To save a jpg with saveas() you have to give a proper figure handle (at least gcf) as first argument and change '.jpg' to 'jpeg' as format specifier (no dot and including the "e").
e.g.:
clearvars, close all
clc
NAME = 'myFig'; % figure name and prefix of jpeg file name
fig = figure('Name', NAME); % creates figure and returns figure handle
plot(rand(100,1)) % plot some random data
saveas(fig, sprintf('%s - F vs V', NAME),'jpeg') % save as jpeg
However, i would recommend to use a vector graphics format or png instead of jpeg, because jpeg could contain ugly artifacts.
