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RA17 spurious signal

Allan
 

I decided to try out one of my RA17 receivers. This was realigned and worked very well a few years back but of course is steadily deteriorating.
Tuning to Radio 4 on 198KHz I found a strong beat note as if the BFO was turned on (which it wasn't), but by tuning slightly to zero beat reception was OK.
Today I decided to work out why there was a beat note. Disconnecting the aerial proved there was a carrier sitting on 200KHz and by experimenting with a signal generator I proved the signal was being generated internal to the receiver and was equivalent to 1mV of aerial signal.
To do this I noted the S-meter reading of the 200KHz signal as 55uV then tuned the signal generator to 210KHz and noticed that 55uV could be obtained from 1mV of aerial signal.
Before I dig out the manual which is of course in one of those inaccessible bookcases I wonder if anyone can explain the spurious signal.
Allan G3PIY

Alf_Fisher
 

Hi Allan,

I've been working on a RA17 that was remarkably dead.
On close inspection I found that a large number of valve heaters were not on. I traced it to a dry jointed link between two tags where the connections to the 2nd VFO are made.  I re-soldered the link and after half a minute the set burst into life.

Regarding your discovery, I have heard this beat note but on reading the manual, on page 9 it quotes its frequency range as 1 -30 Mc/s. Range extends to 0.5Mc/s with slight degradation of performance. 
So going down to 198kc/s is outside its normal frequency range so anything can happen.
There is a 1Mc/s xtal oscillator that it used as a reference to produce the 100kc/s calibration check points.  Its probably the 2nd harmonic on that which you are receiving.
You could try pulling the 1Mc/s xtal and see if the beat disappears!

73, Alf G3WSD



On 30/09/2018 11:02, Allan via Groups.Io wrote:
I decided to try out one of my RA17 receivers. This was realigned and worked very well a few years back but of course is steadily deteriorating.
Tuning to Radio 4 on 198KHz I found a strong beat note as if the BFO was turned on (which it wasn't), but by tuning slightly to zero beat reception was OK.
Today I decided to work out why there was a beat note. Disconnecting the aerial proved there was a carrier sitting on 200KHz and by experimenting with a signal generator I proved the signal was being generated internal to the receiver and was equivalent to 1mV of aerial signal.
To do this I noted the S-meter reading of the 200KHz signal as 55uV then tuned the signal generator to 210KHz and noticed that 55uV could be obtained from 1mV of aerial signal.
Before I dig out the manual which is of course in one of those inaccessible bookcases I wonder if anyone can explain the spurious signal.
Allan G3PIY
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Michael O'Beirne
 

Allan
 
The RA17 is only specified to tune down to IMHz at full spec and at a reduced spec down to 500kHz.  Below that you are into gurgles and odd things.  If you want to listen to anything below 500KHz you have to use a VLF converter such as the RA37 or RA137.  If you want more info on these mail me direct.  I have converters and the manuals.
 
73s
Michael
G8MOB
 

From: Allan via Groups.Io
Sent: Sunday, September 30, 2018 11:02 AM
To: wireless-set-no19@groups.io
Subject: [wireless-set-no19] RA17 spurious signal
 
I decided to try out one of my RA17 receivers. This was realigned and worked very well a few years back but of course is steadily deteriorating.
Tuning to Radio 4 on 198KHz I found a strong beat note as if the BFO was turned on (which it wasn't), but by tuning slightly to zero beat reception was OK.
Today I decided to work out why there was a beat note. Disconnecting the aerial proved there was a carrier sitting on 200KHz and by experimenting with a signal generator I proved the signal was being generated internal to the receiver and was equivalent to 1mV of aerial signal.
To do this I noted the S-meter reading of the 200KHz signal as 55uV then tuned the signal generator to 210KHz and noticed that 55uV could be obtained from 1mV of aerial signal.
Before I dig out the manual which is of course in one of those inaccessible bookcases I wonder if anyone can explain the spurious signal.
Allan G3PIY

Colin
 

They all do that. I think it's mixing with 2x the 100kHz IF. The tone is always 2kHz on radio 4, which is well outside the specified 500kc lower limit in the specs.
I usually leave the calibrator disconnected because it just wears out valves to no end - precision isn't that important when I'm using my fossils and if the set is well lined up, will be within 1kc through the range.
If you take out the 1MHz crystal, the whole shooting match stops working!

73,

Colin mm1aps.

AllanIsaacs
 

Thanks for the offer Michael but I made a converter for my Lime SDR which allows this to tune down to virtually zero frequency so I could use that if I was seriously interested in VLF reception with the RA17.

 

I have a Wavetek 2407 signal generator that’s been giving me trouble for a few years.

Today I noticed something odd. I’d assumed all the RF output range was bad, but today I noticed the output at 500MHz was perfect so I tried 400, 300, 200 then 100MHz.

At 100MHz the output was awful as if a dry solder joint was acting up and making the RF crackly.

I tuned back to 150MHz and it was perfect and by trial and error found it was bad at 137.499 but fine at 137.501.

For the first time I read the manual in detail and found the thing has three internally selectable RF chains. 10KHz to 10MHz, 10MHz to 137.5MHz and 137.5 to 550MHz.

The last is “straight through” but the lower frequencies include a mixer driven by a 512MHz oscillator where they split into two, get processed and then rejoin the “straight through” frequencies to give a range of 10KHz to 550MHz.

Somewhere in the mixer circuitry must be a bad capacitor or a dry joint.

Unfortunately the circuit board isn’t accessible when powered up so it means a lot of trial and error.

I wonder if anyone out there has worked on this sig genny??

Allan G3PIY


From: wireless-set-no19@groups.io [mailto:wireless-set-no19@groups.io] On Behalf Of Michael O'Beirne via Groups.Io
Sent: 30 September 2018 17:39
To: wireless-set-no19@groups.io
Subject: Re: [wireless-set-no19] RA17 spurious signal

 

Allan

 

The RA17 is only specified to tune down to IMHz at full spec and at a reduced spec down to 500kHz.  Below that you are into gurgles and odd things.  If you want to listen to anything below 500KHz you have to use a VLF converter such as the RA37 or RA137.  If you want more info on these mail me direct.  I have converters and the manuals.

 

73s

Michael

G8MOB

 

From: Allan via Groups.Io

Sent: Sunday, September 30, 2018 11:02 AM

To: wireless-set-no19@groups.io

Subject: [wireless-set-no19] RA17 spurious signal

 

I decided to try out one of my RA17 receivers. This was realigned and worked very well a few years back but of course is steadily deteriorating.
Tuning to Radio 4 on 198KHz I found a strong beat note as if the BFO was turned on (which it wasn't), but by tuning slightly to zero beat reception was OK.
Today I decided to work out why there was a beat note. Disconnecting the aerial proved there was a carrier sitting on 200KHz and by experimenting with a signal generator I proved the signal was being generated internal to the receiver and was equivalent to 1mV of aerial signal.
To do this I noted the S-meter reading of the 200KHz signal as 55uV then tuned the signal generator to 210KHz and noticed that 55uV could be obtained from 1mV of aerial signal.
Before I dig out the manual which is of course in one of those inaccessible bookcases I wonder if anyone can explain the spurious signal.
Allan G3PIY

Tony G4NGV
 

Hi. My ra17 is only specced down to about 500khz. It does the same on 198khz. Tony G4NGV


On Sun, 30 Sep 2018, 11:52 Allan via Groups.Io, <allan.isaacs=btinternet.com@groups.io> wrote:
I decided to try out one of my RA17 receivers. This was realigned and worked very well a few years back but of course is steadily deteriorating.
Tuning to Radio 4 on 198KHz I found a strong beat note as if the BFO was turned on (which it wasn't), but by tuning slightly to zero beat reception was OK.
Today I decided to work out why there was a beat note. Disconnecting the aerial proved there was a carrier sitting on 200KHz and by experimenting with a signal generator I proved the signal was being generated internal to the receiver and was equivalent to 1mV of aerial signal.
To do this I noted the S-meter reading of the 200KHz signal as 55uV then tuned the signal generator to 210KHz and noticed that 55uV could be obtained from 1mV of aerial signal.
Before I dig out the manual which is of course in one of those inaccessible bookcases I wonder if anyone can explain the spurious signal.
Allan G3PIY

AllanIsaacs
 

Thanks Tony

All these years and I never noticed the beat note on Radio 4.

Nice to know I don’t have to chase it down although tuning the MHz knob slowly across a strong signal tells me the filter has gone off slightly.

73 Allan G3PIY