K7NVH

Ordered the head extension cable and a mounting bracket for my Icom 706MKII-G last week, and they showed up in the mail on Saturday, so I had a good time on saturday afternoon figuring out how to get the rig mounted in my new car.

The main issue was finding a good space on/near the dash for the head. Unfortunately, due to the large size of the 706 head, and restrictions on where I can place it due to not wanting to put it in front of any of the air bags, I eventually came to the conclusion that the dash wasn’t right right spot for it.

Thought about putting it up in the sunglasses holder, and the head fit there, but none of the cables connecting to it would. Plus how am I gonna get the cables up there anyway.

Eventually I found that it fit nicely with lots of room for cables and whatnot inside the center console/arm rest box. Then I can run the cable under the rear seats and under the floor of the trunk to where I’d mount the body of the radio.

Then came the issue of powering the radio. I thought about how I could run power to the rear of the car from the battery, and have it look nice (seeing as it’s a shiny new car). Short of paying a professional who knows how to get the thousand trim pieces off between the battery and the cargo area, there wasn’t a whole lot I was willing to do. Though, I remembered that there’s an accessory outlet in the cargo area. It wouldn’t be able to supply enough power for transmit, but if I used it to charge a couple of small Sealed Lead Acid UPS batteries, the batteries could provide the transmit current, and the accessory outlet to supply the receive current and recharge the batteries.

Anyway, it seems to be working great, so now I’m all set to be operating mobile in my new car!

So, as pointed out in my last post, I got some HX1 transmitter modules, and hooked them up, however, it appears that the deviation is kinda funky when it comes to APRS. In this line of thinking, I decided to actually make a test of it, and feed the HX1 with a function generator. So that’s what I did.

My test setup was the following, a signal generator, outputting a 2V P-P sine wave audio signal, feeding into the HX1 radio module, connected to a dummy load, being received by a Yaesu FT-8900R transciever, which has the external speaker port connected to an oscilloscope.

A couple of notes about the test setup.

1.) The amplitude of the signal generator was a constant 2V P-P through the frequency range (confirmed with the oscilloscope).

2.) I have no way to get a good reading on the actual deviation of the HX1 using only the audio level of the 8900. All numbers are relative rather than absolute.

3.) I can confirm that the 8900 audio response good at least through 2200Hz as looking at local APRS signals shows the 1200 and 2200Hz tones to have the same amplitude.

4.) Values in the spreadsheet are approximate. They’re pretty close. Also, like I said, they’re relative rather than absolute. So don’t use them for anything!

Enough of the stupid disclaimers. Here’s the results.

As you’ll note. The audio response peaks at about 400Hz, and slopes off as the frequency increases. You’ll also note that the chart starts at 300Hz. That’s because the radio module did not seem to be stable, or would not output anything near a sine wave below about 300Hz.

You’ll also note that for Packet Radio use, this is rather unfortunate, as at 1200Hz the output was at 0.6V and at 2200Hz the output was at 0.215V. With some crappy, lazy, head math tells me that the 2200Hz high tone of the Packet protocol only has about 1/3 the deviation of the 1200Hz low tone. Not a very good setup…

Anyway, here’s the spreadsheet in xlsx format. Do with it what you will. Spreadsheet

I recently purchased a couple of HX1 transmitters for the 144.39 packet frequency from RadioMetrix. I’ve already set up a widget to generate the necessary tones for APRS, so it was a quick matter to connect up the transmitter and the tone generator for a test.

As a reference, here’s a photo off my oscilloscope displaying the output signal from the tone generator.

You can safely ignore the frequency counter. While the tones are switching between 1200hz and 2200hz, it’s kinda hard to count them. Also, I used a 10x probe, so the peak to peak voltage level listed is 2.25V rather than 0.225V. Lastly, the second division from the bottom is 0V, so as you can see, my tone generator biases the output up a bit to about 2.5V.

And next, here’s a video of the computer receiving said signal.

In this video, you can see that for some reason the HX1 module doesn’t modulate as much with the 2200hz tone as it does with the 1200hz tone. However, it does appear to be enough for the system to decode the packets.

I presently use a 2.2uF capacitor to couple the tones into the transmitter, but the results are similar if I disregard the capacitor, and connect the tones directly to the transmitter input.

Hey all, Just been working on assembling one of the High Altitude Balloon telemetry boards, and thought I’d snap a photo or two since I hadn’t shown it here before.

Haven’t put on the transmitter, antenna connector, temperature sensors or flash chip yet, but you can get the general idea of the system.

Each year I help out with UW’s rocketry and high altitude balloon classes. In the past, we’ve been using custom telemetry systems using radios in the 70cm band, transmitting RTTY telemetry down. This has been working well for us, but there are a couple of issues we run into, which is that RTTY can be pretty slow especially if we’re working with decent amounts of data. Secondly, unless there’s a pretty strong signal, it’s easy to get extra, missing or incorrect characters while decoding RTTY. A little while back, we were looking at ways to resolve these issues, and through some chats with my collaborators, we decided that looking into packet might be a good option.

I did some looking into the matter, and looked into two primary options.

One is to generate the 1200Hz and 2200Hz tones in software on the microcontroller in the telemetry system. This is how we’ve been doing the RTTY signals, but packet requires very accurate timing and that the two tones while switching must remain phase accurate. This is certainly not an impossible task, people have done and continue to implement this. The downsides to this are that it’s very processor intensive, and that extra components must be added to clean up the square waves from the microcontroller into a smooth sine wave.

The other option are several IC components that implement Bell 202 signaling. Bell 202 implements the two tones we need, and we just tell the chip which tone we want at a given time. The advantage here is that we offload tone generation to this external chip, which frees a LOT of processor resources, and the tones that come out of the IC are very clean, and remain in phase. The downside is we need to add a separate IC and all of it’s supporting components.

In the end, I ended up grabbing a few of the Bell 202 modem ICs to experiment with. The particular part I got was the MX614DW.

Anyway, point is that I got this IC all hooked up, and attached it to a test system with a gps and microcontroller with an output to my handheld. It ended up taking a little work to implement the AX.25 protocol, but after getting it all set up, I now have a working packet radio transmitter, and have successfully tested it with APRS and the local digipeaters. See the photos below!

Also, here’s some sample code. Most of it is my own work, a bit is inspired by the trackuino project, and other bits are based on work from various people from around the internet and on the arduino forums.

ARDUINO_PACKET

Hey all, A short while ago, I decided to rebuild my rig interface. I had an older one that I stuck together with a bunch of random bits of stuff, and some hot glue, but it ended up working marginally, and was a bit bulky, so I decided to design a PCB for my new one. Bring down the size of the system, and also throw in some nice features, like a USB connection for the data link, and a couple of pots for adjusting the audio levels. Here’s some photos.

For right now I’m going to test using capacitors to couple the audio in and out, but if that doesn’t live up to the job, I’ve got some audio isolation transformers I’ll install instead and see how that does.