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View Full Version : KW-40 7.150 Mhz 40m traps by Unadilla / Reyco



Pushraft
11-07-2008, 04:06 AM
I have a pair of KW-40 7.150 Mhz 40m traps made by Unadilla / Reyco. I was wondering if these would be of any use to me for a newbie setup. I am still experimenting with wire antennas and an attic dipole but I have limited space so a true 40m dipole wont fit in the attic but a 17m will or maybe 20m if I cheat a little and zigzag it up and down a little or use part of an adjacent wall.

I am not sure what traps actually do so could someone explain to me what they do and if they would be of any use for my limited space newbie setup? When I say newbie I dont mean I have my ticket yet I mean I am studying and trying to digest a lot of theory in a short amount of time to ramp up to speed. Is newbie the right term or is there another term normally used for people in my situation? ham wannabe?

Anyway it appears these KW-40 coils were used on a boat because I see a single central feed with a central eyehook for suspending it and two more side mounted eyehooks for suspending the legs of the dipoles down to a pair of dogbone anchor thingies. It appears this was an inverted V setup on a boat using 40m coils.

So that is my question if these coils are of any use for me or if I should sell them to someone who can actually benefit from them? I am thinking I could also erect an inverted V from a high window down to a fence about 45 away (sloped from a 20 foot window down to a 6 foot fence). That is not my preferred method I would rather just chuck a wire up to a nearby tree also about 20 feet off the ground maybe tied to a tennis ball or something. The wire on this antenna appears to be frayed in certain spots so I would probably need to use new wire if I decided to keep the coils but I need advice if they are of any benefit to me.

KJ4AUR
11-07-2008, 03:24 PM
Removed May 07, 2009

WB3BEL
11-07-2008, 03:59 PM
These traps are basically parallel resonant circuits. They are often used in a multiband dipole. The traps are placed in-line with the antenna wires and serve to prevent current from flowing along the entire wire.

As an example if you wanted to make an 80m 40m combination dipole you would put the 40 meter trap ~ 30 something feet from the center on each wire.
When operated on 40m the current would flow on the 40m part of the wire (Between the center feedpoint and the traps). When the antenna is used on 80 meters the whole wire would have current flow. The trap itself would also allow the antenna for 80m to be a few feet shorter because of the traps inductance at 80 meters effectively lengthen the antenna.

Because you have said that you don't have room for any antenna lower in frequency than 40 meters, I doubt that these have any real use to you right now.

Pushraft
11-07-2008, 04:47 PM
These traps are basically parallel resonant circuits. They are often used in a multiband dipole. The traps are placed in-line with the antenna wires and serve to prevent current from flowing along the entire wire.

As an example if you wanted to make an 80m 40m combination dipole you would put the 40 meter trap ~ 30 something feet from the center on each wire.
When operated on 40m the current would flow on the 40m part of the wire (Between the center feedpoint and the traps). When the antenna is used on 80 meters the whole wire would have current flow. The trap itself would also allow the antenna for 80m to be a few feet shorter because of the traps inductance at 80 meters effectively lengthen the antenna.

Because you have said that you don't have room for any antenna lower in frequency than 40 meters, I doubt that these have any real use to you right now.

Unless I use an outdoor inverted V which is only 1/4 WL per leg so that would only be 20 meters per leg for 80m band which is about 66 feet per leg. That is a possibility here although I dont know how the neighbors will react to that. You mentioned for 80m band using 40m traps, the wire antenna could be a little short. How much shorter for the 1/4 WL legs? 1 ft, 2 ft...? Here is the link for the 1/4WL (per leg) inverted V which I am considering. I also have the dogbone insulators which I can probably attach to a 6 foot high fence that will come down from my 20 ft high window. I can just cut the wire to 66 feet or whatever I need and then just angle the V part until it reaches the fence (in 2 places). Then I can just memorize those spots. Would this antenna be too low to work DX? Comments? Suggestions?

http://www.bcara.org/more_wire.html

WB3BEL
11-07-2008, 05:28 PM
I don't know how those specific traps will shorten the 80 meter wires perhaps someone else knows the specs. I will guess that it is a few feet. Its easy enough to verify if you have SWR meter.

The angle between the legs of the wires coming from your window should not be too small. If its less than about 90 degrees, it will be too small an angle.

A 40 or 80m horizontal antenna at 20 ft is too low to be a "good" DX antenna.

You can still work lots of stations, but the signals will be weaker. It will work OK for distances up to 1000 miles. You can work stations who have good antennas even farther. You probably can work Superstations in Europe etc with a bit of patience.

W0IS
11-07-2008, 05:37 PM
am thinking I could also erect an inverted V from a high window down to a fence about 45 away (sloped from a 20 foot window down to a 6 foot fence).

I was under the impression that it was completely, absolutely, and utterly impossible for you to place any type of conductive object outside of the attic for use as an antenna.

If you can run any type of wire, including nearly invisible wire the diameter of a human hair, from the house to the fence, you have many, many, options for excellent performing antennas.

My suggestions are:

(1) Get your license
(2) Put up an antenna of any type, even though you can come up with some reason which will prove to a mathematical certainty that it won't possibly work
(3) Make contacts, notwithstanding the proven impossibility of doing so
(4) Improve antenna, if desired
(5) Repeat steps (3) and (4).

You can make a fine antenna. If you desire to incorporate the traps, I'm sure that will open up many more possible designs.

Pushraft
11-07-2008, 06:15 PM
I can use an outdoor antenna but only at night. I would have to drop the 2 wires connected to dogbone insulators (which I have) out my window at night then walk them over to the fence and attach them with some hooks or even bungie cords. I could make them about 66 feet long each per leg which may make a nice 1/2 wave inverted V dipole antenna for 80m. The thing I am worried about is someone walking inside the "V" while I might be transmitting and getting exposed to strong RF. Also the V will be sloped from 20 ft high on one end to 6 feet high on the other end so that doesnt seem very good either.

Maybe a better solution would be to just put up a 20m attic dipole since I am getting some good activity here on 20m in the morning. I listened in again this morning and heard some clear callsigns and when I looked them up here in QRZ, some of them showed up. The skip distance I appear to be getting here in FL is right around 1000 miles on 20m. Does that seem about right? I am working on cutting down the noise and increasing the signal so intelligibility should get even better.

I appreciate all the help you hams have given me. I obviously made some rookie mistakes but I think I am getting the hang of it now. Even if 160m and 80m are "off limits" to me due to size constraints, maybe 20m and 40m would be good enough to get me started.

M3KXZ
11-07-2008, 06:31 PM
What makes you think there will be harmful levels of RF inside the inverted V at HF frequencies at moderate power levels? Another subject for you to do some reading up on! And EZNEC can be used to provide an estimate of the near field RF strength.

M3KXZ
11-07-2008, 06:36 PM
RF exposure...here's something to get you started http://www.arrl.org/news/rfsafety/exposure_regs.html#table1

M3KXZ
11-07-2008, 06:40 PM
Pushraft "The skip distance I appear to be getting here in FL is right around 1000 miles on 20m. Does that seem about right?"

There is no right or wrong. The skip distance varies with angle of RF, atmospheric conditions, whether it's a single hop or multiple.

Now...what is your name? Just a first name or nickname. I know everyone else's names, and I get fed up typing Pushraft :p

Pushraft
11-07-2008, 06:40 PM
I don't know how those specific traps will shorten the 80 meter wires perhaps someone else knows the specs. I will guess that it is a few feet. Its easy enough to verify if you have SWR meter.

The angle between the legs of the wires coming from your window should not be too small. If its less than about 90 degrees, it will be too small an angle.

A 40 or 80m horizontal antenna at 20 ft is too low to be a "good" DX antenna.

You can still work lots of stations, but the signals will be weaker. It will work OK for distances up to 1000 miles. You can work stations who have good antennas even farther. You probably can work Superstations in Europe etc with a bit of patience.

I could measure the straight line distance from the base of the residence to the fence (which I stepped off and measaured at approximately 40 ft). Then I can use trigonometry to calculate the extra distance for the 14 foot rise (let's say that is 45 feet total), then I can use more trig to find out what angle I need to the fence to get me 66 ft per leg. The fence runs exactly parallel to my window so that should make the calculations simpler.

There are also some trees about 20 ft so as an alternative to sloping the inverted V downwards, I could maybe keep it horizontal with maybe a 100 degree angle between legs. Actually from my view it will be a big 'V'.

All these are possibilites I just have to be careful I dont cause interference with the neighbors.

The attic antenna might be the best for keeping the RF away from other people (except me) and it has the added benefit that it is higher (about 30 ft instead of only 20 ft). 2nd best might be the horizontal V antenna. The worse is probably the sloped inverted V (as far as possible RF exposure to neighbors).

I'll get a PL-259 connector and try the attic dipole this weekend. Should I cut it exactly to 1/4WL per leg for 20m which would be 5m per leg or about 16.5 feet per leg? Since my attic wall is about 30 feet and that is a little short for 20m, perhaps I could use the 40m traps to provide the missing length and just cut the wires to 15 feet per leg. Would that work?

WB3BEL
11-07-2008, 07:01 PM
For putting the dipole in the attic just use the 468/fMHz formula for wire total length. About 33ft or 16.5 ft per side. If you need to bend the wire at the ends to make it fit in the attic, it will be fine. A 90 degree bend with a few feet of wire either end won't change anything significant. The 40m traps wont be any good on 20m antenna.

Pushraft
11-07-2008, 07:36 PM
In my sloped inverted V proposed setup the 40m traps would be in a bad (visible) spot anyway so I guess those are out. Looks like 40m is out. It is either 20m in attic or 80m outside but 40m is a problem. Since 20m is easier and I hear activity already on there I will try that first.

W0IS
11-07-2008, 07:39 PM
then I can use more trig


Looks like 40m is out.

I thought we already decided that trig was a bunch of nonsense, when we concluded that a 40 meter dipole wouldn't fit in the attic. :D

Pushraft
11-07-2008, 09:17 PM
I'll start simple and just try a monoband attic dipole for 20m and go from there. I will also be talking to the owner of the Yaesu rig soon and asking him if he will give me a deal on it since the tuning knob is nonfunctional. If he gives me a discount for the $50-$100 is would cost to fix it, then I'll take the discount and live with the knob not working. I can finely tune by .000.01 Mhz increments anyway using the mic buttons. For example, 14.235.50 then 14.235.51... If I hold that button down it takes about 3 minutes to go from 14.2 Mhz thru 14.3 Mhz without stopping. Someone already told me that is slow enough.

I am making progress.

KE7VZW
11-09-2008, 05:49 AM
Does the Yaesu rig have a CAT port ?

If so, you can tune it using HRD......

Pushraft
11-09-2008, 06:06 AM
Yes it does. It has the CAT system logo on it and the 6 pin CAT port in the back. I wish this rig had a way to disable Tx so I wouldn't have to be so careful around the mic. Any suggestion for the Yaesu FT-767GX until I get my ticket? I use the mic buttons for slow tuning.

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