Taming a Chinese Nighthawk 40m CW Transceiver Kit
CW transceiver kit had a host of problems. With some effort, I got all
of this kit’s many design faults resolved and the transceiver working
nicely. A very satisfying result. Here are the details to quickly and
easily fix your kit.
Figure 1 : The completed Nighthawk 40m CW transceiver, at present without a top cover
IntroductionSome months ago, I ordered a transceiver kit from one of those Chinese suppliers on the internet. Since we cannot get mail delivered reliably here in the desert,
I get items like this kit sent to an address in London. When I next
visit the city, I collect my mail. As you can imagine, a few
months can easily pass between an order, the delivery from China, and
my collecting it.
Despite the delays,this system seems to
work reasonably well. However, when I collected this transceiver kit,
it became quickly obvious that the kit I had received was completely
different to the one I had ordered! The kit delivered was a Nighthawk 40m CW transceiver (夜鹰), but I had actually ordered a “Kangaroo” ( 袋鼠) SSB transceiver kit. (How can anyone mistake a kangaroo for a nighthawk? ;-) )
This was to be just the first of a lengthy saga of problems with this kit.
much time had passed since my order to address the problem with the
supplier in any sensible way, and my verbal Cantonese and Mandarin
skills are non-existent, so I decided to just build the kit I’d
The kit instructions explained - once I’d
translated them from Chinese into English - that the original design
had been “improved in a number of areas”. The claimed improvements
at first glance, this kit should have been a really easy to construct
and get going – The design is 90% based on the well-known and widely
used SW-40+ CW transceiver designed by Dave Benson K1SWL. What could
possibly go wrong? Building it, I decided, would be a nice, relaxing
- Higher transmitter output power (10W instead of 2W)
- Improved rx/tx switching
- Better receiver bandpass filters
- Variable front end receiver diode attenuator
- More stable 11MHz VXO, and
- An on-board CW keyer
first step in kit building is to sort out the parts and check them
against the parts list provided in the kit instructions.
Instructions….? As usual with these kits, there were no instructions
supplied. However, after little searching, I managed to obtain a set of
PDF-format instructions via the supplier’s website. Great! In Chinese….
Ah, not so great.
Figure 2 : The kit of parts contained everything required to build the kit except the
instructions required to build the kit. These were obtained from the supplier. In Chinese.
I can handle that problem. Once I had translated the instructions, I
found them to be quite detailed and accurate, at least as far as the
information required to build the kit and operate the transceiver was
concerned. My translation of these kit instructions can be
downloaded below. Feel free to criticise my Chinese translation skills.
Most of the parts provided were of adequate quality, and
everything on the parts list was in the kit. The PCB was excellent. The
layout made some component labels printed on the PCB overlay a little
hard to read, but there were no significant problems.
the NE602 ICs supplied were quite clearly recycled parts. Corrosion was
evident on almost all of their pins, and the parts had obviously been
removed from the original PCBs with minimal care. Despite that, and
after some cleaning and tidying up with the soldering iron, all of
these chips were found to be working fine.
Little did I know
at this stage that the biggest component problem in the kit was going
to be the variable shielded inductors. The 7 x 7mm “7 MHz” inductors
supplied in the kit were completely different from the now impossible
to find original “42IF123” 10mm x 10mm shielded inductors used in the
SW-40+ design. Internally, the “7 MHz” coils supplied proved to have a
different primary : secondary turns ratio, a critical design parameter.
Nighthawk Kit Design IssuesI
think it’s fair to say that all of the problems I encountered with the
kit can be traced to the kit’s “design improvements”, i.e. the
modifications made to the original SW-40+ design. These changes, IMHO,
meant that this kit, as supplied, could never ever work properly.
problems affect both transmitter and receiver. For example, the
transmitter mixer circuit around U5 (NE602) did not work. The design
changes in the kit resulted in an excessive VXO input level to this
mixer. It could not then generate the required 7MHz transmit signal.
The incorrect inductors supplied for use in the subsequent transmit
bandpass filter also meant it could never work correctly either. In
addition, the filter’s high impedance output was excessively loaded by
the low input impedance input of the subsequent Q6 amplifier stage.
This prevented correct alignment of the filter, a problem reported on
several websites. All told, quite a mess.
In the receiver,
the newly added diode variable attenuator did not work correctly
either. It did provide variable attenuation, but it ranged from a
minimum attenuation of about 20dB to a maximum of 40 dB. Basically,
that circuit simply reduced all received signals by at least 20dB – The
receiver was completely deaf! Like the transmitter, this kit’s receiver
as supplied would never work correctly.
problems can all be easily fixed. With some changes to the Nighthawk
design, based on a number of hours spent with my circuit simulation
software and some bench testing, some extra parts and a bit of circuit
rearrangement got everything working properly. For example, with a
couple of minor changes to the variable diode attenuator, it now has an
adjustment range of about -3 to -27dB. That’s about 5dB more dynamic
range than the original kit “design”, and it has proven to be really
quite nice to use in practice.
Figure 3 : The completed transceiver board. If you look really carefully (Right click for more detail),
you will see a few places where modifications have been done to get everything working properly.
Nighthawk kit also featured changes to tx/rx switching, with the
addition of an antenna changeover relay and a delay circuit to reduce
relay chatter during CW transmissions. I found that a minor change to
the capacitor value controlling the changeover time was desirable. It
doesn’t quite match the full break-in keying capability of the original
SW-40+, but the minor circuit change in this area seem to work fine for
The changes made to the transmitter power amplifier
stages operate well in practice, I’m pleased to say. They appear to be
quite stable and trouble-free. However, another related design error
creates a significant problem. Amateur radio operators often use QRP
transceivers like the Nighthawk in locations requiring battery power.
That demands a low receiver current drain.
strange reason, in this Chinese version of the SW-40+ transceiver, the
gate bias voltage for the final power amplifier FET (Q5 – RD15HVF1) was
designed to use the unswitched 8V regulated supply rail (VCC_8V). This
added an extra and unnecessary current of up to 130mA on receive(!) By
making a minor change to the design, rerouting R29 (4k7) so it connects
to the transmit 8V rail (VCC_8VT), I reduced the receiver current from
160mA to just 30mA, making QRP battery operation of the transceiver
So, what changes are required to get everything working?
Modification Details Modifications
(a), (b) and (c) are critical for correct operation. Modifications (d)
and (e) are highly recommended, but not essential.
a. Receiver variable attenuator
Figure 4 : Receiver RF attenuator modifications (Right-click for more detail)
This modification reduces the minimum signal attenuation to acceptable levels while also increasing the range of adjustment.
- Replace R37 (4k7) with 470R resistor
- Replace R39 (4k7) with 100uH RF choke
b. Transmit mixer oscillator input
Figure 5 : Transmit mixer circuit modifications (Right-click for more detail)
This modification reduces the relay hold time and speeds up the tx/rx changeover.
- Replace C44 (1000p) with 10p disc ceramic capacitor
- Install new 100pF disc ceramic capacitor between pin 2 and pin 3 (ground) on U5 (NE602)
c. Transmitter bandpass filter
Figure 6 : Transmitter BPF modifications (Right-click for more detail)
This modification ensures the BPF operates correctly and can be aligned.
- Remove C27 (220p)
fitted, remove T3 from the PCB. Remove the internal capacitor from
inside the base of the variable inductor. (It is typically a 100pF
miniature tubular ceramic capacitor)
- Install the modified T3 into place on the PCB
- Install a new 3p3 disc ceramic capacitor between pin 3 of T2 and pin 1 of T3
- Install a new 1000pF disc ceramic capacitor (or reuse C44 removed in the previous modification step above) in parallel with R25
- Remove C43 (100nF) and replace it with a new 100pF disc ceramic capacitor
I opted for top-coupling (with the extra 3p3 capacitor) rather than
modify the value of C27. Chances are, your kit could have a different
brand/type of Chinese inductor supplied for T2 and T3. In that case,
the turns ratio could be different, and then we would be back to square
one again with a modificationinvolving C27. Using top-coupling avoids
Here’s a picture showing the capacitors added under the PCB.
Figure 7 : Changes are required under the PCB (See text)
d. Tx/Rx Timing
This non-critical modification reduces the relay hold time and speeds up the tx/rx changeover.
- Change CP14 from 1uF to 470nF
e. Final Power Amplifier (Q5) Bias
This non-critical modification reduces receive current from 160mA to 30mA. Transmitter keying characteristics are unaffected.
- Remove R29 (4k7)
R29 onto the underside of the PCB so it connects between C58/W3 and the
collector of Q8 (VCC_8VT rail). Figure 7 shows that resistor in its new
modification also requires a change to the original (and slightly
obscure) bias setting instructions. The gate bias voltage on Q5
(RD15HVF1) should be about 2V, the gate threshold voltage. This ensures
the PA stage operates in Class-C, suitable for CW transmission. (I was
tempted to modify the PA for Class-E operation, to improve efficiency
still further, but I had to draw the line somewhere in this project!)
correct PA gate bias voltage for your transceiver can vary from 1.8 to
2.3V, according to the datasheet for Q5. To set this value correctly,
we must monitor the drain current of Q5 during transmit, without any RF
input feeding that stage. After the R29 bias modification, this
adjustment is a little more difficult to do because there is no
provision in the transceiver to measure the PA stage current under
no-RF transmit conditions.
But here’s how we can do it AFTER this modification has been made:
the RF drive to Q4 and Q5 (RF PA stages) by place a temporary short
across R25 (I just soldered a wire link across R25 on the underside of
the transceiver in the manual key mode (Ground the ‘dah’ paddle
connection temporarily before turning the power on, then remove the
the key down to turn on the transmitter (The ‘dit’ terminal is now
the manual key input – Ground it to turn on the transmitter)
- Measure the standing current (In my transceiver, it was about 340mA)
- Adjust W3 to increase this value by 50 – 100mA (I set W3 to give 420mA)
- Release the key
- Turn off the power
- Remove the short from R25 to restore RF drive
- Power-up the transceiver again in manual key mode
- Press the key down to turn on the transmitter – You now should have RF drive to the PA
transmitter output is about 10W (12V supply) and peak T2 and T3
slightly for maximum output power across the tuning range (My
transceiver delivers 8W with a 12V supply)
are a couple of areas in the transceiver remaining for me to improve.
One is the keyer. The dit/dah timing ratio doesn’t quite sound quite
right to me when I’m transmitting, although I’m hardly an
expert! I also found the various keyer adjustment steps (e.g.
keyer speed, keyer sidetone) to be too coarse.
this, I’d ordinarily just drop in a ATtiny and some new software but
the PIC12F629 pinout doesn’t allow for a direct plug-in chip
replacement. I’ll have to wait for a very long rainy weekend before I
write new assembly code software for a PIC chip. (And since I live in
the middle of a very large hot desert, that may not be for some time…)
More than likely, I’ll take the easy way out and “shoehorn in” an
ATtiny YACK keyer. It's got loads of features and a ton of adjustments.
The other section of the transceiver I’d like to modify is
the transmitter power amplifier. I think it is possible to make some
really useful improvements there by migrating the design to Class-E,
especially if the transceiver is to be used on battery power. That
would require some fairly extensive changes, but it certainly looks
Putting it in a BoxNow
that i had it all operating correctly, to complete my transceiver, it
needed to be in a suitable box. I did have a perfectly sized aluminium
box, but the BNC antenna connector on the kit PCB made it impossible to
fit the completed PCB in place. Also, I don’t have any metalwork
facilities. Instead, I decided to build a box from blank PCB. That
material is much easier for me to handle.
The result is
shown in Figure 8. I ended up removing the BNC connector to allow the
board to fit in the box, and I fitted my usual “phono” antenna
connector in place of the BNC. I know this will upset some people, but
I have found those phono connectors to be perfectly adequate for QRP
I printed the two knobs I needed on my 3D printer. The
original design for these came from Thingiverse. They just press into
place on the potentiometer shafts.
Figure 8 : An inside view of the completed (modified) Nighthawk transceiver. It’s a tight fit,
and measures about 100mm wide, 40mm high and 130mm long.
sum up, while it was disappointing to discover so many fundamental
design faults with this Chinese kit, and some poor quality parts, I
have to admit to a great deal of satisfaction in hunting down all of
the design problems, one by one, and fixing every single one of them.
is not a difficult kit to build, especially now I know how to fix the
problems. The high quality PCB and the board layout certainly made the
build, and the various modifications, a great deal easier than some
other equipment I’ve worked on in the past, and the finished
transceiver looks very tidy, I think.
With all of the
modifications added, and they are not hard to do, I think this
transceiver now works quite well. I’m not sure it will ever be my
favourite radio, but I do like the final result. It is compact, and the
combination of close to 10W output power and its reasonable receiver
sensitivity gives good results.
If you need an antenna tuner for the Nighthawk, I’ve designed a compact antenna tuner which works nicely. It’s described here on my website.
I hope the information I’ve provided here will help others who may be
struggling with getting their Nighthawk transceiver kit operating
Figure 9 : The back panel of the transceiver records the basic specifications
Translated Kit Instructions: This zip file contains my translation
of the ORIGINAL kit instructions. The modifications described above are
recommended if you wish the kit to operate correctly.
Nighthawk Panel Artwork: My front panel artwork, in case someone wants it
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