Outdoor Under the Eaves Loop vs. Active Mini-Whip Antenna

[Ubbe]

Ubbe - If you have an antenna 1000 feet away from your room, but has poor common-mode properties from the coax, noise from your house / shack can travel right down the outside of the braid to the feedpoint of the antenna, and then right back into your receiver on the inside just like any radiated signal - so be careful. It's why ferrite chokes are popular in many installations.

That's why I have a transformer balun and a magnetic balun for random wires and one balun for dipole work. I had tremendous amount of interferences when I tried a wire going directly to my HF receivers. I need a long coax to seperate me from my house but the neighbours house are just as bad and too close to my fence. I have a ALA loop antenna that works pretty good and a vertical from RF systems that I haven't tried yet. I'm about to set up two 10 fot aluminum poles on the chimney to add to the one I already have and see what I can install to them.

/Ubbe

 

[Lauri-CoyoteFrostbite]

Yes Ubbe, the tuner does not match the antenna if it is between the radio and a run of coax- it matches the coax-- but I never used the term 'coax' --- between it, the tuner- and the 'wire.'

Martin, "Majoco" kindly correct'd my omission - I should have made it clear that the random wire be connected directly to the antenna tuner-- and anyone familar with the standard runs of ham tuners knows there are ports on them for a variety of antennas- including ones called "wire."

Reiterating- the random wire/tuner together are an antenna. If a preamp is desired, it is placed between the tuner and the receiver.
Use coax.

Okay, that'll be all from me--
..........like I said UV, I wish you the best of luck with this-- (send me a PM {personal message} if I can help you out further. )


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Oppps-- a final parting:


Heee hee- I would hope that everyone would not think they have to buy a 2 KW roller- inductor tuner for SWL'ing-- but that would make for an impressive 'radio shack'-- Point that out to your visitors and they will think you are one serious Radio Dude !
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Lauri

 

[Boombox]

To the OP: I'm a little confused. At first you say the mini-whip is 20 ft, and the loop is 10 ft. off the ground. Then, later in the thread you say the opposite.

Your whip is active, and it's higher off the ground. At HF frequencies, higher is always better. Almost any HF or ham antenna handbook will tell you that for HF you want to get your antenna higher off the ground. As for the reason the mini-whip works so well, my guess is that the combination of height, and the fact that (if it is a PA0RDT) it is an active antenna, makes the difference.

As for your solutions for a better antenna than the one you have, I'd try to elevate the loop. Or look into one of the modern amplified loops. Some of them seem to get people amazing results. The others here have a lot of good ideas, also.

 

[ka3jjz]

<snip>
Example: One buys a very simple inexpensive antenna tuner which provides a better match to the receiver for his random wire. Great! But now, with the better match, sure signals smoking strong - the tuner did it's job, but the noise is also raised to ear-burning levels.
</snip>

It's very unlikely that a transmatch - which has no active amplifier - will amplify a signal so strong that the noise will also increase by that much. I've used tuners that were homemade, some from MFJ and even Grove, and never really noticed that. Now an active preselector - yes, that is often a problem, particularly when running one of those at full, or nearly full, gain. There will likely be some gain when using a transmatch, but not a lot.

Mike

 

[ka3jjz]

<snip>
As for your solutions for a better antenna than the one you have, I'd try to elevate the loop. Or look into one of the modern amplified loops. Some of them seem to get people amazing results. The others here have a lot of good ideas, also.

Elevate that loop, get it away from the house, feed it with ladder line into a transmatch that can handle balanced feeds, and you have the workings of a skywire loop. There's even a Yahoo group devoted to the subject Mike

 

[ultravista]

To the OP: I'm a little confused. At first you say the mini-whip is 20 ft, and the loop is 10 ft.

The active mini-whip is 20 feet in the air; 10ft galvanized steel fence post + 10ft of PVC reinforced inside with a wooden dowel. The loop runs the perimeter of my house and it ~9-10ft above the ground.

 

[nanZor]

Mike - for the most part I agree about not needing a tuner for swl'ing under most circumstances. However there are extremes of reactance one can encounter that can put the hurt on a long feedline, where tuning out *system reactance* to a degree can be very helpful.

One example was my so-called coaxial "shielded loops" with no preamp on 160 meters, when the loop size was cut for 40 meters. Having only about an octave of usability (80 meters possible), the tuner helped on 80, and very much so on 160. Tuning was VERY touchy, but brought the overall reactance down to a usable point so that I didn't need a preamp.

And Lauri - get this - I was using a little mobile MFJ tuner to do this - and was so serious about my non-amplified shielded loops that I almost DID get a $$ Nye-Viking tuner with much lower loss at low freqs.

But yeah, one only goes to an extreme like that if they are crazy or have a very specialized need. But no way would I recommend one to someone who doesn't truly need it for something totally special.

 

[nanZor]

Ultravista - like many antennas, common-mode current (the outside facing part of the coax shield) is part of the design.

Yours is vertical, possibly in a spot that has limited noise fields. This is far different to a low to ground horizontal antenna that surrounds your noisy house. Your whip is the equivalent of walking around your property with a small shortwave radio antenna, and finding a spot that works in the vertical position. I've actually used that technique to find a permanent spot on my property for a vertical antenna, despite the common believe that all noise is vertical in nature. Not so, but the myth persists. Eventually, I found a very tiny spot that works, and poured the cement there.

In other words, you are comparing apples to oranges here. There have been quite a few reviews of the mini-whip by people much more professional than I, and I'd just say be happy that it works for you. If you want to find out more about your antenna, look up non-commercial (ie no marketing) reviews.

BUT, there is NO antenna that is guaranteed to work in all environments. Each one is different.

 

[nanZor]

prcguy - you are right, but thought I'd expand on this just a hair for those new to the s/n game.

...
The big loop 10ft off the ground would be excellent for NVIS on the lower bands and would transmit and receive very well in the 0 to several hundred mile range as the signals bounce straight down when propagation is ideal. The signals from the loop on the ground would be maybe 20dB or more weaker but would have some advantage for distant signals off its ends and would also have a very low noise floor where a loop around a house might pick of lots of interfering signals from inside the house.

At first, that -20 to -30db seen in modeling plots is truly alarming. It would be ridiculous to use an antenna like that for transmitting, wasting power. And the on-ground receive loop, while capable of nvis with it's high look angle, ALSO has the low angles too being forced to by being smashed to the ground - not a foot above or 8 feet up under the eaves, but ON the ground.

With receive, some seem to forget that the -20 to -30 also applies to the noise level as well, which the receiver (especially the first mixer) loves to see come down, as it lowers the IMD or intermod products - *additional* noise coming from inside the receiver itself.

Simply, as long as the antenna has a proper look angle, despite it having a -20db spec, the lowered noise floor simply means that even though you may not see your S-meter moving (much), the signal itself sounds LOUD, and armchair copy. Or even weak dx can still be heard - you just turn up the volume a little more.

Just some notes for lurkers - what looks like an immediate -20db penalty with the on-ground antenna, is not much of a penalty - especially for those who have a noisy environment. Guys living on a solitary island in the South Pacific - maybe not so much.

 

[Boombox]

Ultravista, thanks for the reply. It clears it up a bit.

Vertical antennas generally receive low angle radiation better (low angle means the antenna will 'see' more distant skywaves, as they arrive at lower angles) than horizontal loops, and higher is better for SW. Even a 10 ft difference can be substantial. Although a 10 ft difference doesn't seem like much, the 20 footer is twice as high as the horizontal loop.

As Hertzian mentioned if the vertical antenna is out away from your house a bit it might just be enough to counter any noise issues.

And, being amplified -- as I said before, that also can make a difference.

Either way, you're entering the fun world of antennas. I used to build them, but lost interest in it a decade ago. I built a quad loop, a wire yagi, and a V-beam (that really didn't work out well). When they're working well, it feels like an accomplishment. Just coax and wire, and you have something pulling in signals from across the world. It's more fun, of course, when prop is up.

 

[ultravista]

I noticed that on 80 and 60 meters, the loop is comparable to the active mini-whip for amateur stations in California, Arizona, and Northern Nevada - I am in Southern Nevada. So 'local' stations are pretty much the same but elsewhere across the bands, the mini-whip outperforms the loop 10 out of 10 times.

 

[nanZor]

That's great - keep on using it. It seems to be working for you.

Not surprising that a horizontal loop only 8-10 feet or so off the ground under the eaves is poor compared to a vertical. You are in "no man's land" where directivity is a toss-up. You could do one of two things - go to an extreme and THEN compare. Raise your horizontal loop up to 30 to 60 feet, or drop it *entirely* on the ground surface.

There are many dinky active antenna options. The mini-whip is only one of them. It is a viable solution for some. Just be careful with claims of out-performance compared to similar models, or passive antennas. That all changes depending on frequency, time, and propagation.

A similar passive vertical antenna could also be used for comparison up 20 feet:

https://forums.radioreference.com/threads/inverted-vertical-step-by-step.382114/

Which one outperforms the other? Try one!