Elecraft K2 Amplifier Keying Circuit

As some of our members will be aware, I have been building an Elecraft K2 kit radio, and I completed construction this Easter weekend.

When I ordered the kit, I didn’t order the internal ATU or the 100W amplifier option, as I already have an Elecraft KXPA100 amplifier with KXAT100 ATU. However, this amplifier is designed to work with the KX3 radio, and so to get it to work with the K2, I would need to build up a keying circuit.

Fortunately, Elecraft published on their website a neat solution for this. It consist of a couple of transistors mounted on some perfboard, which slots into a PCB header socket intended for the K2′s transporter interface module. Because I don’t have this option, my radio didn’t have the required header socket, but luckily the local electronics store sells suitable headers as part of their Arduino range. I picked up one of these headers, together with the other requisite parts.

The article on the Elecraft website provides a schematic, and some photos of the finished board, but they didn’t provide detailed information about how to build the circuit onto the perfboard. Fortunately, the circuit is quite simple, and wasn’t too hard to work out, but I decided to draw up a diagram which provides a better view of how the components are laid out and the physical connections are made.




The dotted lines show connections running under the board (except the gate lead of the 2N7000 JFET — that runs under the transistor, but along the top of the board).

I built the circuit in the following sequence:

1. put the 8 pin male header under the board on the left side, and solder one leg of the 2.2k resistor to the pin sticking out the top of the board at position A8. This then holds the header in place. The other leg on the 2.2k resistor goes through hole B5.

2. Sit the 10k resistor sitting up on end in hole C5, bend over the top leg and stick it through hole D4. Bend the legs underneath the board to hold the resistor in place.

3. Put a piece of hookup wire (eg. a component lead off-cut from when you built your K2) through hole D3. On the top of the board, bend the wire so it reaches the header pin 2 sticking through hole A2 and solder it to that pin.

4. Mount the right-angle molex receptor on top of the board through holes E1 and F1. Under the board, bend the hookup wire you installed in the previous step so it reaches the receptor pin sticking through hole F1, and solder to the receptor pin and trim. This will hold the receptor in place.

3. The Gate and Source legs of the 2N7000 JFET are the left two legs, if you hold the transistor with the flat face towards you. Bend those two legs backwards, and put the remaining leg (the Drain) in hole C1. Bend the Drain leg under the board down towards the resistors to hold the transistor in place.

4. Solder the Source leg (the left one you bent back) to the header pin 2, which sticks out of hole A2, and trim. Careful not to dislodge the hookup wire that is also soldered to that pin. Trim both the transistor lead and the hookup wire.

5. Solder the Gate leg (the middle one you bent back) to the header pin 1, which sticks out of hole A1, and trim.

6. The drain of the JFET which goes down through hole C1, and the resistor legs sticking through holes B5 and C5 should be bent so they all meet up. Solder the three leads together and trim.

7. The Emitter leg of the 2N2222 BJT is the left-most leg, if you hold the transistor with the flat face towards you. Bend that leg backwards, and put the middle leg (Base) through hole C4 and the right most leg (Collector) through hole C3. Solder the Emitter leg that was bent back to the header pin 4 sticking up through hole A4.

8. Bend the Collector leg sticking through hole C3 so it reaches the molex receptor pin sticking through hole E1 under the board, and solder the leg to the receptor pin.

9. Bend the Base leg sticking through hole C4 so under the board it meets the 10k resistor leg sticking through hole D4, solder the two legs together and trim.

10. Make up a short cable (3″ or 4″) with the molex plug on one end. Solder the side of the cable that connects to the pin closest to the side of the board, going through hole F1,  to the ground lug on the RCA connector.

11. Install the RCA connector in the hole on the bottom chassis labelled “XVTR IN”. Solder the other side of the molex plug cable to the inner conductor of the RCA connector.

12. Plus the keying circuit board into the J13 header socket on the RF board. Connect the molex plug to the molex receptor on the keying circuit board.

And that’s it. Plug one end of the RCA-RCA cable into the new RCA connector on the back on your K2, and plug the other end of the cable into the “PA KEY” RCA socket on the back of the KXPA100. Connect up a patch cord between the K2 ANT OUT and the KXPA100 RF IN, and you are good to go.

Here are some pics of the completed circuit, from above and from beneath.

IMG_0113IMG_0114IMG_0118 - Version 2

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April 2014 Lecture — Beverage antennas

When someone mentions “Beverage Antenna”, if you think of towers of
beer cans or picture fountains of coca-cola, then you need to come to
this month’s lecture at the Manly Warringah Radio Society.

Find out what a beverage antenna really is, why you need one, how it
works, and how to make one yourself. 8pm Wednesday 16 April at the
MWRS club house.

The slides from the lecture are available here.

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February 2014 Lecture – 630m band

On Wed 19th Feb Nick VK2DX gave a technical lecture on the 630m band (472-479kHz).  His lecture covered suitable transmit and receive antenna options (they are different!), as well as hardware and software for scanning the band visually.  He also spoke of propagation characteristics, usually this band propagates via ground wave with a path loss advantage over higher bands however sky wave propagation can and does happen!

Click here for lecture

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January 2014 Lecture – Packet Radio Overview

On Wed 15 January 2014, Matt VK2RQ gave a lecture on packet radio, which provided an overview of what is packet radio and how it works, and described some of the applications for which packet radio is used. Here is a link to the presentation slides in OpenOffice or PDF format. A video recording of the lecture is available here.

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VHF/UHF Summer Field Day 2014

MWRS operated portable during the Sunday morning segment of this year’s Summer Field Day, from the oval behind our club rooms.  This oval is at a high point in Terrey Hills and provides a good outlook in all directions. Operators were Nick VK2FS, Geoff VK2MIA, Matt VK2RQ and Carlo VK2MXC.  In addition we had several club members turn up to say g’day and see how we were going.

Weather was warm and sunny, quite humid as it had rained overnight and the residual moisture was evaporating out of the ground.

For 6m, we used a squid pole supporting an inverted V, with the peak about 7 metres above ground level.  FT-897D radio running on 2 x 12V 7Ah SLA batteries.

For 2m, 70cm and 23cm we used high gain Yagi antennas on a portable mast, rotated by hand.  Unfortunately the coaxial relay for our 23cm equipment was playing up so we didn’t make any contacts on that band. IC-7000 radio running on large blue SLA battery.

Total contacts 19, with a great 6m opening to VK5, VK4 and ZL.  Due to the nice opening, our score for 6m was almost our best category!

We had some carefully calibrated inserts to make the U-bolt bite down on the mast

We had some carefully calibrated inserts to make the U-bolt bite down on the mast

2m, 70cm, 23cm Yagi setup

2m, 70cm, 23cm Yagi setup



7m squid pole, with 6m inverted-V dipole

7m squid pole, with 6m inverted-V dipole

DX on a squid pole! Dom VK2JNA was highly entertained

DX on a squid pole! Dom VK2JNA was highly entertained



Matt VK2RQ and Geoff VK2MIA operating

Matt VK2RQ and Geoff VK2MIA operating


Matt VK2RQ and Geoff VK2MIA operating

Matt VK2RQ and Geoff VK2MIA operating







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VK2TMF’s 555 Contest Entry

555 Contest Entry

Maker: Malcolm Faed

I was excited when the 555 contest was announced to recognize the most used Integrated Circuit ever.

After considering for a while what I could do for the competition, I started thinking about how best to celebrate the 40 years that the device has been around and the 10s of billions produced.

I have often admired home built computers that use discrete components so I though, I will make 555!

This 555 project recreates an operational 555 timer using discrete transistors, resistors, diodes and capacitors.

It may not strictly conform to the competition rules, but I thought it would be fun and original anyway.

Initial Research.
I downloaded a few 555 datasheets from various manufactures only to find that the circuits often have subtle differences. Eventually after some Googling I located a scanned copy of the original Signetics datasheet from dapj Circuits, Including the Equivalent Circuit below.


After inspecting the circuit, I noticed Q19 is rather unusual and has 2 collectors. How can I implement this using discrete components? I decided to simulate the circuit using the brilliant and free Java app from falstad.com to make sure it worked and to quickly experiment with different arrangements for Q19.


This is the simulation. You can run the simulation yourself by clicking the link .

Arranging the resistor on the base of Q19 as in the simulation works perfectly. If I used 2 transistors to replicate the original Q19 design, the circuit did not oscillate.

ConstructionIn order to simply construct the circuit to show its operation and at the same time preserve the original authenticity, I photocopied and enlarged the Philips schematic, glued it to some card and inserted the components through the card and used point to point wiring on the rear of the card.

3Component side of card.



Rear of card using soldered point to point wiring. Drawing pins are used to secure the input and output pins. Much ice cream was consumed during the construction of this project.

A pin was used to poke holes in the card to insert the components. This was a surprisingly quick method of building the circuit. For prototypes of simple circuits I may use this technique again.

the only thing I might do differently is to paste a reverse image of the circuit onto the wiring side of the card in order to avoid wiring errors.

In order to test it works, I attached an LED to the output and suitable timing components, Ra, Rb and C to give an approximate 1Hz flash rate.

the final testing can be seen in the this video.

Making it presentable
The final thing to do is to make the project presentable. I decided the inside of an old data book would be appropriate. I found a copy of a suitable book on the ‘free’ table of my local ham radio club, the Manly Warringah Radio Society.
This was the first time I have used a book as an enclosure. It works well if you are not in a hurry, which I wasn’t. I followed the guide by Bre Pettis from Make Magazine. (Cool guy who I had the pleasure of meeting at a Maker Faire in Austin, Tx.)

One half of the book was cut to accommodate the circuit, while the other half was to house a battery, the 555 timer data sheet and memorabilia.


Right hand side of book contains the circuit


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This highly educational and quirky project is suitable for a rainy day, and is an ideal way to

use up surplus electronic components that may happen to be lying around the workshop.

Basically it consists of a TA7642 integrated circuit that is constructed using discrete

components – i.e. transistors, resistors and capacitors. With the addition of a small audio

amplifier, a complete radio receiver is possible.

The TA7642 is a successor to the ZN414 TRF receiver chip. The ZN414 was well known to

European and Australian constructors of AM radio receivers. It was developed in the early

1970′s by Ferranti in the UK. There are only three connections; input from a ferrite rod aerial,

earth and audio output. The circuit is a TRF (tuned radio frequency) type with all gain at the

received frequency. The chip also incorporates a detector and AGC circuit. Supply is a

nominal 1.5V at 300uA and audio output is sufficient to drive a crystal earphone.

The prototype was made by gluing a copy of the circuit onto a piece of cardboard, punching

holes with a needle, then inserting the components and soldering them together on the

underside of the board. The small jiffy box contains the tuning capacitor, coil, volume control,

an LM386 audio amplifier and a loudspeaker.

The end result did not quite come up to expectations, but nevertheless the project was a

worthwhile exercise. The radio refused to run on 1.5 volts, but instead required about 9 volts

to function. The top frequency achievable was only about 1.0 Mhz instead of 3.0 Mhz as per

TA7642 specifications. A small antenna was also attached to increase the signal level.

VK2RL - TA7642 Cardboard Radio

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2013 Jamboree On The Air (JOTA)

This gallery contains 21 photos.

JOTA time already??  MWRS has hosted activities for the Scouts and Girl Guides for several years and this year was another busy and fun experience!  We had around 180 kids come through the hall over the weekend of 19th-20th October.  … Continue reading

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2013 Flagpole Comp wrap up!

What a great weekend!

As the dust settled and the flags were packed away for next years activities I collected the logs, photos and evidence for review at a casual club meeting. Firstly I have to say for our first comp things went really well, we had contacts from across the land in conditions that were difficult to say the least.

By popular vote points for flags, setup and effort were awarded and the I am happy to announce that the winner is …… Geoff VK2MIA with 152 points.



Not only did Geoff have a flag pole station, he also had a pirate hat, pirate dreadlocks, a sea location, made SSTV contacts and emailed through photos that he had a random by passer take. If that wasn’t enough he also had to deal with someone telling him he couldn’t do “what ever it was he was doing”…

Special mention goes to VK3BQ for his awesome efforts in getting the word out in VK3 about our comp and his great sstv images. VK3YE and VK3BQ for the YouTube video and everyone else who participated in this fun event.

Name Call Points
Garry VK2GAZ 119
David VK2DF 53
Glen VK2FWOO 8
Yves VK2AUJ 32
Geoff VK2MIA 152
Brian VK4LH 53
Peter VK3YE 61
Robert VK2RL 3
Andrew VK3BQ 130
Owen VL2OL 52
Shaun VK2XPP 105
Tim VK2BT 74

If you know of anyone missing please let me know asap..

The trophy was handed out on Wednesday night (Thanks Greg!) and now we look forward to next years INTERNATIONAL Flagpole Comp which will be held on Saturday 20th September 2014.


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MWRS Flagpole Contest

Moon flag

The Manly Warringah Radio Society invite you to celebrate International Talk like a Pirate day, Amateur Radio and Flagpoles by participating in our inaugural Flagpole Contest.

This is a fun and as you can see not too serious contest that will promote Amateur Radio and portable operations. So dust of your rig, get your antenna in the air and try out some new modes with friends.

Why Flagpoles

Geoff (VK2MIA) procured a Flagpole for mobile operations and tweaked the interest of the wider club when he brought it up to the clubhouse one wednesday night. Upon inspection a group buy was in planning, with Shaun (VK2XPP) taking the lead. The club procured almost 2 dozen flagpoles (From here). Once shaun picked up the shipment the club members get right to business, with some great results.

So with all these flagpoles ready for field operations the idea for this contest was born and the point structure was decided upon around the club fireplace with more than a few laughs.


Contest Aims

The winner of the competition will be the person who collects the most points during the day of the competition. The goal of the event is to exercise your ability to operate using a portable antenna across multiple modes and perhaps to get you out of your normal operating comfort zone.

Non-flagpole stations are welcome to participate, but will have to work a little harder to get points.

Rules are as follows

1. The Flagpole station must make up part of the antenna or antenna support.
2. The contest will run all day on the 21st of September 2013.
3. The President / Vice-President’s of the MWRS will be adjudicators.
4. This is a fun event, keep it fun and positive.
5. This event is open to all Amateur Frequencies and Modes.
6. A contact will be the exchange of Callsign, Signal Report and a quick report of your flagpole setup!
7. Log’s are to be submitted using the Competition spreadsheet. (See below)


  • Make a contact with a non-flagpole antenna 1 Point
  • Make a contact with a flagpole antenna  2 Points
  • Make a contact with another flagpole station 5 Points
  • Make a contact with D-Star 10 Points (Maximum of 100 Points)
  • Make a contact with a F call 5 Points
  • Email photo of your flagpole setup to contest@mwrs.org.au 20 Points
  • Send a SSTV Image of your flagpole setup to MWRS on HF 14.314159  50 Points
  • Flag being flown from your flagpole 10 Points (Need photo evidence)
  • Pirate  or funny flag being flown from your flagpole 20 – 100 Points as judged by President

We will make a spreadsheet available on this page for submitting your logs. 

Calling Frequencies

3670 kHz on 80 meters.

7045 kHz on 40 metres.

2 metre repeater 146.875 MHz FM output, 146.275 MHz input


MWRS_Logsheet - Open Office Format

MWRS_Logsheet - Excel Format

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More Hams!!! 5 new foundations and two advanced upgrades!

This gallery contains 2 photos.

Huge thanks goes to Mark and Chris for giving up their Saturday in the name of Amateur Radio. They have helped 5 new Amateur Radio operators get licensed, and held exams for 2 others to upgrade. Club member Lionel who … Continue reading

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MWRS President on 2UE, wrapping up ILLW for 2013



Listen to 2UE interviewing MWRS President Carlo Nizeti after International Lighthouse and Lightship Weekend (ILLW)

After a very successful weekend up at Barrenjoey Lighthouse, we had a chance to talk with 2UE about ILLW and ham radio in general.

Listen to the interview by clicking here




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Lighthouse wrap up!

What a blast! Once again we had a great weekend, and while we are busy consolidating our logs I can give you a video of the events

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MWRS Features in Local Press

Geoff Van der Wagen, Roger Hynes and Ben Menge. Photo courtesy of News Limited

This weekends International Lighthouse and Lightship weekend is a great opportunity to promote Amateur Radio, and with that in mind Club Publicity Officer Richard has done a great job working with the Manly Daily to get us some local press. A journalist from the publication visited the shack to meet with Roger, see first hand the restored Barrenjoey Radio and get some snaps of the guys in action.

I know everyone has their own favourite, but for me Lighthouse is the event of the year so keep an eye out for VK2MB / Lighthouse Portable on the airways!

Read the story at -> http://www.dailytelegraph.com.au/newslocal/northern-beaches/radio-enthusiasts-to-broadcast-from-barrenjoey-lighthouse/story-fngr8hax-1226697925523

Click here to download a PDF of the article

For updates over the weekend check out our Facebook and Twitter accounts!

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Yves VK2AUJ shows off his great KX3 Carry Case

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