[Boatanchors] Mixer Troubleshooting Question For my Homebrew Superhet Novice Receiver

[whitebear1122 at comcast.net]

Hi Bill, Thanks for your comments on the Mate for the Mighty Midget receiver.  Yes I’ve seen your web page on the MMMR.  Aren’t you the fellow that built it into a Heathkit 2’er cabinet?  And I seem to recall a CD disc for the main tuning dial.  It’s good to hear from someone who’s successfully built it.  

Thanks for the links to soldersmoke and gadgeteer, I’ll check them out.   

 

On the crystals, I have 3 crystals now so hopefully between them I can get it working.  These are the military crystals called out in the article.  The 3 should give me filtering for CW and SSB although I don’t have a clue how narrow it will really be.

 

Last night as I was drifting off to sleep I was still thinking over that mixer problem.  I started wondering if I didn’t have the SA set up right, and I wondered if I was over attenuating the signals.  I am not very familiar with spectrum analyzers, just bought a Rigol, and I’m using a 10x divide by oscilloscope probe plus I had a 10 dB external attenuator.  I removed the external attenuator and BINGO there was the mixed IF signal right where it was supposed to be based on the simple mixer subtraction, so the mixer is working!  I was just over attenuating the signal out of caution.

 

Today I’m going to add some capacitance to the HF oscillator and bring it down so that the IF frequency is 453 KHz, not 745 like it is.  I wish the HF oscillator coil came with some variable capacitors across it for fine tuning.  I’ve run out of coil space to add a few turns, so I’ll have to parallel some silver mica’s to it into the ballpark.

 

Thanks Bill.  73, Scott WA9WFA

 

 

 

From: Bill Meara <n2cqr at yahoo.com> 
Sent: Friday, February 26, 2021 6:49 AM
To: boatanchors at mailman.qth.net; whitebear1122 at comcast.net
Subject: Re: [Boatanchors] Mixer Troubleshooting Question For my Homebrew Superhet Novice Receiver

 

Scott:   Oh man, I built one of these.  I have it on my shelf.   It still works.   

 

I too had trouble getting it going.   I found that it was very hard to get good crystals at 455 kc.  The problem was the filter, not the mixer.   I got around this for a time by substituting a 455 kc IF can for the filter.  This left the receiver very broad, but it allowed me to us it until I was able to get a decent 455 kc filter in there.  

 

Lots of info here: https://soldersmoke.blogspot.com/search?q=Mate+for+the+Mighty+Midget

 

And here:  http://www.gadgeteer.us/erart.htm

 

I will dig up the Electric Radio article for you.  I think it was November 1998?   It has details on my temporary substitution of the filter with a 455 kc IF can. 

 

Hang in there.  You are close.  

 

73  Bill  N2CQR

http://soldersmoke.blogspot.com