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Author Topic: 14x70 aluminum skinned mobile home, 40-20m QRP solutions  (Read 10960 times)
W7JCK
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Posts: 11




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« on: June 24, 2013, 09:39:22 AM »

Anything I do has to be pretty covert because of the lease.  I'm expecting to use 5w of CW and mostly on 40/30/20m.  The locations I have are:

1.  Along the roofline of the mobile home- very little seperation is possible.

2.  A short vertical wire in a tree (maybe 30'), no radials possible, but I could run a counterpoise along the coax.

3.  A smallish shed next to the house has internal space for a 4' diameter magnetic loop.

Any suggestions comparing these options?

W7JCK
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N4UM
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Posts: 483




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« Reply #1 on: June 24, 2013, 10:54:44 AM »

2.  A short vertical wire in a tree (maybe 30'), no radials possible, but I could run a counterpoise along the coax.


...I like number 2 using the aluminum skin of the mobile home as the counterpoise
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WX7G
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Posts: 6332




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« Reply #2 on: June 24, 2013, 11:11:05 AM »

The wire in the tree can be worked against the mobile home; the mobile home is the counterpoise, no radials needed. I use a 30' wire in a tree worked against a travel trailer and it works well enough.
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W7JCK
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« Reply #3 on: June 24, 2013, 02:05:11 PM »

Are folks using a resonant wire?  or a random wire and a tuner?
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WX7G
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« Reply #4 on: June 24, 2013, 04:58:44 PM »

I use a random wire (30' give or take a bit) and the ATU in my KX3. It tunes the wire on 80-6 meters.
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KQ6Q
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« Reply #5 on: June 24, 2013, 10:20:27 PM »

I live in a 24x56 metal skinned mobile home. The side skin is aluminum, but the roof is NOT aluminum, it's steel. Mag mounts work. I have FIVE of them, multiple resonator for 20-18-15-10, and singles for 30, 40, 80 and 160. QRP not recommended, as hustler masts and resonators are not all that efficient, but they WORK fine with moderate power (100W). I have counterpoise wires - 2 each, 1/4 wave on all bands but 160, and that band ties into all the others. With 100W, I can make good contacts across the country and in  DX contests, around the world. Not a competitive DXer, but I make plenty of contacts from a treeless mobilehome location. a Remote coax switch - Ameritron RCS-8V - selects the antennas without so many coax runs through the wall.
With limited antennas on a mobile home, QRP will be an exercise in frustration. I do my QRP with resonant wire antennas between trees in the local park.

Fred, KQ6Q
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WX7G
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Posts: 6332




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« Reply #6 on: June 25, 2013, 03:33:14 AM »

I run a KX3 at 12 watts to the 30' wire.
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WX7G
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Posts: 6332




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« Reply #7 on: June 27, 2013, 06:18:44 PM »

I took a look at my trailer and the aluminum panels are painted and slotted together. I doubt there is good electrical contact between them rendering them questionable as a counterpoise. Today I compared the mobile installation against the trailer 30' wire on 20 and 17 meters. Listening to the W1AW CW broadcast on both bands it is approximately 15 dB stronger on the mobile. The mobile antenna is a Tarheel 40A with a 9' whip mounted near the roof line of the vehicle. Based on simulations and base resistance I conclude that it is over 50% efficient on 20 and 17 meters and can serve as a reference antenna.

The 30' wire has two things besides the questionable counterpoise that could account for the poor performance: The last 24" of wire, while insulated, is touching the tree and the KX3 ATU could introduce excessive loss matching the wire.

As a result of this experiment I ordered an MFJ-1796 vertical dipole and it will be installed on the trailer this weekend. I'll report back.  
« Last Edit: June 27, 2013, 06:23:53 PM by WX7G » Logged
WX7G
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« Reply #8 on: July 16, 2013, 05:00:20 AM »

I installed the MFJ-1796 vertical dipole on the travel trailer and have tested it. Installation and tuning were easy. It looks smaller than in the pictures and the neighbors think it's a TV antenna.

Using an Elecraft KX3, receive signals were tested using the W1AW CW broadcast around 0100 Z. The reference antenna is the same as for the 30' wire, the Tarheel 40A and 9' whip mounted on the car. The MFJ-1796 antenna covers 40, 20, 15 and 10 meters and using the antenna tuner in the KX3 was tested on 40, 20, and 17 meters. The mobile antenna was tuned for each band and repeated A-B measurements were performed.


BAND            CAR      MJF-1796   DIFFERENCE
17m              S-5       S-5              0 dB
20m              S-5       S-7             12 dB
40m              S-8       S-8+             8 dB

Conclusions:
The MFJ-1796 works well. I worked the IARU contest and QSO's were easy running 5 watts on 20 meters.
The 30' wire was compromised by one or more problems; touching the tree, poor counterpoise, out of the range of the KX3 tuner.
« Last Edit: July 16, 2013, 05:04:09 AM by WX7G » Logged
W7JCK
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« Reply #9 on: July 16, 2013, 07:59:41 PM »

Thank you for the update.

I haven't committed to my installation yet, but am leaning towards a monoband 30m cw solution at 10' or so (because thats all the height I have).  I think a Magnetic Loop would do well, but I don't feel like that much adventure quite yet.
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