Posts Tagged ‘50MHz’

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50-MHz transverter update (Psst! Newark has cheap 22-MHz crystals)

August 29th, 2015

A few years ago, I built a 50-MHz transverter to operate 6m with my Kenwood TS-930Ses.  I subsequently replaced the two 930s with an Elecraft K3/100 and Elecraft K2/100.  The K3 has 6m and I sold off my TS-700S (and my 6m Mirage brick amplifier) to help finance the internal 2m board for the K3.  The problem with this arrangement is that I can’t be on 6m and 2m at the same time.  I recently assembled and added the SSB board and  transverter interface to my K2 (no time to blog about this but they were straightforward additions like everything from Elecraft), now making it an attractive IF for the 6m transverter (and the Microwave Modules 432 transverter I have on the shelf and the 222-MHz transverter I plan to build sometime).xvtr_50

Enter the problem: Because I was thrifty about building the transverter at first, I had used an inexpensive and widely-available 24-MHz crystal for a 26-MHz IF.  The TS-930S happily worked here (by the way, pro-tip: A lot of guys say that they liked to have the wideband transmit mods on their HF rigs so they could have a wideband signal source for testing/transverters/etc.  The TS-930S will give you a low-level TX out anywhere through the transverter port, even if you don’t have the mod.  Well, at least my PIEXX-equipped 930 did).  However, the K2 only allows a select set of transverter IF bands to be used natively.  Good fortune shone upon my endeavors when I did a quick Google search for 22-MHz crystals and one actually popped up at Newark/Element14 (part number is 86R1720, get ’em while they’re hot)!  Even better news was that it was on closeout for 12 cents apiece!  I splurged and bought five, along with some other parts for another project or two I’ll post about eventually.

I carefully peeled back a layer of dead-bug components, extracted the 24-MHz crystal, and replaced it with the new 22-MHz variety, sacrificing only one 4.7-k resistor, an easily-replaced stock item at K8GU.  The LO came up about 5.4 kHz low and I couldn’t peak it any higher.  So, I’ll either have to futz around with the loading of the crystal or (more likely) load an offset in the K2’s transverter band entry for 6m.

LO_22

The local W3APL beacon popped up at 28.0694 MHz, which is consistent with the offset I observed above.  Now, I just have to get the other interfacing juju worked out to get the K2 to properly command the transverter to transmit and feed it the proper drive level.

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New Radio Thoughts

November 19th, 2012

As I mentioned in a previous post about my trip to the Aleutians, I am the owner of a new radio.  The reasons for the purchase were manifold, but driven by a fundamental shift in the way I view my operating (and living) philosophy.  I had long (at least 10 years) been collecting gear for a two- (or three-) tower contest station.  In this philosophy, the emphasis was on collecting antennas and towers as they became available on attractive terms.  It also meant keeping the inexpensive but well-performing pair of TS-930S HF transceivers for my SO2R setup and the FT-840 for my portable operations.  You can imagine from those past few sentences of description alone that this consumed a non-trivial amount of space and time.

Sarah began subtly hinting that “wouldn’t it be nice if we could clean up that pile of tower on the patio so we could have people over?”  My parents have been slowly migrating my junkbox from their place to ours.  It became increasingly clear to me that as long as we lived in this area it would be unlikely that I would put up the towers.  I started contemplating how to remedy this situation.  I identified a large collection of gear (including the Rohn 45 on the patio) that 1) could be replaced by a new radio, 2) I was not using, or 3) for which I simply did not have a plan.  So, I set out with the following theme to find a new rig:

Excellence in portable operation and competence at home.

I considered four radios:  Ten-Tec Eagle, Kenwood TS-590S, Elecraft K2/100, Elecraft K3/100.

I was strongly considering the K2/100 initially.  Its size and price seemed attractive.  However, when I did the math on what configuration I wanted, it basically ended up a draw with the Kenwood and the Ten-Tec with only a small bump more to the K3/100.  Plus, I’ve built enough kits to know that many of life’s most rewarding tasks tend to look better in the past than they do in the future.  Personal preference, of course!

The Kenwood TS-590S is acclaimed by a number of contesters as “the poor man’s K3.”  It has very similar features and performance numbers at a very attractive price.  I have always enjoyed Kenwoods as well.  But, the one thing that ultimately killed the TS-590S and the Ten-Tec Eagle was their lack of BCD band-data outputs.  The K3 also offered the 2-meter option, IF output (for panadapters), and very easy transverter interfacing.  It was really a no-brainer for me at that point since I had sold off enough gear to cover the cost entirely.

I bought the K3 kit and assembled it.  Anomalies notwithstanding, it amuses me greatly when people announce to the Elecraft e-mail list that “K3 #7777 is on the air”…it’s hard to keep from responding, “Congratulations on assembling your first LEGO kit.”  Unlike the K2, these “modular-kit” radios are very easy to assemble if you have a few hand tools and can follow basic directions.

My friend Oli, DJ9AO, informally asked me to compare the K3 to the TS-930S.  I’ve tested (subjectively) the K3 in a couple of demanding environments and I’m pleased to say that the K3 performed well, even with essentially “factory default” settings.

The K3 wins hands-down the strong-signal handling contest, even with the Inrad roofing filter in the TS-930S.  40 meters in ARRL Sweepstakes CW is a good test for this.  The FT-840 used to have severe mixing products (“beeps and bloops”).  These are not common with the TS-930S, but severe AGC pumping from nearby signals often covered up weaker signals.  Neither of these are problems with the K3.  In fact, the K3 is so good that you can tell just exactly who has key clicks because it’s possible to find two signals of otherwise identical strength on the S-meter and one will be inaudible within a few hundred Hz and the other will continue to bleed through and pump the AGC.  Well-done, Elecraft.

One thing that surprised me about the K3 was its apparently poor performance on the pileups from NA-039.  With the BW cranked down to 400 Hz, the filters rang like a bell in a pileup.  I have the 400-Hz 8-pole and 2.7-kHz 5-pole filters.  Widening the DSP bandwidth out to 700 Hz or so (which switches to the 2.7-kHz roofing filter) alleviated the problem with occasional AGC pumping from louder signals in the pileup.  In a post to the PVRC e-mail list recently, Frank, W3LPL, also confirmed that he prefers the 1-kHz 8-pole filter for CW operation.  Because I had the opportunity, I recently sprung for the special-order 700-Hz roofing filter.  It should arrive in March 2013.  I suspect there is considerable tailoring that could be done to the AGC system but I’m not there yet.  Once I realized that the bandwidth of 700 Hz was a sweet spot, the radio worked great in the pileups.  I have a feeling that I’ll also end up with the 1-kHz filter eventually.  But, I rarely open up beyond 700 Hz on CW so it will be interesting to see what is best.

A few other bright spots:

  1. CW-to-Digital:  This is just plain cool.  Send with the built-in keyer and the radio modulates PSK31 or RTTY for you.  Decode it right on the screen.
  2. Multifunction knobs:  The entire industrial design of the K3 is really unmatched in my opinion.  It has just the right number of knobs and menus.
  3. Options:  They are plentiful and easy to install.  Keeps the initial cost low(er).

I’m extremely delighted with the K3 so far and my shack is getting more compact.  It’s also nice to have a radio with a built-in keyer for once…

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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…

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Improving 50-MHz Transmit Capability

July 28th, 2011

Over the past week in the evenings, I’ve managed to cobble a little PA together for the 50-MHz transverter.  It’s a near-clone of the PA in the Elecraft XV50 using the Mitsubishi RA30H0608M.  Last night, I got it all hooked up and installed in the cabinet.  It broke into oscillation when keyed on CW.

The oscillation was about 50.040 MHz.  I reasoned that it might be the PA output coupling into the nearby TX RF bandpass filters which are followed by 12 dB of gain before returning to the PA.  So, tonight, I added a litle shield between the BPF and the PA board.  That seemed to clear things up and I got about 10 watts out.  There is a 6-dB pad between the last driver stage and the PA, so I should be able to get it up to about 18-20 watts.  But, the first goal will be to check the linearity on SSB.

In other transmit capability news, some boxes and heatsinks arrived for the W6PQL PAs for 903 and 1296 this afternoon.

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Improving 50-MHz Receive Capability

July 23rd, 2011

As I mentioned previously, the receive capability in my 50-MHz transverter seemed to be a little bit anemic.  So, I decided to add a little bit of gain.  Looking at the block diagram for the transverter (shown below in updated form—jumper across the SGA-4586Z to understand what the circuit looked like initially—by the way, full-sized PDF versions of all of my notes and schematics will eventually be available here), I reasoned that I had the following losses and gains:  +10 dB for the LNA (this might be as much as +15 dB, but 10 seems more realistic, if not generous), -3 dB for the bandpass filter, -7 dB for the mixer conversion loss, and -3 dB in the diplexer, leaving me with -3 dB overall conversion gain.

So, I endeavored to find some more gain in the form of a MMIC (which is really what all gain blocks in this transverter would be if I were to do it again).  I have a nice (but dwindling) supply of SGA-4586Z’s that produce about 20 dB gain with a 1-dB compression point around 16 dBm, which is probably a good part for this location.  The idea is to overcome the losses in following stages with robust gain in earlier stages (in order to keep system NF low).  So, I ripped out the existing two-pole BPF and replaced it with this:

I was relatively satisfied that I had everything working with the cover of the transverter off to peak the BPF on the W3APL beacon.  So, I replaced the cover and surprise!  To borrow a poetic description of RF circuit doom from N3UM, the MMIC “amplifier burst into song.”  Bursting into song is a bit of a charitable description for something that sounded more  like S9 power line noise in the IF receiver.  I did not actually know that it was the MMIC oscillating at first, but I started wiggling cables and finally found that if I touched the 12RX (+13.8 volts on RX) line, the problem disappeared.  So, I added the 0.01-uF bypass capacitor to ground on the supply side of 180-ohm bias resistor and the problem was solved.

With the completion of the HF SoftRock with Si570 LO, I now have a tunable IF to play with the transverter.  We had a nice opening to the Southeast and Gulf this morning and I even heard my first DX with the transverter and SoftRock combination—CO2WF.  With the appropriate software, I can configure a the SoftRock as a panadapter with the TS-930S as the transmitter.  More on this in the future.  Best of friends:

The real next step in making the transverter useful is building a 20-watt PA stage.  This should be good for driving a Mirage or TE Systems brick or even something bigger like a 3CX800 or 50-volt solid-state amp…

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SoftRock v9.0 Lite+USB Xtall QRV

July 23rd, 2011

Got the SoftRock v9.0 Lite+USB Xtall working last night.  I’m not 100% sure what the problem was, but I think it may have been due to me programming an ATTiny85 with the latest SoftRock firmware (V15.14), rather than using the supplied ATTiny45 with V15.4.  So, I’m sticking with old version for now.  Not sure if it was cockpit error on my part programming (more likely) or an incompatibility with the new firmware which is designed to work with the Ensemble series of SoftRocks.

As shown in the screenshot from Rocky above, there appears to be a spur that repeats every 1 kHz (see left side of the waterfall).  The right side of the waterfall is with the USB cable unplugged from the computer.  I’m 99% certain this is something internal to the SoftRock because I wrapped a few turns of the USB cable around a big type-31 ferrite toroid and the spurs are still there.  So, need to play with that.

I’m listening to a Es opening to the south on 50 MHz right now using the SoftRock as the RX IF.  Yes, that means that I got the RX on the transverter souped up a little hotter.  I will post something about that later today and place a non-causal link in this post.

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Revisiting the 50-MHz Transverter

July 17th, 2011

I recently resurrected the 50-MHz transverter project and have made good headway getting it working.  On Friday night, I began the process of tapping holes in the PA module heat spreader.  But, despite using plenty of “cutting fluid” (3-in-1 oil), I managed to break a (well-used) tap on the first hole.  Since the maximum (linear) power out of the driver stage is 200 mW, I embraced my inner QRPer and put the PA project aside to give the transverter a try in the CQ WW VHF contest.

The 6-meter Yagi had come down in favor of Yagis for 222 and 432 when the loaner FT-736R showed up.  So, I scampered up onto the roof and moved Yagis around.  I had hoped that this moment would be accompanied by changing out RG-8 coax for LMR-600 and LDF4-50A that are taking up space in the shop and shack.  But, I was not ready to commit to cutting that and I still don’t have LMR-600UF for the rotator loops.  Plus, I should replace the rotator at the same time.  That amounted to too much work for the available time.  I really just need to bite the bullet and install a rotating mast for the VHF antennas that’s not so precarious.

Got everything hooked up late on Saturday afternoon, but had to tend to some domestic concerns and was QRT until later in the evening when I heard my neighbor W4EE calling CQ on six SSB.  Did not know that he had six!  Apparently, this is a new thing for him, too.  He was surprised that I didn’t vibrate his radio off the desk like I usually do!  Told him I was running 200 mW and everything made sense.

Ended up working a few other locals on Sunday including N3UM, who moved me from 6-meter CW to 2-meter SSB for a quick chat.  He just completed the N1DPM active bias mod to his Mirage B2518G, so was eager for an audio report.  Sounds good!  He said my B3016G sounded good on-frequency, but I haven’t gotten the mod actually inserted into mine yet.  Probably that Kenwood (TS-700S) audio making up for the amp’s inferiority…

Eventually, I will be posting more details on the circuit here.  This is one of those projects that I would not encourage anyone to duplicate as I have constructed it.  However, there may be useful features.

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Recent tinkerings (9 Jan 2011 edition)

January 9th, 2011

Several people have commented over the years that I should “write more” on the blog.  I usually respond that I could spend my free time tinkering/hamming or blogging, but not both.  Here are a month’s worth of blog posts as freestyle poetry:

  • A section on my workshop has been added to k8gu.com under Engineering.
  • Discovered that although the SoftRock VHF Ensemble II won’t fit (barely) into the Bud CU-473 diecast box I bought for it, it will fit into an extruded enclosure that housed an ancient X-band radar detector I picked up at Dayton in 2002 in hopes of stripping the Gunn diode assembly and getting on 10 GHz.  Bonus points for thriftiness.  Photos will follow once I finish the project.
  • Did not observe Quadrantid meteor pings with the SoftRock VHF Ensemble II, but did notice something interesting about the W3APL beacon.  Need to investigate.
  • Have more CE/K8GU QSL cards again, finally.  Tonight, I might finish the bureau (and, ashamedly one direct) cards languishing.  Some K8GU (and AA8UP, no kidding) bureau cards are sitting here staring at me, too.  Not a big project, though.
  • Operated the NAQP CW on Saturday (8 January 2011) for four hours and twenty minutes and made 318 QSOs x 128 multipliers for 40,740 points before log-checking discounts.  This total is pleasing to me especially considering that it was almost all leap-frogging SO2R search-and-pounce, which can be very fatiguing.  It’s fun to see the rate meter stay over 100 when you’re S&Ping.  Good Sprint practice.
  • Still the best 30 minutes on the radio every week:  I operated the NS Ladder on Thursday (6 January) night and made my customary 30 QSOs x 24 multipliers for 720 points.  Hopefully, adding 160 will give me some momentum to increase this score back over 1000.
  • We had a spell of 50F (10C) weather on New Years’ Eve.  So, I put the 2-meter beam back up on the chimney.  It was formerly mounted on a steel mast that was ratchet-strapped to the chimney.  A strong wind (>50 mph gusts) before Christmas bent the mast (actually a fence top-rail) and I had removed it.  I cut the bent lower portion of the mast off and attached the remaining top portion with rotator to a “girder” constructed from two pieces of treated 2″ x 4″ x 10′ lumber joined with a half-dozen lag screws.  Again, I ratchet-strapped the entire assembly to the chimney.  The present configuration is much stronger and less prone to damage.  The 3-element 50-MHz Yagi is still on the ground until I actually get the transverter finished, which should be soon (as it has been for 12 months now).
  • Repaired a SoftRock v6.2 downconverter for WF1L and learned that you can solder leads back onto SOIC packages if you’re careful.
  • Have had delightful exchanges with KN6X and ZL1CDP about repairing the TS-930S.  Some of these discussions (and their fruits) may make it onto the site at some point.
  • Back in December, I started integrating the W1GHZ transverters using UT-141 semirigid jumpers with pre-installed SMA connectors obtained on attractive terms from Max-Gain Systems.  Mitsubishi RA18H1213G (1296 MHz) and RA30H0608M (50 MHz) modules arrived from RF Parts.  May have a lead on something less expensive with more gain for 903 MHz via HA1AG.  The big remaining tasks in all three transverter projects are the sequencer and IF interfacing.
  • Also in December, I had dinner with NS Ladder father Bill, N6ZFO, in San Francisco at the Hyde Street Seafood House & Raw Bar, which is a favorite of NA Sprint father, Rusty, W6OAT.  Yes, I did feel that I was in the presence of greatness.  (I had their excellent pork chops since I’m not into seafood, especially raw seafood.)  Like most contesters, Bill’s a super, fascinating guy apart from his radio contesting interests.

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50-MHz Progress

June 14th, 2010

As I mentioned in the previous post, I’ve made some strides toward getting on 6 meters over the weekend.  I assembled the 3-element Yagi last weekend.  It was leaning against a post in our back yard pointing skyward for a few days.  I told Sarah that I was thinking of adding 18,431 more of these antennas so I could compete with the 50-MHz radar at Jicamarca.  She was not amused.  I hadn’t even mentioned anything about megawatts.  Yes, Virginia, the mast in the photo is not square.  The top portion of the mast is a little skewed in the rotor and it’s attached with rusty U-bolts that I’ve never loosened.  I’m still turning the antenna with the TR-2, even though I have a T2X out here now.  I will do that swap eventually.  But, for right now, the TR-2 is doing fine.

In order to start moving the transverter toward its new home in a beautiful rack-mount enclosure that previously housed a 900-MHz digital repeater (not included when I obtained the box, unfortunately), I had to “re-arrange its internal organs”, as a menacing extraterrestrial used to say in Space Quest.  Sarah wonders why I schlep all of this crap from place to place with us.  I’ve had that rack-mount box longer than we’ve been married!  It was just waiting for a chance to serve in my shack.  Anyhow.  You can see the layout above.  Sarah says it looks like a doll house.  Pretty sweet house, if I say so myself.

Here’s another view of the partially-integrated box.  I’m running it off a battery because I don’t have the power supply subsystem installed in the box, yet.  It’s really just a PA and some control circuitry away from operational.  Although, I would like to align the TX side with a spectrum analyzer at some point.

I heard quite a few signals in the ARRL contest over the weekend.  W5ZN comes to mind, as well as a couple of locals like N4QQ, who lives just a stone’s throw away on the other side of the Beltway (aka the wrong side of the tracks).  I suspect that the locals would move the S-meter a little more (like past S9) if I put an IF amplifier in after the RX mixer.  But, I’m not really keen to do that unless I have to.

Schematics will come once I’m finished.  But, nothing about this so far has been rocket science (or brain surgery, as the rocket scientists say).  I’ve just been following the Handbook.

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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.

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