Small Antennas

[Glenn K2KL]

Yep, the same as in "automatic antenna coupler"

Like this model by Harris that is designed to work with ALE systems;

http://www.rfcomm.harris.com/products/tactical-radio-communications/RF-5382H-CU001.pdf

The A in ALE is for automatic. If the operator needs to select a frequency, tune an antenna, or rotate an antenna, it's no long automatic. All the operator needs to do is compose his message and hit send. The ALE system picks the frequency or frequencies and which node or nodes (other ALE stations) to send the message. This is not much different than what you do when you send an email via the Internet. All you do is put in the address of of the recipient(s). You don't care how it get there, as long as it makes it. The DNS system and routers take care of this for you behind the scenes. ALE is similar but the "Internet" connections are RF on HF.

The mil does like logs. But they don't rotate them a whole lot. Many installations are fixed directions. The B&W dipole is "flat" over a 20:1 frequency range. That would make for a mightly big Log to cover such a range at HF. Logs (really multiple logs off one feed) with 100:1 frequency coverage are available at VHF/UHF and microwave frequencies. Most have no more than 6 dB gain though.

[K1JJ]

Right on. It is surprising why
manufacurers continue to mess with the complex matching
and tuning tricks for nested/trapped/crapped yagis and the
like. I would think it would be less expensive to manufacture
a log. Also no tuning or tweaking needed at the factory or
by the user. And they could still charge as much and up their
profits.

I think logs a get bad rap in the ham whirl, so are not in big
demand. Most hams think logs have gain the equivalent to
a dipole and they cover a wide range using a single el at a
time. At least that's been the opinion expressed to me several
times.  There ARE logs out there that suck, like the ones forced
to cover a 4:1++ freq range and/or have very short booms.
They are lucky to be equiv to 2el beams, if that. You need a
long boom and a freq range of 2.5:1 or less to give it a fighting
chance to equal a 4 or 5el Yagi..

All logs use only the elements in their respective frequency "cell".  
For a rough example, on 14mhz, it might use six elements;
the 13.5mhz, 14.0 mhz, 14.6 mhz, 15.4 mhz, 16.2 mhz and 17.0 mhz
resonant elements to form it's pattern. This is equiv to a
good 4 to 5 el Yagi, in my log's case.  The current in each el
decreases dramatically as it moves away from the "resonant" cell...  
ie, the log progressively uses the elements that are available until
they become too short or run out.

To see a good example of performance, all one has to do
is try a few pecker matching tests with Chuck, K1KW [ex-WN1BLN]
on any freq from 14-30 mhz. He has a similar but finished
system to mine with a pair of 60' boomed logs at 110' and 55'.  
No one can touch him even using "Sky Needles" [gag] or other
Yagi stacks, caw mawn.

His system works where other Yagi systems are suspect,
due to detuning from other antennas, towers and guy cables.

T

[wa2zdy]

. . .  As such, a broadband antenna is required and a 3 to 6 dB loss is an acceptable tradeoff to obtain the required bandwidth with only one antenna. It has nothing to do with $600 toilet seats, even though such comments make for a good laugh.

Your point is taken.  I was simply making the point (my opinion only) that the approval of the military being bestowed upon this new short antenna isn't necessarily a sign of it actually being a "good and efficient" antenna.  (Judging from other posts here, many of the users of this forum agree.)  The military that allegedly says this is a well-performing antenna is the same military that has in the past paid insanely for things such as hand tools and toilet seats.

Based on that hand tool and toilet seat example, I'm not real quick to accept "military testing" as the be all and end all of quality.

Certainly the military has uses for antennas such as the B&W dummy dipole and I'm sure even the Maxcomm "thing."   That has naught to do with whether or not the Rhode Island University antenna is any good.  And while it may fill a use the military has, that doesn't mean it's any better an antenna than the other suspect antennas discussed in this thread.

[Steve - WB3HUZ]

I think we agree.

. . .  As such, a broadband antenna is required and a 3 to 6 dB loss is an acceptable tradeoff to obtain the required bandwidth with only one antenna. It has nothing to do with $600 toilet seats, even though such comments make for a good laugh.

Your point is taken.  I was simply making the point (my opinion only) that the approval of the military being bestowed upon this new short antenna isn't necessarily a sign of it actually being a "good and efficient" antenna.  (Judging from other posts here, many of the users of this forum agree.)  The military that allegedly says this is a well-performing antenna is the same military that has in the past paid insanely for things such as hand tools and toilet seats.

Based on that hand tool and toilet seat example, I'm not real quick to accept "military testing" as the be all and end all of quality.

Certainly the military has uses for antennas such as the B&W dummy dipole and I'm sure even the Maxcomm "thing."   That has naught to do with whether or not the Rhode Island University antenna is any good.  And while it may fill a use the military has, that doesn't mean it's any better an antenna than the other suspect antennas discussed in this thread.

[Steve - WB3HUZ]

A couple more articles on the URI antenna.

http://www.eet.com/showArticle.jhtml?articleID=21600147

http://www.commsdesign.com/printableArticle/?articleID=21401977


If the field strength measurements really do show this thing produces the same as a "full-sized" half-wave vertical, then it's legitimate. It shouldn't be that surprising. If they can be fed and/or loaded efficiently, a half-sized or even quarter-sized antenna will produce the same field as a full-sized one (at least in the case of a dipole). The trick is obtaining the efficient feed or loading. I think that is the claim with the URI antenna - efficient loading.

If legitimate, this antenna could be worthwhile for hams with limited real estate.

[W2VW]

Nothing new under the sun. Twill be interesting to see if a patent is granted.
No secret that a properly loaded short vertricle will just about keep up with a full sized one. I missed any mention of what was used as a counterpoise.

[K1JJ]

Nothing new under the sun.
Twill be interesting to see if a patent is granted.
No secret that a properly loaded short vertricle will just
about keep up with a full sized one. I missed any mention
of what was used as a counterpoise.

Yep, even 1/8 wave verticals with BIG copper tubing loading
coils are within a db of a "full-sized" 1/4 wave one. The loss
can be less and depends mainly on conductor sizes and the
ground radial system resistance/efficiency.  

There's a friend in the 75M DX window who runs a 4-square
of 1/8 wave shorties. [31' verticals]   I am always amazed
at how well he hears and the reports he gets. He is close to
the top of the big guns with that system on 75M.

Even loaded 75M Yagis with 90' loaded elements [they should be
140' long with the taper factor] are within a db of a full-sized one.  
As the guys said here, it's all about keeping the loading and
matching losses small. To lose more than 1 db in heat is doing
something wrong, unless you start using vertical elements less
than  1/8 wavelength or horizontal elements less than 1/4 wave
length - you'll start seeing input impedances down below 10 ohms, etc.

BTW, 6M was open tonight - worked a bunch of stations in FL and SW.

73,
T

[Steve - WB3HUZ]

I saw the sun spot number was over 100 today! It's been near single digits within the last month. This is quite an improvement.

[Pete, WA2CWA]

I saw the sun spot number was over 100 today! It's been near single digits within the last month. This is quite an improvement.

6 meters was open to Bermuda, Puerto Rico, a number of Caribbean Islands, and the Northern section of South America on 5/10.

[Glenn K2KL]

My disclaimer.... I'm not an "antenna engineer" but I have spent many hours experimenting with short verticals, in paticular, for the 160-190khz "lowfer band" where even the largest vertical is only a fraction of a wave length and I can tell you there is definately a difference in measured field strength between a short loaded vertical and a taller vertical with less loading. Are they talking about near field or far field measurements? and what about angle of radiation?

A vertical has current and voltage nodes along it's length depending on where and how it's fed and the location of the loading device.

I found that the most effective short vertical was one that used as large a capacitive top hat as possible with as small a base loading coil as possible. Getting the voltage node as high as possible on the vertical was the key, which is what the top hat does.

Just food for thought....




 

Nothing new under the sun. Twill be interesting to see if a patent is granted.
No secret that a properly loaded short vertricle will just about keep up with a full sized one. I missed any mention of what was used as a counterpoise.

[Bacon, WA3WDR]

The counterpoise is covered in the description of the antenna test range, but it basically is wire radials in salt water.  According to the descriptions, the receive location is also on salt water, about 1 mile from the transmit antenna.

To me, it's the combination of high efficiency and relatively wide bandwidth that is impressive in this design.  After examining the typical bandwidth characteristics of 1/4 wave verticals, I conclude that 15% bandwidth for a loaded, high efficiency 1/8 wave radiator may not bend the laws of physics, but it is certainly not shabby.

Now, if we were talking about a 1/100 wavelength radiator with the same characteristics... then we'd be breaking serious ground.

[Glenn K2KL]

I'd be very interested to see a direct comparison between this antenna and a plain old helically <sp?> wound vertical. My good friend K2MME used a 40m yagi with helically wound elements for many years. He swore up and down it was just as good as a full size yagi...... but less bandwidth and heavier than a metal ant (fiberglass elements wound with copper tape)

[WB3JOK]

Here's my short antenna for 40 and 75m:

The little air variable only allowed 125W PEP and was shortly replaced by a Russian vacuum cap (which also tunes 75m without adding a parallel cap).


-Charles

[W2VW]

Here's my short antenna for 40 and 75m:
-Charles

Neat.

How about a picture of the feed loop?

[wa1knx]

Hi Charles,
        great photo shot of your loop!!   When I get back east, I'll try
and put a pix in here of a 3" copper loop I build 20 years ago!  I rid the
losses of the conx to a vacuum variable, by flanging or teeing  out the ends of the loop to copper sheets. silver soldered the sheets. sheets spaced in parallel to form a large air cap. the corner of the sheets were cut to form a "mini" variable, by bending them up and varying the
spacing of the corner "variable cap", I used that  to dial the antenna in. no wires. Virtually no connection losses!  we are talking milliohms of loss here!

      fussy as all get out, super high Q, narrow bandwidth (a good sign of LOW LOSS) I used a copper pipe gamma match. the damn thing played
just great! even inside, but I eventully moved it outside where it worked
better.  Note inside, occasionlly  the wall sockets would "spit" an arc ;;


73 Dean! WA1KNX

[wavebourn]

Charles, it looks like a magnetic field caused cracks on a wall! Great stuff! Did you try to cook a dinner putting it inside of the loop?

[WA1GFZ]

Charles,
DANGER WILL ROBENSON!!!!!!!!!!!!!!!!!!!!!!!!!!!! You are in danger sitting in the field of that antenna with the linear on.  Do your eyes feel dry after
a transmission. Run the ARRL safety program if you want to know how many Volts/Meter.
Dean that was a ciol loop you build....HMMMM was that 20 years ago?

[wa1knx]

hi frank,
     yup, early 80's.  I'd  also modeled,  what might be best described as a
mobious strip (sp?). built from 1 to 2 foot wide copper strapping, I believe
a nearly 100% eff 75mtr antenna can be built table top. wear a lead
jock strap! predicted voltages for 1k exceeded 500kv!

-deano

[WB3JOK]

Charles,
DANGER WILL ROBENSON!!!!!!!!!!!!!!!!!!!!!!!!!!!! You are in danger sitting in the field of that antenna with the linear on.  Do your eyes feel dry after
a transmission. Run the ARRL safety program if you want to know how many Volts/Meter.

Thanks for your concern. But I think I'm safe- I did run the program and the minimum distance is surprisingly small for 7 MHz and 700W PEP, ant gain -1 db, uncompressed SSB (20% multiplier). Also I am sitting in the null of the loop (through the center, perpendicular to the plane of the loop) which the part-65 program doesn't count so there is an additional margin. No, I haven't gotten headaches, sparks off my nose, etc. Anyhow it's temporary and I wil be sitting six feet farther away once I get the sheetrock on another wall finished... (the 100 year old plaster wall already had the cracks!)

Tolly - it would be difficult to cook inside the loop unless the "load" were substantially off-center (null is in the exact center) in which case the tuning and matching might become a problem.

Here's the feed. Sorry it doesn't show up well under the desk but it's simply a piece of 5/16" soft copper tubing with the RG-213 center conductor connected to it. I can tell that the wood frame and metal equipment cabinets are loading it somewhat since the 2:1 SWR BW on 40m is on the order of 60 KHz and it should be more like 30 KHz.

This is my much more portable, remotely tuned 20m loop (which also works on 40 by adding capacitance, but it's 5 db down). Picture is turned on its side, of course



-Charles

[W2VW]

TNX. Nice work.

[Steve - WB3HUZ]

I doubt there would be much difference. The "improvement" in the URI antenna is that the reactive components are cancelled out. One of the articles does touch in the similarity to a helically wound antenna. The claim is that unlike the helically wound design, the URI cancels out interwinding capacitance and any excessive inductive reactance. This mean less loading is needed (more efficient and/or less expensive) and a simpler matching network.

I'd be very interested to see a direct comparison between this antenna and a plain old helically <sp?> wound vertical. My good friend K2MME used a 40m yagi with helically wound elements for many years. He swore up and down it was just as good as a full size yagi...... but less bandwidth and heavier than a metal ant (fiberglass elements wound with copper tape)

[WA1GFZ]

after Nam the Army wanted a small efficient HF antenna. They came to a small loop design with 2 series caps to match the feed line. This was the most efficient radiator of all tried. I had the paper once that followed the whole study. All the popular matching methods were tried and the 2 series caps worked the best. The coax was across 1 cap. They even phased a number of them for gain. Inductors were the worse matching method and the small loop couple method wasn't that great either.

[WB3JOK]

after Nam the Army wanted a small efficient HF antenna. They came to a small loop design with 2 series caps to match the feed line. This was the most efficient radiator of all tried. I had the paper once that followed the whole study. All the popular matching methods were tried and the 2 series caps worked the best. The coax was across 1 cap. They even phased a number of them for gain. Inductors were the worse matching method and the small loop couple method wasn't that great either.

Interesting. Glad to hear small loops work the best  
I can see where inductors would be a problem since the currents can get very high.
Do you have the paper, or a citation so I can look it up? Is it online somewhere? I would like to see if I can improve efficiency over the pseudo-gamma match on my large antenna, or the isolated coupling loop on the smaller one...
-Charles

[wavebourn]

Charles, capacitors may be easily calculated using basic formulas. The problem is tuning, since when you will tune the antenna using variable cap (both ends of it should be isolated from ground!) the ratio between smaller tuning cap and bigger in parallel to feeder cap will change a lot, it means variable load.

      ______________
     |               )
    ---  Var         )
    ---  Cap         )
-----|               )
     |               )
    ---              )
    ---              )
-----|               )
      -------------

[WA1GFZ]

The Army article came out in the late 70s. A friend Dick W1JF SK gave me a copy that I lost in my move to Ca. in 80. They tried a number of configurations and a single turn loop with 2 caps worked the best. They also tried different shapes. Round and 8 sided was best if I remember.