Possible antenna problem

[veedub565]

Hi,  I'm a bit confused by a strange problem I'm having. Hoping it might seem a bit more obvious to someone more experienced.

My 2m rig measures 12W forward power and 1.00 vswr into a 50ohm load. When I connect my antenna I only measure 0.9W forward power and 1.06 vswr.

A few days ago I was measuring 12w forward power with the antenna connected. So I don't understand now what has happened. And I don't understand how the vswr can stay roughly the same,  but the power is so much lower.


Rig = Yaesu FT-480R
Antenna = Diamond X50
Coax = RG213 (8m length)

Ben
M7SCY

Oh and I used adhesive lined heatshrink on the antenna connector (N type) so as to weatherproof it.

[HB9EVI]

how do you measure the swr?

[fourfathom]

how do you measure the swr?

Yes.  Some SWR meters won't give reasonable readings with very low power, and if you have an antenna or cable problem your transmitter is probably backing off on the power to protect the output transistors.

[veedub565]

I'm using a R&S NAS-Z5 insertion unit to measure forward/reflected power and VSWR

[HB9EVI]

very likely you have either a cable or an antenna problem, so the transceiver lowers the output because of the mismatch, so you're measuring garbage.
in such cases you don't get far with an swr meter; if you don't have one of the widespread vnas, I'd recommend you to check the cable with the tdr method
check the antenna for eventual leaks

[veedub565]

Thanks, I'll get and investigate the antenna. Water getting in is the only thing I can think of.

[veedub565]

I'm still getting a signal out by the way. My friend I talk to regularly still gives me an S8 report, although slightly down on the usual S9+

[veedub565]

Fixed it, its the cheap N to PL259 adapter I'm using on the insertion meter.

Thats what you get for buying cheap adapters and connectors.

[HB9EVI]

yea, that's little surprising; the best setup/antenna is worth nothing if you have such a crap in the installation

glad that you found it!