RadioReference on Facebook   RadioReference on Twitter   RadioReference Blog
 

Go Back   The RadioReference.com Forums > HF / MW / LW Monitoring > Receive Antennas (below 30MHz)


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.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #21 (permalink)  
Old 05-22-2018, 5:02 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

8 foot square loop - yeah, needs a little help.

I'm really trying not to run any preamps. But, the 32-foot (8 foot square) loop certainly seems to need a little help below 14mhz. Had to run with a 10db preamp on both the Alinco R8T and Kenwood TS-590 to get the output level at least somewhat near the output the 15-foot square loop provides.

Still, rolling across 8P5A on 20m cw (Los Angeles to Barbados) on my first try isn't too shabby for an 8 foot square loop on the ground. Here, the preamp brought up the overall level, but the 8P5A's signal was just a hair too noisy, so left the preamp off. Not armchair-copy, but still speaker level copy was fine without having to dig it out with headphones.

Having spent time with the larger loop, we'll see how the smaller 8-foot square loop plays tonight on 20 and 40. Will I still hear the Russian "T" and "M" beacons on 7.039.3 khz at 3am? We'll see.

I hope so, because an 8-foot square on ground loop is about the size of your usual "condo lawn".
Reply With Quote
Sponsored links
  #22 (permalink)  
Old 05-23-2018, 3:09 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

8-foot square "log" - workable, but a little too fiddly with the preamp on/off depending on band / signal conditions.

Heard all the vk/zl/hawaiian stations like the larger loop on both 40 and 20, but had to play with the preamp. No Russian beacons - band conditions were just not there like last night. Also frustrating is being able to copy everyone in interesting nets, albeit without moving the s-meter, but the net ops all bailing out because they have S9 noise with the other stations barely above that. Switch to your "on ground loop" for rx guys!

Test: went back to the larger loop, and tried to "improve" it by raising the 4 corners up in the air on 5 foot pvc pipes. More signal output, but turned it into a cloud-burner and lost my low angles.

If I had to describe the log antenna quickly, I'd say it was *similar* but not exactly like a low-mounted inverted vee. But squashed enough to allow for low angle reception too.

Explored this in EZnec by dropping the "backyard v" ends to less than 1 inch above ground. TADA! A very close cousin! Provided of course you *choke and isolate* the feedline.

My invisible inverted vee is doing great. Very happy with it!
Reply With Quote
  #23 (permalink)  
Old 05-25-2018, 12:49 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

20 meter FAIL with "improvement" :

KK5JY was right. Tried to "improve" my loop by taking advantage of the last little bit of space in the yard so that the dimensions were 18 feet, rather than 15 feet on each side. Severely degraded my 20meter northwest reception - KL7xx gone, even the regulars up in Washington state were weaker than usual. I'm always keeping in mind band conditions have a say, but this was too obvious.

His rule was that if you don't want to mess up your highest frequency band omni directivity, don't make the loop larger than 1 electrical wavelength in circumference. I pushed the envelope and started to lose.

EZnec showed the "punched pillow" directivity on 20m when I did that.

I've mentioned before my attempt to "improve" the loop by raising it off ground, more or less defeating the purpose of the project. Even 1 foot above ground helped turn it into a cloud-burner, but this time I noticed that this effect is more pronounced on 14 mhz. At 160 meters - no real difference, at least none that I could hear above the noise. I see no point in raising above ground anyway, but I had to see if some "magic" appeared. No magic.

All this pulling up stakes and changing things around shows to me why most of my "grasswire" attempts in the past never worked. Mainly it was because the directional patterns are sensitive to length, shape etc, and ended up pointing to nowhere.

Example: take K3MT's classic "grasswire" article. I get it. Although I would have choked and isolated the heck out of the feedline. But moving beyond, MODEL that grasswire at say an inch above ground. I won't get into the transmit aspects, but I don't dig the directional lobes for one thing.

AND, although I don't have time to do every physical permutation, if you are doing the "dipole on ground" instead of the loop, try moving the feedpoint away from the center or ends and do an EZnec plot. You may or may not like what you see.

Basically, for these on-the-ground antennas to work to your satisfaction, random lengths make for random and disappointing results. MODEL it and make your changes to get them to your liking before putting down the wire. Shorter, rather than longer may actually be better in that regard.

Last edited by hertzian; 05-25-2018 at 1:25 PM..
Reply With Quote
  #24 (permalink)  
Old 05-27-2018, 1:43 AM
Member
   
Join Date: May 2009
Posts: 2,238
Default

Folded Dipole on ground? (a very skinny loop!)

My "dog" tests compared to my "log" antennas left me preferring the loop. Not by a whole lot, but it seems that there is a bit more output with the loop. The dog, or dipole in this case is only 30 feet long, mainly because I didn't want to skew the omnidirectional pattern at 20 meters. Basically the patterns are the same as the loop from 160m to 20m.

After looking at a folded-dipole version of the same 30 foot length, with wires spaced apart by only 6 inches, and still using a 9:1 isolated transformer / balun, EZnec tells me that this may be more efficient than the straight dipole.

WARNING: I have *NOT* built this yet. I'm runing out of wire and time basically. However, I had to throw this out there since Field-Day is looming, and some may want to try this out well beforehand.

Speaking of contests, while I'm not in it, the CQ contest for cw really has my loop doing an FB job. And my ears aren't bleeding! Even though I'm not banging the s-meter (although some stations are!) with the loop on ground, s/n ratio is much better putting a lot of 80m and mostly 40m noise into the tolerable range. Reduction of listener fatigue is an obvious long-term contest benefit....
Reply With Quote
  #25 (permalink)  
Old 05-27-2018, 3:59 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

15 Meters! / 21 mhz band opening!

15 meters opened up for a few hours! Without consulting EZnec, the 15 foot square loop is larger than 1 wavelength, so I knew that the directionality would be a bit skewed beyond more or less omni. Sure enough, EZnec was right. Without the contest, and current band conditions, I never would have known really.

I'm using Matt - KK5JNY's calculations: 936 / f mhz = loop circumference in feet. AND since we're using insulated wire, I multiply that by a velocity factor of 0.9 too just to stay on the safe side. (for the dipole-on-ground, try not to exceed a half-wave or 468 / f mhz * 0.9) if you want to maintain the omni pattern at your highest frequency...)

The CQ wpx contesters helped me determine that the loop skewed the directional pattern to favor the direction opposite the feedpoint with this loop longer than a wavelength on 15m.

Yep, central and South America, along with the usual short-skip stations. Ridin' the waves with peaks, swells, dips often in mid-exchange with each other. Hanging on the coat-tails of a short-skip station, and then when I couldn't take it anymore, kicked out and spun the dial for another wave. Rad. The Kenwood 590s handled it great, but I actually had more *fun* pushing the Alinco RX-8T around. Much like tossing yourself in the ocean with a boogie-board rather than a full surfboard. What a blast. Props to Alinco for even making an affordable tabletop rx!

With band noise so low on 15m, and the s/n of this loop being so great, any casual spin would make you think it was dead. Then blam - you rip the headphones off your head when that first short skip station blasts away.

I'm happy I'm evaluating this during the bottom of the band conditions. Had I tested this at the top, I would have just assumed it was a case of my feedline common-mode being the real antenna. Not so.

Still, I didn't trust it, and put so many isolation transormers inline, sleeve chokes, more snap-ons, running from battery etc etc that at some point I was degrading the loop with insertion loss and funky frequency responses.

No preamps on either - it just made things louder, and no improvement to the s/n was to be found. It actually degraded my copy. So just the standard amp in either the Kenwood or Alinco was fine.

Stoked! Back to 20m where I just picked up Croatia. Not bad for a dirt antenna...
Reply With Quote
Sponsored links
  #26 (permalink)  
Old 05-27-2018, 9:54 PM
prcguy's Avatar
Member
   
Join Date: Jun 2006
Posts: 6,793
Default

I've been following this thread with some interest but I have no room for any more antennas here, not even on the ground. I picked up a 500W version of my Eyring lay on the ground antenna at Dayton last week and am anxious to try it out if I can find enough space in town to spool it out. Its 300ft long!
Reply With Quote
  #27 (permalink)  
Old 05-27-2018, 10:04 PM
prcguy's Avatar
Member
   
Join Date: Jun 2006
Posts: 6,793
Default

Looking at the manual for the Eyring antenna's they specify different lengths and configurations for various TX/RX frequency ranges and I just noticed they recommend deploying it as a simple 50ft long center fed dipole on the ground for receive only applications.

Looking at the Eyring patent info and also measuring the balun, it appears to be a 9:1, so it should be easy for anyone to duplicate this thing.
Reply With Quote
  #28 (permalink)  
Old 05-28-2018, 1:23 AM
Member
   
Join Date: May 2009
Posts: 2,238
Default

There's *always* room for one more antenna! Glad you showed up - I'll be very interested in what you find out.

I think some key concepts need to be kept in mind:

1) NVIS cloud-burner vs on-ground loop - while the 1 wavelength or smaller loop doesn't have an overhead null just like a cloud burner, it ALSO has low(ish) look angles in the desired direction, but only if you put it on the ground (no image antenna so to speak, and the horizontal E-field is cancelled).

A weird example is listening to a two way qso between Tucson and Germany on 14.200 at 11pm at night. Mostly armchair copy. No antenna has allowed me to do such late night short skip and dx like that. Bizarre.

2) Tx vs rx. Unless one is a masochist, or does a lot of EZnec homework, I suppose you could pump a kilowatt into an on-ground antenna and get Q's. Or, raise it above ground for the high-angle NVIS only thing.

3) I know you know this stuff, but a reminder that *isolation* in addition to common-mode choking is important. The on-ground loop or dipole should not be accidentally grounded. Use a transformer that is physically isolated inside, not your usual trifilar winding sharing a common ground. Not sure what the Eyring uses. If it does use a common ground transformation, just put an external isolator behind it. Radiowavz ISOX (proven with a multimeter not to share input/output connectivity) is just an example.

At the end of the day, receiver gain covers up a lot of sins, but it can't cover up a bad look angle. Can you form the reels into a loop?

ARghh.... reading your info about the Icom 7300 and 8600 makes me want to see what the loop looks like on a waterfall or other display, a real one, not the Alinco.
Reply With Quote
  #29 (permalink)  
Old 05-28-2018, 3:51 AM
Member
   
Join Date: May 2009
Posts: 2,238
Default

WOW - just read the Elpa antenna manual. While designed primarily for dipoles, and not loops, I think it is still worth reading until it makes your head spin:

HFLINK | ELPA Antenna

I understand what the guy from 1990 was trying to say, but talk about too-much-info all at once for every possible combination in the world. You'd need a lifetime to play with all the combos. Now I know why it didn't last. Not because the tech is bad, but the manual *looks* more like a marketing effort to throw every number in the book.

I think that operation and deployment in the field was probably wrong for many - who's going to read that manual?

Anyway not trying to criticise the product, and it actually helps validate some things. Like maybe I really need a version of NEC that deals with wires close to the ground. I'm using the "demo" version. I'm getting better results than expected, but wonder if that is my wishful thinking, or if in fact things are actually better than EZnec demo indicates?

Or am I just being fooled by higher-angled "double hops" when it comes to all the new dx I'm hearing at the bottom of the cycle?

Just note that there are significant differences in lobes between putting the dipole directly on ground, or up at 3 feet on stakes! And of course I'm really interested in rx-only at this point. But yes, that 150x150ft dipole has a nice broadband swr. If you have that kind of room!

I'd really be interested in how well that works for you. You'll be SOTA every weekend from now on!
Reply With Quote
  #30 (permalink)  
Old 05-28-2018, 4:39 AM
Member
   
Join Date: May 2009
Posts: 2,238
Default

Quick note about grounding and isolation....

Grounding is fine, as long as it is between the rig / rcvr and the galvanically isolated transformer. You don't want to ground between the isolator and the antenna.

W0BTU has some pre-wound 9:1 Isolator/transformers for 50Z coax. Or 6.25:1 for 75 ohm cable. I've mentioned the Radiowavz 9:1 balun. But look out for un-uns or those who have a common ground. Not sure if Balun Designs LLC has any physically / galvanically isolated transformers.. maybe - I haven't really looked lately. Anyone specializing in beverages probably has them.

Worst case 9:1 diy air-core isolator / transformer: close-wrap 12-13 turns of thhn household wire around a 1 to 1.5 inch pvc pipe. Attach to loop. Wrap 3 turns of wire over the top of that first winding in the center. Attach to coax. Ideally followed with ferrite choking material. Don't expect top performance, especially at 160 or 12/10 meters. But if you don't do those bands.....

Last edited by hertzian; 05-28-2018 at 5:22 AM..
Reply With Quote
  #31 (permalink)  
Old 05-28-2018, 8:59 AM
prcguy's Avatar
Member
   
Join Date: Jun 2006
Posts: 6,793
Default

I measured my 150W and 500W Eyrng transformer and they both have DC resistance between the input and output, so they could be an autotransformer (unun) or something more elaborate (balun).

I once compared the Eyring 150W single 300ft version on the ground to a ZS6BKW as an inverted V with the apex at 30ft and the ends about 6ft off the ground and the Eyring was about 1 S unit lower than the ZS6BKW. This was on 40m and it was fairly consistent for local NVIS contacts and coast to coast contacts at night. On 160m the Eyring was making contacts that the ZS6BKw could not hear. The Eyring was also very quiet as you would expect.

I'm hoping this new 500W Eyring will be my go to antenna for desert camping as I use a 500W amp while mobile and camping. With 500W it should perform a little better than 100W fed to an elevated dipole on higher bands and it should kick butt on 160m at night.

If you study the Eyring manuals you will see other models that keep adding parallel dipoles spaced 20ft apart. There is a dual version all the way up to an eight dipole version that claims some impressive directional gain. I was offered a eight dipole version at Dayton for a good price but didn't want to take up an entire football field when camping.
Reply With Quote
  #32 (permalink)  
Old 05-28-2018, 9:06 AM
prcguy's Avatar
Member
   
Join Date: Jun 2006
Posts: 6,793
Default

hertz, I've got a bunch of military surplus 9:1 150W transformers good for at least 2 to 60MHz if you want to borrow one for testing.
Reply With Quote
  #33 (permalink)  
Old 05-28-2018, 3:55 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

Thanks prcguy! I'm good - save those for your other projects....

I'm just worried that when I read his manual, he noted that the 8 years of signal measurements from helicopters differed a bit from the nec calculations - notably that the "nulls were softer".

I wonder if that might be due to the 30-foot coax cable becoming part of the system in common-mode. For sure, take at least a sleeve or ferrite choke with you.

Loop goes down permanently! Pulled up the grocery-store zip cord, and replaced it with Super Antenna SuperWire. Mostly to avoid the tangled mess and put some nice connectors on it. It's what I use for ground mount radials because it's so easy to work with.

I'm really interested in your feedback. It will be interesting to see the difference between on-ground rx, or elevated 3 feet or so etc.

At the end of the day, most people might wonder if these are nothing more than dirt-versions of a 20db attenuator! They aren't. Lay one down, but don't expect to bang the s-meter.

That's the thing - and RST report is really so subjective and makes it hard to compare one-on-one.

For example, if I gave a report of "5-9" to a station on the loop, that means he was just tickling my s-meter up to S1 or maybe S2. A station normally 40-over would be about S6-S7 on the loop. Aha, but the s/n makes all the difference. Nothing exact here, but you'll get the feel for it after awhile.

Of course, anything under S9 (S1 tickle) is a judgement call. How do you tell a station that they are "5-5" when the meter isn't even moving?

Last edited by hertzian; 05-28-2018 at 5:43 PM..
Reply With Quote
  #34 (permalink)  
Old 05-28-2018, 5:41 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

Why the loop / dipole is non-resonant and no need to obsess over swr - within reason.

Receiver gain covers up a lot of sins that one would normally obsess over for transmit.

Example: Placing my AA-54 analyzer on the 60-foot (15 feet each side) square loop w/ 9:1 balun isolator, we come up with these values for simple swr:

160m 15:1 or more. Almost infinity
80m 11:1
60m 5:1
40m 4:1
30m 2.8:1
20m 3:1

But does it matter? I can copy weak stations just fine on 160 and 80m. And that's without using a preamp or cranking the audio to ridiculous levels. Just a smidge above what I'd normally use for an antenna in the air.

But at 160 / 80m, the 60 foot loop is just a tad on the small side. If I didn't care about 20m omni directivity, (heh) and had the space, I'd double the size of the loop to 120 feet square. Not so much to make the swr happier, but to make the antenna even more efficient on those bands.

Yes, a tuner did help slightly on 160 / 80m. But not as much as you'd think operationally.

Ideally, I think that there is room for improvement beyond the 9:1 isolator - either in quality or ratio for the low bands.

THIS is where the beverage guys and their specialized transformers might come in handy.

All I need to do is get W0BTU, W8JI or some others to lay down some wire in a loop. Can't wait for prcguy to loop his dipole!

Last edited by hertzian; 05-28-2018 at 5:45 PM..
Reply With Quote
  #35 (permalink)  
Old 05-28-2018, 6:04 PM
prcguy's Avatar
Member
   
Join Date: Jun 2006
Posts: 6,793
Default

It would be interesting to see what an antenna analyzer or vector network analyzer says the impedance is on the various bands and maybe a 6:1 or 12:1 transformer would give a better match. I think the bad match on the lower bands might show up as additional attenuation if you used a lot of RG-58 or other coax that will be very lossy when used under high VSWR conditions.

I did try my low power Eyring laying completely on the ground and with the hot side elevated about 18" on the supplied stakes but didn't see any difference in the dry rocky desert during testing.

Quote:
Originally Posted by hertzian View Post
Why the loop / dipole is non-resonant and no need to obsess over swr - within reason.

Receiver gain covers up a lot of sins that one would normally obsess over for transmit.

Example: Placing my AA-54 analyzer on the 60-foot (15 feet each side) square loop w/ 9:1 balun isolator, we come up with these values for simple swr:

160m 15:1 or more. Almost infinity
80m 11:1
60m 5:1
40m 4:1
30m 2.8:1
20m 3:1

But does it matter? I can copy weak stations just fine on 160 and 80m. And that's without using a preamp or cranking the audio to ridiculous levels. Just a smidge above what I'd normally use for an antenna in the air.

But at 160 / 80m, the 60 foot loop is just a tad on the small side. If I didn't care about 20m omni directivity, (heh) and had the space, I'd double the size of the loop to 120 feet square. Not so much to make the swr happier, but to make the antenna even more efficient on those bands.

Yes, a tuner did help slightly on 160 / 80m. But not as much as you'd think operationally.

Ideally, I think that there is room for improvement beyond the 9:1 isolator - either in quality or ratio for the low bands.

THIS is where the beverage guys and their specialized transformers might come in handy.

All I need to do is get W0BTU, W8JI or some others to lay down some wire in a loop. Can't wait for prcguy to loop his dipole!
Reply With Quote
  #36 (permalink)  
Old 05-28-2018, 6:36 PM
Wiki Admin Emeritus
  Amateur Radio Operator
Amateur Radio
 
Join Date: Jul 2002
Location: Bowie, Md.
Posts: 21,166
Default

Has anyone tried this loop on HF broadcast or utilities? Right now (understandably) all we have are ham-related reports (which really belong in another forum, but I've left this here because of the interest)

Just to supply some examples, Korea (North and South), Japan, China, HFGCS, New Zealand, etc. (yes I slanted these for our West Coast folks, but don't feel bad East Coasters, you can get into this too. Japan and China are very doable on the East Coast, and NZ can be had in the early mornings)

I'd think there'd be a tad more interest if some broadcast or utility observations were made. This seems like a dandy little project for urban lots that are really too small to be used for anything else other than appearances. (My brother has such a lot).

Any takers?

Mike
__________________
co-author, HF Digital Decoding
HF Forum moderator, RadioReference
Friends don't let friends buy Scancat Lite Plus!
Reply With Quote
  #37 (permalink)  
Old 05-28-2018, 7:23 PM
Member
   
Join Date: May 2009
Posts: 2,238
Default

I'd love to hear non-ham stuff too from any other swl's out there...

Most of my non-ham listening is mostly to aircraft atc comms in the 6 and 10 mhz bands. Much improved! Radio New Zealand was blasting in on 31 meters.

At the risk of using marketing lingo, the loop *may* be helping with qsb / fading as opposed to a straight dipole. But don't quote me.

Because of the reduced overall signal output, but not just being an attenuator, I think this would make an excellent antenna for portables!

The old Grundig 750 in particular, which was prone to agc distortion and called for lots of attenuation, might live very happily with this. I knew I should have kept it....
Reply With Quote
  #38 (permalink)  
Old 05-28-2018, 7:41 PM
Wiki Admin Emeritus
  Amateur Radio Operator
Amateur Radio
 
Join Date: Jul 2002
Location: Bowie, Md.
Posts: 21,166
Default

Good thought about using the LOG on a portable. The lower gain might be just the ticket if you're in a high RF area. And another benefit - as it's close to the ground, it's not quite the lightning hazard that a skyloop (for example) would be. An important point if you live in lightning prone areas like in Florida. That doesn't mean you should ever ignore lightning safety, tho.

Remember, all, that loops like these are all about readability, not signal strength. I would much rather listen to a station with a lower signal strength, but less noise and fading, over a station that is being bothered by fading and noise (but strong) any day. Much less fatiguing.

Mike
__________________
co-author, HF Digital Decoding
HF Forum moderator, RadioReference
Friends don't let friends buy Scancat Lite Plus!

Last edited by ka3jjz; 05-28-2018 at 8:10 PM..
Reply With Quote
  #39 (permalink)  
Old 05-28-2018, 9:20 PM
Wiki Admin Emeritus
  Amateur Radio Operator
Amateur Radio
 
Join Date: Jul 2002
Location: Bowie, Md.
Posts: 21,166
Default

I have dumped a message about this thread on the UDXF and NASWA mailing lists. Let's see if we can't shake out a few folks to do some more utility and broadcast stuff using this antenna.

Mike
__________________
co-author, HF Digital Decoding
HF Forum moderator, RadioReference
Friends don't let friends buy Scancat Lite Plus!
Reply With Quote
  #40 (permalink)  
Old 05-29-2018, 11:01 AM
   
Join Date: May 2018
Location: SW UK
Posts: 1
Smile

Quote:
Originally Posted by ka3jjz View Post
I have dumped a message about this thread on the UDXF and NASWA mailing lists. Let's see if we can't shake out a few folks to do some more utility and broadcast stuff using this antenna.

Mike
OK so you have woken me up :-)

I quickly built a KK5JY loop on the ground with 15ft sides and connected it up to my KiWi WEB SDR

http://southwest.ddns.net:8073/?ext=ant_switch

Best directivity should be East West from the SW of the UK. I've added a 12 dB preamp to bring the level of the loop up a bit, but it's still a long way down relative to some other antennas I tried.

Here's an S-Meter grab from the SDR showing the noise floor during pauses in speech and also the peak signal level. I have annotated the approximate dynamic range from each antenna on the graph.

https://forums.radioreference.com/at...1&d=1527610649

It's OK from about 4MHz to 15MHz but not so good on the lower bands.

Try it for yourself and see.

Comments welcome.

Regards,

Martin - G8JNJ
Attached Images
 
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -5. The time now is 9:30 PM.


Powered by vBulletin® Version 3.8.2
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
All information here is Copyright 2012 by RadioReference.com LLC and Lindsay C. Blanton III.Ad Management by RedTyger
Copyright 2015 by RadioReference.com LLC Privacy Policy  |  Terms and Conditions