W7BAS 1296 MHz Transverter Arrival 8/7/11

Not one to sleep, Bruce, W7BAS, has been burning the midnight oil to bring us two new transverters to add to his current stable of 222 MHz and 902 MHz models.  This release is very much like a buying two bookends- Bruce has come up with a 144 MHz and 1296 MHz design (he is also working on another pair of transverters to be released soon- 432 MHz and 2304 MHz).  The 144 MHz transverter is, “very sensitive and quiet on RX. Better than -140 dBm.”  The 1296 MHz transverter  is “better than -135dBm on RX and quiet also.”  Both have an output of ~+17 dBm.

Pricing is as follows:

144 Transverter + Micro-Synth L.O. (user choice of 28Mhz/50Mhz I.F.) = $279.00 (both assembled); $249.00 (XVTR Kit Micro-Synth Assembled)

222 Transverter + Micro-Synth L.O. (user choice of 28Mhz/50Mhz/144Mhz I.F.) = $259.00 (both assembled); $229.00 (XVTR Kit Micro-Synth Assembled)

902 Transverter + Micro-Synth L.O. (user choice of 28Mhz/50Mhz/144Mhz I.F.) = $259.00 (both assembled); $229.00 (XVTR Kit Micro-Synth Assembled)

1296 Transverter + Micro-Synth L.O. . (user choice of 144Mhz I.F.) = $279.00 (both assembled); $259.00 (XVTR Kit Micro-Synth Assembled)

You will note the price increase; but you will also note that with the increased price you are getting one of Bruce’s very excellent synthesized L.O.’s.  This, in my mind, is a better bargain than he was previously offering and you’d be a fool to pass at this price.

Bruce will have these new 1.2 GHz and 144 MHz transverters available August 7, 2011. Order from his website Signalblox.

VK4ZQ’s Excellent Microwave Blog

Roy O’Malley, VK4ZQ, has put together what has to be one of the best blogs about microwaves I’ve seen.  Through his erudite postings, you can learn about his portable microwave setup, how to get on 10 GHz easily and how he designed his rover antenna setup (it’s on its own trailer).  His great attitude and enthusiasm really shows in the quality of his pictures and the text itself.  Good show!  Give Roy a read- you’ll learn something!

Driver amplifer enclosure

Got a friend to lend me his portable drill press so that I could mount the 5 watt 902 amplifier board in its enclosure.  After I drilled the pilot holes, I tapped them and everything fits together quite well.

Now, all that remains is figuring out where/how to drill the SMA bulkhead mounts (and drill, tap and then mount them).

W7BAS LO Review

There are many factors that determine good circuit performance.  Proper design techniques, careful part selection and the attention to detail when it comes to assembly of a device are the three chief concerns of any electronics endeavor.  But that is ex nihilo- upon what corpse is this creation to rest?  In the same way that bodies have dominate sides or particular faculties, so too does the enclosure around which an electronic creation is encased.  Microwaves are their own little creatures, after a fashion, and what you may find from one circuit board sitting on the end of a couple of attenuators, conjoined with the DC blocking adapter which then leads into the spectrum analyzer, can be completely different than what such a board, similarly attached, might produce when it is enclosed, and enclosed in the proper way.

I happen to know this through experience- which, so far as I know, is always acquired “the hard way.”  In my case, I was attempting to wire up my transverter boards to my radio in order to see if it was functioning.  I didn’t have any luck hearing any signals, mainly because I wasn’t properly set up to hear any, and in any case, it was late, I was tired and one loose wire screwed everything up when it energized the transmit section with the wrong voltage.  I caught it pretty quickly but not before the white smoke escaped and I thought I had blown it up.  What a way to go to sleep!

So, I contacted Charles, K4CSO, and asked if he could help.  He graciously offered to see what, if anything, was malfunctioning with the transverter.  As it turns out, apparently nothing is wrong and I caught the overvoltage in time.  What was more interesting was  the performance of the W1GHZ LO.  Paul writes in his paper “902 MHz Transverter for the Multiband Rover,”

“The revised LO board with the combination filter works very well, with a 756 MHz output of +7 dBm, perfect for driving a mixer. The spurious outputs at 36 MHz away on each side are at least 30 dB down, and all other frequencies are more than 40 dB down except for a strong second harmonic at 1512 MHz.”

In this photo, you can see the harmonics Paul was talking about, and yes, they are ~36MHz spaced from the center frequency and approximately 30 dBc as mentioned.

Above is a photo of a sweep from 10 MHz to 2 GHz.  As Paul stated, the LO works as advertised.  But it is dirty.  Very dirty.  I was curious as to why this is the case, as I would like to eventually use this transverter with some power- garbage in and garbage out- and being a good amateur I would prefer to have a cleaner signal.  As I understand it, there is some overlooking of dirty signals the higher one goes in the bands- since no one is there and construction techniques being what they are, you aren’t likely to have a complaint when you are one of the few on the band!

However, that doesn’t answer the question of why there are so many harmonics.  Charles informs me that such even spacing at such a small frequency multiple (in this case, ~36 MHz) is very likely to be the 36 MHz crystal oscillator that is located on the LO itself. One guess is that the signal out of the oscillator is getting into main LO signal via the large ground plane on the bottom of the board.  It’s possible, too, that somehow the signal is getting mixed in one of the MMICs.  It is also possible that once enclosed the transverter may act differently.  In any case, I wasn’t terribly concerned with this until we put the W7BAS synthesized LO on the analyzer.

Confession time:  After reading my post regarding building my W1GHZ transverter, W7BAS offered to send me one of his LO’s, gratis.  I accepted.  I’ve decided to write this review about it and will include the W7BAS LO inside my transverter.  This review wasn’t solicited by giving me a LO and is completely independent of whether I got it freely or not.  I realize I’ve spoken about the W1GHZ LO at great length; you will have to forgive my lack of brevity in this review in the interest of full disclosure- which whether I paid for something or not would, I hope, be the same.  Also, the reason I am rejecting the W1GHZ LO isn’t because it doesn’t meet its published specifications- its because I’ve now got something that is much better.  It should also be pointed out that there is the caveat regarding whether this LO was enclosed or not- as mentioned at the beginning, whether some board was enclosed or not so could make a significant difference in the measurements that are collected.  As both were tested in the same way, one could argue that neither has a testing advantage over the other and would perform the same way in the same enclosure.

From what I’ve read, many people originally didn’t care for synthesized local oscillators because the phase noise was simply too high.  However, cost is always the main issue, and with synthesizers lowering the cost of microwave LO’s, the telecom industry moved towards this technology without hesitation.  This technology was cheaper and cooler to run.  With less heat meaning less waste, the cost goes down further.  While it might not have been at the time the most elegant solution, it was certainly the most expedient one.  Today, the phase noise continues to decrease and there is now wide acceptance in microwave circles, and elsewhere, of synthesized LO’s.

The W7BAS LO drew 40 milliamperes and is designed to take a 12 volt source of DC power- something the W1GHZ transverter is sorely lacking.  When put on the spec an, the frequency readout was incredible- 755.999 MHz.  This is probably intentional (the goal was 756 MHz)- certification shops tend to always under certify some device by just a smidge in order to account for voltage/power differences between the lab in which the item resides and the actual shop that does the certification (and I believe there are other reasons for this in which I am not competent to articulate; I could very well be wrong about this point and could have misinterpreted what I’ve read, so do please be aware of this).

Like the W1GHZ LO, the W7BAS device also had a second harmonic around 1510 MHz. The main signal output was around 8.5 dBm, as sent from W7BAS.  The second harmonic, unlike the W1GHZ second harmonic, was not just -30 dBc down- it was more than -60 dBc, as seen in the following photo:

You will also note the lack of harmonics.  This signal is, in the vernacular, “so fresh and clean” that it honestly couldn’t be practically better.  If it was, I’m not sure what benefit would be achieved (this photo was a 10 MHz to 2 GHz sweep).  Other than the second harmonic, there are no other harmonics of any consequence.  This means that the signal made by the transverter wouldn’t be all over the spectrum (especially with the amplification issue looming in the future) and would be quite clean.  In fact, it may be one of the cleanest on the band!

Considering the purity, but not in any religious sense, of this LO how could you not switch teams from the W1GHZ to the W7BAS?  Admittedly, there is a price difference. The assembled W7BAS LO costs $89 bucks plus shipping.  The other LO costs, all components in with the board and you assemble it yourself, around $25-30 bucks depending on shipping and parts costs.  Why the price difference between two items that do the same thing?  Well, look at the pictures.  One does its task much better than the other.  Will it matter in the long run which you use?  I cannot say as I cannot speak to your needs or environment.  Nevertheless, I would argue that the extra dollars are worth it because you have a cleaner and more precise signal.  With a more precise signal, the less likely it is you have to tune around due to frequency drift, and the less of that you have to do should equal less frustration and effort.  Who doesn’t love that?

I wholeheartedly endorse getting on the synthesized LO bandwagon and can’t think of a better driver than W7BAS.

VK3XDK 3.4 GHz Transverter Available

Graham recently announced his long awaited 3.4 GHz transverter is finally available from him for $150 AU plus shipping.  You can find more information at the following web address:

http://www.vk9na.com/Transverters.html

Please note that the website has not yet been updated to reflect that the transverter is available; also, you may find Graham’s email address located under the blue “Contacts” heading about two-thirds down the page.  Please contact him for more information.

The MIT Radiation Laboratory Series

If you are interested in a piece of microwave history, one could look no further than the RadLad series of papers.  This is an interesting bit of arcana- mainly because the research was released into the public domain, via MIT.  However, there appears to be some corporate skullduggery at play, and the files were no longer hosted by MIT and have since been privately published.  I’m not sure how something that once was public domain isn’t any longer- in any case, that seems to be the issue here.  Grab the paper while you can.

Driver Amplifier for W1GHZ 902/3 Transverter

I recall reading in the recent DUBUS magazine that something every VHF+ user could use was more power.  Naturally, everyone could use more power!  This fact escapes many people who run a barefoot (the all too common 100 watt) transceiver as their main rig.  Many HF users believe 100 watts is the starting point; of course, there is the QRP bunch who do a lot of communicating with a great deal less power.  Nevertheless, there is a large difference between what is QRP on HF and what counts for low power in the microwave domain.  Additionally, there is also a large difference between what counts for QRO between HF and uWave spectrum, as well.

The transverter, as measured so far, puts out about 32mW.  That’s just not very much-  it could get lost in the coax!  So, the plan is to build an amplifier that will take this output and turn it into something respectable (and not so hard to work for the other station!).  Also, I would like this all to fit in the same box- that is, I want the transverter to be plug and play with at least +1 watt output with the xverter boards, switching, sequencing and at least one amp.  After a couple of queries, I found something that I am hopeful will do the job.

A fellow on eBay is selling both a PA module and PCB board for a 5-10 watt (depending on how it is powered and biased) amplifier.  Ultimately, I will be using this to drive another amplifier, but for now, I’m just trying to get my signal above the microwatt level!  As I’ve not yet put mine together, I can’t say I recommend or that I dislike the seller.  I should have the unit built in the next couple weeks to a month or so; if everything checks out, I’ll vouch for the guy and give the sellers name.  The more curious and adventurous will have already looked up this information in the W1GHZ transverter group and will have found some driver amplifier solutions therein.

In other news, I feel like I am getting closer to a container for the xverter project.  After a back and forth email missive with W7BAS, he mentioned that I should check out Context Engineering.  (Also, while Bruce said he was not currently working on any 10 GHz project, he did say he “had some ideas” regarding a transverter.  Stay tuned folks!)  I like the boxes and different enclosures that CE has; that said, not sure what is going to be right for me.  Charles, K4CSO, talks about the solutions to these difficulties as “3D thinking.”  Wish I had more of it.

W1GHZ 902/3 Transverter Measurements and Build Notes

My 33cm W1GHZ transverter is assembled!  However, it isn’t a fully functional transverter because I do not yet have a complete sequencing system in place.  That said, the transverter and LO boards are assembled and plumbed.  I am continually on the hunt for the right kind of enclosure to use for the entire bit of kit and hope to have something soon.

Recently, with the kind help of Charles, K4CSO, I was able to have the device tested and get its measurements checked.  I don’t have the ability to check anything as I have no test equipment, and so I am very thankful for Charles to take time out of his day to lend a hand and expertise.  I was surprised by the results- mainly that they worked at all!  I don’t have a great deal of experience with surface mount soldering and often was concerned that I had cooked some part or other.  Turns out everything works fine!

Considering the cost of these kits, one is getting a new band for not a lot of money.  I secured the transverter boards and parts for $48.  With connectors, switch, sequencer, power parts and eventually some sort of enclosure, I imagine the entire project will cost me $100.  The same sort of thing (recognizing that there are significant differences between the two and that I’d rather have the DEMI if I could afford it) from DEMI would cost over $200 for the kit, and closer to $300.  The next comparable 902/3 transverter kit is from W7BAS and is currently $199 plus $6 for shipping.  So, like I said, you are getting on a new band for not a lot of money- but how well does it work?

I put the LO board together first.  I decided that the best way to approach this would be to solder all the capacitors and resistors in place and then move on to the more delicate MMICs, crystal oscillator and voltage regulator.  This worked very well; if I had it to do again (and I will for my 1296 board), the only difference would be that I would solder the PCB to SMA (coax connector) first.  It appeared to take a lot of heat to get the connector warmed up and as a result it transfered a lot of heat to the board.  If you put this connector on first, you won’t run the risk of cooking the nearby MMIC.  And speaking of MMICs, I used the MAR-6 and MAR-1 from Minicircuits as was listed in the parts sheet by Paul Wade.

After applying some power (the +12 → +8 volt power plant was built using an LM7808 bolted to the ground plane), the current limiter said that the board drew 82 milliamperes.  Not a lot of current!  The LO output was +6.68 dBm, right where it should be for the +7dBm mixer on the transverter board (which had to be jumpered to reach the LO; I used a small piece of brass stock you can get from most hardware stores to jump the trace).  What was odd, however, was the frequency itself was not as close as I would have liked- the LO’s output is 755.985 MHz, off by 15 kHz from the goal of 756 MHz.  Doing a mild heat test of the crystal revealed that with an increase in temperature (unmeasured; used a heat gun), the crystal drifted another 10 kHz and landed at 755.975 MHz.  A better crystal oscillator would be closer to the desired frequency, as the Cardinal one that was supplied had a stability rating of +/- 100 ppm- they make them down to +/- 5 ppm in this particular form factor.  Eventually, even the hobbyist will have some sort of synthesizer to do the heavy frequency (timing) lifting that was once the domain of the crystal oscillator (you should really check out Andy’s, G4JNT, website for some synthesizer projects).

The transverter board itself was fairly easy to put together.  I would warn other folks to mind where you are putting the power supply capacitors for the T/R circuits, as you will want to drape some off the edge, so to speak, and make sure that the wire you want to use is in the right place and soldered down before you put in all the caps.  Alternatively, you may want to place them on the bottom of the board.  Here again, it is better to think of the major parts (plumbing and power) that have to fit somewhere first and then worry about where the little stuff is going to go.

I was pleased that the transverter put out +15.25 dBm (or, approximately 32 mW).  The TX side of the circuit took 187 milliamperes and the RX side of the circuit 120 milliamperes.  The 1 dB compression point (or more formally, P1dB) was at -2 dBm.  So, at least for my transverter, I need to attenuate my radio to -2 dBm output drive in order to avoid saturating the circuit.  Here, I used the following MMICs: A1=SGA3586Z, A2=MAR-6SM and A3=ERA-5SM.

The weak spot in this transverter board design, other than no consideration for built in power on any board that uses +12V input like most do, are the filters.  PCB filters aren’t nearly as tight as something one might otherwise procure from Mouser, but certainly will be at a higher cost than using the hairpin PCB filter.  Here again, we are confronted with price versus performance.  For what I am trying to do, I’ll be able to get by- but for those who like to hack around and make something more than what is given, I believe there are 900 MHz bandpass filters to be had that could tighten up the transverter without doing too much looking.

At the end of things, I’m pleased with the boards.  If you want to try to add a band cheaply, but not expect perfection from your price, I think you have found the right kind of kit.  I can only think of two improvements I would like to make: (1) at some point I’m definitely going to insulate the crystal with some Styrofoam and (2) may even build some shielding over the PCB hairpin filters.  With these two ends tied up, I should have a fairly decent way by which to get on 33cm!