Tuesday, August 30, 2016

Fixing My Astron Power Supply

Some time ago I posted about fixing the front-end of my FT-897 tranceiver which had gone deaf on 6 meters.  I've gotten a number of comments and emails from folks thanking me for supplying those details -- they were able to get their rigs fixed as well.

In that spirit, here's a report of my latest equipment fix.  I have two Astron power supplies for the shack, an RS-35M (the one with the meters) and a RS-35A (with no meters.)  The 35M powers the main rigs, transverters, and accessories.

The 35A was slated to power various VHF and UHF power amplifiers as I bring them on-line.  I bought it used and it started to have problems almost right away. It came up with the correct voltage on the output and could supply a little bit of current (it could run an FT-897 on receive) but as soon as a significant load appears (the FT-897 on transmit) its would cut power.

A little on-line discussion and snooping indicated that it was probably the SCR/crowbar board.  Well, I didn't have a lot of time to horse around with this, so I decided to go for the low-hanging fruit.  I ordered a couple of LM723CNs off of EBay (for a whopping $0.99 shipped!).  This past Saturday I pulled off the cover, removed two bolts holding down that crowbar circuit PCB, and swapped out the LM723 -- happily it's socketed (circled in red).  Screwed the PCB back down, turned on the power supply and Presto!  It's able to put out full current now without tripping the crowbar circuit.

Now THAT's the kind of fix I like -- three minutes of my time and $0.99 of my money.  I hope this helps somebody else get an Astron power supply back in play.

Tuesday, July 26, 2016

Testing Out a Noise Source

Something I've craved for a long time here at ThePalmHQ is an antenna analyzer that can work all the way up into the microwave region.  I have an MFJ-259C and I have appreciated it for use on HF and 2 meter antennas.  But for 222 MHz and above something else is needed.

A video by Adam, 9A4QV inspired me to put together my own analyzer that will work well into the GHz range.  He's posted a video about it here and a more detailed presentation of the same thing has been posted by the folks at RTL-SDR.com here.  Basically, with a noise source, a directional coupler, an RTL-SDR dongle,and some free software we can analyze antennas and filters through all of our amateur bands up through 1296 MHz.  What's especially great is that the total cost of all of this should be around $50!

I tried out the first piece today, the noise source -- a simple device that just honks out an RF signal across a wide frequency range.  These are available for $20ish off of EBay (I got mine here, but there are a bunch of sellers -- just search for "noise source".)  A number of postings on-line note that earlier versions of these boards ran too hot and died.  The good news is that there's a redesigned board using SOT-89 MMICs instead of SOT-86s (be sure to get the 2016 version).  Mine runs hot, but not self-destruct hot.  An added advantage is that this redesign seems to put out a lot more power -- mine averages around -25 dBm across a pretty broad spectrum, whereas earlier versions seemed to put out more like -40 dBm.

I looked at the output on a spectrum analyzer.  It's putting out around -10 dBm at the very low end of the spectrum, has a pretty flat output between 200 - 1500 MHz where it's between -22 and -27 dBm and then it falls off to -40 dBm at 3 GHz.  There's probably useful power above that, but that's the upper limit of this analyzer.

I'm looking forward to sweeping a WA5VJB "cheap yagi" that I built for 1296 MHz as my first real-world application.  If this works out as well as I hope, I may just ditch that MFJ-259 entirely.  Stay tuned....

Friday, October 9, 2015

New antennas, 50 MHz and up!

I just completely reworked the VHF-UHF antennas here at the Palm HQ.  Everything came down, I installed a new rotor, and then put up new antennas on 50, 144, 222, and 432 MHz.  For 50 MHz I have a Cushcraft A50-5S five-element beam.  144 MHz is covered by a Cushcraft A148-10S 10-element yagi.  I built an N6NB 8-element quagi for 222 MHz.  And 432 MHz sports a 22-element K1FO yagi.

These antennas aren't up very high off the ground, but our QTH is at about 1250 feet above sea level and has a commanding view in all directions.

Everything performed very well in the September ARRL VHF Contest.  I have lots of plans to upgrade on all those lower bands, plus push up to 902 and 1296 MHz.  But for now it's simply nice to be back in business for basic VHF and UHF weak signal work.

Wednesday, August 19, 2015

A Proper IF Rig.....Finally!

It has taken me way too long to get to this point.  I have been working off and on (mostly off, I'm afraid) working with and building my own transverters, for almost six years now.  One obstacle I've encountered again and again is the need for a proper IF rig, with an attenuator that switches in and out of the RF path during transmit automatically.

For those unfamiliar with how a transverter works, basically you start with a local oscillator (LO) at frequency X.  You then mix that with an intermediate frequency (IF) Y to get the desired operating frequency X + Y (or less commonly X - Y).  So for example if you start with an LO running at 756 MHz and mix that with the output from an IF rig at 146 MHz, presto! you're operating at 902 MHz.

I have found out the hard way that transverters are fiddly things.  The mixer that combines that IF and LO, for example, can only take a few milliwatts of power.  More than once I've blown the mixer on my transverter because I thought I could hook up an IF rig with no attenuator, just to test the receive path.  I won't accidentally transmit this time.....really, I won't (zork!  smoke......$#%@&!)

I've had a Downeast Microwave (DEM) Transverter Control (TC) kit for a long time now.  This board is particularly good for use with the W1GHZ transverters that I'm building, because it can be configured for transverters with a single mixer.  Well I finally got the thing built, tested, adjusted, and integrated with the rig.  It works great.  Why did this take me so long?  This is not exactly rocket science, eh?  I don't know why.  But I'm glad to have it done.

As you can see from the pictures, I have a Yaesu FT-817 and TC board (in a scrounged enclosure) velcroed together and connected with some stubby cables.  A single Power Pole connector powers both rig and TC with one connection.  Included in the enclosure is a SP4T RF relay that I got from K2TER (thanks Bill!), so that with the twist of a rotary switch (not yet wired in) I'll be able to switch my IF to up to four transverters.  I also rigged up a simple pushbutton allowing me to key the FT-817 while I test the transverters.

So that's the interface.  What about the rig itself?  I'm using a Yaesu FT-817 because I think it makes just about the perfect IF rig.  It can do 28, 144, or 432 MHz IF.  It can be modified to transmit out-of-band for odd IF frequencies (legal to do if you're only generating that RF for a transverter intermediate frequency.)  And of course it can do HF, VHF and UHF FM, satellite, and a bunch of other fun stuff.  I managed to find a reasonably priced FT-817 non-D radio, which was just what I wanted.  The non-D has had some problems with blown finals at full power, but I don't care about that because I'll only be transmitting at around 1 watt all the time.

I'm going to modify the FT-817 further to incorporate the N1JEZ/W1GHZ panadapter (I'll write up that project as it happens), which I'll then use with an inexpensive SDR-RTL (more on that later too) to get a waterfall display.

I adjusted the DEM TC board to give me just about 0 dBm (1 mW) out for 1 watt in (that's the L2 power setting on the FT-817.)  That lets me drop down to around -3 dBm with the 0.5 watt setting or bump up to 3 or 5 dBm if I need a bit more oomph.

So finally I have an IF rig tightly interfaced to a transverter control.  So now I just need to get a W1GHZ transverter on the air.

Tuesday, August 11, 2015

Getting a fresh footprint on 432 MHz at the Palm HQ

I am in the process of upgrading all of my VHF-UHF antennas here at the Palm HQ and made a nice breakthrough last night on 432 MHz.  For some years now all I've had on that band is a cheesy little 6-element beam.  That's not a lot of gain, so performance wasn't great.

I've been getting emails about a Monday night weekly net on 432 MHz run by Steve, N4PZ down in Mount Morris, IL which is a 130 mile shot from me.  Since I recently acquired a 22-element boomer for 432 I thought last night would be a good time to try things out.

I assembled the yagi, attached it to a 9 foot piece of PVC, lashed it to our clothesline pole, hooked up a feed line and routed that into the house.  The SWR isn't perfect, but not bad -- I can probably tweak that a bit for a better match.

I pointed the antenna in Steve's general direction and waited for the start of the net some hours hence.  But then I noticed that Bob, K2DRH, was on the ON4KST chat so I asked if he could give me a shout on 432.100 MHz.  In the meantime I ran outside and swung the beam to point more or less at Bob.  Sure enough, a few minutes later I heard Bob in there (he's also about 130 miles from me) and we were easily able to make the QSO.  Bob thought it should been stronger but since I just guesstimated his direction it probably could have been optimized.

I swung the antenna back toward N4PZ's QTH and not long after that heard him in there calling me.  There was some fading and, as with K2DRH, I'm sure that the direction needed to be tweaked.  But it was good solid copy both ways, even with my measly 10 watts.

When that antenna gets up to 40 feet and I kick in the amplifier I should be very solid indeed on 70 cm.

Thursday, July 25, 2013

The QRP2000 Frequency Generator

I'm back to working on ham radio projects and so it's time to get back to blogging about it too.

I'm still seriously into weak signal VHF-UHF-SHF work, an aspect of ham radio that I never thought would hold any interest for me but which I now find fascinating.  My goal is to build the whole line-up of W1GHZ transverters, from 902 to 3456 MHz (see W1GHZ's documentation and also the Yahoo! group I started for other builders).

To that end I have had serious need of a signal source.  Basically, if you've just applied power to a homebrewed transverter, you need to know whether it can receive something.  A simple crystal oscillator will work, allowing you to hear some weak harmonics.  But I craved something more substantial.  Now I've got it.

I settled on the QRP2000 kit from SDR-kits.  Utilizing the Si570 from Silicon Labs (mine has the A grade, LVDS chip) this unit provides frequency selection via USB control from 3.5 - 1500 MHz.  I just finished mine and it is as cool as can be.

The kit took about 2 hours to complete, including mounting in the custom enclosure highlighted at left.

The only hitch in the building process was that I received a tape of 47 ohm resistors that were supposed to be 4.7K.  I should have checked the values before stuffing them.  But I didn't and of course the board didn't work.  After going over and over my soldering and checking the polarity of diodes and such, I finally on a whim checked the resistance on a couple of the microprocessor control lines and found this mistake.  Fortunately nothing was damaged and stuffing the correct values immediately resulted in a working board.

There are a couple of software applications available to set the output frequency.  The frequency ranges for the "A" chip are spec'ed at 10 - 945, 970 - 1134, and 1212.5 - 1417.5 MHz.  Mine doesn't seem to have any of those gaps and the actual range extends beyond each end--I'm getting continuous coverage from 3.5 - 1500 MHz.

Power-wise I'm getting between -10 and -3.5 dBm out from the Si570 chip, depending on frequency.  My plan is to bolster that by 15 or 20 dB in order to be able to use this box to drive a mixer, so that I can use this dude as an agile LO for any given project.  I'll drop another little amplifier PCB in between the main board and the connector and post an update with the results.

But even without the additional gain this puppy is perfect for a signal source to check out the receive on a transverter. It puts out a nice square wave, so it's rich in harmonics.  I found that running at 100 MHz, the 15th harmonic was only 27 dB down from the main signal.  I currently have a "cheater" 902 MHz transverter at home, to get KC9JTL and me on that band for the upcoming ARRL UHF contest and the 82nd harmonic of an 11 MHz source is a welcome sign that all is well on receive.

This unit has a ton of applications, including some for my day job.  If you need a super-flexible signal source, this is hard to beat.

Next up is to build W1GHZ's RF Power Detector board.

Tuesday, January 10, 2012

Another Ham at The Palm HQ

 I'm happy and proud to say that we have another ham radio operator in our family.  My oldest daughter Emily took a Technician class offered by Ralph Hendrickson, KC9LBO last year.  Just before Christmas she and seven other prospective hams took their exam.  Emily passed her exam with a score of 100% and over the Christmas break she got her call sign:  KC9VEM

I'm also very proud of my son Christopher, KC9JTL, who upgraded to General at the same time.

A big thanks to KC9LBO for taking the bull by the horns and providing the instruction and motivation needed to get a bunch of new hams on the air.

The Palm family amateur radio tradition continues.