Archive for June, 2011

K8GU Field Day 2011

June 26th, 2011

I had not been a big fan of Field Day for many years until last year.  Although ARRL technically terms it “an operating event,” it has most of the features and flavor of a contest.  But, the bands are crowded, there are a few more drunks and lids than your standard contest.  Your local club thinks it’s a great idea to put up a tower and an ancient tribander, but they only do a half-witted job of it making a lot of work for something that could have been smoked by a doublet in the trees. Or, you show up at a random Field Day site, introduce yourself, and offer to operate CW—only to be handed a J-38 or a blank stare.

Last year was different.  Sarah’s branch chief at work is a ham and she’s married to a ham.  Somehow, it came up that I was a ham and soon we had an invitation to Field Day at her mother’s place near the water of the Chesapeake Bay on Maryland’s Eastern Shore.  I was reluctant, but they assured me it would be OK.  They have a tower trailer for a triband Yagi and trees for dipoles on the low bands and they operate 1A.  It was fun.  Sarah enjoyed herself, too, which is a welcome change for a ham radio event!

For a variety of reasons (namely the impending birth of our first child), we elected not to go to the Eastern Shore this year.  After talking to a few guys at the PVRC/W3LPL open house last weekend who implored me to come to their operation (W3AO, the FD of epic proportions) instead, I decided I needed to do something.  Since W3AO was making a run on the all-time Field Day high score record this year, I opted to make a game of running 1D and working W3AO (and their GOTA station, KE3Q) on every band and mode available.  The goal was to not disrupt our weekend too much and to have fun, possibly contending for a plaque offered by PVRC for the most band/mode QSOs with W3AO/KE3Q.

Here’s how things shook out (yellow = QSO, blue = no QSO, red = no QSO possible with W3AO/KE3Q, hashed = no QSO possible with K8GU, but possible with W3AO):

So, I did pretty well with W3AO, all things considered.  I was not QRV on RTTY until Sunday morning (forgot that I did not set that up on the “new” PC yet).  By that time, I missed the really good opportunities to work them on 20 and 80.  I don’t know if I ever would have on 15 and 10.  I did see them spotted on PSK31 (a mode I will never enjoy—one QSO was enough) on 15, but could not hear (erm, see) them here.

It was a bummer not to have 6 meters here and despite 3-4 requests, the 2-meter phone operator(s) refused to QSY to CW with me, even though one told me I was his first QSO in an hour!  It did take almost 10 minutes for them to find a key to work me on 222 and 432 CW!  Thanks for going the extra mile!  I believe my total of 17 QSOs ties K3DI’s record, plus one more with KE3Q, for 18 total.

I worked KE3Q right away on 75 meters, but never heard them again.  I did see QRS Skimmer spots for them on 40 and 20 CW in the middle of the night and at the very end of event, respectively.  But, I do not believe they were QRV on CW on any other bands.

Having 6 meters and digital from the start probably could have increased my totals a bit.  A satellite QSO or two would also have been good.  But, I did not have it in me to get that set up in addition to building microwave gear and getting the baby’s room ready.  Plus the 432-MHz amp I bought recently has been held hostage by the deadlock between Canada Post and their workers.  So, I only have 10 watts on that band until that arrives, making the annual Field Day “Battle for Bandwidth on the Birds” that much more exciting with a small antenna oriented for terrestrial work.

It was a good time, although I think I’ll be itching to go out into the “field” again next year…thanks for the QSOs and the QSYs!

SoftRock v9.0 Lite+USB Xtall

June 25th, 2011

Brian, ND3F (aka N3IQ/R), gifted me a partially-complete SoftRock kit a few months ago on the condition that I put it on the air.  I’m making some progress on that.  I took this photograph to show the SparkFun USB break-out board installed in the Bud CU-124 enclosure.  The whole thing is assembled now, but there is probably a solder bridge somewhere.  This kit is going to be a lot of fun because it’s actually more flexible for experimenting than the present Ensemble II RX kit.

Microwave updates

June 25th, 2011

Apologies for the bad pun in the title.  I was going to call it “Microwave progress” but could help myself when I thought of this one.  Here are some notes from tinkering over the past few days.

1296 Mhz

After learning that the 1152-MHz LO power was -11 dBm, I inserted a MAR-3 MMIC on the 1296RSU transverter board.  W1GHZ shows an MAR-6 on his board, but the ever-astute N3UM noticed that the P1dB for the MAR-6 is 1 dBm, which is well below the nominal 7 dBm level of the ADE-5 mixer.  Unfortunately, the MAR-3 has about 12 dB of gain vs the MAR-6’s 20 dB.  A little bit of skullin’ lead me to my stash of SGA-4586’s (suggested as an economical front end by W9SZ), which can do >20 dB gain with a P1dB point of 16 dBm or so.  Perfect.

Unfortunately, with an 144-MHz IF drive of about 2 dBm, the 1296-MHz output was totally trashed with various mixing products.  I spent about 20 minutes searching frantically for the 3-dB SMA attenuator I’d purchased at Dayton.  But, I never found it—a sign that my organizational scheme has lost control or that I never actually bought the attenuator.  Either are possible.  So, I did the next logical thing—I added a Pi-network attenuator between the SGA-4586 “LO boost” MMIC and the ADE-5 mixer.  If the Dremel tool didn’t make it’s inventor independently wealthy, it should have.  The only SMD resistors that I had on-hand that were realistically appropriate (39.6 and 130 ohms) yielded about 6-7 dB of attenuation, so the effective gain of the SGA-4586/attenuator cascade was probably around 13-15 dB, yielding somewhere around 2-3 dBm of LO.  Blech.  That’s essentially the same as the MAR-3.  The 1296-MHz output with 2 dBm of drive at 144 Mhz was about 2.5 dBm.

The data sheet for the ADE-5 suggests that the conversion loss increases as the LO drive level falls bellow 7 dBm (shocking!), but there are not enough data to show how precipitously it deteriorates.  However, essentially 0.5 dB of overall power gain does not jibe with the amount of gain in the system, which should be closer to 20 dB.  From this standpoint, perhaps the mixing products were due to IF overdrive instead of LO overdrive.  In any event, about 3 dB (instead of 6 or 7 dB) of attenuation in the LO would be a good thing.

902/903 MHz

Fresh off my mixed success with the W1GHZ 1296RSU (which are neatly packaged in Hammond 1590BB-sized cast aluminum boxes), I wanted to give the 902/903 version (which is still loose boards) a try with the spectrum analyzer.  So, I hooked up the 756LO board first.  It made -5 dBm at 756 MHz.  These numbers are more like what W1GHZ was promising.  So, I put the MAR-3 mentioned above onto the 902/903 transverter board.  With 2 dBm of 147-MHz drive, the output was a very clean 16 dBm on 903.  Score!  Must be livin’ right at least half the time.  My last DigiKey order included a 1590BB for that transverter, but the 756LO board is a bit longer and I haven’t yet found a suitable case for it.

3456 MHz

Thought I was done?  Me too.

I admit it.  I’m a sucker for this sort of thing.  Fred, N1DPM, recently posted to VHFcontesting and the “Stanford” VHF lists that he was selling a bunch of spare microwave gear, including a first-generation DEMI 3456 transverter/LO and some amplifiers to get the output up to 4 watts.  Cheap.  He had some 2304 stuff, but ye old project fund is pretty much depleted since Dayton and I always try to keep a little bit in reserve for just this sort of opportunity.  Anyhow, the transverter is set up for 10 watts of drive on 144 MHz.  I gave it 250 mW (24 dBm) from my modified IC-290A (post to follow on this—not rocket science, just bypassed the PA) and the output came up at -9 dBm on 3456 MHz.  Once I remove the attenuator from the input, I should be able to get it up to about 13 dBm.  At least it seems to work on TX.  Need an antenna to try RX because the K3UO beacons are not as close as W3APL.

W1GHZ 1152-MHz LO measurements

June 22nd, 2011

Through some reorganization at work in the past two months, I have suddenly gained ready access to a lab full of RF test equipment again.  Two years is a long time to go without. Apologies for the cell-phone photograph of the screen.

I took the W1GHZ 1152-MHz LO board over to have a look at it during lunch.  I’m seeing -11 dBm at 1152.007 MHz.  I am a bit dubious of the last digit of the frequency (even at 300 Hz RBW) but I’m sure there’s a frequency counter around somewhere.  Anyhow, I need to put a MMIC (or two) on the transverter board.  That should be a nice evening project along with the W6PQL preamp kit that showed up today.

Mirage Active Bias mod, Part 1

June 9th, 2011

After chatting with Terry, W8ZN, about whether to keep or sell the AM-6155s (which I did sell to finance a tower), he suggested that I apply the N1DPM “Active Bias” modification to my elderly “160-watt” Mirage 2-meter amplifier.  I contacted Fred, N1DPM, and he sent me a copy of his paper Linearization of Solid State “Brick” Amplifiers from the 21st Eastern VHF/UHF Conference (1995), along with some additional notes from his notebook.  It’s pretty eye-opening how non-linear the amp is without the modification!  I finally gathered the parts and hacked it together last night.  Hope to test it soon with a “dummy” transistor and then live on the amp. The braided wires go to the thermal compensation transistor which is thermally bonded to one of the RF power transistors.

It probably won’t be ready for the ARRL June VHF this weekend, though.  So, I’ll only be using the amp on CW.  That’s no matter since I haven’t hung the low-loss cable (LMR and Heliax), nor have I received a D1010 432-MHz amp that will be on its way to me soon.  Everything seems to take longer than it ought to!

Recycling LMR crimp connectors

June 4th, 2011

A while back, I came upon about two dozen Times Microwave Systems TC-600-NM connectors that had been improperly installed and cut off.  Knowing that LMR-600 type cable is commonly available, I stashed them for later use.  These connectors cost between $8 and $15 each, so the ability to recycle could offer a substantial savings.  I endeavored to see just what it would take to do so.

The first step is to remove the heatshrink tubing (if installed).  These connectors employed a relatively easy-to-remove heatshrink, which I was able to get off with a sharp knife.  (That probably means that they would have filled with water if they had been used.)

Twist off the old crimp ring with two pair of Channel-Lock-type pliers.

Presto!  (Be sure to do this in a work area where it is easy to vacuum up the small strands of braid that will invariably fall everywhere.)

A butane torch gets the pin off in no time.

Unfortunately, I did not have enough hands to take a photograph and demonstrate the proper technique.  Place the tip of the flame on the widest (diameter) part of the pin and rotate the cut-off coax with the pin hanging down.  The solder will melt and the pin will drop.  Reinstallation can be performed in the exact opposite sequence with the pin sitting on top of the coax.

The secret to this whole operation is the replacement crimp rings.  I originally was going to make them but since I did not know the dimensions, I was searching around the Web.  And, I discovered that Times Microwave offers them individually (part #CR-600).  So, I contacted Joel at The RF Connection and he sold me a bunch of them (second from right below) at an attractive price.

The three rightmost components—connector body, crimp ring, and solder pin, form a complete connector.  You just need to add heatshrink, which is also available from the RF Connection and many other vendors.  The trick to getting a correct installation on the connectors is to be sure that the pin seats (clicks) into the body before crimping the ring.  The whole process of disassembly takes about as long as assembly (minus the stripping step)—just a few minutes.

I recently obtained about 250 ft (80 m) of LMR-600 pieces from various places for about what it costs to fill the gas tank in my Escort.  So, this should be a relatively attractive cable for use at K8GU.