[R-390] R-390a Image problem?
Bob Camp
ham at cq.nu
Sat Oct 20 21:27:16 EDT 2007
Hi
I sure would start checking grounds. Pull the modules and the coax
connectors. Make sure everything (including the inside of the antenna
relay) is shiny and making good contact.
Bob
On Oct 20, 2007, at 7:03 PM, Tony Casorso wrote:
> Hi Bob,
>
> That has occurred to me. The only thing is that none of my other
> radios do this on the same antenna, including my R-392. Plus, the
> signal strength is 40db on the meter. I didn't expect the R-390a to
> be weak in this area.
>
> 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: 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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