[R-390] Got my R-390A working great.

Sun Dec 1 17:08:10 EST 2019

Hello 390 friends,

Well, I did some more testing today and played with the IF gain internal 
pot. Turning the gain down definitely improves the S/N ratio, but not by 
a huge amount. Still it is very significant. Someone asked about 7 MHz 
and I saw much worse sensitivity on 7 MHz vs the other bands. I tried a 
4 kHz band width and saw about -121 dBm in 4 kHz on most bands. (-121 
dBm = 0.2 microvolts.)   8 MHz was -121 as was 26 MHz. 7.5 MHz (middle 
of the band) showed only -117 dBm at 4 kHz. (-117 dBm = 0.32 microvolts) 
The same crystal is used on 27 MHz and my sensitivity there at 4 kHz was 
a bit worse than other bands, but not too bad at -120 or maybe -119 dBm. 
(-119 dBm = 0.25 microvolts)  Then I remembered that my 15 MHz crystal 
for 7 & 27 MHz was NG., and I had dropped in a 7.500 MHz crystal and it 
worked, but not so well.  I scrounged around my junk box and asked my 
brother and he does not have a 15 MHz crystal  either. Someone on this 
list had one and offered it at $8, (He said it was a tad off frequency) 
so I definitely need it.

Looking at the RF output of the crystal oscillator module, 7 and 27 MHz 
have very low output with the wrong crystal installed. It looks like 7 
MHz does worse than 27 MHz.  I need the proper 15 MHz crystal!

If I use a wider bandwidth or a narrower one, those sensitivity numbers 
change and I get better sensitivity at 2 kHz and 1 kHz. Sensitivity 
drops a bit if I measure in an 8 or 16 kHz bw.  That all looks OK.

I ended up turning the IF gain way back and an S9 signal (-73 dBm)  
reads about 54 dB on the carrier meter. The linearity of the carrier 
meter is not perfect, but at least S-9 is good at 54 dB when you figure 
6 dB per S- unit.

This R-390A is just about ready to go!

73

Dave K1WHS

On 11/30/2019 6:13 PM, Alan Victor wrote:
> One other question Dave,
>
> Does your sensitivity track the IF bandwidth for all bandwidths? 
> Appears to be the case and that is the way it should be unless there 
> is post detection noise present. I had that issue in a HB rx I built 
> and required a post detection filter!
>
> 73 Alan W4AMV
>
>
> On Saturday, November 30, 2019, Alan Victor <amvictor at ncsu.edu 
> <mailto:amvictor at ncsu.edu>> wrote:
>
>     Curious Dave,
>
>     What sensitivity do you measure on the 40 meter band say around
>     7.1 MHz.  That band uses the 3rd multiple of the LO and struggles
>     to do as well if mixer conversion gain suffers.
>
>     Alan W4AMV
>
>     On Saturday, November 30, 2019, David Olean <k1whs at metrocast.net
>     <mailto:k1whs at metrocast.net>> wrote:
>
>         Hello BA enthusiasts
>
>         I have been slowly working on getting an R-390A running. I was
>         side tracked for a short time with some carpentry, but had
>         everything working except the carrier meter. The meter was
>         pegged to the left at all times. Funny thing because when I
>         first started work on the R-390A, that meter worked. (?)  Well
>         I finally got some time to work on it again, and found the
>         problem with the meter,  a bad bypass cap in the cathode
>         circuit of the 4th IF amplifier. I did not suspect it as this
>         was a 1967 EAC contract unit and it had modern poly caps in
>         it. Of course I assumed those new looking parts were fine and
>         so I looked everywhere else at first.   The shorted cap looked
>         like a 3 ohm resistor.
>
>         After getting everything running, I decided to tweak up the IF
>         transformers. Just about every slug was badly stuck. I managed
>         to get them sorta loose, but there must be something that can
>         be put on them to make them turn more freely.  Any ideas?
>         Tuning the 455 kHz IF strip improved things a bit.  Going on
>         the higher bands, at 26.5 MHz, I was seeing -125 dBm at 1 kHz
>         BW, and -123 dBm at 2 kHz bandwidth for a 10 dB S/N ratio.
>         This is better than 0.3 uV.
>
>         I listened on the BC band and with an 8 kHz filter, that
>         carrier meter was always up near 100! It hardly ever moved. I
>         had a good beverage antenna on it and could not believe the
>         signal strength. So now I have an R-1051B, an R-390 and a 390A
>         finished. The next step is to work on a couple of R-392s. When
>         I get those running I have to choose which one I will keep as
>         I don't have much room for all of them. What a quandary! I am
>         leaning towards keeping the R-390 from the first Collins contract.
>
>         Dave K1WHS
>
>
>         ______________________________________________________________
>         R-390 mailing list
>         Home: http://mailman.qth.net/mailman/listinfo/r-390
>         <http://mailman.qth.net/mailman/listinfo/r-390>
>         Help: http://mailman.qth.net/mmfaq.htm
>         <http://mailman.qth.net/mmfaq.htm>
>         Post: mailto:R-390 at mailman.qth.net <mailto:R-390 at mailman.qth.net>
>
>         This list hosted by: http://www.qsl.net
>         Please help support this email list:
>         http://www.qsl.net/donate.html
>