Topband: Fwd: Re: More Inv-L matching issues.... BIGGER ISSUE

[Paul Dulaff]

Dan

I understand that your 160 meter station is/was working until you introduced the 374A to the system.

If this is the first time you have manually loaded up the 374A on 160 meters, it may be possible that the amp is tuned up for output on 80 meters. C18 (tune cap) is the only capacitor in the tank circuit, so is possible to reduce its capacitance down to tune on 80 meters when the bandswitch is set for 160 meters.

It is possible to input to the amp on 160 meters, having the output tank circuit tuned to 80 meters and the amplifier develop an output. The amplifier in this case would be acting as a frequency doubler and would output high power at 2X the desired frequency. The impedance at the antenna would be completely wrong in this situation and would explain the immediate failure of the relay box.

As a check, confirm that C18 (tune variable capacitor) is at full mesh (max. capacitance). Tune and load the 374A into a dummy load, slowly decreasing C18 until the first dip in plate current is noted.

Best 73's

Paul - WB2NMI


----- Forwarded Message -----
From: Paul Dulaff <pdulaff at embarqmail.com>
To: Dan Bookwalter <N8DCJ at YAHOO.COM>
Cc: topband at contesting.com
Sent: Sat, 31 Dec 2011 20:21:44 -0500 (EST)
Subject: Re: Topband:  More Inv-L matching issues.... BIGGER ISSUE

Dan

A couple of thoughts...

When transmitting, is the RCS-10 antenna switch inadvertantly changing (switching) antennas (ports) during the transition from receive to transmit, possibly RF getting into the switching circuit causing this ? Do you lose the 12VDC to the switch when changing from receive to transmit ?  Are you trying to support semi-break-in with the RCS-10 ?

The ratings on this switch are fairly good. 16 amps, 1200 volts. I would think that it would need to be feeding an open or a short to fail this quickly at this power level or switching at full power.

Paul - WB2NMI


----- Original Message -----
From: Dan Bookwalter <n8dcj at yahoo.com>
To: topband at contesting.com
Sent: Sat, 31 Dec 2011 17:34:09 -0500 (EST)
Subject: Topband:  More Inv-L matching issues.... BIGGER ISSUE

Ok...

I went and added 9 more radials the SWR is now at 1.2:1 after some adjusting of the air variable....

well , i decided to see how the amp (Alpha 374A) loaded into the antenna , I keyed down with maybe 500 watts and everything went dead again in less that 1 second. So it now appears that I have smoked another relay in the RCS-10 .

One thing about this configuration is that the base of the antenna is about 16" from the RCS-10 , is this too close ? I can probably move it so that it is about 4' away if that is the issue.... I cant afford to keep destroying relays and such....

thoughts ?

Dan N8DCJ


________________________________
 
-----Original Message-----
From: topband-bounces at contesting.com [mailto:topband-bounces at contesting.com]
On Behalf Of Dan Bookwalter
Sent: Saturday, December 31, 2011 2:41 PM
To: topband at contesting.com
Subject: Topband: More Inv-L matching issues....

well about a month ago i put up my Inv-L , it is now ~165ft , I have an air
variable in series , and 12 radials anywhere from 150-250ft long ( going out
to add more as soon as i am done typing this). my SWR wasn't too bad maybe
1.7:1 at the best. Two nights ago I added an amplifier to the mix ~700w ,
well to make a long story short I smoked one of the relays in my RCS-10 , I
am now not too sure what to do , I don't want to keep blowing out relays in
the RCS-10.

I had several responses back then regarding matching etc... , but , in my
haste i seem to have deleted them :-( 

so here i am again asking for advice...

any help greatly appreciated 

Dan N8DCJ
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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UR RST IS ... ... ..9 QSB QSB - hw? BK