[R-390] R-390a Image problem?
Tony Casorso
canthony15 at msn.com
Sun Oct 21 15:19:21 EDT 2007
Hi Jon,
No, I mean using the signal generator I have sine in and not-so-sine out. I
only use the KNUS signal for the spectrm analyzer because of the sig gen
harmonics. On the scope, The sign gen distortion is not really visible. A
little bit of asymmetry in the sine wave will give that second harmonic blip
on the analyzer. In one cycle of the input sine wave, the plate signal goes
up, comes down about half way, goes back up, comes fully down and back up to
the starting point.
I think this may be 'normal'. The plate circuit is tuned to 3.3 Mhz. When I
hit it with the 1.65 Mhz signal it tries to ring at 3.3 Mhz. This combines
with the 1.65 Mhz signal to produce the odd waveform I see.
I'm not sure what to make of this. Either it's normal, or I'm not getting
reasonable attenuation of the 1.65MHz signal through the antenna circuits
(tuned to 3.3MHz), or the Q of the mixer input circuit is too high, or it's
something else entirely.
This is a good reason to have more than one receiver.
Tony
----- Original Message -----
From: "Jon Schlegel" <ews265 at rochester.rr.com>
To: <r-390 at mailman.qth.net>
Sent: Sunday, October 21, 2007 1:03 PM
Subject: Re: [R-390] R-390a Image problem?
> Gee. DC readings look reasonable. I see why now you're hesitant about
> the generator. Yup. forgot about that.
>
> So Tony, when you say sine in - grunge out, you're talking about the
> KNUS's 1650 hHz signal as observed on the grid and plate of the RF amp.
> Just making sure were in synch at this point.
>
> Here's a thought. Watch your grid and plate signals on the scope and yank
> the 1st Mixer, V202.
>
> Jon
>
>
> At 12:49 PM 10/21/2007 -0600, you wrote:
>>Hi Jon,
>>
>>Actually, the signal generator has a fair amount of second harmonic in it
>>so the radio station is cleaner on the spectrum analyzer.
>>
>>I did switch to the signal generator and the scope and I can see the
>>distortion plain as day. Sine wave in, distorted out.
>>
>>Voltages are
>>
>>With no AGC applied:
>>Plate 201v
>>screen 178v
>>cathode 2.1v
>>grid -.5v
>>
>>With AGC applied:
>>Plate 215v
>>screen 201v
>>cathode .22v
>>grid -4.2v
>>
>>These was taken with a signal from the signal generator applied.
>>
>>Tony
>>
>>----- Original Message ----- From: "Jon Schlegel"
>><ews265 at rochester.rr.com>
>>To: <r-390 at mailman.qth.net>
>>Sent: Sunday, October 21, 2007 12:26 PM
>>Subject: Re: [R-390] R-390a Image problem?
>>
>>
>>>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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