Thursday, May 27, 2010

FT-897D deaf on 6 meters no more

As I have already mentioned, during our first roving experience in the September 2009 VHF-UHF contest we found out that my FT-897D had gone deaf on 6 meters. Several guys could hear us clearly, but we could not hear them at all or only just barely. We made a few QSOs, but it was painful. Something was wrong.

I searched several FT-897 forums to see if anybody else had had the same problem, but came up empty. I tried one potential configuration setting solution, but that had no effect. So, I was bracing myself for having to send the rig in and face an expensive repair.

Just by chance, I visited again the blog of Rex Lester, G8UBJ, looking for his transverter interface design for his FT-897. And there on his blog was a posting on his own FT-897 going deaf on.....6 meters. Hey, maybe this was it!

I corresponded with Rex, he told me about what he had figured out had gone wrong, we identified the part, and I ordered some from Yaesu. The part is Q3034 (a 2SC5374) and it resides on the PA board, just below transformer T3006 which is itself just below that yellow relay you see in the picture. Happily, once you remove the cover over the PA board, it's pretty easy to get at.

These are tiny surface mount transistors, smaller than a grain of rice. The transistors were $0.55 apiece from Yaesu. I ordered 5 and they charged me over $10 for shipping (ahem.) Still, if this was really the problem then it would work out as a bargain.

I put the rig on the bench yesterday. Swapping the part took only about 15 minutes--a little hot air to get it off, then tack the new part down while working under the microscope. If you don't have the facilities to work on surface mount parts, please don't try this--you'll screw up your rig and it'll be expensive. You must have magnification, a fine-tipped soldering iron, and a steady hand. A hot air source to remove the part is certainly the preferred way, to avoid tearing pads/traces. But if you have the right tools and technique, go for it.

Last night I did an on-air test with Ralph, KC9LBO and all was back to normal! Thanks a bunch Rex and Ralph for your help on this one. So, 6 meters is back in play and ready for the June ARRL VHF-UHF contest which is coming up fast.

73 de W9HQ

Monday, May 17, 2010

Just a Little IF Padding

My 902 MHz transverter board is stuffed and ready to check out. But first, I need an appropriate IF signal.

I have a 2 meter HT that can be dialed down to 20 mW (13 dBm) on its lowest power setting. That's within spittin' distance of the 0 dBm that I need. So I built an attenuator pad that's adjustable from 10-13 dB of attenuation. Perfect!

It seems like I'm awfully close to getting some 902 MHz RF out of my first homebrewed transverter. Maybe tomorrow.......

Friday, May 14, 2010

1152 MHz LO Working

Okay, today I finished stuffing the 1152 MHz LO board, which goes with the W1GHZ 1296 MHz "Right Side Up" transverter. Since I hit a few landmines with the 756 MHz board, I double-checked a few things before applying power. All looked good, so on she goes.......

And yes, it's working right out of the chute. As you can see from the photo, I'm only getting -8.58 dBm out of this LO, although my test cable which is about 10 feet long is soaking up about 1 dB.

Paul Wade (W1GHZ) says he got -5 dBm out of his prototype, but that some trimming of the R2 and R3 bias resistors on the last two stages of amplification may be necessary for maximum power output. I'm 2.5 dBm off, but I guess we'll see just how much is really needed when it comes time to connect this to the transverter board, which has another stage of amplification for the LO input.

Next task is to get a 144 MHz IF rig to drive this stuff with. The trick is that these transverters only want to see about 1 mW of drive, so it's going to take some finagling to get the output of any of my rigs down to that level. I'll let you know what I figure out.

73 de W9HQ

Wednesday, May 12, 2010

Okay, now it works.....

Alright, that's better. As I said in my last post, the output of the 756 MHz LO board for my 902 MHz transverter (W1GHZ design) was only putting out -28 dBm, so something was obviously wrong. Now, to find out what it was.

Worst case was that I had blown all the MMICs when I accidentally hooked the power up backwards for a split second. (Did I really do that? Uh, well, yeah, I did.) Time to find out. So I pulled C4 and put a test probe on there and sure enough I had 0.5 dBm at 252 MHz out of the first filter stage. So at least I knew that A1 right after the crystal oscillator was working. Phew! Dodged that bullet.

I wasn't too keen on actually slicing the board to test right after the second amplifier stage, so instead I double checked the values of the bias resistors. They were okay. Could it be that running the bias to A2 through a leaded ferrite bead changed the resistance of that path enough to matter? Unlikely, but I removed the ferrite. Same deal.

So I decided to re-flow the solder connections to A2 and A3 and, in doing so, noticed that I had the bias resistor to A3 going to its ground pin, not its output, one via over. Ah ha! Moved that over and....Bingo! 6.68 dBm of beautiful RF at 756 MHz.

Next up......the 1152 MHz LO board for the 1296 transverter.

Tuesday, May 11, 2010

It Lives! .....but it limps....

In a group buy sponsored by W8ISS, I bought the PCBs and parts for LO/transverter boards to build W1GHZ transverters for 902, 1296, 2403, and 3456 MHZ. I have stuffed the LO and transverter boards for 902 and 1296 MHz, but had no way to check them out. I was recently able to borrow a spectrum analyzer for a few weeks, so now I'm scrambling to get as many of these boards up as I can. I've just applied power to the first piece in the line-up, the 756 MHz LO board for the 902 MHz transverter. It's definitely oscillating at 756 MHZ, but unfortunately the signal is at about -28 dBm. The docs for the W1GHZ design say I should be seeing about +5 dBm. Well, I guess that's why they call it troubleshooting. Still, this is extremely cool. I never thought I would be into VHF-UHF-SHF operating, let alone building my own gear for these freqs!

Paul Wade, W1GHZ, has done the amateur community a real service in these simple transverter designs. If you have to buy all the parts outright, you can expect to pay about $70-80 per band which is still darn cheap. But if you can get in on a group buy, that price will drop to sub-$50, which is really incredible. What a fantastic way to experiment with SHF. I have already learned a ton of good stuff and I'm sure both learning and fun have just begun.

73 de W9HQ

January 2010 VHF-UHF Sweepstakes

Okay, time to update this blog more often. My problem—both in blogdom and in other parts of my life—is that I let the best become the enemy of the good. In this case, I always want photos and details all lined up so that the blog posting is as complete and interesting as possible. But then I never quite get around to blogging at all. Enough of that.

My son Christopher (KC9JTL) and I had a great time in the January 2010 ARRL VHF-UHF sweepstakes. One really cool aspect of this contest was hearing so many locals on the air, on both FM and SSB.

As for locals on FM we worked KB9TPG, KC9LBO, K9ALT, KC9OYG, KC9NHQ, KC9KVJ, W9ET, KC9MRV, WX9EP, and N9UNW.

Local contacts on SSB came from WV9E, WV9S, KA9FOX, W9UUM, W9GM, W9RPM, N9ETD, KB9BGN, and AB9HW. (I hope I'm not forgetting anybody.)

I think that's just great, so thanks again for everybody who got on the air!

Christopher and I made a total of 93 contacts. Here's the breakdown:

Freq QSOs Grids

50 27 9

144 52 14

222 9 6

440 5 1

That's almost twice as many contacts as we got last January, which was our first VHF-UHF contest. And conditions were pretty poor this weekend. Hope to do better in June.