He'll be here all week folks!
Don't forget to tip your server.
Reed / WW3A
On Thu, Feb 28, 2019 at 3:23 PM MadScientist <dukeshifi@comcast.net> wrote:
> My ex-wife’s kitchen comment was always, “If you can still tell what it
> is, it’s not done yet!”.
>
> I installed a smoke detector in the kitchen - I used it as a dinner bell.
>
> She did, however, create in me a taste for blackened fish…blackened
> chicken… blackened eggs…
>
> The oven had a nickname - the incinerator.
>
> A friend asked me why I bought a sand blaster. I told him “My job is to
> clean the pans!”.
>
> She had a few recipes that made it into a very famous and important book -
> The Handbook of Hazardous Materials.
>
> Once she dropped some food on the floor. I asked if she was going to pick
> it up. She said "No, the mice will eat it”. I said “No, they have other
> options!”.
>
>
>
> > On Feb 28, 2019, at 2:06 PM, Mike Bryce <prosolar@sssnet.com> wrote:
> >
> > Whoa!
> >
> > That’s a great catch. I’d never would have suspected the Jones filter to
> cause a transmit issue. Are you producing full RF output now?
> >
> > Only once did I find a shorted .01 capacitor and that was in a Drake W4
> wattmeter. I found one of the old micas (the rectangular shaped ones with
> the dots) that was dead short in an old tube audio amplifier.
> >
> > Working with these old radios reminds me of my ex-wife’s cooking—Every
> bite was different!
> >
> > mike, wb8vge
> >
> > “The trouble with quotes on the Internet is that you never know if they
> are genuine”
> >
> > —Abraham Lincoln
> >
> >> On Feb 28, 2019, at 2:27 PM, MadScientist <dukeshifi@comcast.net>
> wrote:
> >>
> >> Thanks!
> >>
> >> I now find that, no matter how long I work on stuff like this, I never
> stop learning new things! I guess that’s part of the reason I do it.
> >>
> >> This Scout came to me with “no transmit”. It did receive.
> >>
> >> I made measurements on the driver stage, based on the schematic, and
> found the “base" voltages to be quite far off (greater than 0.7 volts base
> to emitter) so I assumed that the devices, which at the time I thought were
> bipolar transistors, according to the schematic so I assumed that they were
> bad, possibly from an oscillation problem, so I ordered replacements using
> the numbers on the devices that were in the radio. I had no reason to
> question whether they were bipolar or FET’s since the schematic was quite
> clear on this matter.
> >>
> >> Then, in an effort to test the calibration of my signal generator and
> attenuator for checking sensitivity of an Omni 6 I am repairing, I found
> that the Scout had very weak reception, only showing about S 9 at 0 dBm!
> You could still hear signals but touching the center of the unterminated
> coax connector only produced a barely noticeable hiss, not the screaming
> noise to which I am accustomed in my noisy basement shop.
> >>
> >> I concluded that the receiver also had problems. After a long and
> frustrating evening of following the signal from the antenna terminal to
> the IF board, through the filters etc., I found that the Jones filter was
> attenuating signals by about 40 dB!
> >>
> >> Thanks to a reference on one of the ham sites, I found a link to the
> patent for this filter. That gave a detailed schematic and technical
> description of the filter so I decided to try to fix it. I terminated the
> ends with 50 ohms and applied my spectrum analyzer’s sweep generator to the
> input and followed signal through the filter with the analyzer’s input.
> >>
> >> I didn’t have to go very far. Much to my surprise, the 0.01 uF ceramic
> capacitor coming from the input terminal to the first crystal was dropping
> 40 dB from one end to the other.
> >>
> >> Now I have never in my life seen an open ceramic capacitor, especially
> in low level circuits like this. I have seen them explode in TV high
> voltage supplies and in electron microscope supplies but never in small
> signal applications.
> >>
> >> I replaced the cap and got exactly the passband shown in the patent at
> all control voltages, with only a few dB insertion loss.
> >>
> >> Then after I reinstalled the filter into the radio I checked for TX
> drive at the input to the predriver transistor. I found that I had drive to
> burn! So the Jones filter was the culprit all along!
> >>
> >> Put this one into the archive…
> >>
> >> Gary
> >>
> >> W0DVN
> >>
> >
> > _______________________________________________
> > 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
>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|