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Archive for September 14th, 2008

Life on HF – The MFJ-1796 6-Band HF Antenna for Limited Space

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For those folks who have constraints that do not allow you to put up a big HF antenna then take a look at the MFJ-1796 6-band antenna.  This antenna covers 5 HF bands and the 2 meter band.  HF bands covered are 40m, 20m, 15m, 10m, and 6m.

We’ve been using this antenna for about 8 years on HF with good results.  To have one antenna cover all these bands is a convenience.

At the outset we should say that this review of the MFJ-1796 is for a very special circumstance.  We have made a slight modification to the antenna and we use it in a slightly different position than recommended.

Look at the picture to the left. That is the antenna that MFJ will deliver.  But we have changed it a bit – read on.

The word from MFJ

The quote below is directly from the MFJ-1796 assembly manual and briefly describes the antenna structurally and electrically.

INTRODUCTION
The basic 40 meter quarter wave vertical antenna is 33′ tall and requires a reasonably good ground or counterpoise system to function properly. The usual way to eliminate the requirement for a complicated and space consuming ground system is to center feed a 1/2 wave (in this example a 66′ tall) antenna.

The six and two meter amateur bands are covered with the addition of four quarter wave decoupling stubs. The power rating of the antenna is 750 watts on six meters and 300 watts on two meters.

MFJ solved these problems by combining efficient end loading with a balanced center feedpoint design. The result is a physically small vertical antenna that gives good performance and does not require any type of RF ground system.

The reduction in size is accomplished by adding separate loading coils and capacitance hats at each end of the antenna for the HF bands. The efficient end loading coils are wound on fiberglass forms. The high quality materials and construction of the HF loading system allows a maximum power rating of 1500 watts on 40, 20, 15 and 10 meters. The continuous CW power ratings are 500 watts on 40 meters, 750 watts on 20 or 10 meters and 1000 watts on 15 meters.

Translation

So lets get to the bottom line on this antenna – its a balanced dipole with loading coils (not traps) and capacity hats at each end.  The length of the antenna is 12 feet as delivered from MFJ.  Its as simple as that.

The MFJ-1796 as delivered by MFJ is expected to be used as a vertical and mounted on the ground, on a tripod on a roof, or attached to a chimney.  Its a center-fed vertical dipole that is ground independent – that is, it does not require a counterpoise or grounding system.

Hatching the plan – going Horizontal

Read the rest of this entry »

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Written by frrl

September 14, 2008 at 9:35 pm

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