I just got my XV222 going with the K2 a couple of weeks ago. It works great
but I get some odd behaviour when I transmit on other bands.
The set-up:
-K2 in QRP configuration (with KSB2, K160RX, K60XV with Key Out brought to a
RCA jack, with a bypass cap)
-XV222 in non-K2 / 1mW configuration connected to the K60XV (trn3)
-Microwave Modules 432 MHz transverter connected through an attenuator to the
QRP antenna jack and the External Antenna jack (though a switch) (trn4)
-Key line from Key Out jack to above two transverters is switched (all shielded
cable)
-903 MHz receiving converter alternately connected to the External Antenna jack
(through a switch) (trn5)
-25 watt 144 MHz rig (sharing power supply with all the above)
-10 watt 50 MHz rig (completely separate)
What happened (when switches and K2 set to 222 MHz):
When I transmitted on 6m (10 watts, antenna very close to equipment as this is
an apartment station) the XV222 indicated a transmit IF overload condition
(flashing LEDs). Yes, it's a pretty high field strength, but it should be
about the same as could be expected in a mobile/rover setup (which is how I
intend to use this gear this summer).
When I transmitted on 2m (25 watts, but antenna further away) a relay could be
heard switching in the XV222, the K2 went quiet and the S-meter went to full
scale.
Investigations:
The 2m problem seems to have been solved. I found that the TX IF plug into the
K60XV was not making good ground contact, so it was picking up a lot of RF.
However, it is worth noting that before I discovered the connector problem I
noted that the strange behaviour occurred even with the 2m transmitter
connected to a dummy load, i.e. with very low field strength (probably mostly
radiation from the 2m rig's power cable).
Having fixed the connector contact above, the 6m problem persisted.
I seem to have fixed the XV222 IF overload problem when transmitting on 6m by
making the following modifications to the XV222:
- scraped the paint off the inside of the rear panel under a couple of the nuts
holding the N-type antenna connector
- put a 4.7nF bypass capacitor across the 13.8 V power leads where they connect
to the PC board (for those concerned about safety, it is externally as well as
internally fused).
I did both of these mods at the same time so I don't know which one(s) actually
helped.
But I now have the symptoms initially noticed on 2m when transmitting on 6m.
Apparently the RF is causing the key output from the K60XV to go to ground, but
why the S-meter is reading and the receiver is going quiet I don't understand.
The K2 is not going fully into transmit...with RIT on the displayed frequency
does not change.
There seem to be two issues here...
(1) the XV222 box is not very RF-tight. Probably mostly due to understandable
tradeoffs using of connectors where the shield is not connected directly to the
case. I've made some improvement to that but it is not enough. I'll probably
look at some sort of external grounding strap for the IF and key in connectors.
Maybe a ferrite choke on the power cord.
(2) something in the K60XV or K2 is very sensitive to RF and turns on the key
line. I did try a bypass cap between pins 1 and 2 of P1, with no apparent
effect. Typically disconnecting the TX IF (and sometimes the RX IF) cables
from the K2/K60XV stops the strange behaviour. All 3 K60XV jacks on the K2 are
grounded directly to the case.
I intend to try seeing if I can trigger the key line problem with a low power
50 MHz signal generator feeding into the K60XV jacks, so I can do a more
controlled test, but I haven't got to this yet. I am not sure how much power I
can safely put into the RX jack.
So......any suggestions ? Similar experiences ? Theories on why the K2/K60XV
key line gets switched or why the S-meter goes to maximum for a signal that is
22 MHz from where the K2 is receiving ?
73,
Steve Kavanagh VE3SMA
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