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Portable Digipeaters

On the weekend of May 6th and 7th, the DCARA helped provide communications for the MS150.

During the day of May 6th, the 146.92 repeater was used as the backup repeater and used for the second half of the day.  APRS didpeaters from the DCARA were used to assist in the event on both days.  Portable digipeaters from Guy Story KC5GOI and Gerald Marchant WB5NZV were used for both days.  Both setups will be utilized during the MADD ride.  The pictures below are examples of  the KC5GOI setup.  Pictures of the WB5NZV setup will be posted after the MADD ride. 

The KC5GOI and WB5NZV digis place the radio and TNC at the top of the mast.  Power is feed via 10 gauge zip cord.  Typically feedline used for portable setups has losses of 2 to 4 dB.  This presents 2 issues, degraded transmit power and reduced sensitivity on receive.  Feedline to reduce or minumize the losses tends to be bulky and does not like to be flexed like RG8, RG8x  or RG213 can.  Measurements of 14, 12 and 10 guage zip cord were taken at 30ft lengths.  10 gauge zip cord only loses 0.4 to 0.5 volts where 14 guage lost over a full volt.  Note, these measurements were taken with the radio in a keyed up state.  The loss in the power cord is in relation to the amount of current consumed.  Pull more current, loose more voltage.  Don't forget that the power cord is one long resistor.  The two radios tested (Alinco DR130 and Yeasu 2000H) were able to provide a full 45 watts at 12.1 volts.  Since the radio is at the antenna (well within 2 ft), that is about as much power as you are going to get to the antenna and receive losses are minumized as well.  Since the same amount of power is used to run the radio, I would rather get 45 watts to the antenna instead of 25 to 30.  This is splitting hairs but in an easy to acheive manner. 

The antenna in the KC5GOI digi setup is an Arrow Antenna J-Pole.  I chose this antenna  since it has gain and does not require a ground plane.  That makes it easier to assemble, tear down and store.  The entire setup uses Anderson Power Poles and has a 20 amp fuse at the battery.  The cases were obtained from Lowes and are 4x4x2.  I drilled holes for air flow and installed a fan that pulls air across the heat sink on the radios.  The WB5NZV digi pulls air from the upper left to the fan and is blown out the top center across the heat sink.  The KC5GOI digi pulls air from the bottom of the enclosure and discharges out the top center across the heat sink.  This is an attempt to keep heat build up from occuring.  Even if the radios do not heat up from use, radiant energy will heat up the cases.  I do plan to paint them white instead of leaving them gray.  NOTE: The cases are no longer water tight.

Below are thumbnails of the KC5GOI digi.  The WB5NZV pictures will be posted after May 27th.


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