[ICOM] Icom PW1 Failures - How To

[Adam Farson]

Hi Bruce, 

As I am not a PW1 owner, I cannot speak from first-hand knowledge concerning
ATU operation with the PW1 powered down. The Quadra needs to have its PSU
powered up to provide a through signal path, and the amplifier must be
powered up for the ATU to operate. The ATU will tune if the PA stage is in
Standby. I shall research this question further.

On the SPLITR Unit R7 failure - I took a look at the schematic on p. 10-2 of
the PW1 service manual. (This manual is downloadable from
http://www.qsl.net/icom/  and from
http://www.marcucci.it/english/download/). R7 and R8 are in an RF voltage
divider which feeds D3, the DRIVE detector diode. Assuming 60W RF drive and
a 50-om load impedance in the splitter, the RF voltage across the divider is
72Vrms. This equates to approx. 0.9W dissipation in R7.

The voltage divider is connected to the RF input line ahead of bypass relay
R2; it will therefore dissipate RF power whether the PA stage is active or
in standby. Now consider the case where the PA stage is in standby, the PW1
ATU is off-line and antenna (load) impedance Zl > 50 ohms. The RF voltage
across R7 and R8 will be higher, leading to greater dissipation. In this
scenario, it is quite possible to exceed the wattage rating of R7 -
especially if the exciter's ATU is in the signal path upstream of R7, and is
transforming the high load impedance to 50 ohms for optimum power transfer
from the exciter. 

I would agree that it is not good design practice to place a resistive
voltage divider at a point where it can "see" an RF voltage sufficiently
high to over-dissipate it. Icom should have used beefier resistors for R7
and R8, or used a capacitive voltage divider (as Yaesu does in the Quadra).
Refer Yaesu VL-1000 Technical Supplement, p. 5D-1, Divider Unit schematic.
Please e-mail me off-list if you would like a scan.

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Bruce J. Howes
Sent: 09 June 2005 04:33
To: 'ICOM Reflector'
Subject: RE: [ICOM] Icom PW1 Failures - How To

Hi Adam and group,

Not certain I agree that the antenna tuner in the PW1 functions when the
main switch is off at the PW1.
My ATU internal to the PW1, later serial #, does not work unless the power
is on to the PW-1.
I checked this with Icom, even if 12 volts is applied to the PW1 from the
765 exciter and the PW1 LEDs for the antenna and exciter input are
illuminated, the ATU will not work.
It will only work when the main power switch is on for the PW1.
The ATU will function with the amplifier section off, but not the main power
switch.

As far as determining antenna resonance, its really rather simple, MFJ-259.
The antenna is a 160 meter dipole fed with balanced line.
I am using a Heathkit 2060 tuner and the MFJ to confirm feedpoint impedance
and SWR.

The Icom manual for the PW1 does state on page 16, item 7 "Use the exciters
antenna tuner to tune the line between the IC-PW1/EURO and exciter, if you
have an antenna tuner connected to the exciter." 

I can't believe that the operation of a internal tuner of the exciter can or
should cause a fault in the SWR measuring circuit of the PW1, yet is has
happened to me and others.
Sorry, that seems like a design issue.
Can someone check the schematic and explain the failure of R7 on the
Splitter board any other way?

73 Bruce W1UJR

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Adam Farson
Sent: Wednesday, June 08, 2005 9:44 PM
To: 'ICOM Reflector'
Subject: RE: [ICOM] Icom PW-1 Failures - How To

Hi Harry,

Here is some further clarification courtesy Matt, KK5DR:

...The ATU can be operated without the PA section enabled. It can also be
operated without the PW1 even being powered up. DC power to operate the ATU
and antenna selector is provided by the exciter through the ACC cable. 

These features [Antenna selector & ATU operation with PW1 powered down] are
only provided on later versions of the PW1, S/N 1165 or higher.

The ATU requires at least 60 watts of drive to complete a tune cycle.  

Cheers for now, 73,
Adam VA7OJ/AB4OJ


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of we1x at comcast.net
Sent: 08 June 2005 15:17
To: ICOM Reflector
Subject: RE: [ICOM] Icom PW-1 Failures - How To

Went back and tried it..I stand corrected.

thanks Adam.

Harry WE1X

-------------- Original message -------------- 

> Hi Harry,
> 
> To quote the PW1 user manual, p. 2: 
> 
> When the linear amplifier is OFF, the [AMP/PROTECT] does not light and 
> the exciter's signal is applied to one of the output connectors or the 
> IC-PW1's antenna tuner.
> 
> Ibid., p. 14, top: 
> 
> This antenna tuner is also used when the linear amplifier is turned 
> OFF.
> 
> The Yaesu Quadra can also be configured with ATU on-line and PA stage
> off-line: [OPERATE] key off, [TUNER] key on. 
> 
> The ATU insertion loss is approx. 0.5 dB. 
> 
> Cheers for now, 73,
> Adam VA7OJ/AB4OJ
> 


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