Category Archives: Equipment

More Experiments with EFHW Antennas – Part 2

It’s been a couple of years now since my first post on EFHW Antennas. Notably since then I have acquired a Mini 600 Analyser. Armed with technology it was time to revisit this “no-tune” portable antenna. What followed was 3 months of confusion, learning and experimentation.

Before I go any further I would sincerely like to thank David VK3IL for his patience and assistance over the last 2 weeks in helping me troubleshoot my issues and teach me a bit more about what I was doing along the way.

It all started when I thought it would be a good idea to re-test the end-fed antenna now I have a new analyser as I was preparing ready-to-assemble kits for my local radio club and didn’t want to see people ending up with an antenna that didn’t work as described. To my dismay, the antenna definitely was not working as originally described.

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Hands on with the Mini 600 Antenna Analyser

For a long time now I have had a home-brew antenna analyser based on the VK5JST design. While this has served me OK, the accuracy of the 6m frequency was questionable, as the notes on the side of the tool suggested, and I was really needing something for VHF and UHF with my new interest in satellite and antenna construction.

I had in the past drooled over the Youkits FG-01A, but this again was HF +6m only, and the costs of an MFJ analyser were just wildly out of my range taking into account USD – AUD exchange rates. However we’ve once again seen electronics commoditised over the last few years, and this has led to inexpensive alternatives becoming available. It didn’t take long for the Mini 600, based on the EU1KY design to catch my attention, ticking all the boxes.

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A V/U Handheld Moxon Antenna for Satellites

As per my last post, I have been getting pretty excited about working satellites. However relying on the little ‘rubber duck’ antenna that came with the IC-T90A hand held does limit the range in a way that I could only really work the satellites at high elevation angles. With costs of commercial V/U antennas for satellite work usually over $200 AUD, it was time to build my own.

I did have some constraints around the antenna design:

It had to cost under $50 to make.
No speciality materials required – I could either readily purchase from a shop, or I already had materials on hand.
It had to be made using tools I had on hand.

The last point ruled out making a crossed yagi antenna to my standards as it would require a drill press to successfully fabricate (I am bad at drilling square!)

In the end a quick google found me looking at making a Moxon designed by LY3LP and modified by M1GEO, but I really wanted to get some close ups of some of the more important parts of the build. What follows is an abbreviated build guide with photos. In all, it took less than 2 hours to construct.

Update 22/12/2018 2.15pm – Yep, this antenna is a winner – here is the audio from the AO-91 pass @ 2018-12-22 1342 AEDT. Big improvement – action starts at around 2mins in.

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A 3D Case for the TNC-Pi

TNC-Pi Printed Enclosure

In my last post, one of the things I mentioned was that I built a TNC-Pi shield for my Raspberry Pi, that allows be take part in packet radio. One of the things I didn’t like so much was that I had nothing to put it in to protect the circuits from dust or a misplaced screwdriver shorting out the board.

I was therefore pretty happy to receive as a birthday gift a 3D Printed enclosure designed to hold the Raspberry Pi and TNC from Scott VK7LXX. I’d pointed out the design about a week earlier when looking around, but lacked access to a 3D printer and spare time needed to print.

As you can see in the image to the left and above, it makes quite a comfortable fit. I used a bit of foam to sandwich between the Pi-TNC and the USB ports of the Pi just to prevent any contact of soldered joints with the metal casing around the USB connectors.

Scott tells me this printing was done at a “coarse” level, to speed up the print process and took around 3 hours to print. Those who are eagle eyed will notice that cases bottom is slightly rounded due to an imperfection in the print process – I’m not worried by this because the objective is to protect whats inside, not necessarily be pretty.

3-6 months ago, I was mocking the idea of needing a 3D printer, but I’m not laughing now. I can definitely see myself using a 3D printer to make custom parts in the shack!

Bluetooth Rig Control for $10!

The Bluetooth Dongle. Read below for details

If it’s one thing that continually amazes me is the impact Arduino & IoT are having on Amateur Radio. Things that were once complex pieces of electronics with a complex price tag are now commoditised and available for pennies.

When I first started, a CAT rig control interface could cost up to $200, particularly if on-brand. Taking a look on eBay now, you can find a heap of these Bluetooth Dongles that plug into the back of my FT-817 for generally around $12!

Unfortunately for me, the one that arrived is dead on arrival. It did give me an opportunity to pop the cover and see what is inside. there is not a lot to it at all! To the right of the LED in the picture is basically an AMS1117 3.3V regulated power circuit base, with an HC-05 Serial TTL to Bluetooth Module soldered on as a daughterboard. With only 5 pins in use – +ve, gnd, rx, tx, and LED state, very little needs to be done with these units other than connecting the cables at the right places!

My testing of this unit found that the HC05 board is defective. I have confirmed all power is going to the right places, and it is correctly wired, but unfortunately the unit does not broadcast a bluetooth device ID. This is the big catch when buying from eBay – you get what you pay for! lucky for me the seller is willing to send a replacement unit.

I think however I will eventually purchase one of the units made by K6VHF (His eBay store here). Its ridiculously more expensive, but I will get a unit that has been assembled and tested properly by someone familiar with the radios – and given I spent about an hour of my time today troubleshooting the defective one, with unknown quality of the replacement, that may be money well spent.

I’ll give an update when I have a working adaptor!

Building A linked Dipole

It’s been a little while since I have posted, and its not because I haven’t been doing anything. I’ve been getting my portable station even more portable that before. Ov er the past 3 weeks where I have had a spare evening I have been putting together a new portable station that is even more lightweight than the previous setup featured in my post on Peter Murrell Reserve. Key to this has been producing a linked dipole.

Linked dipoles provide the benefit of creating a single-wire antenna that is resonant on multiple bands without a tuner by “linking” together lengths of wire with clips. While there is no limit on how many links you make, it may not be practical to make the dipole suit everything between 1.8 and 450 Mhz.

I ended up going for a 5 band antenna – 6m, 10m, 15m, 20m, 40m.

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Stuffing the Smoke Back In!

This post will end the saga where I let the magic smoke out of a somewhat expensive commercial antenna.

Today a package arrived in the mail from china which greatly excited me. In it was 100x 10k ohm 3 Watt carbon film resistors from eBay, costing around $8 including delivery. with these, some Veroboard and a little bit of patience I was rebuilding the resistive loads in the antenna. one of the old loads is on the left and the new home brew one is on the right. The damaged resistors are marked as 10k ohm, but measuring them with a multimeter gave a reading of 1.1k ohm.

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Letting the Smoke Out I

Above is a rather fine example of letting the smoke out. My last post talked about replacing a dipole that had worked well for many years but suddenly not so much. With the options of breaking it all apart to check the inside pieces, or throwing out the antenna, I chose the former.

What you are looking at is a very cooked load. Originally 9 10k ohm resistors in parallel are now well in truly charred. behind this (as evidenced by red winding wire) is a ferrite rod with a coil wrapped around it, in parallel with the resistor bank. These loads are used to give the antenna its low SWR across all bands.

Cooking the loads occurs when you forget there is a difference between Px and Py power and also forget that most baluns/loads can take a greater amount of the former over the latter. In this case my new radio allowed me to transmit 100 watts of PSK31, when the antenna was only rated for 50 watts.

It’s not out of the realms of possibility to repair this, should the ferrites in the loads and balun still be in working order. However when you take into consideration that I am would probably need to replace most of the stainless steel wire, obtain replacement resistors and still end up with a balun of questionable integrity (due to aforementioned power excesses), it may be time to recover what I can from the antenna and throw out the remains.

New HF Antenna for Home – an OCF Windom!

When I made up the 4:1 balun earlier this week, I didn’t realise that I would be putting it to use by the end of the week!

Ever since I got active again, the commercial multi band dipole that I had been using for many years was no longer working optimally. When I first purchased it, it had an SWR of < 1.8:1 across most bands, but recently the SWR had had risen to around 2.5:1 across most bands. After discussing and troubleshooting the issue with the antenna manufacturer, it was decided the cost to replace faulty parts exceeded the original purchase price of the antenna.

It was time to replace the antenna.

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Building A Balun

Testing the Balun with 200 Ohms and an Analyser. Looks good to me!

Baluns have always been a bit of a homebrew boogeyman to me, mainly due do what appeared to be some sort of magical winding technique around a toroid. However, given the prices of baluns these days seems to range from $60 AUD upwards, given I have all the parts already at home to make one (“free”), I decided to bite the bullet and learn how to make one.

I’m not going to bore you with the details on how a balun works here, other than to say I think they are useful for connecting coax to antennas. Ladder line, while more efficient, doesn’t have a very good use-case for my applications and good quality ladder line is also expensive and difficult to obtain compared to the plenty of coax I already have available to me.

Shout out to VK6YF whose diagrams for the 4:1 Ruthroff voltage balun were what I used. Some people will be quick to tell me that it was odd to make a 4:1 balun when I am not using ladder line – I agree (and in hindsight should have made a 1:1 balun), but this was about learning how to make a balun.

You can imagine my surprise after being having my build peer reviewed by my good friend Murray that other than a dry joint that was soon fixed, the balun actually worked! to put this in context, two previous attempts at building a balun had resulted in wildly varying SWR and resistive load that on the whole didn’t look much better than just using a piece of wire.

Anyway, now that I know I can build them, I will obtain another jiffy box to build a 1:1 balun for use with my upcoming portable dipole!