter antenna. But yes, it does have low-angle capability. BUT, that does not mean you should get disappointed when you do an A / B comparison with say a 160 foot long Inverted L running up 60 feet. No way.

If I *had* to come up with a comparison, I would say the "dx capabilities" of the LOG, at least on 80 - 20 meters is nearly equal to that of my Hustler ground-mounted mobile whips with proper radials. Actually more so, because my ears aren't bleeding, I'm putting in much more behind-the-dial time to be there when dx is around.

Basically, that means for MY setup, dx means usually hearing the big-guns. But I'm ok with that. I didn't lay this down to hunt dx specifically.

That being said, from Los Angeles, my personal best so far is armchair ssb copy of a ZS6 in South Africa. In the meantime, I'm also hearing Russians, Japanese, South Pacific, New Zealand, Australia, East Coast, Central and South America, Caribean and only one or two Europeans so far. No, for the most part they aren't daily "phone patch" quality. (Showing my age). Of course CW helps a lot too.

About the only thing I haven't heard yet are the South Pole stations, running 5w ssb to a buddipole on an ice-covered patio table. Don't expect to.

STATIONS HEARD DON'T MEAN SQUAT. Just because the reviewer didn't hear them, doesn't mean that *I* didn't! In other words, everything is relative. If you have a water tank from the 1800's buried in your backyard with the loop over that, you may only hear down the street. Perhaps my rocky-soil conditions are helping.

OH, and this is on a simple Nasa / Target HF3 inexpensive marine ssb receiver with a 3.8khz filter designed back in the 90's for casual boaters.

If I put in some serious dial time with my Kenwood TS-590s, things might be a bit better.

The main point is that I didn't lay one of these down to win any dx contests. I don't think anyone ever claimed that to be the point of it all. Yet somehow, I'm hearing my fair share, even if they are just the big guns so far. I'm happy with an antenna so close to the worms doing that, yet meanwhile doing a very nice job at other angles.

Last edited by hertzian; 11-09-2018 at 6:14 AM..
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  #127 (permalink)  
Old 11-09-2018, 1:55 PM
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Default Sorry for that

Apologies all around for that emotional dump. I guess I got tired of bench-racers.

Be suspect of hearing nothing OR things too good to be true. Have you isolated any common-mode problems making the coax part of the antenna and ending up with lobe pointing straight to Keokuk, Iowa?

Not singling out Keokukians - I'd love to hear from you!

If anything, I'm wondering if sky-noise will be an issue if/when the cycle improves. Until then when I find out, I'm having a blast.
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  #128 (permalink)  
Old 11-09-2018, 1:57 PM
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What's a bench racer?
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  #129 (permalink)  
Old 11-10-2018, 3:04 AM
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It's a racing reference for those who talk specs about what combo of parts will be faster, better etc, (and usually why yours sucks) but don't actually own a racing vehicle themselves, or aren't really active at all in the sport.

Basically it means talking a knowledgable game, but not taking all the variables into consideration. Usually easy to beat at the track when all the spec-talk blows up on the dyno in his garage.

Nobody at RR is doing this - it was "helpful" 3rd party private email.

Last edited by hertzian; 11-10-2018 at 3:09 AM..
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  #130 (permalink)  
Old 11-10-2018, 1:04 PM
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Originally Posted by hertzian View Post
It's a racing reference for those who talk specs about what combo of parts will be faster, better etc, (and usually why yours sucks) but don't actually own a racing vehicle themselves, or aren't really active at all in the sport.

Basically it means talking a knowledgable game, but not taking all the variables into consideration. Usually easy to beat at the track when all the spec-talk blows up on the dyno in his garage.

Nobody at RR is doing this - it was "helpful" 3rd party private email.
That is why I try to include some type of "If it works for you, is what really matters." thing, when talking about theoretical. (Unless there is actual danger. If it is legally "questionable" then I tell them so, and let them decide what level of legal risk they are willing to take on.)

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  #131 (permalink)  
Old 11-12-2018, 5:45 PM
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I'm over it - just a bad week. All good now.

This does make me wonder how much of the dx I am hearing is really a higher-angle multi-hop rather than a single hop.. It would take a far better dxer than me to determine that.

I suppose too that also depends on the antenna on the other side - if they are putting out a higher-angle lobe in addition to their low angled ones. Maybe I'm hearing the energy from those? Time to get out the charts.
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  #132 (permalink)  
Old 11-14-2018, 2:25 AM
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Default Poor ground means better response

Maybe this is why I have better results than others. I have a very poor ground environment. Good news for us desert-dweller types.

How bad? So bad that after pushing the metal lawn staples into the ground for about an inch, I have to use a rubber mallet and carefully pound them down. More often than not, I bend them.

So I modeled with EZnec using a real high-accuracy ground as usual, but changed my ground to what K2AV calls a very poor ground, 0.001 , 3

Now the numbers are coming up better.

If I change it to what K2AV calls "ghastly" ground, 0.0005, 1 , then things start to swing towards the feedpoint and skew pretty badly. I don't think my ground is that bad.

LAZY VEE test:
For fun, I tested out a vee. Thinking about the guys that for whatever reason can't lay down a loop, nor a dipole with it's center feed. Perhaps the VEE would be more convenient. I ran 17.5 foot sides to the vee.

Yes, that works too. I only had it up for a day, and didn't spend much time on 160 - in fact I didn't hear any locals, but had limited time before I went back to the loop.

Modeling suggests that the VEE configuration is always a generic omni, so it doesn't matter how you lay it down. More like a perfect sphere.

There is obviously any number of ways to lay these things down, but at least the loop, dipole, and now the vee have predictable patterns - mostly omni, but the loop and dipole have a bit of directionality if you want to take it that far.
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  #133 (permalink)  
Old 11-15-2018, 3:12 PM
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Default ZF9CW Cayman Islands

I heard Stan, K5GO operating as ZF9CW on 40 meters at about 3am local time blowing my front end out, working a string of JA's.

From LA to the Cayman's may not seem like such a big deal, but dx doesn't always have to be a 6 degree angle hop.

Op runs a variety of rx antennas, like bogs and flags. Although the omni pattern of an on-ground loop is the total opposite of what you desire with bogs and flags, it makes me wonder what if he tried using say a larger one, like a 120 foot loop for 160-40, or even a 240 foot one for 160-80 - even with the omni response.

Different reels and rods for different fish - but sometimes the wrong ones will pull up something interesting.

My first thought would be due to the supposedly good soil conditions, a bog or log may not perform as well as a classic elevated beverage, or simple vertical - taking the loss of super high gain and directionality of a LOG into account of course...

However, if one is space-constrained, the convenience of a LOG or even a DOG just outside the shack would be worth a try....

Last edited by hertzian; 11-15-2018 at 3:29 PM..
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  #134 (permalink)  
Old 11-17-2018, 6:00 AM
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Default Added a "cable tv" ground loop isolator at rig end

In preparation for another project at vhf, I decided to try one of those physical / galvanic cable-tv type isolators at the rx side of things. It is an "Ancable" model. Others seem similar. Works, BUT

I may be going overboard with isolation.

These things are typically designed to operate from 5mhz to 1ghz. I gave it a shot anyway, and sure enough, AM BCB is attenuated a bit. Ok, I'm not doing BCB dx'ing and it seemed to actually help calm the front end of the inexpensive Nasa / Target receiver.

160 seems a bit attenuated, but I didn't do a lot of testing there. 80m likewise, but to a much lesser extent. Hearing all the usual stuff, but hard to tell any degradation by ear.

Overboard - point of diminishing returns?

1) Have an isolated 9:1 at the feedpoint.
2) Have a good common-mode-choke at the feedpoint.
3) 30 foot run of coax
4) Sole antenna attached to receiver run on batteries.

And now this. I have no way of measuring this - other than the RigExperts antenna analyzer noticing a few minor dips and peaks compared to the original plot.

Because it doesn't see to be hurting (other than BCB and 160), I'm going to leave it attached just behind the rig anyway.

Honestly, I'm not sure it is a major improvement, BUT I *may* have a slightly lower noise floor. Noticed that I pulled back on the rf amp driving the Nasa / Target ssb receiver a little bit more than usual.

I probably wouldn't even notice with the Kenwood or Alinco.

Thing is, I discovered that these "cable tv" type rf ground loop isolators may be entirely desirable on higher frequency rx-only projects, like VHF / UHF etc at the feedpoint, and possibly at the shack end too. We'll see...

Last edited by hertzian; 11-17-2018 at 6:11 AM..
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  #135 (permalink)  
Old Yesterday, 5:17 PM
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Default Swapped loop leads to isolated transformer

It shouldn't make any difference right? I noticed a very minor one.

An imaginary 20db improvement was noticed on skywave signals.

Joking aside, I did notice the slightest of improvements to a local noise source. Not enough to write home about, but hey, an improvement by merely swapping the leads cost me nothing.

Modeling says it shouldn't make any difference. Skywave reception very hard to tell.

BUT, modeling is one thing and real-world another. For whatever reason, the swap, while not logical, was noticed on a very very weak local noise signal, but I had to look (listen) real hard. Re-swapping it back and forth confirmed it.

I'm just saying - it shouldn't matter, and for practical purposes it really doesn't. But if there is a *major* noticeable difference, than something is actually wrong.
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