CQ DE VK7BEN

Just another Amateur Radio Operator

Category: Equipment

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:

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.

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.

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