[R-390] R-390a Image problem?
Jon Schlegel
ews265 at rochester.rr.com
Sun Oct 21 14:26:24 EDT 2007
Tony,
What are stage DC voltages doing?
Also, can you reproduce the behavior with the sig gen at the input
instead of KNUS's megavolt/meter signal. If so, conditions would be
more controllable. You could easily see behavior over level change, etc.
Jon
At 12:11 PM 10/21/2007 -0600, you wrote:
>Hi all,
>
>I looked at it with the spectrum analyzer this morning and I did not
>see any oscillation. What I did see is that I have over 100Mv of
>signal from the KNUS broadcast station at the balanced antenna
>terminals. It is reduced to about a quarter of that by the antenna
>circuits (tuned to 3.3Mhz) so 20+ millivolts is going into the RF
>amplifier. There is no visible signal at the second harmonic (3.3
>Mhz) going into the RF stage. At the grid of the first mixer with
>the receiver tuned to 3.3Mhz, the broadcast band signals including
>the huge KNUS signal are gone (below the floor of my spectrum
>analyzer) but there is about a 1 millivolt signal at 3.3Mhz. It
>would appear that some kind of non-linearity in the RF stage is
>creating a strong second harmonic in the RF stage.
>
>Tony
>
>
>----- Original Message ----- From: "DW Holtman" <tubestuff at comcast.net>
>To: "Bob Camp" <ham at cq.nu>; "Tony Casorso" <canthony15 at msn.com>
>Cc: <r-390 at mailman.qth.net>
>Sent: Saturday, October 20, 2007 6:28 PM
>Subject: Re: [R-390] R-390a Image problem?
>
>
>>Hello,
>>
>>I also have a 50KW broadcast station in my area. It causes problems
>>on both of my R-390A's, 51S-1 and R-392. The cross over distortion
>>is mostly heard in the broadcast bands. I built a highpass filter
>>with about a 3MHZ roll off. Put it in series with the antenna lead,
>>going into the multicoupler and it works great. Ended the problem,
>>can still receive broadcast bands with the filter inline because
>>they are so strong.
>>
>>Best,
>>DW Holtman
>>WB7SSN
>>
>>----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>To: "Tony Casorso" <canthony15 at msn.com>
>>Cc: <r-390 at mailman.qth.net>
>>Sent: Saturday, October 20, 2007 4:21 PM
>>Subject: Re: [R-390] R-390a Image problem?
>>
>>
>>>Hi
>>>
>>>By any chance are we chasing a ghost here?
>>>
>>>I used to have a 50KW AM station a stones throw away from my
>>>back yard. My long wire could get a reading on a Bird Termline
>>>with a good matchbox in between. It was always amazing to me
>>>just how different radios would and would not pick up which
>>>harmonics of that station.
>>>
>>>See if you can get a signal generator you trust. Check the radio
>>>and see what it's really doing. If the front end of the radio is
>>>running ok, and it's properly aligned, there may not be anything
>>>wrong with the radio.
>>>
>>>Bob
>>>
>>>On Oct 20, 2007, at 1:13 PM, Tony Casorso wrote:
>>>
>>>>I just finished checking the injection level at the first mixer.
>>>>It seems more than adequate at 1 volt rms but I don't really know
>>>>what is supposed to be. First mixer cathode is at about 8.5
>>>>volts (manual says 9.7).
>>>>
>>>>I have a spectrum analyzer over in the corner. I might be able
>>>>to use it to look for oscillations in the RF stage. Maybe I'll
>>>>have time later today.
>>>>
>>>>Tony
>>>>
>>>>
>>>>
>>>>----- Original Message ----- From: "Jon Schlegel" <ews265 at rochester.rr.com>
>>>>To: <r-390 at mailman.qth.net>
>>>>Sent: Saturday, October 20, 2007 10:55 AM
>>>>Subject: Re: [R-390] R-390a Image problem?
>>>>
>>>>
>>>>>Tony,
>>>>>
>>>>>Some further thoughts. Again, I'm not really familiar with
>>>>>the 390 yet so these are just some general ideas.
>>>>>
>>>>>Could the screen or suppressor/cathode of the RF amp be
>>>>>lifting off of RF ground (bad C229, C227?). This could cause
>>>>>some instability. Another possibility along these lines is a
>>>>>problem with the parasitic suppressor, E212, or something
>>>>>downstream from it. E212's presence in the design is tip off
>>>>>that the stage could be *hot*. If the stage is oscillating at
>>>>>some frequency that's not immediately obvious (VHF range?), a
>>>>>non-linearity could be created that might generate the 2nd
>>>>>harmonic of 1650 kHz that you are seeing. You could try to
>>>>>*sniff* the existence of an oscillation using other receiver(s)
>>>>>you may have on hand. Use a short wire probe as the search
>>>>>receiver's antenna, put it next to the RF tube and start
>>>>>searching for any signs of life.
>>>>>
>>>>>Regards,
>>>>>Jon
>>>>>
>>>>>
>>>>>
>>>>>At 09:42 PM 10/19/2007 -0600, you wrote:
>>>>>>Checking the injection levels is a good idea. I'll try that tomorrow.
>>>>>>
>>>>>>Tony
>>>>>>
>>>>>>
>>>>>>>From: Bob Camp <ham at cq.nu>
>>>>>>>To: Tony Casorso <canthony15 at msn.com>
>>>>>>>CC: <R-390 at mailman.qth.net>
>>>>>>>Subject: Re: [R-390] R-390a Image problem?
>>>>>>>Date: Fri, 19 Oct 2007 23:06:32 -0400
>>>>>>>
>>>>>>>Hi
>>>>>>>
>>>>>>>Stage voltages are a good idea if you have a VTVM. With an
>>>>>>>RF probe you can also check the injection levels at the
>>>>>>>mixers. Low drive to a mixer can cause all sorts of odd
>>>>>>>things. Your 17 MHz crystal oscillator may be a bit "sick" for instance ....
>>>>>>>
>>>>>>>Another stupid thing to check - did somebody put a couple
>>>>>>>of diodes up in the antenna relay to "overload protect" the radio?
>>>>>>>
>>>>>>>Bob
>>>>>>>
>>>>>>>
>>>>>>>On Oct 19, 2007, at 10:48 PM, Tony Casorso wrote:
>>>>>>>
>>>>>>>>I see what you mean about AGC. I checked it anyway. -11 volts on a
>>>>>>>>strong local station. I swapped tubes with no improvement.
>>>>>>>>I wonder if the stage bias could be wrong? I guess I
>>>>>>>>should measure the voltages just to be sure.
>>>>>>>>
>>>>>>>>When I said 1st RF stage, I guess I forgot this was an
>>>>>>>>R-390a. Part of the cost reduction removed one of the RF
>>>>>>>>stages didn't it? There is only one.
>>>>>>>>
>>>>>>>>The antenna is a 100 foot longwire.
>>>>>>>>
>>>>>>>>Tony
>>>>>>>>
>>>>>>>>
>>>>>>>>----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>>>>>>>To: "Tony Casorso" <canthony15 at msn.com>
>>>>>>>>Cc: <R-390 at mailman.qth.net>
>>>>>>>>Sent: Friday, October 19, 2007 8:36 PM
>>>>>>>>Subject: Re: [R-390] R-390a Image problem?
>>>>>>>>
>>>>>>>>
>>>>>>>>>Hi
>>>>>>>>>
>>>>>>>>>I'd swap it for another tube just in case.
>>>>>>>>>
>>>>>>>>>With no input to the radio, there should be pretty much no
>>>>>>>>>AGC to the front end. It may be the problem, but only indirectly.
>>>>>>>>>
>>>>>>>>>If the radio is fine with no front end tube, you
>>>>>>>>>probably have one very large antenna.....
>>>>>>>>>
>>>>>>>>>Bob
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>On Oct 19, 2007, at 10:17 PM, Tony Casorso wrote:
>>>>>>>>>
>>>>>>>>>>Aha! The 1st RF tube is correct (6DC6) but when I remove
>>>>>>>>>>the tube and put a small cap from pin1 to pin 5 (grid to
>>>>>>>>>>plate), the receiver works fine and NO image. I'm going
>>>>>>>>>>to check the AGC to that stage.
>>>>>>>>>>
>>>>>>>>>>Tony
>>>>>>>>>>----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>>>>>>>>>To: "Tony Casorso" <canthony15 at msn.com>
>>>>>>>>>>Cc: <R-390 at mailman.qth.net>
>>>>>>>>>>Sent: Friday, October 19, 2007 7:13 PM
>>>>>>>>>>Subject: Re: [R-390] R-390a Image problem?
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>>Hi
>>>>>>>>>>>
>>>>>>>>>>>I'd check the grounds as Jon suggested. The R390 can pick
>>>>>>>>>>>up "stuff" from the power line pretty easily. The AC
>>>>>>>>>>>line filter works both ways with a loose ground ...
>>>>>>>>>>>
>>>>>>>>>>>Next up would be to start swapping front end tubes. You
>>>>>>>>>>>may find that you simply have a defective tube. You may
>>>>>>>>>>>also find that somebody "improved" the design by putting
>>>>>>>>>>>in a tube that didn't belong there.
>>>>>>>>>>>
>>>>>>>>>>>Bob
>>>>>>>>>>>
>>>>>>>>>>>On Oct 19, 2007, at 8:58 PM, Tony Casorso wrote:
>>>>>>>>>>>
>>>>>>>>>>>>Hi Bob, I'm using the balanced input. I bought a twinax to BNC
>>>>>>>>>>>>adapter so one side of the balanced input is grounded.
>>>>>>>>>>>>
>>>>>>>>>>>>Same antenna doesn't bother the R-392.
>>>>>>>>>>>>
>>>>>>>>>>>>Tony
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
>>>>>>>>>>>>To: "Tony Casorso" <canthony15 at msn.com>
>>>>>>>>>>>>Cc: <R-390 at mailman.qth.net>
>>>>>>>>>>>>Sent: Friday, October 19, 2007 6:52 PM
>>>>>>>>>>>>Subject: Re: [R-390] R-390a Image problem?
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>>>Hi
>>>>>>>>>>>>>
>>>>>>>>>>>>>Which antenna input are you running into? The situation you
>>>>>>>>>>>>>describe would be pretty typical if you run a long antenna into
>>>>>>>>>>>>>the "unbalanced" input.
>>>>>>>>>>>>>
>>>>>>>>>>>>>Bob
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>On Oct 19, 2007, at 8:31 PM, Tony Casorso wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>>Hi everyone. This is my first post to the list
>>>>>>>>>>>>>>although I've been following it for a long time now. A
>>>>>>>>>>>>>>few months back I bought a 67 EAC R-390a. The only
>>>>>>>>>>>>>>problem I had was an open Z-503 AGC coil. I replaced
>>>>>>>>>>>>>>that and did an alignment and the radio seemed to be
>>>>>>>>>>>>>>working real well. Sensitivity was very good on all bands.
>>>>>>>>>>>>>>Recently I've noticed broadcast stations coming through in the
>>>>>>>>>>>>>>3Mhz band. A local station on 1650KHz is about 40db
>>>>>>>>>>>>>>at 3300KHz on the R-390a. I don't hear it on
>>>>>>>>>>>>>>my R-392. Even moving the 2-4MHz RF slug rack
>>>>>>>>>>>>>>by hand, I still hear the station (although it does
>>>>>>>>>>>>>>get a bit quieter). There are several other stations
>>>>>>>>>>>>>>coming through as well on other frequencies. I didn't
>>>>>>>>>>>>>>notice anything odd when I aligned it, everything
>>>>>>>>>>>>>>seemed to peak like it should.
>>>>>>>>>>>>>>Looking around at other frequencies with my
>>>>>>>>>>>>>>signal generator, I started noticing all kinds of
>>>>>>>>>>>>>>harmonic responses, but that is probably (at least
>>>>>>>>>>>>>>to some degree) just my signal generator (a
>>>>>>>>>>>>>>Boonton 102C). I'm pretty sure something is wrong here but I'm
>>>>>>>>>>>>>>scratching my head trying to think of
>>>>>>>>>>>>>>a good explanation. If the BC station harmonic was
>>>>>>>>>>>>>>that bad, I'd hear it in my other radios I would think.
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>Ideas anyone? How do I track this one down?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>Thanks,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>>Tony
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>>>>>>
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>>>>>
>>>>>
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