Tuesday, August 28, 2012

TS-120 Tribulations

I recently picked up a Kenwood TS-120S at a hamfest for what I thought was a fair price. I asked the seller if there was anything wrong with it and he showed my how sometimes the PLL would unlock and pushing on a particular connector would 'fix' it. "No biggie" I thought, "loose connection, a little NoAlOx will fix it". Also there was no mic. I brought the rig home with a CB mic I found for a dollar.

Once home, the rig's true nature quickly became clear. USB reception was only possible with the IF shift knob was turned fully clockwise. USB transmission was impossible. LSB transmission sounded like crap. Turning the power higher than a watt or two caused the finals to oscillate with full 100W power forwards and reflected. The audio was crackly and the PLL lockup issue was a significant annoyance. Sometimes after TX the RX sensitivity would dive.

After way way too much time on the bench, I finally have these issues resolved to my satisfaction. 10m TX audio is still distorted, but I get good audio reports on other bands and have made several contacts on 20 and 40 meters.

I suspect this radio will eventually find it's way into my Jeep.

Here is a full list of the work I did to resurrect this rig.


PA Board

Distorted TX audio & CW tone

  • Exciter output sounded great but PA output sounded like garbage. Properly adjusted base currents; still sounds bad on 10m, other bands OK

Preventative Maintenance

  • Resoldered all transistors.
  • Applied fresh heatsink compound.

 

RF Board

Preventative Maintenance

  • Replaced D2,3,4,5 and 8 on RF board with new 1N914 parts. D8 showed high reverse leakage in circuit, but that may have been caused by an alternate path to ground.

Finals Oscillating

  • Applied SB-844 to resolve PA oscillation; R47, R50, and C61 already had the updated values, from the factory I think; Did NOT add series diodes due to possible RX IMD degradation; Did add AVB bypass cap.

 

IF Board

Loss of RX sensitivity after TX

  • I found that sometimes after TX, RX sensitivity would be lost, and a bonking the rig would bring it back. Replaced IF board relay RL1 with new part. See also filter board repair.

 

Filter Board

Loss of RX sensitivity after TX

  • I found that sometimes after TX, RX sensitivity would be lost, and a bonking the rig would bring it back. Replaced Filter board relay RL1 with new part. See also IF board repair.

Preventative Maintenance

  • Applied SB-051 Final Protection mod

 

AF Gen Board

Symptom: Crackly RX audio, PLL unlock (dots on display)

  • Re-soldered broken joints on Q3 & Q7 on AF board; solder cracked due to thermal cycling and insufficient solder from the factory; I would check Q2 also.

Preventative Maintenance

  • Replaced C10, C11, C13 and C16

 

CAR Board

Symptom: USB BFO frequency low

  • At first, USB reception was only possible with the IF shift knob cranked fully clockwise. During alignment it became clear that the USB BFO frequency could not be brought into spec. It's supposed to be 8.8315MHz, and the highest I could get was 8.8314MHz, which is a big problem. This is probably due to the crystal aging. I got the CAR board set up so I could play with it in vivo and experiment with adding additional capacitors in parallel with C22. I found a 1pf cap lowered the resonant frequency just a bit. I then put the 1pf cap in series with C2 22pf USB CAR osc fixed cap. That brought up the frequency into the useful adjustment range of the trimcap, making it possible to complete the carrier point step of the alignment procedure.

 

Misc

  • Drilled holes in sides of front panel to access front assembly screws without removing panel; this makes removing the RF board much easier; loosen shaft coupler front set screws; remove front panel screws; pull front panel forward to free shaft from coupler; remove rf board screws; angle front panel down, remove RF board by sliding up and back off the shaft.

 

Alignment

  1. Checked PSU voltages, OK
  2. Adjusted USB & LSB car outputs; OK
  3. Adjusted CW CAR; NOT OK! Behaves oddly; rx freq = usb freq; tx freq is offset lower; procedure calls to adjust VR2 to set CW car osc rx freq but adjusts tx freq instead (sigh). Need to review TS-130 manual for potentially improved procedure.
  4. TX/RX IF shift; OK
  5. Center RIT; OK
  6. Carrier suppression; nulled by ear with a second receiver
  7. Carrier point; adjusted first using factory procedure, then by ear listening to RX signals
  8. Adjusted final PA base current; OK

Twiddled RF board output balanced mixer balance trimpot; oops; how to fix? Not documented in svc manual.

Still To Do:
  1. Apply SB-037 VOX Operation Pick-up Time
  2. Apply SB-816 Band Pass Filter Change
  3. Adjust CW CAR
  4. Add speech proc
  5. Add DSP (or a notch filter at least)

Friday, August 10, 2012

Area 2m Repeater Report

Here's a list of 2m repeaters I can hit from my QTH in Barre Vermont, using my Yaesu FT-1500 50 watt mobile rig (38 watts measured) into a 1/4 wave vertical, up about 18 feet.

FREQ CALLSIGN LOCATION Report Notes
145.150 WB1GQR Bolton 59
145.410 K1VIT Fayston 59
146.625 W1BD Williamstown 59
146.760 W1UWS Mt Ascutney 22 QRN
146.880 W1ABI Killington 59
146.940 W1CTE Mt Mansfield 59 QRM
147.150 W2UXC Plattsburgh NY 44 DX!
147.390 N1IOE Barre 59

Codec2 - Next-Generation Digital Voice for Two-Way Radio

Codec2 is an awesome, new, award winning, free as-in freedom, open source, digital voice codec. Codec2 was developed primarily by David Rowe Ph.D., VK5DGR, specifically to avoid the intellectual property encumbrances of the digital voice codecs currently in use.

By now you've probably heard of D-STAR. What you may not know is that the voice encoding protocol (codec) used by D-STAR, AMBE, is a proprietary patented trade secret.* Under no circumstances may you inspect, dissect, examine, or modify the codec. This is not in the spirit of amateur radio! Unfortunately most of the other digital voice codecs in use today suffer from similar encumbrances.

In 2008, well-known open source advocate and Amateur Extra Bruce Perens, K6BP, recognized the danger of closed codecs, and began to advocate and evangelize the need for a free as-in freedom codec for hams. Thankfully, Bruce was able to recruit successful open source codec developer David Rowe to our cause. David has an impressive and extensive digital voice resume, and he co-developed the Speex codec, one of the most popular VoIP codecs on the Internet today.

Dave et al have designed Codec2 and created a free open source reference implementation, released under the GNU Lesser General Public License, meaning that it's free and easy to incorporate into other software, even commercial applications. The reference implementation is written in C and targets Linux, with work on Windows compatibility underway (Cygwin is already supported). I was able to download it and easily compile it on my Ubuntu Linux box and encode/decode some sample audio files. I think it sounds GREAT, even at it's narrowest bandwidth!

The reference implementation includes an FDMDV softmodem optimized for use with Codec2. Remember that a codec converts one digital stream to another digital stream; it must be modulated on an analog signal to be transmitted over the air. The FDMDV modem works with your sound card, much like PSK31 or SSTV, and is optimized for HF. The FDMDV modem may also be used with VHF+ FM radios, although an optimized GMSK modem is planned for such operation.

Not only is Codec2 free, but David has managed to produce a codec of truly superlative technical quality. On HF, Codec2 bandwidth is as narrow as 1.1khz; HALF of SSB! On VHF+, 3kHz channels should be easily attained, with 2kHz channels possible depending on radio quality. That's ½ to ¼ the bandwidth of other popular codecs such as AMBE. Power efficiency is easily double that of existing codecs, and hence range is substantially improved. Sound quality is excellent for a voice codec. Depending on the modem used with the codec, amplifiers may be non-linear, hence cheaper and more efficient. The bottom line is that Codec2 beats the snot out of all other digital radio voice codecs!

Because Codec2 is a free and open specification, it is not an “unspecified digital code under FCC rule 97.309(b)”, and may be legally used for international communications. Contrast this with the situation in France, which has completely banned D-STAR due to the closed nature of AMBE.

On July 24 the ARRL announced David Rowe as the recipient of the 2012 ARRL Technical Innovation Award for his work on Codec2. The Board noted that Rowe “has been a major leader and the primary technical author of an open-source CODEC2 protocol, designed to address the impediment to the development of amateur digital voice posed by closed-source protocols.”

Codec2 and FDMDV are currently usable, but are in an “alpha” stage. Development and testing are well underway, including on the air testing. There's a GUI in the works, but right now it's just a collection of command line utilities and libraries, so that's a bit of a hurdle for less technical folks. I hope we soon start to see Codec2 support in the popular PC SDR apps, and DSP radios like the K3 should be able to support it with a firmware upgrade. I for one am looking forward to trying Codec2 on the air, and I'll be sure to report my findings when I do.

For more information:

* If you were in the D-STAR presentation at the 2010 RANV HAMCON, you may have caught me giving the presenter, Cal Calvitto, WA1WOK, a little friendly heckling about AMBE (Sorry Cal, nothing personal, and I did enjoy your presentation). Yes, D-STAR takes a lot of heat. Yes, the codec situation is unacceptable. It's also pretty lame that Icom trademarked it even though JARL invented it. And the rigs cost a fortune. That said, I have reviewed the D-STAR specification, and aside from those issues, I think it's actually a pretty good system. If the issues can be surmounted, then I would be happy to see D-STAR with Codec2 become widely adopted by the ham community.

Wednesday, August 8, 2012

Weather Radio DXing

I recently built and installed a 1/4 wave vertical antenna for the 2m ham band. I used an aluminium boom from an old TV antenna for a mast; it's not super strong, but it's a light antenna. After trying to think of a way to homebrew a mount, I ended up using this 24" stand off mount to install it on the house under the eves, right outside my shack. I'd say it's up about 20 feet.

I hooked it up to my cheap new scanner, which has a WX button that scans the weather band. I thought it would be fun to listen to the dulcet tones of the NOAA voice synthesiser for a while and log all the NOAA weather stations I could hear. Here's the list with notes:

Call Location Miles Report
KIG60 Mt. Mansfield, VT 27 Full quieting.
WWG50 Burke Mtn., VT 38 Full quieting.
KZZ41 Mt. Washington, NH 59 Mostly quieting, solid copy.
WNG546 Moose Mtn., NH 38 Very little quieting, poor copy.
WXM44 Mt. Ascutney, VT 54 Mostly quieting, good copy.
KSC43 Gore Mtn., NY 86! Full quieting, excellent copy!

There you go, six stations, including one 86 miles away, past the Green Mountains, way over on Gore Mt. in New York! Must be an inversion!

Tuesday, August 7, 2012

Radio Shack PRO-2038 Scanner Review

I wanted a way to have a permanent receiver in the shack for monitoring local VHF/UHF amateur activity. Something I could just leave on all the time and never be tempted to remove from the shack and put in a car. I could have just bought a ham transceiver, but I decided a scanner might be a better fit for a couple of reasons:
  1. Cost: I got my scanner for $20 shipped. It being so cheap I will be less tempted to ever take it out of the shack, because I have real radios for that. If I really feel the need to have a scanner in the car or in the field, I can cheaply buy another one.
  2. Speed: Scanners are blazingly fast, even old ones. Most ham radios scan very slowly, especially the older cheaper ones. With lots of channels programmed, you're lucky if it ever stops on any activity, and if it does half the time you just catch the squelch tail.
  3. Frequency coverage: Even cheap scanners cover 28mhz through 450mhz; some go up to 900MHz.
I found a Radio Shack PRO-2038 scanner on eBay, and won it for $20, shipped. I know it's a rebadged Uniden, but I'm not sure the equivalent Uniden model.

Being somewhat new to scanners in general, I was a bit surprised to discover how it "really" worked. It's billed as a "50 channel" scanner. The reality is more complex and, unfortunately for amateur use, limited.

It has six "banks", the first five of which are pre-programmed with relevant frequencies; Fire, police, air, weather, marine VHF. Then there's the "Private" bank, which is where you put your ham channels. Unfortunately the "Private" bank only has 20 channels. So what about the other 30 programmable channels? Turns out they are in the fire and police banks, so you can add new frequencies to those banks. You COULD use them for ham stuff but then you'd also be scanning 500 police frequencies at the same time. Also you can only scan one particular bank at a time, so if you want to monitor fire AND police, or fire AND amateur, SOL; buy two scanners (or one with a more flexible memory system). I guess those are the limits of circa 1993 scanner technology.

The bottom line is that, for amateur use, this is a 20 channel scanner. That's adequate for me. I don't think there are more than 20 active VHF ham channels that I can pick up from my QTH. I programmed all 20 channels and most of them are silent 24/7. Some are distant repeaters and I may just be out of range. Others are local repeaters and simplex freqs with zero activity; sad.

The built-in speaker fires down, which renders speech unintelligible when the unit sits on a flat surface. With an external speaker, the audio sounds fine.

I get crud on 146.550 sometimes. Sometimes it sounds like a pager, sometimes it sounds like music. It's a bit odd because there are no strong transmitters in my immediate vicinity. I keep that channel locked out much of the time, which is unfortunate, because my area does have some activity there.

Overall I'm satisfied with my purchase. I can monitor pretty much all of the active VHF/UHF channels in my area and it scans a lot faster than most ham rigs. If you live in an area with more activity, you might want a scanner with more channels.