New test equipment: Siglent DSO and AWG

I recently decided to step up my test equipment game by getting a digital storage oscilloscope (DSO) and an arbitrary waveform generator (AWG). These will come in handy for fixing stuff, or when making electronic devices. 

The AWG (left) and the DSO (right)

After some research, I chose instruments made by Siglent for four main reasons. First, they are both very capable instruments for their price. The nearest competitor is Rigol, but Siglent beats them in almost all specs and operations, for just a few $ more. 

Second, these devices are made in China. The very stable genius/convicted felon/insurrectionist in clown makeup says he's going to impose tariffs on everything from China. That means the prices of these instruments may rise dramatically in the coming months, so get them now or maybe never.

The DSO is the SDS804X which is a 12 bit (8.4 bit ENOB, SFDR 35 dBc), 4 channel, 2 Gsps, 70 MHz BW scope. Siglent also makes 100 MHz BW and 200 MHz BW versions of this scope with greater memory depth. In fact, all three scopes use the exact same hardware, the only differences are the model number labels on the front panel. The higher BW and memory depth models simply enable those features in firmware. 

This brings me to the third reason for buying these devices instead of others. Someone figured out (or leaked from the factory) a keygen that enables you to turn on the wider BW and memory depth so you can turn your 70 MHz scope in to the 200 MHz BW scope. Of course, making the modification voids the warranty, so it's a good idea to make sure everything works as it is supposed to before upgrading. If you had a warranty covered problem with the scope, maybe it could be downgraded back to 70 MHz BW before trying to get service, but who knows if there's a log file somewhere showing the mod and subsequent unmod.

The fourth reason for buying two Siglent products is that they can talk to each other via USB or network. That can be useful for certain types of measurements. More on that below.

The scope comes with 4x switchable 1x/10x, "70 MHz" probes. However, the 70 MHz probes are identical to the 200 MHz probes, minus some accessories that come with the 200 MHz probes. So even after the "upgrade" the probes will be fine.

I bought the DSO new, via amazon, and the AWG, used, via ebay. 

The DSO: SDS804x

When I started working as an engineer back in the early 80s, a scope with 1/4 this one's capabilities would have weighed about 80 lbs, and would come on a wheeled cart, and would have cost about 2 year's pay.

What sort of capabilities? The ability to do math on the captured waveforms is a big plus. That includes, among many other built in functions, the ability to do Bode plots (aka frequency response curves), and Fast Fourier Transform that converts time domain data captured by the scope to frequency domain - i.e. spectral - plots. Rise and fall time measurements, signal frequency, etc., with full statistics are just a couple button pushes away. Captured data can be stored on a thumb drive and then imported into Matlab or similar software for more heavy-duty number crunching.

Dual trace analog CRT based scopes could not monitor two points in a circuit simultaneously because the CRT could only provide one electron beam. A two channel scope typically alternated between the two channels, sweeping one trace then the other one the CRT. There was something called "chop" mode that would rapidly switch the sweep back and forth between the two channels to "sort of" monitor two points in a circuit at the same time, but you had to be very careful about interpreting what the scope was showing you in that mode.

OTOH, a single sweep on an analog scope showed the waveform in real time. There were also DSOs that used CRT displays, so they could capture a waveform and display multiple traces on the screen from memory. They suffered from the same limitations that today's DSO do, except these days the memory and A to D converters are much cheaper so today's DSOs use much more of both.

DSOs typically have multiple A to D converters and can sweep multiple channels simultaneously, so you can monitor multiple points in a circuit in "real-time" (within the limits of the sample rate, of course).

Like dual trace CRT based scopes, DSO's require constant vigilance to avoid being fooled by  what the scope is showing you. The Siglent scope always displays the sample rate and memory depth on the screen. That's not just for convenience. The actual BW of a measurement is 1/10th of the sample rate. Though the spec says it's a 200 MHz BW scope, that is the maximum BW it can achieve when it's using 1 channel operating a 2 GSPS and using the full 100 Mpts memory. The sample rate, and BW drop as a function of the memory depth, sweep setting, and the number of channels in use. For example, if I am using one channel and set the scope to 100 ms/div, it runs at 100 MSPS and uses the full 100 Mpts in memory. That's 10 MHz BW, not 200! If I turn on a second channel the memory is split between the two and the sample rate drops to 50 MSPS with only 5 MHz BW in each channel. If you're looking for a transient that lasts a few picoseconds, you're not going to see it.

There's a very good explanation of DSOs vs analog oscilloscopes here.

As the article linked above points out, DSOs can do a lot of math that the old analog scopes couldn't. Rise time, fall time, period, frequency, skew between channels, etc. can all be displayed, and since the numbers are calculated from the waveform in memory, you can set up multiple measurements and display them at the same time. It also presents statistics on the measurements including min/max, mean, standard deviation, etc.

The scope also does dozens of things geared toward factory production of electronic gear that I'll never make use of. The 243 page user manual (and several others) is here.

The AWG: SDG1032x

The AWG is a two channel, 14 bit, function/arbitrary waveform generator that works up to 30 MHz. Another keygen enables it to be bumped up to 60 MHz because it uses the exact same hardware as the SDG1064x AWG. I had some trouble getting the keygen to work on my AWG, but I'll keep trying. In the meantime 30MHz is fine.

The AWG has dozens of waveforms built in, and can use data generated by free software called EasyWave and entered via network to create almost any waveform you might want/need. It also has multiple modulations built in, and the two channels outputs can be combined or synced. The manuals are located here.

Sine wave specs for the AWG. Distortion at audio frequencies isn't spectacular, but adequate for many tests.

Siglent has a bunch of app notes that explain how to use their scopes and AWGs to make different measurements here.

So what can you do with this stuff?

I recently bought an Advance Paris A12 stereo amplifier. Among it's many features are two line level subwoofer outputs with switchable LPF frequencies of 75 and 150 Hz. I have inquired about the slope of the LPF and have been unable to get a response anywhere. So how about measuring it?

If I connect the AWG, the DSO, and the amp together like this:

The test setup. Channel 1 of both the AWG and the DSO are for the reference signal. Channel 2 is for the device under test (DUT-  the amplifier). There are BNC connectors on the AWG and DSO, and phono connectors on the amp.

I can set the DSO to do a Bode plot that will cause the AWG to sweep the signal frequency while it monitors the output from the amp and plots the gain and phase difference between the input and output signals. The AWG is set so that channel 1 and 2 are synced meaning their frequency and phase are locked together- as one changes, the other will change equally, under control of the DSO. The DSO will compare the signal coming through the amp to the signal coming directly from the AWG and plot the differences in amplitude and phase vs. the frequency. 

There's a good explanation of Bode plots here.- I'm going to have to do some studying- it's been a long time since I dealt with this sort of thing.

To verify my settings, I connected the AWG channels 1 and 2 directly to the DSO channels 1 and 2 and ran the sweep. The image below shows essentially zero difference in amplitude and phase as it should. The minor differences seen may be due to differences in the two cables I used- one was a BNC to BNC cable, the other a scope probe, just poked into the AWG output jack, and/or the limited resolution of the scope.

Bode plot of the AWG connected straight through to the DSO, frequency swept from 10 Hz to 5 kHz.

The LPF in the amp can be switched from 75 Hz to 150 Hz, so I ran two tests, one for each LPF setting, sweeping sine waves from the AWG over a frequency range from 10 Hz to 2000 Hz, measuring 20 points per decade. I set the AWG to 100 mVrms out so I wouldn't overload the amplifier, and disconnected the speakers and subwoofer before running any of the tests. I adjusted the volume control on the amp to get the test signal close to the 0 dB line on the Bode plot.

I connected the amplifier using two BNC to RCA (phono) cables with the LPF switch set to 75 Hz and swept again. This time I turned on two cursors (X1, X2) on the amplitude trace as well as 3 dB point, gain and phase margin measurements (P1, 2, and 3).

The 75 Hz LPF test. The DSO says the 3 dB point is 80 Hz (P1, lower left), and cursors say it's at 81 Hz. It probably varies a little depending on where you start. P2 shows gain margin. P3 is supposed to show phase margin- not sure what happened there.

I switched the LPF to 150 Hz and ran the test again.

The 150 Hz LPF filter test. I've turned on cursors and a couple measurements. The cursors show the 3 dB point of the filter is at 166 Hz and the scope's measure of the 3 dB point is 167 Hz. The scope and I probably chose slightly different starting points for the measurement.

The DSO can save the data from these plots as .CSV files like this one from the 75 Hz test:

Instrument Name,SDS824X HD

Serial Number,SDS08A0X806378

Software Version,3.8.12.1.1.3.8

Awg Type,USB

DUT Input Source,CH1

DUT Output Source1,CH2

DUT Output Source2,None

DUT Output Source3,None

DUT Channel Gain,Auto

Sweep Type,Simple

Awg Amplitude,0.1V

Awg Offset,0V

Awg Amplitude reference level,1V

Awg Load,HighZ

Awg Amplitude Unit,Vrms

Sweep Mode,Logarithmic

Start Frequency,10Hz

Stop Frequency,2000Hz

Sweep Line,50

Sweep Log(dec),20

Amplitude Mode,Vout/Vin

Amplitude Axis Type,Logarithmic

Amplitude Axis Range,-92dB,-28dB

Phase Unit,Degree

Phase Axis Range,-120Deg,80Deg

Bode Data

Number of Points,48

Frequency(Hz),CH2 Amplitude(dB),CH2 Phase(Deg)

10,-0.316206946,176.898533

11.2201845,-0.301349145,174.827017

12.5892541,-0.295593542,172.720797

14.1253754,-0.285307544,170.482712

15.8489319,-0.282871402,168.078595

17.7827941,-0.278952734,165.495564

19.9526231,-0.276636798,162.72877

22.3872114,-0.283139497,159.650485

25.1188643,-0.286777113,156.27685

28.1838293,-0.302849299,152.508918

31.6227766,-0.325629345,148.256579

35.4813389,-0.37922284,143.414019

39.8107171,-0.448551886,137.938013

44.6683592,-0.57699543,131.685234

50.1187234,-0.785198164,124.551014

56.2341325,-1.1070296,116.547249

63.0957344,-1.58892266,107.680373

70.7945784,-2.27801731,98.1979734

79.4328235,-3.19725386,88.408361

89.1250938,-4.36847629,78.6493903

100,-5.76128114,69.3966066

112.201845,-7.33886852,60.8239298

125.892541,-9.07129381,53.1396052

141.253754,-10.8753204,46.4291769

158.489319,-12.7822801,40.5519963

177.827941,-14.7305102,35.324053

199.526231,-16.6876153,30.6849254

223.872114,-18.6739893,26.8189145

251.188643,-20.6655185,23.2595056

281.838293,-22.6610596,20.0543472

316.227766,-24.6691554,17.3480928

354.813389,-26.6556163,14.7279327

398.107171,-28.6618495,12.4576434

446.683592,-30.6646106,10.2932372

501.187234,-32.6885167,8.5660686

562.341325,-34.6574611,7.25368276

630.957344,-36.5675565,5.67887063

707.945784,-38.7709119,2.96040434

794.328235,-40.6839971,0.931052533

891.250938,-43.4931255,-4.32564563

1000,-44.6084714,-1.41852283

1122.01845,-46.6796759,-4.34549142

1258.92541,-48.7276961,-5.72869398

1412.53754,-50.9672037,-6.92954931

1584.89319,-52.9628139,-10.5570804

1778.27941,-54.8710069,-11.4217083

1995.26231,-57.0067772,-13.761997

2000,-57.1240924,-13.1864203

From the plots and the data, we can see that the 75 Hz filter hits the -3 dB point at about 80 Hz, and the slope after that is about 12 dB per octave (or 20 dB per decade), making this a 2nd order LPF. The 150 Hz plot and data show the 3dB point to be about 160 Hz, with the same 12 dB per octave slope.

Why does knowing this matter? If you were going to drive a subwoofer that didn't have it's own crossover you'd want to know how much of the higher frequency energy is going to be presented to the sub's amplifier/driver. It would also be very useful if you were building an active crossover to drive a bi- or tri- amped set of speakers. Or if you were restoring old audio gear and wanted to see if the tone controls were behaving right, or wanted to see the limits of their effect. It has many other uses for tuning higher frequency circuits, too.

FFT

Another one of the interesting things the DSO can do is called Fast Fourier Transform (FFT). That is a process whereby time domain data is converted to frequency domain data and plotted. It essentially turns the scope into a crude spectrum analyzer.

I hooked the scope to my CD player and played a steady 1 kHz tone from a test CD, then ran FFT and plotted the result.

Spectrum of a 1 kHz test tone played from a test CD on my VRDS-20 CD player. The first 8 harmonics are listed. Note the sidebands on either side of the 1 kHz spike. Those are 120 Hz offset from the 1 kHz tone, indicating some ripple from the power supply is getting into the output of the CD player.

This is no substitute for a real audio analyzer (or spectrum analyzer) as the DSO noise level is high and ENOB is only 8.4, but you can see power supply ripple in the signal and the relative levels of some of the harmonics. The results also depend on the selected "window" used to make the measurement. Some window types are more accurate for amplitude and others more accurate for frequency.

I will be exploring other measurements and options in the future and my test cable collection expands, and I study and practice a bit more. A DSO can become a hobby all by itself!

A New Bike: Priority 600X

Note: I wrote most of this post back in April, but never got around to posting it. I believe Priority no longer sells this specific model of bike, though they sell others using the Pinion gearbox.

I've been commuting back and forth to work on my Priority Continuum Onyx (referred to as PCO from here on) for about 3 years and it has been wonderful! The sealed Enviolo CVT in the rear hub and the Gates belt drive have been absolutely perfect. But time marches on... I retired in September last year and no longer need to commute daily, though I still ride the bike around town, even through most of the winter.

The mean streets of Milwaukee are cracked and potholed a lot like I remember Tijuana in the 80s. I decided to get myself a bike with some suspension and fatter tires to make the ride more comfortable. I started watching youtube videos of some of the Priority bikes and was really impressed with the Pinion gearbox bikes. 

The Priority 600X has a Pinion C1.12 gearbox at the cranks instead of the PCOs CVT in the rear wheel. I have always been a bike geek and love to try different transmissions. I saw the Pinion gearbox a few years ago and found it interesting, but most bikes with that gearbox cost $4-5k, often more, and that was a bit too rich for my blood. $3k has always been the far upper limit of what I could see ever spending on a bike.

I don't know if it was coincidence or the result of some artificially intelligent Google surveillance of my viewing habits and interests, but I got an email from Priority Bikes promoting a spring sale. Among others, they were offering an incredible deal on the 600X. The bike normally sells for $3500, but it was $250 off and there was an ordering code that knocked it down another 25%. I couldn't resist! I don't know how they can sell that bike at that price and stay in business. I'm guessing they were getting rid of inventory of this bike prior to selling the newer models.

The Priority 600X is an incredible machine. It has a 110 mm travel Wren suspension fork that is owner-serviceable (unlike the Cannondale headshock in my old MTB). It also has a very low maintenance (oil change every 10k km or once a year) Pinion C1.12 gearbox, a maintenance-free Gates CDX belt drive like the Onyx (CDN), four piston hydraulic brakes, tubeless capable WTB rims and tires. You can see all the details at Priority's site, and a bunch of youtube reviews here.

The bikes 2.4" wide tires and suspension fork mean it will be great on the pot-holed streets and good for off-road riding, as well. The frame is built to have bags and carriers, so it's super versatile.

I also ordered a trailer hitch and bike rack to fit my car. I didn't order a roof rack because the bike is relatively heavy (~32 lbs) and I don't like the idea of having to lift it that high. I also figured that if the bike gets muddy I don't want to try to carry it inside the car, where it will be hard to fit anyway, due to the 29" wheels.

A few people liked my review of the PCO, so after I get through all the other stuff, I'll go into some detail about the bike that you might not find in other reviews. You can skip down to the Bike Details section below if you prefer to skip the other stuff.

Arrival!

The bike arrived 4 days after ordering and within minutes I had it out of the box, preserving it for future shipment via airlines. As usual, the packing was perfect and the bike came out of the box without any damage whatsoever. I took pictures of the way it was packed so that if I ever want to ship the bike via an airline, I will know how to pack it up so it arrives undamaged.

It's here!  It's here!

This is how it gets packed for shipping. No damage at all!

The usual goodies: pedals, shock pump, touchup paint, bash guards for shock, tools, and manuals.

Here it is, about a 1/2 hour later, fully assembled!

My bike came equipped with Tektro Orion 4P brakes, Goodyear Peak 29 x 2.4" TC tires on WTB KOM Tough i35 rims, WTB Volt saddle, and Wellgo B087 platform pedals. Note: the tires and rims are tubeless capable, but the bike ships with tubes installed.

When I separated the front wheel from the rest of the bike after taking it out of the box, I was impressed by the size of the wheel and tire. It looks like something that should be very heavy but it was surprisingly light.

Assembly was pretty easy- unwrap everything, mount the pedals, turn the stem around 180 degrees, mount the handlebars, and install the seat. I also checked belt tension, tightness of screws all over the bike, headset tightness, brake caliper to disc alignment, etc.

Next I studied the shock manual and gave it some air as suggested, then took it outside to bed-in the brakes. That involves getting up to speed and then squeezing one of the brake levers until the bike slows to walking speed. At first is squeaks and vibrates, but you speed up and do it again, and again, and again, and eventually the brake starts slowing the bike smoothly and quietly. Then you repeat the whole process for the other brake. Fortunately, I live on a relatively steep hill and the getting up to speed part was super easy.

The Pinion C1.12 Transmission

The ride back up the hill gave me a chance to test the low end gears of the of the Pinion transmission. I was impressed! The lowest gear seems like you could ride the bike up a tree if you wanted to. I was used to shifting the Enviolo CVT on the Onyx, and shifting the Pinion gearbox was similar. I found that shifting required a little more muscle than I had expected, but I was wearing heavy winter gloves, so maybe the gloves were forcing me to grip the shifter harder. It may also be the tension on the shift cables is a bit higher than it needs to be. That can be adjusted, but I'll wait until I've ridden the bike a while to give the cables time to stretch. 

Gear shifts were instant, but you have to time your pedaling pressure a bit when shifting so you're not putting too much of a load on the gearbox during the shift (like the Enviolo hub in the Onyx). You don't have to stop pedaling, just reduce pressure momentarily. The shifter clicks at each gear position, so as soon as you feel /hear the click you can start mashing the pedals hard again. To me it seems like it's easier to shift down than up because you don't have to time the shift to your pedal stroke as much- the gearbox seems to tolerate more pedal pressure when downshifting. Rotating the shifter forward increases the gear ratio, rotating back reduces it for climbing. You can shift through the entire gear range while stopped.

I remember the old Sturmey-Archer 3-speed hubs I rode as a kid. If you worked the shifter carefully, you could put the thing between gears and the pedals would just turn without moving the bike. I tried to do the same thing with the Pinion gearbox and could not get it to do it, so you probably don't have to worry about shifting and having the pedals suddenly go limp while you're barreling down single track on rocks or roots, or worse, while pedaling a heavy load up a steep hill.

Wren Inverted Shock Fork

I played with the shock settings a bit and found it very responsive. There are so many adjustments you can make it will take me a while and some off-road riding to set it up just right. My old Cannondale with a headshock, and the only adjustments were the air pressure and damping. The Wren shock has a lockout for street riding, though with the potholes we have in Milwaukee, I may leave the shock active most of the time.

I've been riding it for months now, and find that I have to top-up the pressure in the shock every couple weeks to keep it working consistently.

Lights and Reflectors

Since I'll be riding around town on the bike, and frequently at night, I did my usual thing and put reflective tape on the wheel rims after I peeled off all the WTB stickers and wiped the rims with IPA. I used blue, fluorescent yellow, red, and white reflective tape randomly arranged between the spokes on the rims. I'll probably add more reflective tape to the cranks and head tube.

I also bought a bright headlight that has a large battery and a "smart" taillight that senses when you're braking and lights up at maximum brightness like a car's brake lights.

Headlight and Wahoo GPS/computer. I made the headlight mount from a piece of aluminum angle stock.

Here's The Hitch

I want to be able to transport the bike easily so I shopped for hitch receivers that would fit my car. Draw-Tite and Curt seem to be the most popular brands on amazon.com, both getting many good reviews. I don't want the bike and rack bouncing and swaying around so I chose the Curt 11473 over the Draw-Tite 24944 after studying pictures of the two. The Curt hitch seemed to be the more sturdily built of the two. I also bought a hitch tightener. 

The hitch arrived on the same day as the bike and I took it to the Milwaukee Makerspace to install it. Three hours later it was finished, with most of that time spent dealing with the little plastic fasteners used to hold all the splash guards and the lower bumper cover (the black part) in place. I managed to put it all back together without any leftover parts, and the sensors on the rear bumper still work!

The hitch is solid as a rock!

Bike Carrier

I ordered a bike carrier, too, and went cheap. Big mistake. The carrier I ordered hangs two bikes by their top tubes. It can tilt back to allow access to the back of the car, which seemed like a good idea. There are two main problems with this rack. First, the top tube on my bike is tilted which means the bike hangs on the carrier tilted, putting the front wheel about 7" off the ground. That's a bit too close for comfort. Second, the hinged joint that allows the rack to tilt out of the way of the hatch wobbles. There's no easy way to stabilize it. Ugh. It turns out the rear hatch clears the bike carrier and bike without tilting, so maybe that feature wasn't that important.

The wrong bike carrier. Maybe it would have worked OK if I had hung the front end of the bike by the fork/downtube joint, but it was a bit too wobbly, even with a hitch tightener in place.

I returned the carrier and ordered another- a Swagman "platform" type that holds the bike's wheels and has a clamp that comes down over the top tube. Much better! It can hold two bikes, and I set it up so my bike goes on the back side of the carrier. That leaves enough room to open the car's hatch, even when the bike is on the carrier. If there's a second bike on the carrier, that may not work so well.

The bike and Swagman XTC 2 platform carrier on the car. Both wheels are now about 14" off the ground. The bike is 75" long and the car is 69" wide, so the wheels stick out a bit on either side of the car. The center clamp that comes down on the top tube is supposed to be located at the top-tube/seat-tube junction, but that would require shifting the bike about a foot to the left and leave the front wheel sticking out, far beyond the side of the car, just waiting to bang into something. The bike is completely constrained as shown, so it's not going anywhere.

The Swagman platform carrier folded up. 

Another view of the bike carrier mounted on the car. The central post can be folded down so it doesn't block the back-up camera when there are no bikes on the carrier, but then you have to leave the wheel trays down as shown.

I added a hitch tightener to minimize wobble and sway- but there wasn't much to start with, so maybe this isn't really needed. The bolt at the left is the hitch pin that comes with the bike carrier and threads into an insert in the carrier that holds it tightly- the hitch tightener might not be necessary. I'll probably use it anyway because it will be one more thing that a potential thief will have to deal with and it might slow them down a little.

Another view of the hitch tightener. That's a 1/2" stainless U bolt. One 19mm or 3/4" wrench can be used to tighten bolts on the hitch and the tightener. You can also see the cotter pin that comes with the bike carrier.

I have a bunch of tools, but didn't have a socket deep enough for the bolts on the hitch tightener, so I ordered a ratcheting wrench specifically for the purpose. I'll just keep it in the car with other loose parts for the bike carrier so I'll always know where it is when I need it.

When you travel with a bike on a car carrier, you're going to have to stop to eat now and then. How do you ensure the security of the bike(s)? I ordered a locking hitch pin that comes with a steel cable. No, it isn't super high security, but it will stop someone from simply walking up and taking a bike off the carrier. When you put the bike(s) on the carrier, you loop the steel cable through the wheels and frame(s) and anchor the end of the cable on the hitch pin. It's a little difficult to get at, but it's better than no security at all. My bike only has to be a little more difficult to take than the one on that other car, over there. Of course, if someone is prepared to cut the cable they will make quick work of stealing the bike.

New Bike, New Other Stuff

Sometimes, the best part about getting a new bike is getting all the other stuff to go with it.

Top tube junk carrier. It's big enough to fit my Pixel 7 Pro phone, still in its case. There's plenty of room for glasses, ear buds, wallet, keys, snacks, etc.- you know, all the stuff you need to carry that they don't put pockets in bike clothes for. Over the several months I've been using it, the velcro that holds the phone in place has become very weak. I don't recommend this bag.

The Enfitnix Cube tail light, with auto on/off and brake light functions, mounted on the seat post. It also comes with a mount for the seat rails, but I didn't have room for it there. The light twists on and off the mount, so it's easy to take inside to charge (or to steal!). The battery is supposed to last between 4 and 14 hours, depending on how you set it. The button that turns it on and sets operating mode is a little too easy to push. I paid about $22 via amazon.com, but you can buy similar lights via aliexpress for about $5.

 

Fenders

I'm going to be riding the 600X around town (I sold my beloved PCO via Craig's List) in addition to off-road, regardless of the weather, within reasonable limits. That means fenders are a must. The problem is fenders made for MTBs are mostly intended to protect shocks, bearings, and the rider's face from mud thrown up off the trail and tend to be very short so they won't get caught on branches.

The 600X's inverted Wren fork makes it difficult to fit a front fender. Most forks have a bridge just above the wheel that moves up and down with the wheel and makes a great attachment point for a fender that follows the motion of the wheel as the shock compresses. MTB fenders are usually designed to attach to the fork's bridge. The Wren fork on the 600X has no such bridge, so the only attachment points for a fender are the upper stanchions. If you want the fender close to the tire, it has to attach to the lowers that move up and down with the wheel as the fork compresses. The problem with that is the fender has to be about 15" away from the axle and you need something that long to support it. You can mount a fender using the upper stanchions but it won't follow vertical motion of the wheel. OTOH, if you're riding on streets, you can lock out the fork and mount the fender low enough on the upper stanchions to put the fender close to the wheel.

A fender for the 600X rear wheel isn't too big a problem because unlike the front wheel, nothing moves up and down, so attaching it to the seat stays should be fine.

After a lot of searching, I found the Mucky Nutz fenders to be the most likely to provide most of the coverage I wanted to keep my clothes clean when riding on wet streets. I ordered them via ebay.

Mucky Nutz rear fender on the bike. It's plenty long at the back, but a bit short at the front end. I may have to figure out how to add an extension to get more coverage toward the front. The fender is held in place with velcro straps that come with it, so it's easy to put the fender on in wet weather and take it off in drier weather.

Mucky Nutz fender on the front wheel. I wish it were longer at the back- I may need to figure out how to extend it. Velcro straps secure it to the upper stanchions. I can keep it close to the tire as long as I lock out the fork so the wheel doesn't move up and down. 

The fork has no bridge to secure the front fender and it seemed a little too wobbly just strapped to the stanchions, so I designed and printed a bridge specifically to hold the fender. It friction fits over the upper stanchions, gripping them tightly, and Velcro tape secures the fender to the bridge. It greatly increases the stability of the fender.

Mucky Nutz fender mounted on the front wheel with 3D printed bridge. I printed it with black TPU filament. It grips the two stanchions tightly without any retaining straps, and improves stability of the fender. We'll see how it holds up when exposed to weather. 

Closeup of the 3D printed bridge. The fender has slots for the Velcro straps that secure it to my printed bridge.

CAD render of the bridge. The holes for Velcro straps match the holes in the fender. It took about 20 minutes to design it and I only had to print two versions to get the dimensions right. Printing with a 1mm nozzle in 0.5mm layers at 30 mm/sec took about 1 1/2 hours. Everything you see is 5mm thick.

It takes just a minute or two to attach the fenders, so when the weather is bad I'll put them on and when the weather is nice they're coming off.

Tubeless? Tubes?

I watched a lot of YouTube videos about running tubeless tires on MTBs. Under some circumstances it seems like a really good idea, (riding in areas with lots of thorns, etc.) but otherwise the maintenance seems troublesome. I'll probably use tubes for the foreseeable future.

I picked up a couple spare tubes - I got TPU tubes that are super thin and light. You can buy a 2-pack of 29" Cyclami tubes via amazon.com for $26, or buy the same package via aliexpress for $10. Guess which I did. On-line reviews indicate that they are lighter, harder to puncture, retain air better than butyl tubes, and are difficult to patch reliably. I chose the Cyclami tubes because they have threaded metal stems- a lot of the TPU tubes have plastic stems that can break, and won't work with screw-on pump connectors.

One of two Cyclami TPU tubes ordered for $10 from AliExpress. That's a 29" tube and only 62 g! Very small and easy to carry on the bike. I bought two tubes and they came with some cleaning wipes and a couple patches (regular bike tube patches won't work with TPU tubes). I chose these tubes for their threaded metal stems- most TPU tubes have plastic stems to reduce weight, but that makes them incompatible with a screw-on pumps, and plastic stems can break. Note: the valve cores of these tubes are not removable, so I probably won't be putting any sealer in these tubes.

One of the butyl rubber tube that came in the wheels. 4X heavier than the TPU tube! That's almost an extra half pound in each wheel that you have to spin. Yikes!

Size comparison. Which would you rather carry as a spare? You can carry 4 of the TPU spares in the space (and weight) of one butyl tube.

When I received the TPU tubes, I immediately set about replacing the butyl rubber tubes that came on the bike. That presented a new problem: how do you get the tires off the rims? Tubeless capable wheels and tires require a very tight fit and I found that I couldn't get a tire lever between the tire and rim no matter how hard I tried. Back to YouTube to search for the answer. The trick is to lay the wheel down with the tire deflated, then step on the tire with your shoes to force it in toward the center of the rim. Once you get it started, it's pretty easy to get the rest of it to go. Once the bead is all pushed into the center of the rim, you can grab it in one spot and pull it over the rim. Then you can pull the tube out and stuff the new one in. 

I started this post in April, and now it's December. I've had one flat tire caused by a piece of glass. I patched the TPU tube per the instructions and found that it was flat again a day later. I opened the wheel up and inspected the patch and found it wasn't entirely stuck to the tube. I applied some localized pressure to it for a couple minutes and put it back and it's been holding air for about 3 months now.

One claim about TPU tubes is that they leak less air than butyl tubes. I haven't found that to be the case. They seem about the same to me and I find myself topping up the tire pressure every few days. I typically run the tires at 40 psi on the streets.

Pump

I got a small pump to carry on the bike for just-in-case. It's a Crank Bros Klic HV pump. It's a great design that includes a flexible hose, valve adapter, pressure gauge, and CO2 cartridge fitting in case I don't feel like pumping (but don't use CO2 with TPU tubes!).

The Crank Bros Klic HV pump. It's 260mm long and about 30 mm in diameter. It comes with a mount that bolts on the bike. When it's closed up like this everything is sort-of protected from mud and dirt. It contains a flexible hose with screw-on adapter for Presta and Shrader valves, a pressure gauge, and a CO2 adapter so you can inflate your tires that way (don't use CO2 with TPU tubes!). It takes 300 strokes (I counted!) to fill a 29x2.4" tire to 35 psi with this type of pump, so I hope I don't get many flat tires.

Pedals

The bike came with Wellgo B087 pedals as did the PCO. I took one of the Wellgo pedals off the bike and tried to open it to see what the bearings and seals are like, and found that I didn't have a socket that could get inside the pedal to unscrew the lock nut. Hmmm. 

I bought some very slightly used, large size Crank Bros Stamp 7 pedals via eBay for the 600X. The advantage is that they fit my big feet better, are easily serviceable, and the traction pins are adjustable and replaceable. The one's I got happen to be a metallic blue color that matches some of the parts on the Wren fork. 

Stamp 7 pedal in metallic blue.

The new pedals match the fork air cap and lockout lever!

Rack/Bag

When I ordered the bike I ordered the same Axiom rack I had on the PCO. I also did some research on pannier bags and found one I liked- a Rhinowalk knock-off of an expensive Ortlieb bag. It is water tight (well, rain proof- not sure about getting it wetter than that) and can carry a lot of stuff. It goes on and off the rack quickly and easily.

Heavy duty rack, the same one I used on the PCO, fits over the rear fender, no problem.

Bag on the rack. I have tested this bag in pouring rain. Not a drop got inside.

I had one small problem with the bag. It uses a similar clamp system to the Ortilieb bag it copies, that has clamps that slide along a rail to allow you to space the clamps to fit your rack. I found that the clamps moved easily when I pulled up on the strap that releases them to take the bag off the bike. I fixed that with a couple drops of super glue.

Bike Details

The bike's frame has internal cable routing for a dropper seat-post. It also has a quick release seat post clamp that I'll probably replace with one that requires a tool so my seat is less likely to get stolen. The seat post diameter is 30.8 mm.

The large frame that I ordered has cranks that are 170 mm long. The ground clearance to the pedals is 130 mm, quite high off the ground compared to a street type bike, meaning that when you're riding on the street you can pedal through turns without worrying about the pedals hitting the ground.

The bike comes with a heavy-duty kick stand that is set far back on the frame. It's far enough back that you can roll the bike backwards while the kick stand is down without the pedals hitting it. I haven't noticed any heel-strike while pedaling. 

The belt drive is Gates CDX type rated for a very wide temperature range. Both the front and rear belt pulleys have 32 teeth. Both are made of stainless steel, and since the tooth counts are the same, I'd expect the two to wear at about the same rate. The 32 tooth crank pulley is pretty small, giving it lots of ground clearance when riding off-road.

The wheels are quick release, with 15 mm through-axles. It appears that the rear hub has a standard freewheel (is that what it's called these days?) so the wheel is dished to make room for it. I would have thought that with the belt drive and a single cog, and a disc brake rotor on the opposite side, there would be no need to dish the wheel, but I guess it doesn't work that way.

More New Stuff

I don't like to wear padded bike shorts (what a ridiculous concept!). The Volt seat that came on the bike is pretty good, but after riding the bike for a few months I wanted to see if I could find something more comfortable. I did some digging and found recommendations for something called an "Infinity" seat. I looked them up. Yikes! $400 for a bike seat! These things are made in LA by a company started by a chiropractor, and used by almost all the Race Across America riders because of the comfort. I checked to see if I could pick one up on eBay and and yes, you can, for about $300, but they go fast. I got an email from Infinity offering 15% off, so I ordered a seat figuring that if I didn't like it, I could always sell it on eBay and only lose $50 in the process.

Most of the infinity seats have a leather cover, but I didn't want to have to worry about taking care of leather if I'm out in rain and snow, so I bought the seat with the "marine vinyl" cover. I am pleased to say that it is every bit as comfortable as the reviews said. So far the longest ride I've done is 25 miles in a day, but the seat is no longer a comfort issue.

Infinity seat and Suntour suspension seat post. There is a neoprene cover over the mechanical bits of the seat post to help keep them dry.

One thing I discovered early on is that you'd better not pick up the rear of the bike by the Infinity seat- it will distort enough for the rails to pop out of the back of seat frame and then you have to use a screw driver to release the front end of the rails, get the back end inserted back into the seat frame, then screw the front down again. I've trained myself to grab the rack when I want to lift the back of the bike instead of the seat, so it's no problem.

The suspension fork does a great job soaking up bumps and potholes on the streets, but rear end of the bike (and my butt) take a bit of abuse when the rear wheel goes over the same bump or into the same pothole. I decided to look into suspension seat posts. After reviewing several YouTube videos about them, I bought a Suntour post for about $100. There are more expensive posts out there, but the reviews didn't really find the extra money worth spending. There are also cheaper seat posts out there from unknown Chinese manufacturers. I didn't want to gamble on one of those.

I'm pleased to report that the Suntour seat post is "all that and a bag of chips!" It is not a shock absorber, just a spring that compresses on the bumps and takes out the bone-jarring that accompanies them. There is a preload adjustment screw that you can set to compensate for your weight. I set it so it doesn't compress when I'm riding normally- it only compresses when I hit a big bump. I weigh 197 lbs and the spring that comes with the seat post is fine. If you weigh much more than that, you can get a stiffer spring (for added $, of course). 

Riding is getting very comfortable between the Infinity seat and the Suntour seat post. Now I have to work on hand/arm comfort a bit...