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Old 01-10-2016, 04:44 PM   #1
ke0me
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Default apartment balcony stealth antenna

We are stationary until the end of May in a 2nd floor (of 3 floor) apartment.

The only ideas I can come up with are:

1- a random length wire antenna and antenna tuner ( max length about 25 feet)

2- clamp on railing mount (might be too visible)

3 - some kind of an end fed wire ( again max of 25 feet)

it also has to be cheap since it is only for a few months.
Interest is mostly short rag chew on 20-15-10, so might get away with a short wire.
RF grounding for noise reduction is a concern also.


Suggestions are encouraged!
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Old 01-10-2016, 06:06 PM   #2
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Build a twin-lead j-pole for ten meters and use the tuner on 15 and 20. It'll be about 23 feet long, I think. Flexible, so you can roll it up for storage. Just dump it off the balcony and let it hang. Pass the coax at the near end through a toroid (mix 31 or maybe 43) to keep RF off the outside conductor and to reduce local noise. No ground plane required.
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Old 01-10-2016, 08:14 PM   #3
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Maybe a couple of hamsticks in a dipole arrangement?
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Old 01-12-2016, 08:52 PM   #4
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thanks, i'll try some of your ideas when I get some time in the next few weeks.

Carl, I haven't bought toroids for eons, where is a cheap place to get them (assume radio shack, if we still have one, wont carry them) ?
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Old 01-13-2016, 08:33 AM   #5
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I buy mine on eBay usually. Look for mix 31, it's modern and works at HF and VHF. The ones I'm using on J-poles came from an eBay vendor in England.

J-poles work fine without toroids (though some RF comes down the outside of the feedline), so don't delay building J-poles just 'cuz the toroids haven't arrived. When they arrive, add them.
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Old 01-13-2016, 04:05 PM   #6
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I have a ultimaxx 100 end fed. It comes with 24ft of wire and tunes 80-6 meters. It worked ok but I replaced the wire with 44ft of wire and it's a little better. For a limited space it serves the purpose. I've made digital contacts as far away as Indonesia.
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Old 01-13-2016, 07:00 PM   #7
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I'm planning a 20-meter J-pole to hoist into a tree. The design procedure is the same as a twin-lead J-pole (or any other J-pole), but for the matching section I'm gonna use RG58 instead of twin-lead (it's a bit shorter that way because the velocity factor is 0.66 for RG-58 and about 0.80 for twin-lead). The antenna part, instead of being twin-lead, will just be wire.

It'll be easier to build, too. Instead of soldering the end of the feedline into the appropriate matching point in the matching section, I'll make the matching section from two pieces of RG-58 with PL-259s and a UHF tee between. Then the feedline connects at the tee.

Also it'll be easier to deploy. The matching section, being coax instead of twin-lead, can be left rolled up -- the only part that has to be unrolled and hoisted (or dumped off a bridge or balcony) is the radiator wire (about 34'4" long).

I've got the lengths all calculated, and I've got some RG-58 coming from an eBay vendor. I've also calculated the sensitivity of the antenna to errors in the lengths of the three parts.

It turns out that the antenna is very insensitive to an error in the top part of the two-piece matching section. Errors in the bottom part of the matching section will affect the minimum SWR, and errors in the radiating section (the long wire on top) will affect the resonant frequency but not the minimum SWR.

The radiator impedance (at the point where the top part of the matching section meets the radiator wire) is very uncertain, so some experimentation will be required to get the optimum length of the bottom part of the matching section.

If the radiator impedance is, for example, 2000 ohms (a good guess), then the top part of the matching section should be 9 times the length of the bottom part. The total length of the matching section should be λ/4, which is 90 electrical degrees, so 1/10 of that is 9 electrical degrees, and the square of (sin 9 degrees) is about 1/40, giving an impedance ratio of about 40 between the bottom of the radiator (2kΩ) and the tap (the tee, where we attach the feedline and want 50Ω). 2000Ω/40=50Ω, so that's about right.

I'll build the top part of the matching section as calculated, and the bottom section a bit long, and the radiator a bit long too. Then I'll hang it up and start testing and cutting.

First, of course, I'll measure the velocity factor of that RG-58. That's easy. It's Belden 9907, and Belden says it's 0.66, but I'll measure it anyway.

Who knows, it may actually end up working.
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Old 01-13-2016, 08:41 PM   #8
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Let us know how it works out.

PS- I brought the radio eqpt in from the trailer to the warm apartment today. I'm letting it sit a few days without turning on anything to ensure there is no condensation.

(As dry as it is in this apartment, I may want to look at static reduction!)

Now, what about a ground??????
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Old 01-14-2016, 08:37 AM   #9
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Have you though about a screw driver antenna for the apt? I kind of looks like a bird feeder.
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Old 01-14-2016, 04:43 PM   #10
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Quote:
Originally Posted by N3LYT View Post
Have you though about a screw driver antenna for the apt? I kind of looks like a bird feeder.
That may be the best idea of all, except that it's a bit expensive. But you can use it on the RV, too.
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Old 01-14-2016, 08:28 PM   #11
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I googled "slinky antenna" and got this site, among others.

http://www.nonstopsystems.com/radio/...io_antenna.htm

This guy goes on about the limited space and need to be sneaky in his apartment. Maybe something here for you.
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Old 01-30-2016, 04:05 PM   #12
ke0me
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Default tvi and antenna for apartment

I have ordered some toroids from MFJ, hope they will stop some of the tvi.

repositioned the 25 foot random wire slightly ( and lifted up the aluminum blinds!), much better matching now.

dc ground is a connection to the hot water heat pipes in the apartment, that dropped the noise level a noticeable amount, but its still way high.

I would like to get a screwdriver type antenna, depends on how much money I make in the next 2 months ( got a temp job doing tax returns till April 15).

has anybody used the MFJ apartment antenna? this is the basic unit that tunes with clips on the coil. its rated highly, thinking about it for both the apartment and the 5er.
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Old 01-31-2016, 08:56 AM   #13
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Quote:
Originally Posted by ke0me View Post
I have ordered some toroids from MFJ, hope they will stop some of the tvi.

repositioned the 25 foot random wire slightly ( and lifted up the aluminum blinds!), much better matching now.

dc ground is a connection to the hot water heat pipes in the apartment, that dropped the noise level a noticeable amount, but its still way high.

I would like to get a screwdriver type antenna, depends on how much money I make in the next 2 months ( got a temp job doing tax returns till April 15).

has anybody used the MFJ apartment antenna? this is the basic unit that tunes with clips on the coil. its rated highly, thinking about it for both the apartment and the 5er.
I have bought two HS screw driver antennas at ham fests for $150 total they IMHO are not the best made but they work as well as any. They will have to be taken apart and cleaned up and the tuning spring in the top will have to be replaced (HS web site has them $16) but after that you'll be on the air for little money. One lives in my camper and the other is a loaner for our ARC.
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