Archive for November, 2011

SoftRock Ensemble RXTX IF modification

November 12th, 2011

This is a pretty simple modification that converts a SoftRock Ensemble RXTX SDR RF interface board from “common-IF” (RX and TX share the same antenna port) to “split-IF” (RX and TX have separate ports).  Split-IF is the standard for high-performance transverters on the 50-, (70-), 144-, 222-, and 432-MHz amateur bands.

So, I had a look at the RXTX schematics (here, here, and here) and considered the following options for where to break the RX and TX portions of radio:

The purple dots were the first option.  Unfortunately, these locations on the actual printed circuit board were not easily accessible to miniature coax and this process would involve significant surgery to perform and restore the modification.  The second alternative I considered was the red Xs…jumpering over the BS170 PA transistors.  By this time, I was looking for a way to avoid butchering the original circuit too much.  So, I elected for option three, which was to install a second T/R switch at the antenna jack (golden circle).  This had at least two advantages, the first of which was being minimally invasive.  The big advantage, though, is that the radio could be operated at its design output and run through a fixed or step attenuator on the TX side to the transverter.  This meant that I would be assured of having a reasonably clean signal to work with if I configured the radio correctly.  It also meant that I could operate the radio as designed if I simply disabled the the second T/R switch and connected the antenna to the default port.

So, here is the modification that I came up with using parts I had in my junk box.  KB9YIG ships the Ensemble RXTX with a couple of spare BS170 FETs that can be used in place of the 2N7000.  I just had a lot of 2N7000s and thought I’d save the BS170s in case I ever burnt one in the RXTX.

The interface to the transverter is through a DB9 connector.  PTT for this transverter is +12 volts (as done with the TS-930S) on pin 6.  Pin 1 is ground.  Pins 2 and 3 are shorted together in the transverter cable connector to enable the modification in the SoftRock.  The right portion of the schematic with the relay driver and Omron G6Y relay is based on the T/R switch from W1GHZ’s “Multiband Transverters for the Rover” that I decided not use on the microwaves when I found a cheap source of SMA coaxial relays.  An I2C decoder would be great to put band data on the other pins to select a transverter (or transverter cascade for the microwaves).

The whole mess works great from a switching standpoint.  When I key the PTT on Rocky or PowerSDR, it switches the TX line and keys the transverter.  I’m a little ambivalent about the quality of transmitted signal that’s actually coming out.  I think it’s good enough if you live in a sparsely-populated area, but I have a lot of VHF neighbors that I’d rather not upset.  So, I need to do some more testing on this—a lot of it is getting the RXTX and PowerSDR configured correctly.  It appears that the I/Q channels are flipped on my sound card (Audigy 2 ZS) between transmit and receive.  I don’t know if that’s a wiring error in my breakout box or whether it’s normal.  Spectra to come at some point…

SoftRock Ensemble RXTX

November 11th, 2011

A few photographs of my latest tinkering—a SoftRock Ensemble RXTX.  This unit provides all of the hardware necessary to have a software-defined radio (SDR) transceiver that uses a computer soundcard for ADC and DAC.  It is available here as a kit.  They are kitted in batches of 20-100 every few weeks and usually sell out within 24-48 hours.

I originally had little interest in doing a full SDR transceiver (preferring receivers only) until it occurred to me that I could modify the RXTX as an IF strip for VHF/UHF transverters like many have done with the FlexRadio Systems rigs.  So, I have developed a modification that is minimally invasive to the operation of the RXTX.  At build time, you choose a nearly octave-wide “super band” for operation.  This one was built for the 20-30 MHz band, covering the 15-, 12-, and 10-meter Amateur bands, as well as the 25-28 MHz IFs that I (will) use with present and planned transverters for the 6-, 2-, 1.25-, and 0.70-meter bands.

I’m not sure I have the enthusiasm to build another SoftRock.  There are a lot of trifilar transformers to wind.  The final result looks pretty good and seems to work.  I’m going to put it on the spectrum analyzer soon to see how clean the output is and how I should balance the drive for the transverters.  Then, I will also include a write-up of how the modifications are done.  (I promise that writeup is the same place as the control circuit schematic for the 50-MHz transverter!)

Here, you can see the W1GHZ relay board for doing split-IF T/R switching.  If the transverter control cable (DB-9) is disconnected, the SoftRock switches to common-RF for regular 15-/12-/10-meter operation.

(No?) Nonsense Radio

November 10th, 2011

The November 2011 issue of QST contains an Op-Ed that really left me shaking my head more than normal.  The author bemoans the complexity and feature sets of newer handheld radios and pines for the days of his IC-02AT.  He goes on at length about the “unnecessary” receive capabilities (NOAA weather broadcasts, AM/FM radio, etc) and how he has to search for the manual every time he wants to program a repeater offset.

Well, as someone who recently upgraded from a radio just slightly newer than the IC-02AT to a “modern” HT, he’s wrong on nearly every account (except the micro-/mini-USB port, which I would wholeheartedly support for charging purposes).

  • Eliminate extraneous features.  Too bad we all have different definitions of this.  I think scanning is a worthless feature, but like NOAA/NWS weather broadcasts.  In fact, my wife is delighted that we now have a battery-powered AM/FM+NOAA/NWS radio again that I will always be able to find and will guarantee that it works.  Did you hear that, guys?  My non-ham wife actually likes my HT and uses it to listen to FM radio!
  • Eliminate multilevel menu trees.   I’m just dying to replace my cell-phone-sized VX-3r with a knob-covered brick.  I’m sure you are too.  It’ll look great in my shirt pocket.
  • Eliminate the proprietary programming cables.  Maybe I’m not a typical ham, but I only have about ten memory channels programmed into my VHF/UHF FM radios and they took about 10 minutes to program through the front panel (my bad, menus).  The mini-/micro-USB port is a good idea for charging, though.
  • Allow for a battery pack that uses disposable batteries.  Last time I checked, most radios have this option.  Did I miss something?
  • Create an inter-vendor standard for user interface.  What if they standardize on Icom?!?!  The last Icom VHF/UHF FM radio I used received a “grade of S, for ‘stupid'” from its owner.  That was in 1993.  All of the Japanese manufacturers will be put out of business by the factory owned by the Chinese military that produces their products before this happens.

He should buy another IC-02AT if he liked them so much.  I bet for a Jackson or two, you could have a nice one…complete with the 6x AA battery holder.  Heck, buy two or three for spare parts.  I think I have the Service Manual around here somewhere if I didn’t already sell it.

On a more serious note, there are lots of no-frills radios available out there, even brand new ones with factory warranties.  Until recently, at least, the money in VHF FM radios was in two-way, government, and public safety, not amateur.  There are a lot of amateur rigs at the “low end” of the market that share a lot in common with their commercial counterparts.  And, of course, you can always buy used Motorola gear on eBay if you desire ultimate performance and ruggedness.

CW Sweepstakes 2011

November 8th, 2011

So, K3KU, who won last year’s Maryland-DC certificate in A-power (150-watts, no DX cluster) for Sweepstakes CW posted to the contest club e-mail reflector a few weeks ago noting that although he had won that I had nipped at his heels with 7 additional hours of operating left on the table.  I responded to the reflector that he had operated long and made more contacts and therefore deserved the win…but, that I was highly motivated by that fact this year.

I tried not to let Sweepstakes consume my home life before the contest since contesting is a major disruption for a married couple, let alone a couple with a four-month baby.  So, I did not start setting up and testing the logging software, etc, until Saturday morning of the contest.  As long-time readers know, I replaced TR Log for DOS in the Spring with TR4W on Windows XP.  I also replaced the real-time keying interfaces (basically an NPN transistor and a resistor attached to a serial or parallel port) with a K1EL WKUSB.  This combination worked flawlessly for the most part, although there were a few glitches I need to fix.

Last year, 80 meters was excellent.  And, for a city lot station, I have a pretty good setup on 80 (full-size vertical and a K9AY RX antenna).  So, even when I had a slow start on 40 meters with the second radio on 20 meters, I had high hopes for a bottomless pit on 80…that never happened.  And, something—perhaps related to the lawn mower incident— is wrong with the K9AY.  So, I had a solid S9 buzz on 80.  When I worked K3AU (op K2YWE), he sent ‘A’ as his precedence and a serial number that was 20% higher than mine.  In fact, every time I heard him, that geometric relationship in our scores held.  I was worried but plowed forward.  The high bands were clearly in good shape because there was always a clear run frequency on 40 and 80.

I operated from the start at 2100 UT on Saturday pretty much straight through until 0700 (3 am local, actually 2 am after the Standard/Daylight time change) on Sunday morning.  Slept for about 4.5 hours (an even multiple of 90 minutes, I might point out) and was back at it again.  Having not spent much time on 20 the night before, I was keen to get there and was well-rewarded for doing so after scraping up what I could on 80 and 40.

I never really worry about multipliers in SS.  Like the “Soviet Russia” jokes go, “In Sweepstakes, multipliers work you.”  But, the fact that K3AU was kicking my butt and the fact that I had only 70 sections (out of the possible 80) on Sunday morning was a bit of a motivator to set score aside and make an effort to get “the Sweep” of all 80.  My normal (low-sunspot) strategy is to call CQ all day Sunday on 40 meters with the second radio S&Ping on 20 and vice versa.  With two more bands definitely in play, this was a different experience.  Since I finished the W3NQN filters, I now felt confident that I wasn’t going to destroy my receivers operating SO2R on 15 and 10.  However, I soon noticed that there was quite a bit of RF getting into the computer.  When I was CQing on 20, keyboard entry to the computer was choppy.  It’s very difficult to line-up a second-radio contact when you can’t enter the call!  Some ferrite will fix this.

So, I ended up using the second radio mostly as a multiplier monitor.  First, I found KE0A (North Dakota) on 10 meters with a roaring pileup.  I kept CQing on 40 and 20 with 10 in my right ear until the pileup died.  I dumped my call in and worked him on the first try while running off a dozen or so guys on the left radio.  SO2R WIN #1!  The same thing happened with the elusive VY1EI (who deserves a massive medal—Northwest Territories).  However, VY1EI’s pile-up management technique involved moving around in frequency.  So, I just waited for him to move and I had the good fortune of being able to study his habits for a half hour without losing rate on the other radio.  SO2R WIN #2!

With VY1EI in the log, I only needed Nebraska for the Sweep.  And, I was rewarded when W0PQ answered my CQ on 20 at 2242 UT.  So, with the Sweep out of the way, I pressed on trying my best to stay motivated and keep the rate up.

Although running (calling CQ) is mentally easier, I found search & pounce much more effective from a rate standpoint for a lot of the contest.  I probably should have done even more.  TR4W guessed that I made 441 QSOs by running and 294 by S&P.  It also says that I called CQ 3870 times.  That’s a pretty bad return on investment.  Anyhow, here are the numbers from 3830 for the interested:

                    ARRL Sweepstakes Contest, CW

Call: K8GU
Operator(s): K8GU
Station: K8GU

Class: Single Op LP
Operating Time (hrs): 21
Radios: SO2R

 Band  QSOs
  160:    0
   80:  182
   40:  330
   20:  170
   15:   31
   10:   22
Total:  735  Sections = 80  Total Score = 116,000

Club: Potomac Valley Radio Club

Those numbers include 10 dupes (at least two of which duped me several times).  But, the score is calculated as 725 x 80 (x 2).  Last year, I lost 12 QSOs with two additional penalty QSOs.  I’m not optimistic about this year.  Last year’s #3 finisher in Maryland-DC is claiming 738 x 80 in 24 hours (and an effort to improve his accuracy).  And, K3KU is claiming 716 x 79 also in 24 hours.  So, I may have to settle for a spot down in the rankings again this year.  After the contest, K2YWE fessed up that his K3AU effort was actually a last-minute switch to Unlimited…so, at least I have a chance despite some mediocre performance on my part this year!  It all comes down to the log-checking.

DXpedition QSLing

November 1st, 2011

This post might better be titled “supporting things that you value.”  A recent large-scale DXpedition to a “new one” just started sending out QSL cards in the past few weeks.  I have seen a bit of traffic leaking onto the regional contest club’s e-mail reflector about QSLing this operation and today someone complained that QSL requests that included donations were being processed rapidly and that he had not yet seen his. He was thoroughly chastised by a number of people on the reflector (including one of the DXpedition operators who went on at some length about the cost of the DXpedition) before the thread was (wisely) quashed by the moderator.

I composed a short reply very early in the melee, but decided (also wisely) not to contribute it because it really had little to do with contesting.  So, I’m writing here in hopes that someone finds it interesting.

When I was a new ham, I won a copy of the ARRL Operating Manual at a hamfest.  It sounds inane now, but I read the thing cover to cover.  In the chapter on DXpeditions, the author writes, “A donation should never be a condition for receiving a QSL card.”  That has stuck with me through the years.  The fundamental question is: why spend tens of thousands of dollars on the effort only to hold the operators who worked you hostage for a donation that might cover your QSLing costs if you’re lucky?

But, life is rarely black and white and most DXpeditions understand the futility of that question, so the situation outlined above rarely happens.  In the present scenario, the DXpedition stepped into the gray by prioritizing donors ahead of non-donors.  I have no problem with this.  In fact, as I began to write in my reply, it is a matter of supporting things that are important to you.  If having a card for the “new one” is important so you get on the Honor Roll for this year’s DXCC Yearbook, how much is that worth?

This falls into the same category as people who used to complain about the results of contests sponsored by CQ magazine being unavailable for free online.  Well, if you want the results, buy the magazine!

Enough ranting…did somebody mention that CW Sweepstakes is this weekend?  SWEEPSTAKES!