[Elecraft] KPA100 SWR bridge adjustment 160m & 80m

[Koert Wilmink]

Dear all,

Please find my emails to Elecraft support below. Is there maybe somebody with additional tips?

Thanks!!

73 Koert PA1KW



-----------------------------------------------------
Hi Gary,

Sorry for my late response, but I had not the opportunity to work on
this earlier. I moved houses and that took longer than expected.

I did check the HV bias and that is 135volts. The diodes are ok and the
voltage on TP4 2mV on receive and 240mv on transmit (tune).
I did connect a good dummyload close to the KPA100.
I did the re-adjustment of the SWR bridge but this provided me not the
required results. The best results with adjusting C1 on 5 Watts is:

160m 1.8-1
80m 1.3-1
40m 1.0-1
30m 1.0-1
20m 1.0-1
18m   1.0-1
15m 1.0-1
12m  1.0-1
10m 1.0-1

Please help......

Best regards and 73,

Koert Wilmink
PA1KW

PS.
All the best for 2008!!

Gary Surrency wrote:

> > Did you check to see that the HV bias at the left side of R11 is at least
> > 100VDC, and the higher it is - the better? I like to see 120-150VDC
> > there.
> > Too little HV bias, or a damaged diode or error in the t-r switch, can
> > allow
> > too much RF to leak through the t-r switch when in transmit at high
> > power.
> > That can cause the KPA100 PA stage to self-oscillate and produce HI
> > CUR and
> > high SWR. The problem will be worse on the lower bands from 160m to 30m,
> > since the RF transistors have higher power gain at lower frequencies
> > and the
> > KPA100 typically will produce higher RF output on the lower bands.
> >
> > If damage has occurred to the MAX1406 RS232 IC, or to any of the parts in
> > the KPA100 t-r switch, it may load down the HV bias too much or allow too
> > much RF leakage through the t-r switch to provide the needed input to
> > output
> > isolation.
> >
> > You must see a low null voltage at TP4 of less than 10 millivolts (on
> > 40m or
> > 80m) when a good 50 ohm dummy load is connected as closely as possible to
> > the KPA100's antenna connectors. Do not have a SWR meter, wattmeter, coax
> > switch, or long cable inserted between the dummy load and the antenna
> > connector on the KPA100. Most rigs will null down to about 1-3 millivolts
> > with a very close and direct connection to the dummy load. Also, the
> > flange
> > of the SO-239 antenna connector should be installed so it is on the rear
> > panel, not on the inside.
> >
> >
> > If the antenna was left connected when there was a thunderstorm nearby,
> > lightning can damage the 1N5711 diodes in the KPA100 SWR sensors.
> >
> > If the diodes are OK, there should be about 98-100K ohms between their
> > cathodes and ground when tested with an ohmmeter. You can do this at the
> > side of the trimmer pots that connect to the diodes too.  Connect the
> > postive ohmmeter lead to the cathode, and the negative lead to a ground
> > point on the tuner.
> >
> > Then, if your meter has a diode test function, there should be about
> > 0.38 to
> > 0.40VDC of diode drop across the 1N5711 diodes, with the + lead to
> > anode, -
> > lead to the cathode.
> >
> > The diodes are easier to replace if one lead is clipped. It can be
> > done from
> > the top of the PCB without removing the heat sink, if you are very
> > careful,
> > have good desoldering tools and skill, and you pretrim and form the
> > leads on
> > the new diodes. Leave a little extra lead length above the PCB for easier
> > soldering.
> >
> > Also check to see if the calibration of the null cap, and the FWD and
> > REFL
> > cal pots still check out OK.
> > While the PA shield is off of the KPA100, be sure to check the
> > tightness of
> > the screws in PA transistors Q1, Q2 as they do tend to loosen.
> >
> >
> >
> > -- 
> > 73, Gary AB7MY
> > =========
> > gary at elecraft.com
> > Elecraft Technical Support   
> >
> >
> >
> > -----Original Message-----
> > From: Koert Wilmink [mailto:koert at wilmink.com] Sent: Tuesday, July 03,
> > 2007 1:26 PM
> > To: 'Gary Surrency'
> > Cc: 'CSinfo'
> > Subject: RE: PA1KW: RE: High SWR on 160M and 80M with dummyload
> >
> >
> > Hi Gary,
> >
> > Yes I have the new value of C31 installed. It is impossible to lower SWR
> > reading with C1. Other bands are perfectly working well. Any other
> > suggestions?
> >
> > 73 Koert PA1KW
> >
> > -----Oorspronkelijk bericht-----
> > Van: Gary Surrency [mailto:support at elecraft.com] Verzonden: Monday,
> > July 02, 2007 8:34 PM
> > Aan: 'Koert Wilmink'
> > CC: 'CSinfo'
> > Onderwerp: PA1KW: RE: High SWR on 160M and 80M with dummyload
> >
> > Koert,
> >
> > Is C31 in the KPA100 t-r switch the new value of 0.22uF, 63WVDC? This
> > change
> > is specifically to address oscillation and high SWR problems on the lower
> > bands of 160m-30m if there is too much RF feedback through the t-r
> > switch at
> > high power.
> >
> > The new value of C31 (0.22uF, 63WVDC) applies only to late model KPA100
> > kits, or to older ones that have had the KPA100UPKT modifications
> > installed.
> > Info on that mod kit is on our website at:
> >
> > http://www.elecraft.com/order_form_parts.htm
> > All parts requests should be sent to parts at elecraft.com for the quickest
> > response. I'm not at the main office in Aptos, CA. I'm located near
> > Phoenix,
> > AZ and have no stock of parts here other than for doing repairs.
> >
> >
> > -- 
> > 73, Gary AB7MY
> > =========
> > gary at elecraft.com
> > Elecraft Technical Support 
> >
> > -----Original Message-----
> > From: Koert Wilmink [mailto:koert at wilmink.com] Sent: Sunday, July 01,
> > 2007 2:08 AM
> > To: support at elecraft.com
> > Subject: High SWR on 160M and 80M with dummyload
> >
> >
> > Dear Elecraft,
> >
> > I've a high SWR on 160 and 80M with my K2/100 # 5618. With a dummyload I
> > cannot get the SWR meter adjusted right. I cannot get it lower than
> > 1.9-1 on
> > 160M and 1.7-1 on 8oM. On all other bands it's exactly 1.0-1. Any
> > suggestions?
> >
> > 73 Koert PA1KW
> >
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> > 3:35 PM
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