Building the NN1G Mark II XCVR

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From: Bruce Lifter (bal@ccd.harris.com)
Date: Tue Jan 25 1994 - 19:57:29 EST


Our next local club meeting's program is going to be on QRP. I provided
the following article to be included in the corresponding newsletter. I
though you all might also be interested.

73, Bruce

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Building the NN1G Mark II XCVR
by Bruce Lifter, KR4AQ

I was interested in building a small QRP rig that would fit in my brief
case that I could take with me when I'm out of town. I really did not want
to dump $200 into a kit for fear it would not perform that well and I might
not get it working. I ran across a few references to the NN1G rig via various
internet sources. It was getting pretty good remarks about it and, most
important, it was inexpensive ($59.95). This seemed like pretty low risk,
so I went ahead and ordered one from Dan's Small Parts and Kits.

The NN1G Mark II is a 1.5 watt single band superhet transceiver. It
was designed around three NE602 IC's (double balanced mixer and oscillator
all on a single chip). The rig has a VFO based on the Hartley oscillator and
has a crystal filter. According to the documentation provided, the rig is
supposed to draw about 30 mA on receive and about 215 mA on transmit.

The kit comes with two silk screened boards (one TX, one Recv), all
board mounted components, a 10k audio pot, and a nice air variable
capacitor. The air variable is optional. He sells the kit for $10 less
without the air variable. The Air variable he sends depends on what he has
on hand. The one I received had a 7:1 reduction drive built in. The kit is
for either 80, 40, 30, or 20 meter bands. I ordered the 40 meter kit.
The builder must supply the case, hook up wire, and all knobs and connectors.

The documentation that came with the kit consisted of a circuit diagram,
2 pages listing the parts included, 2 pages of parts layout diagrams (one
for the TX board and one for the Recv board), an article describing the
original NN1G rig by Dave Benson (NN1G) from the January 93 QRP Quarterly,
2 pages of information on building and aligning the NN1G Mark II transceiver
(written by NN1G), and a page on putting the NN1G Transceiver on 80/40/30
meters, apparently from another edition of the QRP Quarterly.

This is definitely not a Heath kit! The documentation gives very little
instruction on how to put the kit together. There is a few tips provided
on building such as not putting the chips in sockets for it may cause one
them to oscillate at VHF.

I started by checking the parts provided against the parts list. Everything
checked out OK except for two capacitors that were supposed to be 47pf which
measured on my multimeter as 470pf. They were marked with 470 which can
be interpreted as either 47 or 470.

Not having much experience in building XCVRs, I decided to solder it all
together, mount it in its case and then jump right into the alignment procedure.
I won't do that again. I got to step 3 in the alignment procedure and found
that the local oscillator was not oscillating. This drove me crazy for about
a week. To make a long story short, I ended up desoldering all the IC chips
and methodically replacing every component in the VFO circuit. The bottom line
was that a single 330pf NPO capacitor was bad. The worst part was that I had
taken out the bad capacitor, measured it and then put it back in the board
again only to later find out that it was the guilty party. I still don't know
whats wrong with the cap, it checks out with my meter.

Once I got the LO to oscillate, things went much smoother. I plugged the ICs
back in the board and completed the rest of the alignment with little trouble.
The alignment procedure was easy to follow and well written.

I installed the rig in a Radio Shack 3 X 5.25 X 5.875 metal cabinet. The
boards and air variable fit with plenty of room for future modifications. I
have already made two minor mods to the rig. First I added a trimmer cap
in parallel to the air variable. This allows me to easily change the start
and end frequency of the rig. (The rig has about 80k hertz coverage with
air variable supplied with my kit.) The mod does not seem to affect the
stability of the VFO. The other mod was also pretty minor; I placed a diode
in series with the power supply for polarity protection.

The rig seems to operate quite well. My only complaints so far are in the audio
portion of the rig (all of which should be fixed shortly with further
minor modifications). The kit, as it comes, does not seem to be able to drive
anything other than a set of head phones. The LM386 used in the audio section
is supposed to have another 20 dB of gain in reserve. Dan is sending me
a mod sheet that will allow the rig to easily drive a 5 inch speaker. My
other complaint is that the side tone audio is to low while transmitting.
While testing with a strong station across town, I could barely hear my side
tone while transmitting. A mod to cure this is already floating around
Internet.

Overall I am very pleased with this kit. My main rig is an ICOM 737 without
a CW filter. The Mark II is actually easier to listen to at night during noisy
band conditions due to its filter. I think I'm ready to build another one for
20 or 30 meters. I talked to Danny Stevig (of Dan's Small Parts and Kits)
today and he tells me that he currently has the kits on special, 4/$200 mix
and match the bands.

One more note,... special thanks to Doug Snowden, N4IJ and Dave Rush, WO4Z
for their patient help in my struggle get the LO working.

--
Bruce Lifter                                                      MS: R5-202
Harris Corporation                             email: blifter@ccd.harris.com
Controls Division           Amateur Radio Packet: KR4AQ@N5AUV.#MLB.FL.USA.NA
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