Newbie Issues


Ed Gable
 

Hello.  New to group.  Just built a Blue Jumper and the TX took right off with 5W into 50 ohms. From reading past emails I too had trouble with Q2 oscillating.  I had a 40 year old NOS MPF102 in stock but that also brought no joy with tight feedback turns and  22 pf added.  Tried a U310 and it took right off and oscillated but I think it's too weak.  I hear a very weak hiss even though audio amplifier chain is working OK.  I have my TEK scope on TP1 and see a nice clean 7 Mhz signal at 0.25Vp-p signal that is smoothly controlled by REGEN.  Seems to me that might be too low.  I can hear FT8 signals.  Using a HP-8640 sig gen my minimal discernable is -70 dBm, kinda deaf!  The RX current draw is only 10 Ma, not the 23 Ma. as suggested.  Is that because there is no audio signal (hiss) in output stage?  The ATTEN control seems to work properly.  Is a U310 a good enough substitute for what seems to be a successful J310?  (I had a U310 in my junk box)  Any ideas from you experienced Jumpers out there?  73,  Ed Gable  K2MP


N7RKC, Mike
 

Hi,  I replaced the MPF102 with a Fairchild NOS unit I had in my junk drawer.
I then replaced the C-20 Cap with a 0612 COG microwave grade cap.
The size of the cap in proximity to the other components has a large effect on sensitivity & the tuning range.
Receiver now works like a dream.  Minimum detectable signal is measured at 3uV with a HP 8648 Signal Gen.
Hopes that helps
//Michael Taylor - N7RKC  (Agent 076)


On Thursday, May 20, 2021, 12:52:53 PM MDT, Ed Gable <egable@...> wrote:


Hello.  New to group.  Just built a Blue Jumper and the TX took right off with 5W into 50 ohms. From reading past emails I too had trouble with Q2 oscillating.  I had a 40 year old NOS MPF102 in stock but that also brought no joy with tight feedback turns and  22 pf added.  Tried a U310 and it took right off and oscillated but I think it's too weak.  I hear a very weak hiss even though audio amplifier chain is working OK.  I have my TEK scope on TP1 and see a nice clean 7 Mhz signal at 0.25Vp-p signal that is smoothly controlled by REGEN.  Seems to me that might be too low.  I can hear FT8 signals.  Using a HP-8640 sig gen my minimal discernable is -70 dBm, kinda deaf!  The RX current draw is only 10 Ma, not the 23 Ma. as suggested.  Is that because there is no audio signal (hiss) in output stage?  The ATTEN control seems to work properly.  Is a U310 a good enough substitute for what seems to be a successful J310?  (I had a U310 in my junk box)  Any ideas from you experienced Jumpers out there?  73,  Ed Gable  K2MP


Jim, N5IB
 
Edited

Hi Ed,

Since a regen is most sensitive and selective right at the onset of oscillations your detector is doing its job and its level is good.

Are your red/green LEDs working correctly? They consume 10 mA or so of that 20+

It may be tough to get a good MDS measurement because the Rx input impedance is more than likely not a good match to the sig gen.
The real test of sensitivity is can you her all the way down to the ambient band noise.

Do I understand you correctly that you hear no background hiss or noise but still hear signals?
What are the voltages measured at the pins of U1?

U-310 ought to be fine as a sub for J-310.
If I'm not mistaken the U-310 is good well into the UHF range, since its noise figure has a 450 MHz specification. Its current and threshold voltage specs are in a good range.

Jim, N5IB


Ed Gable
 

Hello Jim:  Thank you for your prompt and helpful response to my plea for assistance to my BJBlue issues.  I regret I've been tied down with family needs but am now back and the Jumper is working great.  I'll be brief (yeh, good luck with that :>)   My RX issue was all with Q2.  First MPF-102 was DOA.  Second 40 year old junk box 102 oscillated was also problematic.  Read on the 4State news group of J310's working well and found a U310 in the junk box which was the whole problem.  It worked right away, 7 Mhz looked OK on TP1, but really unstable, noisy and rough sounding signals and no hiss but more of a buzzing sound.  I have an older but nice HP spectrum analyzer with a rarely used FET Hi-Z test probe.  With that on TP1, poof,  there it was a nice 300 MHz spurious band of junk.  I got a J310 from a friend instead of that UHF rated U310 I had been using and everything instantly fell in place with 22 pf installed and the 4 turn link now readjusted from super tight to "normal."   You asked about the LED current.  I actually had not wired the LED's yet but now running about 24 Ma in RX with some peaks when pushing audio harder.  Yes, I'm hissing when I want to and hearing background noise with no signal is the norm.  Frequency range is good and I'm tweaking for linearity over the range but probably as good as it can or needs to be.  So the end result is good, it's been a fun project with just some bad luck in the beginning.  Thanks for all that you do for the group.  Warm regards, 73  Ed Gable  k2mp

-----------------------------------------

From: "Jim, N5IB"
To: main@4SQRP.groups.io
Cc:
Sent: Thursday May 20 2021 7:43:45PM
Subject: Re: [4SQRP] Newbie Issues

[Edited Message Follows]

Hi Ed,

Since a regen is most sensitive and selective right at the onset of oscillations your detector is doing its job and its level is good.

Are your red/green LEDs working correctly? They consume 10 mA or so of that 20+

It may be tough to get a good MDS measurement because the Rx input impedance is more than likely not a good match to the sig gen.
The real test of sensitivity is can you her all the way down to the ambient band noise.

Do I understand you correctly that you hear no background hiss or noise but still hear signals?
What are the voltages measured at the pins of U1?

U-310 ought to be fine as a sub for J-310.
If I'm not mistaken the U-310 is good well into the UHF range, since its noise figure has a 450 MHz specification. Its current and threshold voltage specs are in a good range.

Jim, N5IB