AmateurRadio.com

My “first” KX3 during its early days at KG9DW.

I heard back from Elecraft yesterday, and my KX3 is officially toast. You see, it wasn’t ever designed to have 120VAC applied to the external power connector. As I feared, the current transitioned through the control board, wiped out some components, traveled across the leads to the RF board, took out multiple components, and then exited through the well grounded antenna connection.

Talking through the options, fixing it is cost prohibitive. The guys at Elecraft are working on an option for me, so I’m hopeful I’ll have a working KX3 back in the shack in the next couple of weeks. In the meantime, I’ve got a loaner radio from a buddy in the shack. It transmits fine but its receiver is so, so deaf compared to the KX3. It’s like going from an iPad Air to a Palm Pilot.

In the comments of my last post about this mistake, the suggestion of fusing along with a diode was brought up. I’ll definitely be putting more thought into my power supply cables after this costly error.

With my KX3 on the fritz (boxed up, ships out tomorrow) I won’t be able to join in on the fun in chasing K1N on Navassa Island. But I did manage to sneak in some time this evening on K2SDR’s internet enabled software defined radio station. Just listening to the CW pileup makes you wonder if you’ll ever be good enough to pick them out of the pile! Here’s a view of what 20M CW is like….K1N is the station on the left…the rest to the right are in the pile!

There’s two ways I learn best – studying other people’s mistakes, or making my own mistakes. Today I was the subject of the mistake. My Astron power supply has two meters on the front…one for voltage and one for amperage. I noticed a few weeks ago that the ammeter was reading way too high. I rechecked the voltage, and all was fine. My loads hadn’t changed, and my other ammeter wasn’t showing anything amiss. I cracked open the case and found the simple pot to adjust. Since I needed to put a load on the supply to set the ammeter I left the AC plugged in. Just as I was connecting up the load, I dropped a lead. Well crud, that wasn’t a nice snap or crackle. I blew the AC fuse, which was quickly replaced. I went on with the procedure, buttoned everything back up, and went to check out the radios. Unfortunately it wasn’t just a fuse that gave up its magic smoke. My Elecraft KX3 refused to power on. Sitting back a few minutes and thinking through what had happened, I realized I had just exposed my beloved radio to 120V across its DC input. I opened up the KX3 but didn’t see anything obvious that I was up to servicing – but I did sniff the board and caught a whiff of magic smoke. A few google searches, a visit to the yahoo group, and the KX3 is packed in a box readied for a trip back to Elecraft. Another mistake, another learning opportunity. And did you know that magic smoke comes from $100 bills? It must, because that’s what it costs when I have to have other people put it back in my radios.

I was very time limited this evening, so I only spent a few minutes on the NAQCC cw sprint for January. I worked AA7VW Vern in Oregon, and KD3CA Don in Pennsylvania. My last two sprints had quite a few more contacts, but I also worked all two hours then. Work ran long, and then after a late dinner I found myself in the shack working on two fixit projects that I didn’t want to put off another day! I turned on the KX3 and listened to the melody of cw while soldering a new connector on a mic and fixing a fussy (but new) power supply. If you’re looking for a fun little contest, I’d recommend trying the NAQCC monthly sprints. Even if you’re not a member, you’re always welcome to join in.

So you’ve played with DSTAR enough that you’ve decided you want to host your own repeater. Well congratulations! Welcome to one of the most challenging and satisfying activities in your ham radio “career”!

Here’s what you’ll need if you want to build a DSTAR repeater.

1. Antenna
2. Feedline
3. Lightening protection (suppressor, in addition to a proper ground system)
4. Duplexer (a flat-pack mobile unit will work if you’re in a low RF environment. If there are other transmitters around, you’ll want larger cavities – a band-pass/band-reject unit.)
5. A repeater site – as high as you can get, with easy access for maintenance
6. Internet access – including a public facing ip address so users can route directly to you from other repeaters
7. Power supply – 12V at whatever amps you’ll need
8. Miscellaneous cables…all good quality!

As a quick side note, all of the principles for analog repeaters applies to digital systems. Checkout www.repeater-builder.com for tons of good information.

Phew. Now that you’re done with the antenna system and internet access, you’ll need to make a decision. Are you going to go with the ICOM system, or a home-brew system?

For an ICOM system:
1. Radio module for the band you want to be on ($700 for UHF)
2. Controller module ($850)
3. Computer running Linux to run the gateway software (figure $300 for a solid system)

That’s $1850 in addition to items 1 through 8 above.

The other option is a home-brew system. I’ve built two of these already – one from Kenwood radios, and one from Motorola radios. Either of these requires access to programming gear/software, so you may have other costs you need to consider.

For a home-brew system built on Motorola radios:
1. 2 CDM 1550 UHF radios (one for TX, one for TX) – $300 from eBay
2. Raspberry Pi with SD Card to run the G4KLX gateway software ($50)
3. DVRPTR modem – http://dvrptr.net/ ($120)

For the CDM radios, you can’t run them at 100% power – these are mobile radios, and they are rated at 50% duty cycle or lower at full power. I’m using 30 watt radios at 10 watts. The transmitter doesn’t seem to mind this power setting, even when run for 2 hours continuously. Because of the acknowledgement packets that are sent after user transmissions, duty cycles easily get 100% during normal DSTAR use. Hold a net, or a long QSO, and you’ll find your transmitter melted if you try to run it at too high of a power setting.

You can add a power amplifier after the transmitter if you need more power. I’ve not found this to be necessary with the proper antenna and site. If I can hear the remote units, they can hear me. More power hasn’t been necessary.

I’ve also had success with a Kenwood TKR-820 repeater. But….programming these for me is harder. Alignment is a bunch of coils and takes some time. They have a built-in power supply. You really need to narrow-band the units, as that’s what the users’ radios are expecting. It will work wide-band, but it won’t work as well. The system needs to be narrow on both the repeater and user side.