@Vintage-MR600 These seem good, do you have a picture of them. John vk3hjq

@Vintage-MR600 Do you have a spec sheet on these antennas. It depends what the gain figure (dBi) is at 700MHz too, it may not be 15dBi. So 15dBi to dBd - 2.15 = 12.85 dBd (dB) 12.85 - (2 x 1.3dB...

@Vintage-MR600 Shorter is always better at these high Frequencies. Remember 3dB is 1/2 your signal loss in both Transmit & Receive. Examples below using LMR400 coax over 5mts (16.4042 feet) & 10mts...

@Vintage-MR600 Usually more height means more signal. Do a temporary setup outside & see what signal strength you get. John vk3hjq

@Vintage-MR600 @ 700MHz (698) which is the lowest Frequency used, then its 856.5mm (85.6cm) between the 2 antennas. John vk3hjq

@Vintage-MR600 It depends on the lowest Frequency used, here is the Formula to work it out. As for the length of the coax, the shorter the better. (more cable = more loss) John vk3hjq