A 3D Case for the TNC-Pi

TNC-Pi Printed Enclosure
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!

HC-05 Interface Board
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

IMG_1989It’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!

Loads

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

Oops

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!

OCFWindom

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!
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!

 

Yaesu SCU-17 – The Missing Manual

Yaesu SCU-17 Unit
Yaesu SCU-17 Unit

Although it is almost certain that future generations (and the more expensive versions!) of radios will have rig control and digital mode keying built in with just a USB cable to go between radio and computer (such as Yaesu’s FT-991), for previous generations of radios, such as my FT-DX1200, the Yaesu SCU-17 Interface is required to act as that bridge between radio and computer.

There is nothing particularly special about the interface – you could make one yourself at home if you wanted. It consists of 2 USB to Serial ports, a sound card interface and a little bit of wizardry to wire it all together. As for me I’d rather just spend the money to save myself the hours of frustration of putting one of these together (and troubleshooting issues) and end up with a professionally made, compact unit.

However what I wanted to address was the distinct vagueness of documentation around that covers how they operate.

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Testing Coax for Faults

It’s been a while since I was regularly operating my station and much of the coax that is in use has been exposed to the outside environment for over 10 years. I know the best way of testing coax is by using specialised sweep tools, but having only basic testing equipment available I though I should ask the Ham Radio community over on Google+. I think Google+ is an entirely underrated social platform, and I find myself leaning towards it’s use more and more.

Some of the advice coming back I expected, such as investing in an MFJ-269 or FoxDelta Analyser (which is good advice by the way, I see an antenna analyser being next on my purchasing list). However, I think Tim (VK2XAX) provided me with some excellent advice to get started:[mks_pullquote align=”left” width=”600″ size=”12″ bg_color=”#eaeaea” txt_color=”#000000″]

Yes there is a couple of things you can do with basic ham shack items:

  1. stick your power/SWR meter on a small patch cable with a dummy load directly on the output of a 2m radio. Set you power out to precisely 10 watts aka 40dBm call this p1. Remove meter from rig. attach suspect cable to rig. attach meter and dummy load to end of cable and measure power again without touching rig output power. call this p2.
    p1-p2 = loss for your cable.
    look up spec sheet for your cable e.g. RG213 has a loss of ~15db@100MHz for 100m so 15/100 = ~0.15dB loss per metre. e.g If your cable is 34m in length then it should have a loss of ~5.1db aka about 3.5w.
    If your 34m cable shows a different value to 3.5w then you should be able to calculate that loss and work out how much worse than the specs it is.
  2. If you have a big dummy load, stick that on the end of the cable with the SWR meter at the radio and pump up the power to max and see if there is any SWR – there should be none. If there is SWR then the cable is most likely damaged in some way that is causing reflection These are good “rule of thumb” tests to check your cables.[/mks_pullquote]

Tim then went on to detail in a separate Google+ post a demonstration of his testing.

I was quick to check out the second of the two items, as high SWR was my immediate concern (The SWR without ATU seemed a little higher than I remembered, ranging between 2-3:1). I was pleased to find that it is not the coax contributing to the SWR (which means I need to look at the balun next…). The loss measurement will also come later.

Other more obvious inspections I have done are:

  1. Continuity – just use a multimedia so find any obvious issues like open circuit, or short circuit  between the conductor and ground.
  2. Visual – Inspect Coax and connectors for any physical signs for deterioration such as oxidisation around the connectors and ground braid and  any indications that the outer jacket of the coax has been damaged or has become brittle, allowing water to enter the coax.

I have unfinished business with the Coax and dipole, so I am sure there will be a post in the future providing a continuation of the testing.

 

 

Back on 6m

6m Dipole
6m dipole finally in the air

I’m finally back on the 6m band. It wasn’t a cakewalk, with the dipole generally un-cooperative with the element parting ways with the Acro-bat insulator, and then finding the masthead pulley rope (pictured to the right in the photo) was no longer going up to the masthead, meaning that I needed to lower the mast to replace it.

1:1 coax balun made by VK7ZIF is the centre-feed, and I took the time to redo the PL259 connectors and waterproof them prior to reinstalling to make that particular joint a lot stronger than last time. It was this joint that led to the antenna’s demise a few years ago.

Plugged in, and tested, works a treat with low SWR, which was how I remembered it.

I’m looking at building a new and improved version of this antenna at some point using 2mm multi-strand stainless marine stainless steel wire, much the same as my HF dipole.