[VHFcontesting] Better late than never, K9ZF/R June VHF recap

[Nate Duehr]

On Jul 4, 2008, at 4:20 PM, Dan Evans wrote:

> think it had ever seen RF before.  At least it looked new:-)   Lastly,
> was my trusty old Par Moxon for 6 meters.  The Moxon goes up, the  
> cable
> is run, and then Murphy strikes!   The SWR test at around 7:1!!!    
> Holy
> cow!  What happened?  It worked fine last September.


Dan,

Just checking here... how did you measure the SWR on the Moxon?  If  
you were using a Bird or other external wattmeter and not to internal  
metering in the FT-897, good.

If not, beware that the FT-857/FT-897 (same radio deck inside) have  
had some funny issues -- especially early non "D" models -- with 6m.   
I've seen everything from "Yaesu has a fix for this, send your radio  
back to them."  To people saying the problem is just screws backing  
themselves loose inside the radio, causing the grounding internal to  
the rig to get squirrelly.

But whatever the reason, the symptom is the same.   Key the rig, say  
nothing, and watch it start oscillating and putting out full power  
continuously in SSB mode.

I attempted to use my "trusty" FT-857 for the 6m rig in my 2007 Rover,  
and found that it was doing this silliness when hooked to the dual 6m  
square loops (stacked) on my 12' mast on the Jeep.  Plug in the  
FT-847, and zero problems and 1:1 SWR.

The false SWR readings from the FT-857 were because the rig goes  
*hideously* spurious when it's in this "feedback loop" scenario and  
most of what it's throwing out is out of band.  A regular wattmeter  
sees all sorts of reflected power back, and shows a high SWR, but if  
you look at it on a spectrum analyzer -- it's just "grass" everywhere.

I only mention it because 6m problems on certain antennas come up  
regularly on the FT-857 YahooGroups list.  Perhaps that's what you  
were fighting and the Moxon is fine.

--
Nate Duehr, WY0X
nate at natetech.com