On Apr 25, 6:30*pm, JIMMIE wrote:
On Apr 25, 4:22*pm, Owen Duffy wrote:



Chuck Forsberg WA7KGX N2469R wrote :

I installed a Diamond X-200A antenna just above a Thunderbird TH5MK2
tribander. *Due to a short mast, the Diamond is virtually sitting on
top of the Thunderbird.

The lead-in consists of some 20 feet of 9914f and 50 feet of 9913,
connected with UHF connectors.

Ok, from TLLC (http://www.vk1od.net/calc/tl/tllc.php) you have about
1.1dB of line loss if everything is in good condition.

The measured SWR minimum is at 147.7 MHz and 1.2:1 at the far end of
the coax. *The MFJ 259B reads 1.9:1 at 144 mHz. *Presumably the SWR is
a bit higher at the antenna connector.

I assume all readings were made with the same instrument.

Your load end VSWR at minimum is close to 1.3, which is typical of those
type of things. The frequency of the minimum does seem a bit high.

If I use a longer mast to raise the Diamond above the tribander, can I
expect the resonant point to move to the specified 146 MHz and the SWR
at 144 to go down? *How much separation is needed?

I am a bit surprised that it is that far off, and wouldn't expect a lot
of change in raising it... but you only know if you try it.

Have you used / measured it in other scenarios?

Have you measured the VSWR characteristic using a conventional
reflectometer style instrument at modest power? Does it agree with the
'259B?

Owen

Owen, didn't you write a paper on stacking antennas.

Jimmie

Perhaps I was thinking about Ian White.

Jimmie