Re: [TenTec] Keying lockup problem continued

[Ken Brown <ken.d.brown@verizon.net>]

Hi Bob,

Thank you for the helpful suggestions. I don't think that proximity of 
the antenna is a factor, and some more details follow which explain why 
I think that:

I have had the Omni VI and Titan operating for over a year without 
encountering this problem before. Previously I had been using a 238 
tuner with the only antenna I have up. I got a 253 Autotuner, which has 
provisions for connecting the keying loop through it, so that fault 
conditions in the tuner can prevent the transmitter from keying until 
the fault is resolved. So I hooked up the keying loop through the 253 
and everything worked fine, until I went to 160 meters and had the 
lockup problem. When I first discovered the problem I was tuning into a 
dummy load. It is a really good oil bathed non-inductive resistor that 
can handle full power and is probably good up to 450 MHz or so.

Since putting one more device in the loop required one more RCA to RCA 
phono cable, I went out and bought a few at Radio Shack. The new cables 
I bought seemed nicer than the old ones I had been using, so I went 
ahead and replaced all of the cables in the keying loop with the new 
ones. When I discovvered the problem, the first thing I though of was 
that I had a faulty cable that was more susceptable to RF ingress than 
the cables I had been using before. I put one of the old cables back, 
and the problem was gone. I thought that was the end of the story, until 
I tried tuning up on 160 meters last night. When I switched from the 
dummy load to the antenna, I had the lockup problem again. It seemed 
like it happened at a slightly higher power level than before, or more 
accurately I should say that I did not have to reduce the power output 
to as low a level to get the lockup condition to release.

I considered whether I could just reduce power a little bit to prevent 
the lockup, and wondered if there might be some effect on my keying 
envelope at a power level that did not lock the system up. So I decided 
to listen to my signal with another receiver. I used my Paragon for this 
and that is when I discovered that with the key up and no sidetone from 
the Omni headphones, in the locked up condition, even though the Bird 43 
was still indicating that same power output, I could not hear the signal 
on the Paragon. So in the locked up condition the TX signal either 
shifts frequency or spreads out in such a way that it now longer makes 
the sound of a CW signal on the same frequency as the key down signal. 
Fearing some kind of parasitic oscillation that might damage my tubes, 
or perhaps an out of band signal causing QRM who knows where, I decided 
not to try to figure out where the signal went. I left the radio room 
for the night and took the Omni, Titan and 253 documentation with me.

Studying the manuals I discovered a few interesting things. The manuals 
show several different ways to interconnect the transceiver, tune and 
amplifier, depending on exactly what equipment you are using. Some of 
the diagrams are not applicable to my situation. Of the diagrams that 
are most applicable I found that some show the TX OUT of the transceiver 
going first to the 253, then from the 253 to the amplifier, and from the 
amplifier back to the TX EN of the transceiver. Other diagrams show the 
loop going to the amplifier first and then to the tuner, before 
returning to the transceiver. This may not be of any significance, since 
it is just a loop, and breaking the loop anywhere should disable the 
transceiver from transmitting. On the other hand keying the amplifier 
while preventing the transceiver from transmitting might not be so good 
for very long.

Another interesting thing I found in the 253 manual is that the relay, 
K6, which is used to break the keying loop, is on the KW BRIDGE PAD 
BOARD. This board has the SWR bridge on it, and full Titan RF power goes 
through it. So there may be a significant path for RF to get into the 
keying loop, regardless of how good my cables are. I'll test this theory 
by just not connecting the 253 in the keying loop. In the long term 
though, I want the safety of having the 253 able to prevent the Omni 
from keying. So I'll have to do something else. Perhaps an external 
relay that is activated by K6. I don't know what the solution will be, 
and I'll keep you posted as the saga continues.

Ken N6KB





Robert & Linda McGraw K4TAX wrote:

> Better cables may not be the answer.  Most likely it is RF getting into the
> transceiver via any of the cables connected to the rear connectors on the
> transceiver.  Key, audio in/out, PTT, power, speaker, etc etc.  I'd suspect
> that it is RF being radiated from the antenna that is being picked up.   Is
> the antenna for the band causing the problem closer to the radio than others
> that do not cause the problem?
>
> Additional bypassing on the inside rear at the connectors might work.  Don't
> over do it as excessive capacity could have a negative effect on the
> required in and out signals.  Start with .001 mf and work your way to .01 or
> maybe a .05.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "ERichard Roberts 3rd" <olesalty@adelphia.net>
> To: <tentec@contesting.com>
> Sent: Wednesday, September 24, 2003 7:29 AM
> Subject: Re: [TenTec] Keying lockup problem continued
>
>
>  
>
> > Ken, I have had the same problem. Where are you getting the better cables
> > from.
> >
> > Tnx
> > Richard
> > W1OS
> > ----- Original Message -----
> > From: "Ken Brown" <ken.d.brown@verizon.net>
> > To: <tentec@contesting.com>
> > Sent: Wednesday, September 24, 2003 4:28 AM
> > Subject: [TenTec] Keying lockup problem continued
> >
> >
> >    
> >
> > > Hi all,
> > >
> > > I posted a message a few days ago about a problem with my Omni VI and
> > > Titan getting locked in TX. The problem seems to be related to RF pickup
> > > by the QSK control cables between the Omni and the Titan. I thought I
> > > had solved the problem, only to have it happen again tonight. I am
> > > expecting that better quality cables will solve the problem. Another
> > > detail I discovered tonight is quite interesting: I turned on another
> > > receiver to monitor my signal, heard my signal where it should be when I
> > > key the Omni. When not keyed, and locked up by the RF into the QSK
> > > cables problem (I presume) I did not hear my signal, even though the
> > > Bird 43 wattmeter is indicating the same power output as when keyed. I
> > > do not have a spectrum analyzer, or other way to quickly see where (in
> > > frequency) the RF is, and I am certainly not going to let this continue
> > > while I tune the other receiver around to find it. Better just to fix
> > > it. Interesting though.
> > >
> > > Ken N6KB
> > >
> > >
> > >
> > > _______________________________________________
> > > TenTec mailing list
> > > TenTec@contesting.com
> > > http://lists.contesting.com/mailman/listinfo/tentec
> > >
> > >      
> > _______________________________________________
> > TenTec mailing list
> > TenTec@contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
> >
> >    
>
>
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>
>  

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