160 meter AM without a 160 meter antenna

[W1UJR]

Don't have a 160 meter antenna, or space for such?
Here is an idea!

Take the KA1KAQ Collins KW-1, add a large broadcast dummy load, a "T" coax connector, a 75 meter dipole and a few hundred watts of RF and you are on 160 meters.
And you have a good footwarmer as well.

Of course Marconi Aerial Wax was liberally applied.

Clearly most of the power was burned up in the dummy load, but some RF did manage to get out.
So how did it work?
Actually quite well.

Tried it on 1945 KC with Todd, KA1KAQ late Saturday evening, Q5 here in Maine.
Bill, KC2IFR was in on the QSO as well.
But I can't claim credit for the idea, its based on the Barker and Williamson Folded Dipole design, you know, the one with the "matching network" suspended in the middle.

Kurt Sterba would be proud. 

[Ed-VA3ES]

I'm just in the midst of putting my dipole back up, (after 8 years).  The last time I was on 160, I used my end-fed-Zepp.  Fed with balanced line, and run through a tuner. It worked OK, but not great.  I did manage to work guys in the north-east.   I expect the dipole (also fed with bal. line) will perform the same.  What else can I do; I have a postage-stamp lot. 

[k4kyv]

For a couple of years before I got my radial ground system installed back in the early 80's, I operated 160 using my 80m dipole, fed with open wire line, as a quarter-wave dipole on 160.  Not with the feeders tied together and working against ground, but as an actual dipole with a tuner.  I got good signal reports all over N. America with this antenna.  Of course, it helped that this dipole was on average about 110 feet high.  But this has been successfully done with much lower antennas.

One thing I found was that it was extremely sharp tuning.  I could move +/- maybe 5 kc/s before the tuning got too far off.  The first year I used it, I ran down to the tower to readjust the tuner every time I QSY'ed.  The second year, I had a reversible DC motor installed to remotely tune, but by then I had my radials installed, so it never got a tremendous amount of use before I began using the quarterwave vertical on 160.  The vertical outperforms the short dipole everywhere except for stations about 50 miles away, where there is a skip zone, i.e. the groundwave fizzles but it is still too close for good skywave propagation.  I still used the dipole to talk to stations in Nashville, which is right in the middle of my skipzone.  At the time, I QSO'ed regularly with several stations in the Nashville area, and they always reported that the dipole was about 30 dB stronger than the vertical.  Often, signals from the vertical were lost in the urban electrical hash, but the dipole produced armchair copy.

One of the guys in Nashville went SK, and the others eventually drifted into other endeavours, so I no longer regularly talk with stations in Nashville on 160.  In addition, I accidentally ran over the motor control cable with a lawnmower. Now the dipole is very rarely used on that band.

[Todd, KA1KAQ]

Yes, I am living proof of the last statement!

As Bruce stated, I was able to work 160m with the dipole-T-dummy load system. Bill was quite loud, and I heard Bruce well enough to carry on the contact. We started on 1885 and moved up to 1945. Sure, the dummy load got a bit warm, and sure, I did hear a few *SNAP* sounds followed by accompanying sparks in the PA compartment, but BY GAWD it worked! When you add in the fact that the 75m dipole is in the trees (literally) out back, maybe 15-20' at its apex, it's even more amazing.

Not that I plan to run this way a lot, or even again, but it was pretty fascinating and netted my my first and second 160m contacts ever. Cool.

But get this: as fun as the contacts were, something even more interesting took place. I was hearing images from the local BC station whenever Bill or Bruce keyed up, which was a bit interesting at best, annoying at worst. Bruce mentioned hearing some CW on our carriers from what? Drift nets in the North Atlantic! I listened a bit and was hearing them also, a couple of letters or letter/digit combo followed by a long dash. VERY cool!

So now I'll be looking to get a real antenna system set up for 160, despite having to pull it down in a few weeks or months to move. In the meantime, I'll be listening!

[K1JJ]

We talked about this before, but, if I remember correctly, using a 75M dipole fed with good quality, homebrew openwire, on 160M is within a db or so of a full-sized coaxially fed one.

Using 75' elements on 75M rotary Yagis that should be 140' long is commonly done with 1db losses according to modeling.  

For the wire dipole, the key is to pay attention to the current points. Make sure at least #10 wire is used on both the feedline, flat top and always have a strapping tuner designed to handle low impedance feeds.. The input imedance can be very low (12 ohms?) on a one-half sized dipole, thus the problem with conductor size, even using openwire.


The  'T' system:
Using a dummy load a with 75M coaxial fed dipole and a "T" split should give a 3db loss in the dummy/antenna split, a ~1db loss in the 1/2 sized dipole, and maybe 3-4db? loss in the 100' long mismatched dipole coax. (just a guess)   So if the system is down 7-8 db from a full sized dipole, that's not too bad. It's like reducing power from 375 to 75W... Sometimes it's hardly noticable under good local cornditions.


T

[WA1GFZ]

There was a guy on 160 a couple weeks ago who was using a 3 wire 75 meter dipole
with open wire feed. He called it a cobra ant. The extra wires made the resistance lower. He was just as loud as other guys.

[Jim KF2SY]

Frank,
that Cobra antenna is the "cobra lite" which uses a linear loading techinique with 3 wires on each leg.


url for cobra antenna:

http://www.k1jek.com/

Jim KF2SY

[K1JJ]

"To Serve Man"     "Hey stop them, it's a cookbook!!!!"

heheheheh....

[WA1GFZ]

Gee, I would prefer them in parallel and live with the low z input or maybe hang vertical elements to get length. what do you think Mr. vu

[WB1AEX]

Hi,

Just another comment regarding the linear loaded 140 foot center fed (sold commercially as the Cobra Senior). It is roughly the same length as a 75 meter dipole, but loads very nicely on 160 meters through 6 meters with a tuner. Two local friends in nearby towns use them, and they work quite well. In both cases, they did not have the room to run them straight. Theirs are zig-zagged all over their property to get them to fit. Generally, they are about 3 - 6 db down from my half wave on 160 meters, but they make up the difference by running more power. The commercially made units as seen at   http://www.k1jek.com/  are very well made and work great right out of the package, but you can roll your own using rotor cable. They blow the popular G5RV antennas out of the water. When you think about what they are doing with this antenna, there's actually 420 feet of wire on each side, a total of 840 feet to load into. Pretty slick.

Rob, WB1AEX

[Ed-VA3ES]

Hi,

Just another comment regarding the linear loaded 140 foot center fed (sold commercially as the Cobra Senior). It is roughly the same length as a 75 meter dipole, but loads very nicely on 160 meters through 6 meters with a tuner.

Hmmmm.... might just be what the Doctor ordered!  Might solve my 160M problems handily!

Thanks for the tip, guys!!

[K1JJ]

The JEK antenna shown is really a dipole fed with openwire, except that it has a unique matching system.  It's the same concept as a folded dipole that gives 300 ohms or in this case, the three wire configuration gives an even higher input match. This is good for openwire.

The performance of a 140' three wire dipole fed with openwire - and a standard coax dipole cut for 75M are identical on 75M. They have the same pattern. But when using that three wire antenna on the higher bands, the pattern becomes multi lobed - This can be a problem at freq X 4 when the broadside direction is now a big null. (cloverleaf pattern)

It would be interesting to model it and see what input impedance a 140' three wire config gives on the higher bands, and 160M too. An antenna matcher is needed, of course, so it appears that the design is simply trying to raise the input for the openwire and make a standard tuner usable on 160M where the imedance of a 1/2 dipole is too low for many tuners.. For example, on 160M, a 140' dipole would be down around 12? ohms. By using the three wire config, they are bringing it up to a more reasonable level to match the openwire to minimize losses from IR drop. At least I THIONK that will happen on 160M with a shortie dipole.

Maybe somebody will model a three wire and report the  input impedance on 160-10M.

T

[k4kyv]

What's old is new again! About 25 years ago, a character by the name of Sonny Irons sold a gizmo called the "Maxcom Instant Antenna Matcher". It was nothing more than a couple of noninductive resistors in a metal box...To protect his "secret" from prying eyes, Irons potted the boxes. To save money on potting compound, Irons put pieces of scrap PC boards into the boxes. He used to sell these things for up to $800...quite a profit for a couple of resistors, a metal box, and some insulators!

The MAXCOM automatic antenna matcher turns out to be a little-known and rarely used device. I first read about the matcher in an article written by Gordon West in the December 1983 issue of Worldradio. Gordon performed a product evaluation of the MAXCOM and gave it such a glowing report I purchased one. After several months of using the MAXCOM, I, too, was impressed and purchased a second unit for my marine SSB.

http://www.southwindssailing.com/articles/9907/HamRadio.shtml

[Steve - WB3HUZ]

Yes, the short, ladder-line fed dipole can work pretty well on 160 meters. I did it for many years. Started out with just a 75 meter dipole, 120 feet long. Then I added 30 foot vertical sections on each end, like below (ignore dimensions).




Then I added linear loading sections (30 feet of ladder line) to each leg. This made the total amount of wire in the antenna 300 feet. The tuning was not nearly as sharp with these arrangement as compared to just the 120 foot long version. Like below.



The height was about 50 feet on average, the center was probably about 65. Even it this relatively low height, I made hundreds of contacts on 160 meter AM, most of them running no more than 100-200 watts. It works.

Joe, N2YR, took the idea a step further and juggled some of the lengths on the above arrangement so he could use coax feed. He's used it the last two years and it works FB, on par with another AMer local to him that was using a full-sized 160 meter dipole.

[Ed-VA3ES]

The performance of a 140' three wire dipole fed with openwire - and a standard coax dipole cut for 75M are identical on 75M. They have the same pattern. But when using that three wire antenna on the higher bands, the pattern becomes multi lobed - This can be a problem at freq X 4 when the broadside direction is now a big null. (cloverleaf pattern)

This is not a consideation for me since I have a tri-bander for 20 thru 10 M.  This dipole will only be for 160, 80 and 40 M.   Any idea how this antenna will perform on 40?   My old end-fed-Zepp worked  gang-busters on 40.

[K1JJ]

This is not a consideation for me since I have a tri-bander for 20 thru 10 M.  This dipole will only be for 160, 80 and 40 M.   Any idea how this antenna will perform on 40?   My old end-fed-Zepp worked  gang-busters on 40.

Ed,

A 140' dipole on 40M should have an optimum bi-directional lobe that is about 35 degrees wide each way. So, you need to aim it right or off the center stations will drop off very fast.  You will see about 2.5db gain on both fronts. Non-rotatable, so a problem.

I wud recommend using it for 75/160M for a standard 80 degree wide broad figure 8 and put up a 40M coax fed dipole if you have the room. The coax 40M dipole will also have a coverage of about 80 degrees either direction broadside. Big difference for coverage.

73,
T

[Ed-VA3ES]

Ed,
A 140' dipole on 40M should have an optimum bi-directional lobe that is about 35 degrees wide each way. So, you need to aim it right or off the center stations will drop off very fast.  You will see about 2.5db gain on both fronts. Non-rotatable, so a problem.
I wud recommend using it for 75/160M for a standard 80 degree wide broad figure 8 and put up a 40M coax fed dipole if you have the room. The coax 40M dipole will also have a coverage of about 80 degrees either direction broadside. Big difference for coverage.
73,   T   

Excellent info, Tom.  One more question...  How will a 80M, balanced fed dipole work on 160,  vs.  that "Cobra Antenna"? any ideas?   I'm seriously thinking of getting that "Cobra Antenna', but not if the difference will be slight.

Your idea of a separate 40M coax-fed dipole is good; I have the room.  The orientation of all dipoles will be E/W, or main lobes N & S.   I need to work east/west  to work friends in Montreal and Toronto, on 40.

[John Holotko]

Last time I tried operating 160 with an 80 meter antenna. I tied the ends of my open wire feed line for my 80 meter Inverted Vee together and ran the Johnson Viking 2 into it along with what  I thought was a decent ground. I keyed up the transmitter  and moments later I noticed the smell of something burning. I instantly unkeyed and started hunting down where the smoke was coming from. Eventually I found it. Turns out  the smoke was coming from my network switch. Apparently enough stray rf got into it to induce enough of a current to pass through the switch's  components and cause them to overheat. Surprisingly the switch still works fine. So I figure I'll have to try a different config for 160. I am also on a postage stamp here so I am limited in whatI can put up antennawise.
 

[K1JJ]

Excellent info, Tom.  One more question...  How will a 80M, balanced fed dipole work on 160,  vs.  that "Cobra Antenna"? any ideas?   I'm seriously thinking of getting that "Cobra Antenna', but not if the difference will be slight.
Your idea of a separate 40M coax-fed dipole is good; I have the room.  The orientation of all dipoles will be E/W, or main lobes N & S.   I need to work east/west  to work friends in Montreal and Toronto, on 40.

John Holotko,

For a limited space area, probably the best bang for the buck is a 160M inverted 'L' fed against ground.  Try to get as many radials down as possible and try to get the vertical and flat top about equal in length. Make it at least 140' or LONGERr (1/4 wave)  to give a higher feedpoint impedance and less dependency on the ground system. Otherwise, do the best that you can. A flat standard dipole is about best for local work, but the L is a close SECOND only because it needs a very clear perimeter (houses, etc) for the lower vertical angles - it will exhibit some ground losses unless you do up an elaborate radial field.



Ed, VA3ES,

Your question on the three wire Cobra antenna... well, I think what I need to know is what input impedance does it exhibit as a 140' dipole on 160M? My older antenna modeling software won't do parallel ines like that, so maybe someone can do it that has the later software. In other words, normally there is ~12 ohms there... but this technique may bring it up to something more reasonable. On 75M it should be fine as is.

Personally, I'm not crazy about that commercial brown openwire stuff. They use it for both the flat top and feeders. It is prone to rain sheeting, so drifts horribly for  high impedance applications, like where is used here. It's also solid #18? or so... thin wire. There are still gonna be high to low impedance swings throughout the system on 75 or 160M, so you will still have to deal with loss.

I would do a conventional, heavy single conductor dipole fed with heavy openwire. You may need to config your tuner or build it for low impedance fed series tuning... or experiment with feedline lengths. On 160M, the  loss from low impedance should be low with #10 wire throughout. I would get a 500' roll of #10 stranded wire from a supplier like Home Depot. Put up as long a dipole as possible with double end insulators. Then stretch out two lengths between two trees and slide on the open wire spacers.  Pull it real tight and and tie each spacer with #14 solid copper. You can use cheap 3/4" electrical plastic pipe for the spreaders. (That gray type or get Lexan rod, etc) Just cut into 5" pieces and drill a hole in each end. I also use them for end insulators - stack a few in series for a real low RF path, or use conventional ceramic series insulators.. This is for 75/160, so not as critical as the higher freqs.

At least that's what I would do...

73,
T

[Vortex Joe - N3IBX]

Bruce - Let me know if you want to do any 160M tests with me at my QTH near Philadelphia. You sounded pretty FBOM the other night when I heard you on 75M. No reason for it to be different on 160M!

Regards,
           Joe N3IBX

[nq5t]

I bet he'd make a killing on the new crop of "amateur radio operators" graduating from our VE test sessions! He was just 20-25 years too early with his scam, oops, I mean, product.

This has come up before.  They are (or somebody is), of course, still in business.  http://www.maxx-com.com/OurModels.html

The blue-light internet special on a 200 watt model is $395.  1200 frequency jumps per second, and 100Khz to 1.3 Ghz coverage all in one little box, all solid state and powered by the RF from the transmitter (according to one review).     

You can have a 2 kw model for $595.

Grant/NQ5T