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Author Topic: A shortened antenner that works  (Read 29749 times)
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The Slab Bacon
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« on: November 23, 2007, 09:21:24 AM »

I finally got this scanned in so I figgered I would post it for all to see and / or complain about. With all of the discussions lately about limited space antennas, this is what I have been using for some years now with great success. Many of you that have been to my qth have seen it, and many of you that have worked me have heard it, so I do know for a fact that it works quite well. If I can hear them, I can work them. And noone ever seems to have any trouble hearing me. I usually run QRO, but have also been heard running pissweak low power as well when condx warrants.

Mine is hung 35' off of the ground, and I have used it from 160m to 10m with pretty good results. It works very well on 75m and kicks ass on 40m. The 160m performance leaves a lot to be desired, but that is to be expected from a 60' long antenner. I have been using it on 75 for the main station anrenna for some years now.

Here are a few notes to consider.
1. since it is a non resonant antenna, none of the dimensions are real
critical.
2. Use BALANCED feeders only, something fairly heavy gage to handle heavy feedline currents. 14ga crappy brown stuff is the absolute minimum, if you are using it on 160, consider 12ga or heavier.
3. do everything you can to minimize I/R losses, this is critical to putting out a good signal.
4. USE A ROBUST TUNA, ONE CAPABLE OF MATCHING A VERY LOW IMPEDANCE LOAD AND HANDLING HEAVYFEEDLINE CURRENT! No MFJ junk or crappy ham grade stuff if you plan to run real power, you'll smoke it!! My tuna is a large HB single ended "T" type unit in a box the size of an R-390 and I use a large HB ferrite balun wound with #10 silver teflon wire and 4lbs of ferrite. Again do everything you can to minimize the I/R losses. Anything that is getting warm means you have power that is NOT getting to the antenna. Heat = loss!!

I hope this will help some of you that like me are space challenged to get on the air and have some fun!!

I kinw that there will be some nay-sayers out there that will swear it wont work well, but the proof of the pudding is in the eating, and i have been "eating" well for some time now. Say what you wish, I KNOW that it works!!

                                          The Slab Bacon

* short ant.pdf (483.04 KB - downloaded 911 times.)
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W4EWH
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« Reply #1 on: November 23, 2007, 10:36:50 AM »

My tuna is a large HB single ended "T" type unit in a box the size of an R-390 and I use a large HB ferrite balun wound with #10 silver teflon wire and 4lbs of ferrite.

Bacon,

Please post a diagram of your tuner: I'd like to know more about it -

  • Is the balun on the input side like the "ARRL Tuner", or on the output?
  • Would a balanced design make a balun unnecessary?
  • I assume you float the low side of the T network inside the box. What kind of clearance is needed?

Thanks!

Bill, W1AC
http://billhorne.com/
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The Slab Bacon
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« Reply #2 on: November 23, 2007, 11:07:44 AM »

Bill,
     A balanced tuna would definately make the balun unnecessary.
However you would have to make the tuna capable of matching to a low-Z load, Basically a "step down transformer" if you would.

No, I dont float the bottom leg of the coil in the tuna as I run a very short run of coass to the balun. (About 6') to escape all of the metal in the storage closet behind the tuna. The tuna is just a simple "T"
series cap in, coil to ground, series cap out with wide spaced bread slicers and a large rollie duck from a broadcast transmitter.

You have seen the whole setup when you were here back in the spring. You even commented about the antenna.

                                               The Slab Bacon
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W7SOE
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« Reply #3 on: November 23, 2007, 12:07:16 PM »

I would also like construction details of the tuner. 

Someday I will try to get my HB 813 transmitter on the air an the matchbox won't cut it.

Thanks

Rich
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The Slab Bacon
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« Reply #4 on: November 23, 2007, 01:11:14 PM »

I would also like construction details of the tuner. 

If I get a chance I will sketch it out over the weekend. But I will have to bring it in to work next week to scan it in.

It is so simple that you really shouldnt need details. 2  400pf wide spaced breadslicers, and a large edge wound ribbon roller inductor in a big box. Your basic "T" type tuna. Or as Chris (W2JBL) calls it ----
the worlds largest MFJ tuner!! (I prefer a T type as it affords a very wide range of matching) the Balun is a 4:1 design right out of the ARRL handbook, just supersized and fed massive amounts of steroids. I did experiment with and wind a lot of different balun designs and then sweep them. I found that the 4:1 adds the least reactive component of its own to the mix, no matter what the operating impedance was.
1:1s were very impedance specific.

                                                The Slab Bacon
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W4EWH
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« Reply #5 on: November 23, 2007, 03:46:08 PM »

Bill,
     A balanced tuna would definately make the balun unnecessary.
However you would have to make the tuna capable of matching to a low-Z load, Basically a "step down transformer" if you would.


I'm going to use a link-coupled tuner, like Brent W1IA, so I think that will give me the choice of ratio I'll need.

No, I dont float the bottom leg of the coil in the tuna as I run a very short run of coass to the balun. (About 6') to escape all of the metal in the storage closet behind the tuna. The tuna is just a simple "T"
series cap in, coil to ground, series cap out with wide spaced bread slicers and a large rollie duck from a broadcast transmitter.


Well, they say the memory is the second thing to go: I know you showed me the setup after Timonium, but I forgot.

I was assuming that you had the balun on the input side of the tuner, since the ARRL design puts it there, and that would (I think) require isolating the bottom of the "T" network from ground. It's good to know that a 4:1 design doesn't necessarily have to be on the input side of the tuner.

BTW, did anyone ever come up with an "official" name for your antenna? My brother and I were debating if it was a "crooked dipole", or a "divorced folded dipole", or possibly a "broken barrel dipole", but the definitions got more hazy as the afternoon wore on and the 807's warmed up.  Roll Eyes

73, Bill
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The Slab Bacon
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« Reply #6 on: November 24, 2007, 01:38:46 AM »

No, we havent come up with a name for the ant, but.......................
since I built the tuna in a 19" rack mount box and had nowhere to put another rack cabinet, I cut a hole into the wall and racked the tuna into the wall. Henceforth it is now called "the hole in the wall tuner"

                                                            The Slab Bacon
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KF1Z
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Are FETs supposed to glow like that?


« Reply #7 on: November 24, 2007, 07:49:33 AM »

Saw this ant in an old handbook....

Or at least in with the folded dipole, they mentioned leaving the center disconnected...to give the ability to use it on more than one band...

On the freq it's cut for the top "appears" shorted, and on higher freqs, it is open...
Something like that,,

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Steve - WB3HUZ
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« Reply #8 on: November 24, 2007, 10:21:39 AM »

That's what Frank is using, a 60 foot long folded dipole, with the top leg open and the bottom leg fed.
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The Slab Bacon
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« Reply #9 on: November 24, 2007, 10:50:37 AM »

>snip<
 "Saw this ant in an old handbook...."

That is where I got the idea from!! Steve sent me a page scanned from a very old handbook some years back, and I said "what the hell, I'll try it". The rest iz history. There are many very good antenna ideas that have been forgotten about since the introduction of coass and rice boxes that wanted 50 ohm coass feeders. Over the years many people have come to shun antennas that had to have balanced feeders in favor of the easier to install coaxial cable designs.

But that is why they invented the tuna!! Sometimes you just gotta do what you gotta do!
always remember that a compromised antenner is still way, way better than none at all, and if you can find one that works well you can have your cake and eat it too!

                                                                               The Slab Bacon
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AF9J
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« Reply #10 on: November 24, 2007, 11:05:16 AM »

You bet those old Handbooks have some good antenna ideas!  Back then, more people rolled their own antennas, rather than buying them.  So they had more antenna stuff in the handbooks.  A case in point - I got on 160 back in 1986 from of all places, an apartment!  I got the design for a shortened helical vertical (basically a rubber duck on steroids), from a 1972 Handbook.  It wasn't the greatest, but it got out with my FT-101B.  A few years later, it was no longer listed in the Handbook.

Slab, as for your antenna - it's almost like folded dipole, but I'd say it's closer to a dipole combining  both capacitive and linear (although not in the traditional sense of having the ends droop down) loading.

73,
Ellen - AF9J
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K3ZS
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« Reply #11 on: November 24, 2007, 01:29:42 PM »

I am using a short antenna when on 160M, it is 135 ft fed with #14 window balanced line.   I am using an MFJ 989C T tuner but I am using a hefty DX Engineering made-for-tuner type balun on the output side, not the crappy one in the tuner.   These things work much better than the one in the tuner both for balance on the low bands and power handling capability.   I have no connection or interest in DX Engineering but using one made for 10KW continuous power makes this configuration usable and effective.
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W8EJO
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« Reply #12 on: November 24, 2007, 05:01:46 PM »

Are the top & bottom wires electrically connected? I'm trying to model it with 4nec2.

Terry
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Terry, W8EJO

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ka3zlr
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« Reply #13 on: November 24, 2007, 05:31:13 PM »

Good Afternoon,

 I can attest to the vertical helix, built one here for 160 some time ago using schedule 40 plastic pipe with a 70 foot resonator off the top, used on ssb phone works great...then i turned it into one of my receiving antennas it does a great job for vertical receiving, i like it alot....

jack ka3zlr
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KF1Z
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Are FETs supposed to glow like that?


« Reply #14 on: November 24, 2007, 06:06:22 PM »

Are the top & bottom wires electrically connected? I'm trying to model it with 4nec2.

Terry
W8EJO

There is a "left wire" and a "right wire".

It's a folded dipole, that is "snipped" in the middle, above the feedpoint.

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W8EJO
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« Reply #15 on: November 24, 2007, 06:21:03 PM »

Are the top & bottom wires electrically connected? I'm trying to model it with 4nec2.

Terry
W8EJO

There is a "left wire" and a "right wire".

It's a folded dipole, that is "snipped" in the middle, above the feedpoint.


OK thanks. That wasn't self evident from the drawing.
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Terry, W8EJO

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W8EJO
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« Reply #16 on: November 28, 2007, 02:35:36 PM »

Vertical & Horizontal patterns @ 3.8mhz.


* SLAB BACON SPECIAL H 3.8.jpg (118.12 KB, 390x390 - viewed 577 times.)

* SLAB BACON SPECIAL V 3.8 .jpg (116.12 KB, 390x390 - viewed 515 times.)
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Terry, W8EJO

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WA1GFZ
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« Reply #17 on: November 28, 2007, 02:45:40 PM »

Yup and on 160 it is all high angle so all you need to do is match the very low Z.
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Steve - WB3HUZ
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« Reply #18 on: November 28, 2007, 09:17:58 PM »

To really tell what is going on, you need to do pattern comparisons with a dipole at the same height. I ran those sims. See image below.

In the sim of the AHE antenna, at 3.8 MHz, the feedpoint impedance is Real(Z) = 11.3874, Imag(Z)  = -305.197. Using W9CF's feedline calculator, at the end of 70 feet of 450 Ohm Window line (this is my guess on the length in use at AHE radio) the Z is 107.34 +j1124.1. Loss in the feedline is 2.76 dB. The 107 Ohms resistive isn't bad, but there sure is a ton of inductive reactance for the tuner to deal with!

So, from the antenna plot, we see that the AHE antenna is down about 1 dB compared to a dipole, when there is NO feed loss. A dipole cut for 3.8 MHz and fed with 70 feet of RG8 would have feedline loss of 0.27 dB. Adding in the 2.76 dB of feedline loss to the AHE system, it would appear the Frank's antenna is about 3.5 dB down from a dipole. This doesn't include tuner loss. Who knows what the loss in Frank's tuner is. Can't be much based on his signal. But for giggles, lets do some simulations.

Using W9CF's tuner simulator and plugging in the Z numbers calculated at the end of 70 feet of feedline, tuner loss is only 0.3 dB. This simulator is set up for a typical T-type tuner with two series caps and a shunt coil. The simulator finds the lowest loss setting of the components for minimum SWR. In the simulation above, the caps had a Q of 2000 and the coil a Q of 100. There's likely a little more loss in the balun. But looking at the size of the one Frank made, it's probably small. So, worst case, Frank's antenna is about 4 dB down from a dipole. Not bad considering the size!

I've always thought Frank's set up was within 3dB or so of a full sized dipole. The cool thing is, according to the transmission line sim, almost 2dB could be gained by using 600 Ohm open wire line!


* ahecomdip75m.gif (11.27 KB, 639x385 - viewed 485 times.)
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w3jn
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« Reply #19 on: November 29, 2007, 06:56:30 AM »

I think the orange Super Bee parked underneath it gives Frank an extra couple a dB or so   Grin
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The Slab Bacon
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« Reply #20 on: November 29, 2007, 09:14:26 AM »

I think the orange Super Bee parked underneath it gives Frank an extra couple a dB or so   Grin

thatz right!! The 440 sixpack in the super bee gives it that real "high performance" signal!! Grin Grin
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The Slab Bacon
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« Reply #21 on: November 29, 2007, 09:49:58 AM »

All kidding aside, thats why I posted it. I know that it works well. All that have ever worked me know that it works well. Compromise antenna or not, it might help a few others that are "space challenged" like myself get on the air!

Steve,
       believe it or not I have been planning some homebrew feeders but just havent had the time lately to do it. Ifin it aint broke dont fix it! I just cant seem to find that one missing part that I need for the hb feeders, you know the round tuit Wink

                                                      The Slab Bacon
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The Slab Bacon
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« Reply #22 on: November 29, 2007, 01:28:18 PM »

yea, but I'm on the air Grin  Cool
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Steve - WB3HUZ
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« Reply #23 on: November 29, 2007, 05:33:23 PM »

And with straight pipes, it's loud too!

It's talkers versus doers, Frank.


I think the orange Super Bee parked underneath it gives Frank an extra couple a dB or so   Grin

thatz right!! The 440 sixpack in the super bee gives it that real "high performance" signal!! Grin Grin
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Steve - WB3HUZ
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« Reply #24 on: November 29, 2007, 08:09:15 PM »

No, Mopar only!
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