Attempting Amateur Satellite Contact with the TM-V71A

If you haven't read my last blog post, I've been taking a break from using my vertical antenna until I can get some proper coax cable set up, in order to reduce the SWR. In the mean time, I built a coat-hanger Yagi antenna using the instructions described here:

http://www.amateurradio.bz/4_dollar_satellite_antenna.html

Here is a picture of the finished antenna:

Using this antenna, I've made 5-10 attempts to listen to the SO-50 FM repeater satellite, and in each case, I would either hear nothing at all or about 5-10 seconds of good signal around the middle of the pass. I'm using the dual-band Kenwood TM-V71A radio, and have been following all the proper procedures for listening to a satellite, including no squelch and adjusting the frequency for Doppler shift. I haven't tried transmitting to the satellite at all, since I can barely get good reception on the downlink frequency.

I was getting frustrated, and posted the above details on the Amateur Radio Stack Exchange website:

http://ham.stackexchange.com/questions/5195/why-can-i-barely-hear-the-so-50-satellite

One of the users there suggested that I might not be compensating for Doppler shift, and sent me the following link that suggests what increments to use when adjusting the frequency:

http://www.amsat.org/wordpress/wp-content/uploads/2014/01/Work_FM_Sats-20131010.pdf
(see the chart on the last page of the document)

It was at this point that I realized the problem. My radio only adjusts the frequency 25 kHz at a time on the 70 cm band. The SO-50 downlink frequency is 436.795 MHz. My radio will only receive on 436.825 MHz, 436.800 MHz, and 436.775 MHz. At first, I was adjusting across these values for Doppler shift, but wasn't hearing anything at all on 436.825 MHz or 436.775 MHz. I eventually gave up and just left the radio tuned to 436.800 MHz during the entire pass, since it was closest to the actual downlink frequency.

The chart above suggests adjusting the frequency 5 kHz at a time over the duration of the pass. This explains why I was only getting a signal for a few seconds at the middle of the pass. I likely got signal only when the satellite was at the 436.800 MHz point in its Doppler shift range. Adjusting 25 MHz up or down would be over-compensating and skip the signal frequency entirely.

EDIT: I wrote the following paragraphs before I realized that you can change the step frequency setting on the radio. The step frequencies that I mention refer to the default settings.

I did not realize this important detail when I purchased the radio. I bought a dual-band radio specifically because I wanted to do satellite contacts. Upon further research today, I noticed in the manual for the TM-V71A that it comes in three types, K, E and M4. The K and E models will only tune by 25 kHz at a time on 70 cm, but the M4 model will tune 10 KHz at a time. I did not know at the time of purchasing the radio that this would be an issue. I checked, and apparently I have the K model.

If you happen to be considering a purchase of the TM-V71A or any other dual-band radio for the purpose of satellite contacts, pay close attention to the step frequency in the downlink band of the satellite from which you intend to receive a signal.

In conclusion, I guess this means that I can't make satellite contacts with my particular radio. I didn't see any mention of a way to adjust the step frequency, so I assume that I would have to purchase an M4 model, or some other model of dual-band radio.

This is frustrating and disappointing, especially on top of my existing frustration with my coax cable issues for my vertical antenna. There just seem to be so many road blocks and details that you need to know, when just getting into the hobby and deciding what equipment to use. To be honest, it's making me lose interest in amateur radio somewhat, because part of the original appeal is gone, due to my equipment situation. I spent $420 on this radio, and now I can't do some of the things I was hoping to do with it.

EDIT: Good news! I figured out how to change the step frequency setting on my radio! I can now change frequencies in the 70 cm band by 5 kHz at a time. I will attempt more satellite contacts with this new setting and report back with an update.

High SWR

The other day, a local ham came by with his SWR meter to help me troubleshoot why my signal wasn't reaching very far. The SWR reading ended up being so high that it was off the chart. It is likely due to a combination of factors: using improper impedance coax, using three coax joiners in the line, and possible water damage to one of the outdoor lengths of coax.

I've decided to order proper coax, and to mount my antenna higher up in the air. Both of these changes should dramatically improve my signal, as well as prevent damage to my radio from high signal reflections in the feed line.

Additionally, the local ham helped me tune my antenna properly. I had not realized that the length was adjustable, in order to tune to the middle of the 2 metre band. This should also help improve my signal. I will post an update once I get new coax in place and a higher mount for my antenna.

Clearing a Memory Channel on the Kenwood TM-V71A

It's been a fun past few days! I've made my first few contacts, and tested the range limits of my radio. I managed to hit a repeater (although with poor signal) that was about 17 km away from me. I'm not sure if that's normal or if I might have a high SWR, as I don't have an SWR meter yet.

Anyway, today I was trying to clear out memory channels on my Kenwood TM-V71A. According to the manual, you go into memory mode by pressing the MR button, tune to the channel you want to clear, power off the radio, then power on while holding the MR button. This should bring up a menu prompt asking if you want to clear the channel, and you press the tuning control to confirm.

I managed to do this for all but one of the channels that I wanted to clear. When I powered the radio on while holding the MR button, it would just turn on as normal, and not prompt me to clear the channel. After trying a few times, I realized that there was a reason it wasn't working, and this reason didn't seem to be mentioned in the manual. If you have both bands on the radio set to the same channel, it will not allow you to clear the channel.

The solution was to switch to band B by pressing its corresponding volume control knob, tune to a different channel, switch back to band A, and then go through the memory channel clearing procedure. This allowed me to clear the channel properly. It took me a few minutes to figure out though, as there is no indication by the radio or in the manual that this was the problem. When I Google searched about this issue, I couldn't find anything, so hopefully this helps someone with the same problem!

Finally Finished Setting Up

I've finally had a chance to set up all my radio equipment so that I can use it! I got my first contact this morning, and it was very exciting! The following are some pictures of my antenna setup and station.