Archive for May, 2010

Odds and Ends

May 25th, 2010

Yesterday, I revisited this post listing on-going projects from December 2009.  Some things have changed, some remain the same.

The computer stuff has all been crossed-off the list, except that the home server is off-line with a dead power supply (or motherboard).  I’m somewhat loathe to spend any money on it, but I should be able to pick something up.

While it would probably have been cheaper to buy one of the HF/VHF/UHF combo radios, I’ve set off stupidly down the trail of building (and interfacing) transverters.  I am just three amplifier stages away from having 3-5 watts on 50 MHz!  …plus the interfacing.  I’ve decided that interfacing transverters to radios is more difficult than actually designing and building the transverters themselves.  I built the 903-MHz W1GHZ transverter during the Winter, but haven’t tried it on the air just yet.  W8ISS announced recently that he had some leftovers from the group buy of W1GHZ transverter parts, including boards for 2304 and 3456 as well as some G6Y relay kits.  I bought the lot.  I have enough MMICs and chip caps in the shop to build these and since I’ll need to order a couple of mixers for the other transverters, I can hit the Mini-Circuits minimum order.  Sometime.  Microwaves may all get pushed off to Fall and Winter.

Through a strange coincidence, my wife and I independently decided that it would be a good idea to move my ham shack.  The new location is closer to the center of activity in the house, which means I’ll operate more radio and be more accessible to her while I’m doing it.  But, the feedline and rotator cable no longer reach my 144-MHz Yagi.  Fortunately, I’ll be able to raid the K8GU coax stash shortly.  In the mean time, I’ve been missing what appear from the Hepburn maps to be epic tropo conditions.  Stuff happens.

QSLing, notably my favorite QSL topic—bureau cards.  All bureau requests for KP4/K8GU have been processed.  I ran out of CE/K8GU cards with 10 to go.  I will run some more of these from a photo printer in the next couple of days.  Piles of PJ2/K8GU, K8GU, and (go figure) AA8UP cards remain.  I will get the PJ2 cards done this weekend since I have a box of cards on-hand.  K8GU and AA8UP cards are awaiting a redesign.

Although it sounds like a lot, relatively little is getting done on any of these things thanks to an outdoor project at home.  More on this in the future.

TS-930S PA mod — first try

May 25th, 2010

As I wrote recently, I have been tackling the low-frequency instability problem in the TS-930S PA unit.  My first attempt was to add several bypass capacitors to from the supply side of L7 to ground (through a lug on the Q7 mounting screw a short distance away).  This should tame the drivers, although the problem is not there.

The hum came back when I pushed the power beyond about 50 watts.  The push-pull MRF-422 final amplifier circuit in the TS-930 comes from Motorola EB27, with a few small modifications.  However, it is not clear to my untrained eye where additional precautions could be taken.  I have a hunch that my next target will be this portion followed by the 2SC2075 pre-driver stage if I come up empty on the finals.

More on the TS-930S PA

May 21st, 2010

I’m not sure that I’ve shared this on the blog, but I’ve long known that the reason that my “troublesome” 930 burns up PA drivers is a low-frequency oscillation.  This mechanism was also mentioned by Leeson in his comprehensive list of 930 upgrades and repairs.  At first, I thought that the 28-volt power supply’s filter capacitors might be the culprit—insufficient ripple-suppression.  After all, the oscillation sounds like it has a 60-Hz component (I’ve never tried to measure this because I’m concerned about blowing up more transistors).  I finally completed the capacitor replacement last night, realigned the power supply voltage and PA bias levels…and the oscillation is still there, just as I increase the drive past the point where I get 50 watts out.

There is a good Helge Granberg article in the September/October 1980 issue of RF Design titled “Good RF Construction Practices and Techniques.”  I would like to get a copy of the original article because Motorola, in their infinite wisdom, reprinted the article as AR164 but neglected to include the list of references.  Granberg devotes an entire section of the article to instabilities, a full of half of that section to low-frequency instabilities.  This is the area I will focus on first:

Causes for the low frequency instability are usually inadequate collector DC feed bypassing or an extremely poor ground in that area.  Two or three RF chokes together with various values of bypass capacitors from 1000 pF to several uF may be required in the DC line to stabilize the circuit.  (See examples in Reference 1.)

Ah, Reference 1, where (who) art thou?

If I ever get to the bottom of this problem, there should be a useful body of work and notes to prevent this from happening repeatedly to others.

A License to …

May 13th, 2010

Jeff, KE9V, posted a note today about all of the bellyaching that goes on over the Hamvention venue at Hara Arena in Dayton, Ohio, also occasional home to Bill Goodman’s North American Gun and Knife Show (“Tell a buddy, bring a friend…Don’t you dare miss it!” the jingle goes).  In fact, according to the Hara calendar, it appears to host almost monthly gun and knife shows.  But, I digress.  I’m delighted that Hara is near my in-laws’ home should I ever wish to make a last-minute appearance—yes, it’s tempting to get in the car tonight.  And, I digress farther.  The point of this post is to explain the pervasive grumbling, finger-pointing, and misinformation, that spews forth from a vocal minority of the amateur community.

I was sitting in 8th grade math class adrift in daydreams as the teacher reviewed yet another topic from a prior grade.  Clearly, this was a widely-perceived problem, because one of my classmates persisted in talking to several others around her.  Finally, the teacher became so exasperated that he asked, “Young lady, do you have a license to talk?”  Of course she did not, but I chuckled noting that, as a newly-minted General class amateur radio operator, I had a license to talk.  I tucked that away for future use and went back to whatever it was I was daydreaming about.  And today, some 16 years later, the thought sprung into my mind as I read Jeff’s blog.

Another curious coincidence contributed to this confluence of cogitation.  As I was eating my lunch, I happened across an old KK7B paper from the Proceedings of Microwave Update ’94 entitled “Simply Getting on the Air from DC to Daylight.”  It’s not a particularly technical paper.  It is about the art of doing radio and it was fun to read.  In the first three paragraphs, he writes,

In the not-so-distant past, the primary emphasis in amateur radio was putting a station on the air…Sometime in the ’70s the ARRL stopped calling amateur radio a technical hobby and started referring to it as a communications hobby.

Brilliant.  I’d like to update that for the present,

In the not-so-distant past, the primary emphasis in amateur radio was communication via radio…Sometime in the ’00s, realizing that it had lost the communications game to telecom deregulation, mobile phones, and the Internet, the ARRL stopped calling amateur radio a communications hobby and started referring to it as an emergency service.

So, where does that leave us?  Well, we have a technical license exam structure impressed upon a group of people who are enthralled with communication but use the Internet because it’s easier.  No wonder anybody who reads about ham radio on the Internet thinks we’re up a creek!

I’m going to go make a CW contact or melt some solder to cheer myself up.  In the end, we have a license to communicate via radio.  Let’s use it.

Platform Agnostic

May 6th, 2010

Are you?  Objectivity trumps hype.

Transverter Common-IF Box

May 1st, 2010

I weighed the pros and cons of tapping the low-level TX and RX lines inside of my FT-840 (the TS-930 brings these to the rear panel) versus installing an attenuator in the TX line.  I opted for the attenuator instead of doing surgery on the radio.

The circuit is not particularly remarkable:  the transceiver RF jack goes to a relay T/R switch.  The TX side of the relay goes through a hefty 20-dB attenuator to a BNC jack.  The attenuator is rated at 5 watts continuous duty and considerably more at lower duty cycles, perfect for this application.  The RX side goes straight through to a second BNC jack.  The TX circuit is normally closed (and RX normally open).  This minimizes the chance of accidentally dumping 5 watts into the RX side of the transverter.

50-MHz RX LNA (Day 2)

May 1st, 2010

Built a little low-noise amplifier for the RX converter today using one of the BF981s I received the other day.  The design is based on the dual-gate MOSFET VHF preamp in the 1993 ARRL Handbook.  My local noise level was too high to credibly optimize the match on the beacon alone.  But, it did improve my ability to hear it on the 10-meter dipole.