Some examples of the Squid Pole interface box built by NERC members
Click on each photo to see a larger image.
This first image is of the prototype and this version has been built by most club members. Band selection is done by jumper leads with 4mm plugs and sockets.
These three images are of the version built by Trevor, VK5ATQ. In this version Trevor has used a three pole switch to select the 80, and 20 Metre coils or straight through for 40 Metre
These images are of the two versions built by Phil, VK5SRP. Phil has also used a three pole switch. Details on how to build these at the end of this page.
Early in September 2015 Les (VK5KLD) came to me for some technical help. He had started building the Squid Pole interface at the NERC technical night but it had turned into a UFO, an unfinished object. I took this on as an oppertunity to make another easier to build version with a three position switch and using a readily available Jiffy Box. Rummaging in my box of boxes I found an AZtronics/Altronics H0151 158X95X53 mm grey plastic box, ideal for this new try at the project.
The two coils are mounted with 25mm PK screws driven into small holes drilled 60mm apart on one side of the coils. The Beehive trimmer is accessed through a hole in one end of the box. Two poles of the three position switch are used, one pole switches the antenna wire from the 80M coil, straight through for 40M and to the 20M coil. The other pole switches the input from the coax connector to the coils and straight througn in the 40M position.
Building the VK5SRP version of the Squid Pole Interface
Parts list
- Twelve Metre of insulated multi-strand copper hookup wire - the copper inner is 1mm in diameter
- Five Meters of enamel copper wire approx 1mm diameter. Diameters smaller than 0.7mm need a couple fewer turns and greater than 1.2mm need a couple more turns. That might sound counterintuitive but it is caused by the inter-turn coupling which reduces as the wire gets thicker.
- 200mm of 42mm PVC pipe
- Five 3mm by 9mm metal threads with star washers, nuts and solder lugs.
- Four 12mm small PK screws
- 3 position 2 or more pole rotary switch with a pointer knob
- Two Bannana sockets (I used a black for the Ground/Radials and a White for the radiating element).
- One coax socket
- One 25pF mica compression trimmer capacitor or better still, a bee-hive concentric trimmer if you are lucky enough to have one.
- A roll of good insulation tape
- AZtronics/Altronics H0151 Jiffy Box (158X95X53mm) or similar
Proceedure - The radiating wire and the loading coil
- Cut a 10.1 Metre length of the hookup wire for the radiating wire. This includes the wire wound round the loading coil.
- Cut a 30mm length of 42mm diameter PVC pipe for the off-centre loading coil former.
- Drill two 2mm diameter holes in the PVC to thread the radiating wire through. Each hole is positioned about 3mm in from each end of the PVC, the exact spacing will vary depending on the wire you use. You can re-drilled the holes closer to the coil and trim the PVC for a neat finish.
- Wind 7 turns of the radiating wire round the PVC former, poking the wire through the holes as illustrated.
- Make sure that you position the coil on the wire so that it is exactly 4.7m down from the top of the wire.
- Connect a banana plug to the bottom end of the wire.
- Terminate the top of the wire using one of these methods:
- Tape a small Rawl Plug to the top of the wire leaving the bottom of the rawl plug free to slide onto the top of the squid pole.
- Use a fishing swivel to clip onto the tiny eyelet on the top of the squid pole
The resulting length of wire + coil is used as the radiating element on all bands.
This length of radiating wire with the loading coil is now ready for use on the 40, 30 and 15M bands without the interface coils. The rotary switch will connect the coax socket from your rig to the bannana socket you plug the end of this wire into. No other coils required for these frequencies.
Next we build the 80 and 20m coils
The 80 Metre coil: Primary 25 turns of enamelled copper wire, Secondary 5 turns of hookup wire
- Cut a 70mm length of 42mm diameter PVC pipe for the 80m coil former.
- Drill a 3.5mm hole near one end of the PVC and install a solder lug with 3mm bolt, nut and star washer.
- Bare 2cm of one end of your spool of enamel copper wire, scrape the enamel off with a sharp knife and tin the copper. Now feed the enamel wire through the small hole in the solder lug and solder it.
- Wind 25 turns of the enamel copper wire neatly and tightly onto the PVC former.
- After winding all the turns on, cut the wire so you have about 25mm remaining. Use some electrical tape to hold the wire in place wile you drill a 3.5mm hole near one end of the PVC and install a solder lug with 3mm bolt, nut and star washer.
- scrape the enamel off with a sharp knife and tin the copper. Now feed the enamel wire through the small hole in the solder lug and solder it.
- Solder a length of spare radiating wire to the enamel wire and wind 5 turns of it over the bottom end of the enamel wire winding leaving enough spare as a tail to connect to the rotary switch that goes to the coax socket input from your rig or ATU.
- solder a short length of hookup wire to each of the solder lugs, the one that is fixed to the lug where the secondary coil is soldered goes to earth on the coax connector and a bannana socket for the radials. The other one will connect to the 80M position of the rotary switch that switches the radiating wire.
- When the windings are in place cover them tightly with insulation tape.
The 20m coil: Primary 10 turns enamelled copper wire, secondary 2 turns of hookup wire
- Cut a 70mm length of 42mm diameter PVC pipe for the 80m coil former.
- Exactly the same technique is used as for the 80m coil above. Drill a 3.5mm hole near one end of the PVC and install a solder lug with 3mm bolt, nut and star washer.
- solder the enamel copper wire to the lug and wind on 10 turns. After winding all the turns, cut the wire so you have about 25mm remaining. Use some electrical tape to hold the wire in place wile you drill a 3.5mm hole near one end of the PVC and install a solder lug with 3mm bolt, nut and star washer.
- depending on what type of trimmer capacitor you use you will have to devise some way of mounting it so it is accross the primary winding. One way to do this would be to drill another drill a 3.5mm hole near one end of the PVC and install a solder lug with 3mm bolt, nut and star washer then mount the trimmer capacitor accross the twp solder lugs.
- Solder a length of spare radiating wire to the enamel wire and wind 2 turns (secondary coil) over the bottom end of the enamel wire winding leaving enough spare as a tail to connect to the rotary switch that goes to the coax socket input from your rig or ATU.
- Solder a short length of hookup wire to each of the solder lugs, the one that is fixed to the lug where the secondary coil is soldered goes to earth on the coax connector and a bannana socket for the radials. The other one will connect to the 20M position of the rotary switch that switches the radiating wire.
- When the windings are in place cover them tightly with insulation tape.
- Mount the 25pF trimmer so that it is electrically wired in parallel with the enamel wire coil.
Tuning the 20M coil
Tune the 25pF trimmer for maximum received signal strength at 14.2MHz. Fine tune it by adjusting it for minimum SWR at low power output on the same frequency.
If the tuned circuit is working properly there will be a single very obvious spot where RX and TX work brilliantly. If you have an antenna analyser you can tune it perfectly and expect to achieve a nice 50 ohm non-reactive load.
Connecting to your ATU
For portable use it is highly desirable to position the ATU right at the bottom of the squid pole. That way there is no coax between the ATU and the squid pole and thus no RF coming back down the coax into the portable radio shack. Stray RF with a poor earth is usually overcome when the ATU is at the base of the antenna because that configuration provides properly matched coax running back into the vehicle or tent. The perfect solution is a remote ATU and if you are doing much portable work you should rush out and buy one now.
This version of the Squid Pole interface is based on an project by Phil (VK7JJ)
My edited version of the above web site in PDF
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Written by and Copyright, Phil. Storr © Last updated 8th September 2015
