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Author Topic: QRP antenna questions  (Read 6542 times)
KA4NMA
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Posts: 357




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« on: June 08, 2013, 09:13:15 PM »

I am disabled and am looking for an antenna to use indoor with my FT-717ND.  I know these antenna's are a compromise.   I am looking for suggestions, reviews, for sale or free.  If possible 75m-6m or a portion are the bands I am interested   The key is compact, self-contained able to move it around in my apartment or able to take it with me to treatments, etc.  I have limited ability to build an antenna.
,
I am thinking of something like the MFJ walk about multiband or single band antenna or one of the eBay clones.  I would not direct connect one of these to my radio.  I would use some sort of mount with a few radials. 

Is the miracle ducker tl or one of their other models worth it?  I have seen clones on Ebay.  How about wonder wand?

I have also considered a whip (4-6ft) attached to my MFJ random wire tuner.  An Alexloop would be good, but it is out of my budget. I have also looked at a compact base loaded whip, such as what MFJ sale.

Randy ka4nma
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AF6WL
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Posts: 146




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« Reply #1 on: June 09, 2013, 09:33:35 AM »

How about the MFJ 935B loop tuner @ $209
Just add a length from a roll of of 1/4" or 3/8" soft copper tube $20 + ground wire terminals $2  ( or use RG-8 / wire for portable operation )

For 20m and above it's remarkable efficient for the size

 
« Last Edit: June 09, 2013, 09:53:58 AM by AF6WL » Logged
K2CMH
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Posts: 278




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« Reply #2 on: June 10, 2013, 06:34:23 AM »

I don't know about CW, but my guess would be that on SSB that you will not have much luck considering you only have 5 watts, will be using a severely compromised antenna, and on top of that, will be using it indoors.   If you are able, I would seriously consider getting either a higher output radio or a small amplifier (50-100 watts) for the 817 if you are going to try and do SSB.  I think if you are wanting an easily portable antenna, a magnetic loop of some sort is probably your best bet.
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KQ6Q
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« Reply #3 on: June 10, 2013, 08:51:01 PM »

A solution which would fit your budget would be the basic MP1D Superstick ($120) (you WILL need the radial setup, or cut your own and use the MP1B basic model - $80), and if you can't clamp the antenna to a metal table the TM1 Supermount from http://newsuperantenna.com will be useful - this is not the ideal solution, but it will let you have a resonant antenna on 40 through 2m, and cost around $110. An Alex Loop would be best, and a Buddipole setup would be next bestr, but they would cost several times as much. Creating your own radials with wire and crimper would save you some bucks. on the MP-1 setup. I have it stowed in my roller bag for QRP in the park - though full size dipoles work better if you have trees to string them from.
Keep in mind that with QRP and limited HF antennas, you'll have better luck making contacts on CW.

Fred, KQ6Q
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K5LXP
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« Reply #4 on: June 11, 2013, 06:19:39 AM »

Frankly I think your most realistic option is to enlist the aid of some local hams to put up a real antenna for you.

You've got too much working against you with what you propose - QRP, compromise antennas, operated indoors.  2 of those 3 are iffy at best, and all three I believe is futile.

Even a low dipole or end fed would be very inexpensive, easy to put up and very effective.


Mark K5LXP
Albuquerque, NM
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WX7G
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Posts: 6317




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« Reply #5 on: June 11, 2013, 08:23:17 AM »

You want something you can take with you and set up very easily. If you don't mind the 20-10 meter bands only the MFJ-1780 Box Fan antenna fits the bill.
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K3VV
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Posts: 13




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« Reply #6 on: June 11, 2013, 10:27:11 AM »

As others have said, low power and indoor antennas are going to make it difficult for you to make contacts.

I think the longest wire you can manage hooked up to your random wire tuner might be a place to start.  You'll need quarter-wave counterpoises for each band you want to work connected to the tuner's ground lug. They'll have high RF voltage on them, even at low power -- use insulated wire and tape up the ends. 

SSB is probably hopeless.

You might be able to make contacts on 20-meter PSK and CW, though 20m CW is kilowatt alley.  17 meters is another possibility.  I've worked people on CW and PSK with low power and indoor antennas on those bands.

I'd try 20m PSK if I were you.  Assuming you don't live in an RF-proof building -- metal, foil-insulated, whatever -- you can make contacts. 

This doesn't address portability I realize, but it's a place to start. 
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KJ4FUU
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Posts: 162




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« Reply #7 on: June 12, 2013, 10:53:13 AM »

How new is the apartment? A lot of newer buildings have WAY too much metal in them for an HF antenna to get anywhere, especially at QRP levels. If it is a modern building, your best option might be something along the lines of a vertical that sits on a window ledge and shutting the window holds the antenna in place. MFJ has a couple of those, but I don't know how well they work, since I've never used one.

For some bands, it might be possible to set up a Ventenna HFp inside, as long as you don't have a ton of metal in the structure of the apartment.

In any case, you will be readable on CW more than SSB.

73,

-- Tom
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KA4NMA
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Posts: 357




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« Reply #8 on: June 14, 2013, 07:20:58 PM »

The apartment is a older unit.  It is a 4plex with all units on the ground.  The window (and my shack) faces the main driveway of the complex.  It would be hard to put up a window sill antenna.

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W1JKA
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Posts: 1821




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« Reply #9 on: June 15, 2013, 03:42:58 AM »

Got Gutters?,If not how about a tree out front,if so a bird feeder/house on a 6 ft. post with thin vertical wire to overhead branch from roof of feeder /house.Bury wire from under window to  inside/outside post base.I put my matching unit inside the bird house.
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GILGSN
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Posts: 208




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« Reply #10 on: June 15, 2013, 10:39:58 AM »

You can probably forget 75m! You will have much better luck with 10-20m with an inside antenna. As some have pointed out, CW will get out, SSB will be much harder. I have used my buddistick inside with some success, and a homemade magnetic loop up to 40m, but it is 6' in diameter.. Size matters.

Gil.
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W4MMR
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Posts: 7




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« Reply #11 on: June 27, 2013, 06:41:51 PM »

Randy,
First - a web site to see is K3WWP.  He is big on QRP and has information about his experiences.  His website is http://home.windstream.net/johnshan/  John has a lot of different antennas - not too portable - but it may give you some ideas for wires in the house.

I am not sure if you have a car but you could put an HF antenna on the car to use and run a cable to the house.  I have used to use a 102 inch steel CB whip and tune that from 10 - 40m.  Not very efficient but it worked.  I have a trailer hitch and use a "tenna hitch" mount.

I use delta loops in the house for QRP operation to include CW and PSK-31.  These are monoband antennas made of wire and hung in the shape of a triangle with the flat part on the ground (in my case).  I attach the antenna to a balun like the BL2 from Elecraft   http://www.elecraft.com/mini_module_kits/mini_modules.htm  and hook regular coax to it to my radio.  Works very well.  I live in SC and talked with Texas on PSK-31 with 5 watts off the open side.  The delta loop I cut was for 15m and I tuned it for 10m, also, easily with my TS-480sat.  I was shocked at how well it worked and the receiving ham could not believe I was at 5 watts.

Delta loop ideas can be found here:  http://w5sdc.net/delta_loop_for_hf.htm  This is a good site to learn about the delta loop.

Good luck and if you have any questions, you can get my email from my QRZ.com listing.

mark
W4MMR
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KA4NMA
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Posts: 357




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« Reply #12 on: June 27, 2013, 07:21:36 PM »

Thanks for the links.  I liked K3WPP website. My apartment is small and I only have room for a 6m or maybe 10m delta loop.  I wonder how to scale them for 6m and 2m?

Randy
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WB6BYU
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Posts: 13567




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« Reply #13 on: June 28, 2013, 12:10:43 PM »

Standard formula for the length in feet is 1005/f(MHz), though in practice you'll
have to make some adjustments to center the SWR curve where you want it.

Impedance is typically matched using a quarter wave section of 75 ohm coax.

There is nothing magic about the delta shape - many other closed loops will work
as long as you don't fold it back on itself too much.  One of my favorites is to use
about the same length of wire but make it rectangular with one dimension twice
the other.  When fed in the middle of the short side it will be very close to 50 ohms
and not need any further matching.  The polarization is that of the short sides, so
"wide and not so tall" gives vertical polarization and may fit on a window for 2m.
For horizontal polarization the short sides with the feedpoint would be at the top
or bottom.

If you have space you can stack one loop above and one loop below a common feedpoint:
if these are dimensioned for a 100 ohm impedance then the pair will be very close
to 50 ohms, and will give a bit more gain.
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KT4EP
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Posts: 15




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« Reply #14 on: June 29, 2013, 07:20:53 PM »

I don't think you will like the MFJ walk about,, I have one, its not that easy to use.   And will probably be more expensive than what you want to pay for.   For just inside your apartment, maybe a loop around the ceiling fed with 450 ohm? Have to use a tuner for multi band.   More portable, maybe a painter's pole?  Have to make some coils,though, and have some sort of counterpoise running around the baseboard.  I've done both of these and they work.   In fact, I had a 20 meter loop in my living room but my wife didn't like that too much.
When I first got started, I had 10 meter dipole in my living room.  It worked fair enough for CW work.
KT4EP
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