Richard,

Interesting situation. You are short by a couple of inches from what one
would expect. I wonder if you have to take into account the few inches of
line inside the meter. Does the manual say anything about that? You should
certainly count the length of any connectors/adapters as part of the line
length.

Here is something else you could do. Connect a 50 Ohm, or so resistor from
the MFJ to the cable. Then a diode (1N914, etc) from that junction to a DC
voltmeter. Now adjust the frequency for minimum DC voltage. You may have to
interpolate between the two points where the meter goes to 0. If it tunes
too broadly, make the resistor 0. I have done this with a 'scope, but not a
voltmeter,

Tam/WB2TT

"Richard" wrote in message
om...
What would be the best way to adjust a quarter wave of 75 Ohm twin
line using an antenna analyser? I just connected mine across the
analyser (open circuit) and looked for the freq where a short showed -
is that likely to be accurate? At 10.1 MHZ I ended up with a 15.7 foot
line which seems a bit short (low velocity factor).

73

Richard
G3CWI

Tarmo Tammaru wrote:
Interesting situation. You are short by a couple of inches from what
one would expect. I wonder if you have to take into account the few
inches of line inside the meter. Does the manual say anything about
that?

Recent MFJ manuals recommend using an external coax T-adapter with a 50
ohm load on one arm, and looking for the dip in SWR reading
(short-circuited quarter-wave, or open-circuited half-wave). That does
not require accounting for any extra length inside the meter, only
inside the T-adapter itself.

You should certainly count the length of any connectors/adapters as
part of the line length.

Certainly. If you don't like math, then plan to install the resonant
line in the same way as you tested it, using a T-adapter.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek