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 Post subject: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Tue 14, 2019 1:56 pm 
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Joined: Jan Sun 06, 2013 2:14 am
Posts: 271
Location: Butler, PA
Hi All
Im ready to build my 20 meter dipole but i have some questions.

1) do i need the above balun for a HW-32A
2) should i cut the antenna for the middle of the General frequency
3) need opinions on the 20/40 trapped type dipole, i own a DX-40 as well
Thanks for all your help.

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Tue 14, 2019 7:54 pm 
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Joined: Nov Sat 07, 2009 11:37 pm
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Location: Sayreville, NJ 08872
Cadmandu wrote:
Hi All
Im ready to build my 20 meter dipole but i have some questions.

1) do i need the above balun for a HW-32A
If you're going to feed the antenna with coax, the balun will keep the RF from creeping down the feed line which is not a good thing.
2) should i cut the antenna for the middle of the General frequency
If that is where you plan to operate.
3) need opinions on the 20/40 trapped type dipole, i own a DX-40 as well
I don't get the connection between a DX-40 and a trap dipole. Trap dipoles work if you're pressed for space. Also, dipoles (and generally any wire antenna) can zigzag to fit them into a smaller area

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Wed 15, 2019 12:34 am 
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Joined: Aug Thu 20, 2015 3:09 pm
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Location: Albion, CA, USA, 95410
As noted above the balun will work if you are feeding with coax. I have one of those and though it looks cheaply made it seems to work ok and has been in the air for a few years now. Trapped dipoles work but have limited bandwidth. If you have a general class license then yes, cut for the middle of the band. Are you going to use an antenna tuner?


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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Wed 15, 2019 7:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3665
Location: Monterey California USA
You don't HAVE to use a balun, it just divorces the coax from the radiation pattern. If money is an object, don't bother buying one.

Trap dipoles have narrower bandwidth that separates but are convenient. Unless you want to operate all over the band, you don't need a tuner.

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Wed 15, 2019 7:53 pm 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 9307
Location: Ohio 45177
Whatever you do, if you intend to keep it up for awhile, best make a really good connection to the coax at the antenna center and seal the transition such as connector putty or something over the connector so it is absolutely air tight. That black sealant used to be sold at Radio Shack. Black sticky stuff and if used properly, moisture will not get in there under any conditions. A balun will not hurt. The w2AU is lighter than another balun I have. That is only an issue when the antenna is not supported in the center. I put up a 20M dipole. The analyzer said it was just a bit short, more resonant towards the top of the band. That was easy, I put about a 6 inch piece of wire at each end hanging down at the insulator and trimmed them till it was where I wanted it tuned. You should have a decent match across the phone band if it is resonant in the center of that phone section. I did not think the HW is particularly a CW rig so you can stick with best SSB match versus having to compromise for the two modes. Many years ago I used black vinyl tape on some connectors but that stuff does not hold up over time. Unravels. They make that self-bonding rubber tape stuff now and that can make a good seal in most cases. The stuff that sticks to itself, not other stuff, and fuses together where it overlaps. Used to be a commercial and military product but I have seen it for sale to hams now.

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Wed 15, 2019 8:34 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: S. Dartmouth MA 02748-1225 USA
If a balun is not used to terminate a balanced antenna, the downlead or feed line becomes part of the radiating pattern. That, can distort the desired pattern and/or cause RF in the shack ,raise havoc with the transceiver, especially a solid-state one. RF losses will rise. A match box can be used but it will have a trade off for the good match vs efficiency...

Baluns are cheap for the job they do.
Be aware NOT to use household silicone sealant, this has acetic acid cure and corrodes the connectors over time. There is safe electrical silicone sealant but it is costly. An alternative is electricians varnished cambric tape, followed by electrical putty for void filler then an over-wrap with electricians electrical tap for outdoor use. The net result is a similar joint protection as used in electrical service as well as the ability to remove the material if the connection should fail. The cambric will keep the sealants from sticking to the connector.. A silicone connector grease can be used to keep the plated connector surfaces from corrosion.

A UV proof rope trolley could be used or a center suspension point. The antenna wire could be hard drawn strand or solid copper. Do not solder any joint under tension as the heat of the soldering will soften the copper and that location will be the weakest point. For those exposed tension connections, electricians come to the rescue with something called a bronze burndy clamp two of those will support the load of a 20 meter dipole easily. Use three in a line for 80 & 160. An application of silicone grease will protect that joint for a year or do the varnished cambric thing.

YMMV

Chas
WA1JFD

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Thu 16, 2019 2:09 am 
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Joined: Sep Wed 10, 2014 2:01 am
Posts: 1969
Location: Costa Mesa, California
I use a fan dipole that is really just three dipoles--15 meter, 20 meter, and 40 meter connected at the coax feed point. They are separated by some plastic spreaders that hold the wires about 16" apart so one rope at the end can be used to lead to a tie point. I have a system where I can lower one end and the center to reach the balun connection point in case the antenna develops problems. I have a RigExpert 54 antenna analyzer that really makes tuning the antenna and adjusting any antenna tuner simple and effective. I also have my antenna where I can disconnect it when weather threatens. I leave the antenna disconnected when I am not using the shack. My location is in the mountains and quite susceptible to lightning strike. The disconnected antenna end is placed away from my house in a small jar upside down so water can't penetrate the fitting.

Norm

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Thu 16, 2019 10:43 am 
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Joined: Jan Sun 06, 2013 2:14 am
Posts: 271
Location: Butler, PA
Thanks a lot of good advice was given. I will be cutting for the center of the general phone band around 32' 9"" OAL and using an Alpha Delta C center connector and a Johnson Machbox 250 plus a HM-102 SWR meter. How much power can I expect to radiate using the above station with my HW-32A assuming that the transceiver is working as designed?

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 Post subject: Re: 1:1 Balun Dipole Unadilla W2AU
PostPosted: May Thu 16, 2019 7:46 pm 
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Joined: Nov Sat 07, 2009 11:37 pm
Posts: 2184
Location: Sayreville, NJ 08872
Cadmandu wrote:
Thanks a lot of good advice was given. I will be cutting for the center of the general phone band around 32' 9"" OAL and using an Alpha Delta C center connector and a Johnson Machbox 250 plus a HM-102 SWR meter. How much power can I expect to radiate using the above station with my HW-32A assuming that the transceiver is working as designed?

Effective Radiated Power (ERP) = (gain of antenna with respect to isotropic radiator) X (input power to antenna)
To be really accurate, you need to determine input power at the antenna. Remember, this is not a lossless system, Cables, wires, connectors, matchbox, swr meter all have some finite resistance and can be considered lossy. RF losses generally transforms into generated heat. Also, whatever RF reaches the antenna, you don't want of portion of it to be reflected back to the transmitter because that also reduces the amount of ERP.

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http://www.classicradiomanuals.com


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