EMRFD Message Archive 13432

Message Date From Subject
13432 2017-01-01 18:51:07 jwolczanski 20m XCVR with "discrete Gilbert Cell Mixer" completed
In September 2016 I received some great advice on the build of a discrete version of a NE602 (Gilbert Cell) mixer.  Well, it's at home in my finished (Except for cosmetics) 20 meter direct conversion transceiver. 

I've up-loaded photos of the top & bottom compartments in my (KI4IO) folder.

Here's a description
Photo PC260003.jpg (bottom compartment)
12:00 position (top of photo), then counter-clockwise
1)  The "discrete NE602" mixer board.  EMRFD page 5.11, figure 5.28
2)  Pre-amplifier.
    First is 88mH filter from SSDRA Page 77
    Remaining is from R2Pro pre-amp
3)  W7ZOI Peaked low-pass filter (I love this circuit!)
4)  600 Hz (optional) band-pass filter - stock design from ARRL handbook
5)  Audio amplifier from EMRFD page 9.41, figure 9-74
6)  Long board in center is LO mixer and amplifier.  I mix the 4MHz VFO with a 10MHz crystal. 
Note the pair of mercury wetted relays which switch the antenna and audio
(I had dismal luck with T/R switches)

Photo PC260002.jpg (top compartment)
1)  top board is the transmitter from EMRFD page 5.20 figure 5.50
2)  Middle board is 4.000 to 4.075 MHz LO - also has +/- RIT capability
3)  Control board - perf board
    Relay Control circuit from SSDRA, page 176, figure 83
    side-tone from ARRL handbook
4)  metal box is tuned circuits from RX front-end

Made quite a number of contacts.  Output is 2 Watts.  I think I can get more (TX rated for 4 Watts) but I've already fried one IRF510 playing with the bias.

I've only now come to appreciate the role of headphone sensitivity in receiver gain (duh).  Initially, I thought the "NE602" had too much gain...then I swapped earphones.  The real sensitive earphones are a pair of "Alinco Magnetics".  They also seem to be more sensitive to hiss/hum.  The 2ND pair of earphones, which mate perfectly with my new transceiver are a pair of "Trimm Featherweights".  I told a ham buddy, "I feel like Goldylocks!....these headphones are too sensitive....these headphones are just right!"

I've made quite a number of QSOs...the first batch  when the receiver was bread-boarded down in the workshop....and now a bunch with the receiver all "boxed" up.  I'll get the front panel painted, etc., and will bring my new "baby" to FDIM.

I'm deeply appreciative of the EMRFD book and the work that went into it.  It allowed for this rather fun Lego-style of building (I tried a number of different circuits!).  Thank you EMRFD authors!

Jerry Wolczanski
Warrenton, VA

13434 2017-01-02 09:14:46 Alan Jones Re: 20m XCVR with "discrete Gilbert Cell Mixer" completed
Hi Jerry,
I like to archive all your rigs on my computer for future reference.
I especially like your discrete NE602, which I have yet to build but plan to.
Can you send me the schematic for your 20 meter transceiver?
I think you told me that you build your own enclosures?

Congrats on making all those contacts with your new rig!


13435 2017-01-02 15:59:26 jwolczanski Re: 20m XCVR with "discrete Gilbert Cell Mixer" completed
Hi Al!

There's actually 11 different circuits and they're all from the referenced publications.  When I go to build a circuit, I usually re-draw it on a 14" x 17" sketch sheet.  I can then draw various doodles, including pin-outs, toroid types, turns, design notes, measurements, or changes in the margins.  I don't have electronic versions of these. 

I've listed all or most of the various publications that I used in building this rig.  If you need any more detail, shoot me an e-mail and I'll do what I can.

and then there are the copyright issues.........