K3s IF-Out level


Daniel Sloss
 

What is a normal signal output level from the IF-out jack (going to the P3)? I mistakenly (I think) connected my RigExpert antenna analyser to the coax for the K3s IF-Out instead of the receive antenna coax. The P3 signal has dropped right off, so I'll have to see if I blew a component on the RF board. Any suggestions where to start? 73 VK2NAD


Paul G4KZY
 

Hi Daniel,

I have seen it mentioned that there is about a 6dB loss from the RF in to the IF out without the preamp switched on.  This would increase to say 4dB gain with the preamp selected.  There is a level specified in the P3 menu which defaults to -5.8dB and which allows you to accurately set the loss from the K3 antenna to the IF out connector.

It is not clear whether your Rig Expert was inadvertently connected to the K3s IF Out or the P3 input.  You could check the P3 input if you have a signal generator.  If you have a second HF receiver you could check the K3s IF out for signal level.

The Rig Experts seem to produce about 13dBm or 20mW of power which is quite high for a receiver but I would be surprised if it was high enough to cause damage through immediate power dissipation. 

The P3 schematic shows that it uses a small 1:4 transformer on its input and can also be fed by what looks like a bias-tee 5V signal.  I would look here for signs of damage.

The IF out on the KXV3B comes directly from the K3s main board connector J2 where it arrives having been buffered by Q10.  A bad Q10 could easily cause loss of signal strength.

Good luck with it.

Paul G4KZY


Daniel Sloss
 

G'day, Paul. Many thanks for taking the time to share your thoughts. I'm 90pct sure I connected the RigExpert to the K3s IF-out, thinking I had the coax from the receive rx-in antenna. The P3 seems to be working, although I need to connect it to some other transceiver that has an IF-out. An antenna connected directly to the P3 IF-in provides more amplitude than when I connect the K3s IF-out (even the strong signals read well below S-0 on the P3). The K3s seems fine otherwise. I've been poring over the K3s schematics and might have to poke around J2 with an o-scope to see where the signal disappears. Mind you, with my level of electronic troubleshooting, the equivalent of a mechanic with a hammer.

Thanks again. 73. Dan VK2NAD


Daniel Sloss
 

Hi Paul. Tracing voltage in the K3s shows roughly 12V all the way through Q10 and the front side of C68, but nothing on the J2 side of C68. I connected the K3s IF-out to my KX2 antenna input and searched around and could not find a signal. I think the K3s buffered IF-output is supposed to be around 8.215MHz. I don't know how to check/trace RF levels. Reading up on that now. Dan


Paul G4KZY
 

Hi Dan,

If you have more than a few volts on the source of Q10 then it indicates that Q10 is damaged.  The source is the node with C69, R9 and Q10 connected.  So if there is 12V across C68 you have a problem.  You probably have in excess of 50mA flowing through R9, assuming that hasn't failed too, as it would be dissipating more than 1/2 watt like this, and probably warm to the touch.

Remove Q10, check the resistance of R9 and fit a new device for Q10 and, if necessary, R9.  While Q10 is out of the circuit it is worth checking the value of R8 and R89 too.  With a working Q10 I would expect the voltage at R9/C68 to be in the region of 2V or so.

Good luck and 73,

Paul G4KZY


Ray Maxfield
 

Great incite ! 

WA6VAB  Ray K3

 

 

From: Paul G4KZY
Sent: Saturday, September 25, 2021 6:21 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3s IF-Out level

 

Hi Dan,

If you have more than a few volts on the source of Q10 then it indicates that Q10 is damaged.  The source is the node with C69, R9 and Q10 connected.  So if there is 12V across C68 you have a problem.  You probably have in excess of 50mA flowing through R9, assuming that hasn't failed too, as it would be dissipating more than 1/2 watt like this, and probably warm to the touch.

Remove Q10, check the resistance of R9 and fit a new device for Q10 and, if necessary, R9.  While Q10 is out of the circuit it is worth checking the value of R8 and R89 too.  With a working Q10 I would expect the voltage at R9/C68 to be in the region of 2V or so.

Good luck and 73,

Paul G4KZY

 


Daniel Sloss
 

Thanks, Paul. It's not easy to diagnose over the internet, especially when my descriptions aren't precise. The voltages I mentioned were not "across" components; rather between the circuit and the chassis ground, but there is certainly more than a few volts across C68. I'll do more investigating but you're diagnosis is very helpful.

I've had a look for replacement Q10 JFETs; the J309 isn't produced anymore so I think I need to order one or the other of the J310s.
https://au.element14.com/on-semiconductor/mmbfj310/transistor-jfet-n-sot-23/dp/1095137

Anyway, I'm patient and persistent, so if I don't damage more components, I'll get there eventually. It will take some time given the way packages are (not) moving around the world.

73. Dan VK2NAD


Paul G4KZY
 

Hi Dan,

From the data sheet the J310 looks like a reasonable alternative.  It has a higher Gate Source Cutoff Voltage than the J309 which suggests that the DC source voltage will be higher than the J309, leading to the source voltage (voltage across R9) going up from about 1.3 V to maybe 2.5 V and the current through the FET and R9 will therefore increase from about 6 mA to about 11 mA.  R9 will dissipate more power but it should still be under 30 mW so not really a concern.  Q10 is a source follower configuration amp so the voltage gain is (just below) unity and the change in the DC conditions should not materially affect the small signal gain.

I'd be interested to hear how you get on.

73,

Paul G4KZY


Ray Maxfield
 

https://www.electronic-spare-parts.com/descript/j/j_309.htm

 

Found this site…… WA6VAB  Ray

 

 

From: Paul G4KZY
Sent: Monday, September 27, 2021 1:32 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3s IF-Out level

 

Hi Dan,

From the data sheet the J310 looks like a reasonable alternative.  It has a higher Gate Source Cutoff Voltage than the J309 which suggests that the DC source voltage will be higher than the J309, leading to the source voltage (voltage across R9) going up from about 1.3 V to maybe 2.5 V and the current through the FET and R9 will therefore increase from about 6 mA to about 11 mA.  R9 will dissipate more power but it should still be under 30 mW so not really a concern.  Q10 is a source follower configuration amp so the voltage gain is (just below) unity and the change in the DC conditions should not materially affect the small signal gain.

I'd be interested to hear how you get on.

73,

Paul G4KZY

 


Keith_WE6R <keithtrinity@...>
 

It is rare for the Q10 circuit to get damaged, but I have seen it happen if energy comes in the IF OUT line.
Q10 is available from us, Elecraft # E580042 
Also we get it from DigiKey; MMBFJ309LT1GOSTR-ND https://www.digikey.com/en/products/detail/onsemi/MMBFJ309LT1G/919590 

Make sure R8 is at 13k (we changed it early on). Our # E500374  https://www.digikey.com/en/products/detail/panasonic-electronic-components/ERJ-6GEYJ133V/83068
Check the other resistors in that circuit, I think you can ohm them in-circuit.
Keith WE6R Elecraft K3/K4 Tech


Daniel Sloss
 

Thank you, Keith. Energy in the IF Out is what I think I did, inadvertently, with the RigExpert when I connected to the wrong coax lead. The MMBF J309 chip seems to be out of stock everywhere and no longer produced. Do you think the J310 chip would substitute? I'll try to order a J309 from you guys, but the US Postal Service has suspended parcel deliveries to Australia due to Covid. It's a mad world. Many thanks for jumping in. 73. Dan VK2NAD