FY6900 20/30/40/50/60/80/100MHz DDS Function Signal Generator Dual-CH Arbitrary Waveform Generator Source Frequency Counter(FY6900 20M)

I already have a couple professional-grade signal/function generators, by the likes of HP, etc; and pro-sumer ones by Rigol and Siglent. But they are all frequency limited to no more than 60MHz. Since I have been working on repairs of some faster frequency counters, I wanted a faster signal generator to test them with, but could not justify $1000++ for the "good" ones. This model sold on Amazon as "GuliTech", is marked as "FeelElec" and supported by a "FeelTech" website (BTW, the English version is http://en.feeltech.net/). The model number is FY6900, and it comes in a few different models, with progressively higher frequency top-ends and corresponding prices. I bought the 100MHz version, which is the fastest one in this series. Note that the basic model number does NOT change according to the maximum frequency.I have not had a chance to do a thorough test yet. I have hooked it up to a few frequency counters, and an oscilloscope. All waveforms are digitally synthesized, and during a quick view on my 'scope, they appeared to be cleanly formed. I verified that the generator output usable signal up to its rated maximum of 100MHz, but noted that this is ONLY for sine waves......it appears that square waves are limited to 25MHz, and pulse, ramp and triangle waves are limited to 10MHz. This makes sense, because a limited DDS like this is unlikely to have the 'oomph' to generate higher frequencies complete with all the necessary harmonics to comprise the more complex waveforms.This generator was TWO identical channels, like two independent signal generators on one box. They can be synchronized, or not, and via a pair of rear-panel BNC jacks ("SYNC IN" & "SYNC OUT"), they can be synchronized with other signal generators.Also on the rear panel are two more BNC jacks; one for "Trig/FSK/ASK/PSK" and the other for "VCO IN 0-5V". Also also, there is a proprietary-looking 8-pin connector "TTL OUT" with pins GND, 5V. Rx, Tx, A, B, C, D, which I have not explored at all, and a USB-B connector, which I also have not investigated.The front panel has a 'soft' power pushbutton (it does not really disconnect the generator from the AC Mains...there is a rear panel switch for THAT), a 2.5" (diagonal) color LCD screen, five 'soft' function buttons whose context depends on what is on the screen at the moment, six "Function" buttons (Wave, Mod, Sweep, Counter, VCO, System), a non-clickable parameter adjustment knob, a pair of Left/Right cursor buttons, an "OK" button, and the two "Channel Select/Channel On-Off" buttons adjacent to their associated BNC output jacks. There is also a third BNC jack, which is for the Frequency Counter functionality.For basic operation, you turn the rear panel power switch on, then turn on the screen with the front panel 'soft' power button, select the parameter (e.g. frequency, amplitude, offset, duty cycle) using the function buttons, then use the cursor buttons and the knob to adjust whatever you have selected. Note that this does NOT have a keypad for direct numerical entry of parameter values.Most of the screen is occupied with parameters, and a thumbnail of the current waveform, for one of the two channels, with a smaller segment of the screen dedicated to a overview of the other channel. To select a channel to be the current primary, press its associated button, and the screen will change to highlight that channel's parameters at the expense of the other channel. The same buttons can be used to turn the channels on and off. A short press selects a channel to be primary, and a long (1 second-ish) press toggles the channel on/off, as indicated by the button being illuminated or not.When setting parameters such as frequency, you can change only one digit at a time; select the digit using the cursor buttons, then use the knob to roll that digit until the desired value is shown. This can be a bit tedious when trying to get all the digits of resolution the way you want them.One annoyance I noted was that both channels on mine default to ON upon power-up. There might be a way to save preferences......I forgot to mention the power cord and other cords. This device comes with a rather short IEC type power cord (about 3 feet long); the real power switch is part of the IEC socket. If it were any longer, its weight might well pull the device off the table, since it weighs so little (22oz or 600 grams), and the case is also small at about 7.5"W x 3"H x 7.5"D (190mm x 76mm x 190mm). The two included BNB-to-BNC cords are similarly short, as are the two included BNC-to-alligator clip cords. The case feels flimsy, but is reportedly made from ABS and is probably adequately rugged. The carry handle/tilt bail/kickstand is of the same material and DOES have the ability to be folded out of the way on the bottom of the case; it has only one useful angle for propping the device's front up.A frequency counter is built in, and to use it the COUNTER function button must be pressed. It can be used at the same time as one or both of the signal generators. I have not delved into this more than just a perfunctory validation of basic functionality.So, no much like serious test equipment, but I think pretty decent bang for the buck.This does not come with a printed manual. A business card was in the box of the one I bought, directing me to a website URL that was all in Chinese. A Google search found the URL I referenced above, and that one is in English, and does include a DOWNLOADS webpage, where several PDF files of manuals can be obtained in English (including a WORD document describing how to open the case). I have not actually read the downloaded manual yet.