[SOC] Matching G5RV

[Bob Nielsen]

On Mon, Aug 18, 2003 at 05:51:00PM +0100, Paul Bartlett wrote:
> Hi All,
> 
> I have a conundrum to solve.
> 
> I have a K2, a full size G5RV (104') and an ex-miltary ATU (Redifon type
> A.C.U.9) kindly loaned to me by Paul MW3PWA.
> 
> The ladder-line phasing section of the G5RV terminates in a 50R co-ax
> connector and is immediately followed by a 10 turn co-ax 'choke balun'
> (about 6" in diameter). There's then a 30' run of co-ax to the shack.
> 
> The ATU takes an RF input via a BNC connector which runs to the K2.
> Disassembling the ATU I see that the hot input passes to a bank of
> switchable capacitors down to  ground and thence to variable series inductor
> (rather nicely made).
> 
> There are three output terminals: Earth; the other end of the inductor; and
> a third terminal connected to the second via a high-voltage cap which value
> I can't determine.
> 
> Questions:
> 
> Is the ATU sensibly usable at all with my mix of antenna and feed? If so,
> how?
> Do I need a further balun after the ATU to match the unbalanced feed?
> Should I ground the ATU via it's EARTH terminal?

Paul,

This is a simple L-network.  It will (depending on L and C values)
match impedances which are lower than the output impedance of the
transmitter.  If you want to match a higher impedance, turn the unit
around (the lower impedance is connected to the series inductor, while
the higher impedance is connected across the shunt capacitor).  It is,
therefore, somewhat limited in matching ability.  You should probably
ground the unit.

73,
Bob, N7XY