DC Receivers

I was over at the workbench this afternoon working on some Direct Conversion receiver ideas.

My original plan was to use a NE602/SA612 with my signal generator and a LM386 op-amp. It is not designed to be a incredible piece of hifi gear, but the hope was that it would be quick and dirty receiver. For what ever reason I seemed to struggle with the SA612 on the breadboard. The LM386 provided audio but the SA612 did not seam to want to act like a mixer which is a problem.

After screwing around for a while I decided to take an even simpler approach, use the trusty SBL-1 as a passive mixer. --Bingo, 2 minutes of setup and I was hearing CW on the computer speakers.



Audio Clip from the DC receiver

The audio clip sounds pretty poor as it was just a computer mic near the speaker. The person calling CQ was very easy to follow so the breadboard mess was functioning as a direct conversion receiver.

When time permits I would like to go back to the workbench and figure out why I was having problems with the SA612... it should be really simple... but clearly it wasn't.

The DC receiver is not long for this world, it is a stepping stone as I begin to work through receiver theory and more complex designs.

73 de NG0R

Sorting parts

I sorted the parts this afternoon. With the arrival of a bunch electrolytic capacitors I started a new parts box just for electrolytic caps. (I have another box for ceramics, another one for small trimmers, etc.) 

The larger caps on the right side of the tray are for a project to fix my HP606A signal generator.

73 de NG0R

Parts arrive!

Several orders from various vendors have arrived this week.









It is always fun to get parts in the mail let alone several orders.

• The box of parts is a Mouser order for some various electrolytic capacitors and SA612 mixer.
  
• The red & black 16 gauge zip line is for making some "low power" power cables for various projects.
• The UHF-->BNC adapters are for connecting various projects to the test gear at the work bench.
  
• The final bag of parts is 30 amp Anderson Power Poles.

73 de NG0R

Weekend notes

The weekend here was kind of a bust for me.... (It feels like that without having a project success of some sort)

• Saturday morning I decided to relax and visit my workbench with the intention of building a direct conversion receiver on a breadboard. One little issue; I did not have any through-hole capacitors that were good at audio frequencies for a DC block. ---argghhhhh
  
  
• Saturday afternoon I took my elderly HP606A signal generator over to N0FP's QTH for some troubleshooting. The last time that I tried to use it I was not getting any significant RF out of it. It is a nice 1959 vintage signal generator with plenty of tubes. One little issue, I am scared to death of tubes... those high voltages can kill you if you don't know what your doing. 
  
  We were able to get the RF going again but the CW tone sounded horrible. We spent 3+ hours trying to figure out why the tone was so harsh.  We swapped out tubes, measured the voltages, checked caps, replaced diodes in the rectifier bridge, but still never resolved the problem.
  
  
• Saturday evening I bagged-up 15 bags of parts (mainly resistors) from my various bulk orders. (N0FP was looking for some resupply items for his parts box.)
  
  
• I then placed a couple of orders for 12 & 16 gauge red/black zip line for making power cords, some Anderson Power Poles, and some UHF-->BNC adapters. (ebay was my friend)
  
  
• The remainder of the evening was spent with the family eating pizza and watching a movie.
  
  
• Sunday morning was spent getting groceries. (The three kids eat a lot of food during the course of a week.)
  
  
• Sunday afternoon I cleaned the desk at the operating position of the radios.
  
  
• I spent about 30 minutes talking with N0FP and W0RK on 75m SSB. (A clean operating position makes it easier to play with the radios.)
  
  
• I then spent the remainder of the afternoon looking for parts at Digikey and Mouser. I pulled together a big order of parts, most of which was electrolytic capacitors. (Some for the DC receiver project, some for the HP 606a repair, some for the parts box.)

Now that I look back at the list that was a lot of stuff. I still am left wanting for some small project success to be able to call the weekend a success. --Clearly I am having an issue trying to relax.

73 de NG0R

St Cloud Hamfest

N2BEN (10) and I went to the St Cloud hamfest yesterday.


Like all good hamfest we saw the three requirements to call it a hamfest: 
tubes, crystals, and old soldering irons.






There was actually quite a bit of interesting ham radio gear on hand. It is nice to see radios at a hamfest vs all of the computer stuff from past years. There was quite a bit of newer gear in addition to some older gear.



After the hamfest several members of the Meeker County Amateur Radio Club met for lunch. You will notice that Roger is experimenting with some new callsigns...


And we have proved that Jason AA0II does NOT eat all of his vegetables!


Overall we had fun getting out of the house for 1/2 of Saturday with the mini road trip to St Cloud.

73 de NG0R

Early Morning

A picture sunrise picture from the camera phone from earlier in the week.

K2 SSB Testing - Follow-up

Back in late January I discovered that my K2 was putting out a lot more power on CW than SSB & LSB. After posting some messages on the Elecraft reflector Geoff GM4ESD looked my original test data and wondered out-loud if the cause might be an alignment issue.

Fast forward past a couple of business trips out of town, being sick, and a hectic work schedule and I am finally getting back to the workbench to follow-up on the troubleshooting.

This afternoon I went back through the various calibration and alignment steps (largely around the BFO and filters.) Sure enough I noticed that one of the filter settings for Filter1 looked odd. I reset it back to where the book suggests the value should be. (Note-to-self: The filter settings are somewhat complex if you don't use this portion of the K2 menu very often.

The latest test:



The original test:


That is a very impressive improvement in the levels. I am not sure what is causing the funkiness on 12m but I am not sure that I really care at the moment since I don't think that I have ever made a Q on that band.

This looks quite a bit more usable at 28mhz CW & SSB which is important since I am using this an IF radio for 3 transverters. I will need to reassemble part of the station to be able to re-test the K2 with the transverters after the bench time. --I won't really know if I solved my problem until I can run that test.

73 de NG0R

ATS4 Evening 4 - The Fix!

I replaced C55 and that was the magic fix.  It was supposed to be a .1uF - 104 but who knows what it really is since it is an unmarked SMD part.  I had a 1uF - 105 in the proper SMD size on my parts shelf. It was about a 20 minute repair end-to-end.

That made a huge difference in the amount of audio that is available to the headphones.

73 de NG0R
73 de NG0R

Modern Archimedes

http://xkcd.com/857/

Wow... there is some commentary.

Tension (

http://xkcd.com/859/