Due to my own laziness...

[Opcom]

I ended up accepting a friend's offer to repair one of my R-390A's. Usually I fix things my self, but this gentleman has much experience on them and is only 20 miles away and to be straightforward, a set of this kind deserves an expert. I am very glad I accepted his kind offer.

The rig is a Stewart-Warner and has sensitivity of MDS -134dBm @ 2KHz.
I am not quite sure what that means (minimum detectable signal?), but -140 was the noise floor of the H/P network analyzer at work. The 0-100 "S" meter shows "10" at -93dBm

My friend has a couple of racks of the finest H/P gear. At home. Amazing what one can have for personal gear when one is -serious-. It was much a better idea that he repaired and aligned it than if I had done it.

drool now.. as my total cost for this was 6 new tubes and an antenna switch. The radio was previously given to me inoperative for repair or parts. All I can say is Texas has the best sto' 's. I owe my buddy big time for this.

I think I have "the shack receiver" now.  I can't wait to hook up the 40FT wire and tune around a bit. BTW the antenna tower project is on hold till the summer heat is gone.

[W1VD]

A brief explanation of MDS, blocking and two-tone DR testing:

http://www.w1vd.com/Receivermeasurementbasics.html

Tests on another R-390A:

http://www.w1vd.com/R-390A.html

The above measurement was made in the .1 bandwidth position...which wasn't actually the measured bandwidth. IIRC it was more like 300 - 400 Hz. That would make a bandwidth factor of 7 dB ... 400 Hz vs 2 kHz measurement. 

[WA3VJB]

Don't sweat your having outsourced some TLC for your R390A.
Now you have a receiver that's ready to go.

I've had three R390 and R390A experts care for the examples I use. Howard Mills, W3HM, has done a great job on two R390, and Chuck Rippel, WA4HHG, did a totally fine job on a high serial number, 1967 EAC R390A.

Both men also used the 2kc selectivity position as a "standard" for sensitivity measurements.  I don't find this (nor more narrow) setting a very practical basis to evaluate a receiver primarily used for the reception of AM.

Nonetheless, what I find is that the sensitivity is of less importance than a good alignment at being able to minimize any intermod and provide a real-world performance reference.

I had a Motorola that was extremely sensitive, but needed an alignment. It's practical performance was not very good compared to a 1966 EAC of average sensitivity but well-aligned. This was demonstrated by Greg, K3EWZ, who convinced me the first problems come not from a lack of sensitivity, but poor intermod performance.

All in all, these receivers are really satisfying for use on wholesome AM, even when a spec or two is a little sub-par.

You've perhaps seen this site:

http://r390a.com/

[Bill, KD0HG]

Don't use the coax 'wire' antenna input, always use the twinax balanced antenna input. Use a balun (best) or simply ground one pin to use it. The twinax connectors are common, used by some IBM computer systems.

You lose some front-end selectivity by using the wire antenna input.

[The Slab Bacon]

Don't use the coax 'wire' antenna input, always use the twinax balanced antenna input. Use a balun (best) or simply ground one pin to use it. The twinax connectors are common, used by some IBM computer systems.

You lose some front-end selectivity by using the wire antenna input.

If you're lucky, (and you've been livin right lately) you can even find adaptor connectors that go into the "twinax" connector, have one pin allready grounded, and the other one terminated into an SO-239. I have found several at local hamfests for somewhere around $1 in the miscellaneous junk boxes under the tables. Most people dont have a clue what they are so they just about give them away.

[WA1GFZ]

When I had an R390A I built the balun inside the twinax adapter.

[flintstone mop]

OK who was the tech or shop or Ham op who did this wonder???
I have heard a few good things about a Rick Mish.

Fred

[Opcom]

Francesco Ledda did it. He collects some rather special military radios and repairs them all himself. The 390 is simple compared to some of the radios he has. He also likes atomic clocks.

I was going to send them to Rick, but put it off for 3 years!..  I was afraid to crate them and risk destruction at the hands of a shipper. So I figured I woiuld never get around to it and they sat and sat.. Francesco lives 20 miles away.

[Opcom]

I have been noticing now that the set has been on for about 6 hours, that about every hour or so but intermittently, the signal seems to disappear. Turning the set to standby and back restores it sometimes, turning the set off for a few seconds and then back on always restores it.

NOTE I do not blame Francesco for this, he charged me nothing and was just going to get it working because it was really dead. He also found a bad cap. He did not spend the normal amount of time as he would on some of his rigs (weeks+ of burn in, tedious fiddling, etc..), he just did me a favor and got it back and did the book alignments. I am perfectly happy to work this little problem. I have isolated it to an area not depending on these functions (they still have effect): audio, bandwidth, BFO, RF gain, AGC, bandswitch.

I am in love with this radio. It reminds me of my first R-390A. Having it working and listening to all these stations through a Stromberg-Carlson 30W amp and S-C "Custom Four hundred" coaxial speaker is making me very happy. The plastic radios, even the TS-430, barely sound half as good. I want to fix my SX-28 now.

I am listening to radio havana on 6MHz at S+40 using a 40FT piece of wire 8FT off the ground. (the meter goes from 0 to 100 and this seems to reflect relative dB of carrier). I think this is the feed that must secretly be used for the TV news, they sure spout the same things. Time to change the channel, what a spewing of stuff they do from Havana. haha it's a free world I suppose.. WWV 5MHz comes in the same. This radio is really accurate!! the atomic clock on my wall changed at the exact moment the radio's WWV signal predicted!

So what about this meter-of-100dB-range anyway? I am not sure where "S9" is on this beast..

[w5omr]

So what about this meter-of-100dB-range anyway? I am not sure where "S9" is on this beast..

Hi, Patrick.  Long time no eQSO.

John Mohn/W5MEU (sk - R.I.P.) was about the best when it came to restoring R-390's and BC-610's.  At one time, I counted a dozen (or more) 390's and a smooth half-dozen '610's at his place.  One of each was to go to Bob/W5PYT.

Instead of giving S-meter readings, John would give Microvolt readings. 

Now, of course, this is always subjective and I don't mean to start a war, but *I* have always known 50uV to be equivalent to S-9.  When John said "your putting 135uV in over here..." that was a signal to be proud of!

The Hallicrafter R-274/SX-73 meter is calibrated in db.  -40, -30, -20, -10, 0, 10, 20, 40, 60, where -0- is ass'u'me'ed to be S-9.  10, 20 40 above 0 is _(xx)_db/S-9.

Hope that helps!

[Opcom]

So what about this meter-of-100dB-range anyway? I am not sure where "S9" is on this beast..

Hi, Patrick.  Long time no eQSO.

John Mohn/W5MEU (sk - R.I.P.) was about the best when it came to restoring R-390's and BC-610's.  At one time, I counted a dozen (or more) 390's and a smooth half-dozen '610's at his place.  One of each was to go to Bob/W5PYT.

Instead of giving S-meter readings, John would give Microvolt readings. 

Now, of course, this is always subjective and I don't mean to start a war, but *I* have always known 50uV to be equivalent to S-9.  When John said "your putting 135uV in over here..." that was a signal to be proud of!

The Hallicrafter R-274/SX-73 meter is calibrated in db.  -40, -30, -20, -10, 0, 10, 20, 40, 60, where -0- is ass'u'me'ed to be S-9.  10, 20 40 above 0 is _(xx)_db/S-9.

Hope that helps!

Hi Geoff! It has been a very long time.

According to the sensitivity tag on the radio and assuming 50 ohms to the coax input, S9 would be -97dBm and reside at the "40" on the meter of this radio. I can hear some signals clearly even though they are at 0 or 10.. imagine telling someone they are 30dB under S-9 and you have good copy! If the noise is 10 over S9, and so is the OM you are copying, what DO you say?

The level of background noise has alot to do with it so I am not sure S-9 means anything as a signal report unless compared to the background noise. Come to think of it, giving signal reports in uV or dB above the floor might be a good idea. But most hams might go "Huh?"

I have noticed that different MHz positions seem to pick up more background noise than others when the ant. is grounded (shorted). I've heard that it can be a result of a few "tired crystals" or a resistor in the band oscillator. Not touching anything..

Gee there is some nut ranting on 5070KHz.. must be hard into clipping his limiter, very loud audio. (03:14 zulu)

[Steve - WB3HUZ]

30 dB under 9 is about S4. On a quiet band, that's a good signal. On a noisy band, that's a PW signal.

You are correct, it's signal-to-noise ratio that really matters. Even giving out uV reports are somewhat nebulous since the antenna factor must be included. If you know that, then you can tell someone the actual field strength that is impinging your antenna (much more useful). But still not as useful as SNR.

So what about this meter-of-100dB-range anyway? I am not sure where "S9" is on this beast..

Hi, Patrick.  Long time no eQSO.

John Mohn/W5MEU (sk - R.I.P.) was about the best when it came to restoring R-390's and BC-610's.  At one time, I counted a dozen (or more) 390's and a smooth half-dozen '610's at his place.  One of each was to go to Bob/W5PYT.

Instead of giving S-meter readings, John would give Microvolt readings. 

Now, of course, this is always subjective and I don't mean to start a war, but *I* have always known 50uV to be equivalent to S-9.  When John said "your putting 135uV in over here..." that was a signal to be proud of!

The Hallicrafter R-274/SX-73 meter is calibrated in db.  -40, -30, -20, -10, 0, 10, 20, 40, 60, where -0- is ass'u'me'ed to be S-9.  10, 20 40 above 0 is _(xx)_db/S-9.

Hope that helps!

Hi Geoff! It has been a very long time.

According to the sensitivity tag on the radio and assuming 50 ohms to the coax input, S9 would be -97dBm and reside at the "40" on the meter of this radio. I can hear some signals clearly even though they are at 0 or 10.. imagine telling someone they are 30dB under S-9 and you have good copy! If the noise is 10 over S9, and so is the OM you are copying, what DO you say?

The level of background noise has alot to do with it so I am not sure S-9 means anything as a signal report unless compared to the background noise. Come to think of it, giving signal reports in uV or dB above the floor might be a good idea. But most hams might go "Huh?"

I have noticed that different MHz positions seem to pick up more background noise than others when the ant. is grounded (shorted). I've heard that it can be a result of a few "tired crystals" or a resistor in the band oscillator. Not touching anything..

Gee there is some nut ranting on 5070KHz.. must be hard into clipping his limiter, very loud audio. (03:14 zulu)

[w5omr]

[quote author=Opcom link=topic=21077.msg148944#msg148944
According to the sensitivity tag on the radio and assuming 50 ohms to the coax input, S9 would be -97dBm and reside at the "40" on the meter of this radio. I can hear some signals clearly even though they are at 0 or 10.. imagine telling someone they are 30dB under S-9 and you have good copy! If the noise is 10 over S9, and so is the OM you are copying, what DO you say?
[/quote]

Tell 'em "this ol' boat anchor is 50+ years old and I'm not sure how accurate the meter is, but I can hear ya head-n-shoulders above the noise, so you got a good Q-5 signal here, OM!"
;-)

In another thread/topic I was talking about putting an S-meter on an AR-88 (once owned by Bob/W5PYT that came to me via WD5JKO).  I remember when using that rx, with no meter, that the bottom line was, either I heard 'em.. or I didn't. 

I've since come to the conclusion that S-meters cause 'bias'. 

What -really- comes across in AM transmissions is 'audio'.  This is, after all "Amplitude" Modulation.  A properly modulated AM signal running 40 or 50w, will sound louder than a 100w signal that's only 40 or 50% modulated.  There might be more background noise, but the audio will punch through on the lower powered, properly modulated rig.

Back in the old days, the Johnson Viking Ranger was known as "The Magic Box"... that little bitty (comparatively speaking) transmitter packed more audio punch than any of it's +3db output counterparts.

Bottom line... if you can hear 'em, work 'em!

yeah, it's been a while.. I'm jonesing for a good buzzardly AM fest.  Were it not for a previous work commitment, I'd run over to San Antonio Labor Day weekend and fire up the 250TH rig.

[WA3VJB]

The two most useful technical references to signal strength are:

Strapping.

Piss-weak.


Everyone understands.

[Opcom]

I just use the meter to find the carrier at 0.1KC BW then open er up. Besides, real men leave the AGC off and use the RF gain control as intended. Here's its place in the dining room for now. It deserves the nice 30 watt amp and speaker cabinet.