Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Sep Mon 21, 2020 5:27 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 24 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: KKMoon FY-6800 DDS Signal Generator
PostPosted: Dec Sat 29, 2018 4:53 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
Hi All,

My great wife forced me to select a Christmas gift this year. (I'm one of those who never needs anything)

Under severe duress, I asked for a new Signal generator, specifically a KKMoon FY-6800 DDS Signal Generator / Counter. Its under $100 and that made it interesting.
Attachment:
FY-6800.jpg
FY-6800.jpg [ 55.21 KiB | Viewed 4415 times ]


As with most Chinese items, documentation is very limited. The generator arrived with NO written info of any kind. After some web searching I found the PC software and User Guide.

Manual can be had here:
http://en.feeltech.net/index.php?case=archive&act=list&catid=6

I'm starting to learn to use the new toy and I must say my overall impression is pretty positive...

PROs
>> PC Interface is great! Simple USB cable. Much more convenient than reaching over the radio under test to fiddle with the knobs.
>> Waveform quality looks very good, I dont notice any artifacts.
>> No issues seen with ground loops, etc.

CONs
>> I have not been able to get a swept signal to be modulated. Seems that it is a one or the other proposition.
>> I can find no output for scope horizontal sweep drive. This makes the sweep function pretty useless as I cant sync the sweep to my scope. Found a good workaround on the web which uses channel two ramp function as the sweeper scope horizontal defelection signal.
>> There is not a marker output. I could use channel two if it weren't already being used for sweep function. However, if everything is calibrated properly, center of sweep should be the target frequency - not yet fully verified.

Is anyone else here working with one of these. Since this is a 'learn as you go' process, it would be great to share what we have learned. I have no doubt that there are other options that I haven't thought of.

The pictures shown below indicate the relevant setup parameters for various jobs, circled in purple. The sweep section is x'ed out in red since I have not yet figured out how to get any real use out of it.

Tim


Attachments:
AMSweep.JPG
AMSweep.JPG [ 235.65 KiB | Viewed 4446 times ]
FMDiscriminatorSweep.JPG
FMDiscriminatorSweep.JPG [ 203.26 KiB | Viewed 4446 times ]
Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Thu 03, 2019 5:15 am 
Member
User avatar

Joined: Aug Tue 28, 2018 9:22 pm
Posts: 2414
Location: Sanford Fla 32771 (USA)
I'll be interested in what others have to say, particularly in relation to the sweep operation. No way to sync the scope is really bad from my humble opinion. Looks like they packed a 1000 options in this but may have forgotten some of the simple requirements (like scope sync).

_________________
Paul of Florida ….I had my patience tested. I’m negative.
https://paulsironhorse.smugmug.com/


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Thu 03, 2019 5:56 am 
Member
User avatar

Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7167
Location: Liberty, Missouri
For some reason I can't get the manual to open, so a couple questions.

what is the frequency range?

How low does the output level go?

Have you done any leakage testing?

Any mention of stability, phase noise, or spurious content of the output?

Thanks

_________________
Pics, Bold & underlined text, are usually links.

https://mikeharrison.smugmug.com/

Mike


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Thu 03, 2019 8:32 am 
Member

Joined: May Wed 23, 2018 6:28 am
Posts: 525
I can't get the manual to open either. Its an 11mB rar file that won't unpack.

From memory, the low end 14 bit generators have a VCO. I think the 2nd channel is used to modulate the first, and that sweep is intended to be controlled by the VCO which needs a 0 to 5V source. I've never had to deal with this, but it seems like it takes a ramp from another generator to get both AM and sweep at the same time. It may also be that you can feed external modulation into the trigger/FSK... input and control the sweep with 2nd channel.

I have an Siglent SDG 1025 which I believe can manage both without another device, but I'm sorry, I don't sweep in my shop very often, which my wife complains about.

I think if you Google "FY-8800 + modulation + sweep", you might find something, if you are patient.

John


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Thu 03, 2019 12:29 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
The chinese site seems to have a more current version of the user guide...
http://feeltech.net/index.php?case=archive&act=list&t=wap&catid=6
This may have a better version of the rar file.

I wonder why some use rar compression rather than using the common zip compression?

They list the specs on this page...
http://en.feeltech.net/index.php?case=archive&act=show&aid=61
(link corrected)

Probably best taken with a grain of salt :wink:

To clarify sweep results. I am able to get a good practical linear sweep using the channel 2 signal in ramp mode. The ch 2 output drives the scope horizontal as well as sweeping ch 1 in FM modulation mode.

The problems with this are twofold...
1: Ch 2 is used for sweeping so it cannot be used to AM modulate the ch 1 signal.
2: The nice built-in sweep features are useless as they don't provide a way to sync the scope. (I have to believe that I am simply missing the boat on this issue, hard to believe they'd design a sweep capability with such a flaw)

Update on computer interface...
I find that it fully controls the generator but has a quirk.
When changing a parameter, say frequency, in order to get the change to properly set up the generator, you must hit modulation mode again.
Not too much of an inconvenience, just takes a little getting used to. It would be more straight forward to have a transfer button to be sure all changes get transmitted.

I used this generator to do full AM and SW alignment on a panasonic RF-2200, a tedious job. The computer interface, as well as not needing to verify frequencies made the job quick and easy.

Tim


Last edited by Tkilboy on Jan Fri 04, 2019 5:05 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 1:55 am 
Member

Joined: Sep Tue 12, 2017 3:04 am
Posts: 142
Location: 251 Moon Lane Spring City, TN
Sounds like you making headway. I continue to learn with mine. I rebuilt a used attenuation box and it has helped with the preset 5 volt signal and knocked it down to RF ranges (yes, I can dial the Feeltech down, but I think it's just easier to run it though the box). This makes setup a little easier. I have collaborated with another member here and was able to figure out most functions. But like you, I have not figured out modulating the swept signal. At this point, I'm believing my unit either does swept or modulated, since both modes require both channels at the same time. Overall I like the unit and it doesn't take up much room on the bench. Some here seem to be quite negative toward it and not certain why. Bottom line, what we do here is not exactly going to make anyone rich..........except in knowledge.
I think you're about where I am with yours, but here's the thread I began if there's anything to gain. http://antiqueradios.com/forums/viewtopic.php?f=8&t=348120&hilit=Feeltech


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 2:21 am 
Member

Joined: Jun Thu 12, 2014 4:03 am
Posts: 76
Tim:

Congrats on the Christmas present ... as a self-admitted test equipment junkie, I am always on the lookout for the next new thing, and a 60 MHz function generator for around $100 is pretty remarkable. As to your sweep issues, I have a couple of comments. First, you are correct that the unit does not offer a separate trigger or ramp output to sync the scope X-input to the sweep output on the Feeltech channel 1. Don't know why. I think you've already figured a work-around by using the FM mode (rather than sweep) on Channel 1 and a ramp output on Channel 2. As an alternative, as John suggested above, the VCO function (set for frequency) will work while in the sweep mode, using a ramp of 0-5 volts at maybe 60 Hz to drive both the VCO input and the scope X-input. The voltage at the VCO input will vary the frequency between the start / stop you set up in the sweep function, but you'll have to experiment a bit to see exactly what those voltages need to be to get the sweep width you want. I'm not understanding exactly why you want to amplitude modulate your swept signal for alignment purposes, but perhaps I'm just missing something.

One caution about the KKMoon implementation of the sweep mode. It is a stepped sweep, rather than a perhaps more "traditional" phase-continuous sweep. There is a contradiction in the manual about this ... early in the text they imply that the total sweep time can range from 0.01 to 999.99 seconds, but in the spec pages in the back they restate this as 0.01 to 999.99 seconds/step. Very different. Also, Page 33 has the "step size" formula:

Step value =(End value — Start value )/(Sweep time*100)

This implies that if you set the sweep time to 10 msec, you will only get 1 frequency step between your start & stop points. In your example, the radio IF would only see discrete frequencies 440 and 470 KHz toggled back and forth, and would never get 455 KHz at all. If you chose to set up a 100-point detailed sweep, it will require a full second to complete, which for me makes the IF passband hard to visualize and adjust due to flicker on the scope.

One last possibility. The KKMoon has a mode called SYNC (manual page 39), which is not very well described. It says that Channel 2 can be made to mirror Channel 1 in terms of waveform, frequency, amplitude, offset, or duty cycle. Its not clear how Channel 2 (as a ramp) would behave if frequency SYNCED to Channel 1 during a sweep. I could envision that the Channel 2 ramp could be triggered by the start of a frequency sweep in this configuration, but you'd have to experiment to see if it actually works this way.

Good luck, and I hope you keep us posted as to your progress.

Jim


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 4:10 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
Thanks for the feedback and ideas.

My reasoning for wanting to have an option for Sweep + AM modulation would be in those cases where the scope is measuring across speaker voice coil. I suppose this would not be a very common requirement, but it would require sweeping of a modulated rf signal. Not a critical need, but I did not expect it to be unavailable.

The other gap I see is lack of an available marker oscillator. I would like to see the target IF center frequency on the scope. I dont want to assume that 455kHz or 10.7mHz are actually located at the center of the sweep ramp.

I had expected that this unit would include 2 useful oscillators plus a sweep controller. Since the sweeper lacks a scope output, I think it has very limited usefulness.

Thanks again for the ideas, it helps me be sure I'm understanding how to best use this new toy.

Overall, I'm very happy with the overall performance, it allows me to perfom an alignment much more quickly - and its not fun to use. :D

Tim


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 5:03 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
Corrected link to FY6800 specs...
http://en.feeltech.net/index.php?case=archive&act=show&aid=61

Link given above also corrected.


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 12:11 pm 
Member
User avatar

Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7167
Location: Liberty, Missouri
Quote:
...Ch 2 is used for sweeping so it cannot be used to AM modulate the ch 1 signal...
Why would you want to modulate the signal while you are sweeping? The purpose of sweeping is to determine the "shape" of the filter being tested, be it a receiver front end, an IF strip, or the proper adjustment of a discriminator, and nothing having to do with AM modulation or demodulation characteristics.

Quote:
...The nice built-in sweep features are useless as they don't provide a way to sync the scope. (I have to believe that I am simply missing the boat on this issue, hard to believe they'd design a sweep capability with such a flaw)...
When Sweeping, the ramp IS the "X" signal, that is, the signal that makes the scope trace move left to right on the screen. The response amplitude is the "Y" signal from your detector, what ever that might be.

In the simplest form, here is what a sweep setup looks like.

Image

If you want more detail;

Image

Setup as shown in the diagrams above, should give you Displays that resemble the two pics below. The actual "shape" will of course depend on the filter you will be testing.

Image


Image

Though not a particularly good pic, this shows all the equipment I use for sweeping. The sweep generator is in the rack with "-19" shown on the display, and the box on the table is the detector.

Image

The box on the bench is a simple logarithmic detector using an Analog Devices AD8703 IC.

Clicking on any of the pics in this posting will take you to more pictures on my pic page.

Image

----------------------

The data sheet for the generator shows it will allow you to do IF sweeps, and its capable of supplying fairly decent audio signals. Both of these functions are very useful and will definitely give you a big step in the right direction, but....

Those aside, the spec sheet for the generator isn't very impressive from an "RF generator" point of view. They imply a lot, but the actual "data" just isn't there, a classic case of "A lot of Sizzle, but not much Steak". This is typical of many Chinese low cost offerings now days.

It performs a number of functions, but only the specifications having to do with audio frequencies have any reasonable values. I suspect, if you pursue radio repair, especially communications receivers, you'll find yourself looking for an RF generator not too far in the future.

Edit:fixed link

_________________
Pics, Bold & underlined text, are usually links.

https://mikeharrison.smugmug.com/

Mike


Last edited by Mikeinkcmo on Mar Fri 01, 2019 12:29 pm, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 6:09 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
Hi Mike,

Thanks for the info! I like your Sweep Setup schemes.

For my purposes, I look for the fastest most efficient way to verify a reasonable IF shape. Often, the most convenient way is to just attach the scope to the hot terminal on the volume control to grab the dc offset audio signal or just hook up to audio amp or speaker voice coil.

I believe any of these will show the IF shape in the form of the swept audio envelope, but for this sweep plus modulation is required.

I took the liberty of marking up one of your schemes to illustrate what I'm thinking.
Attachment:
Markup_SweepGenSetUp-L.jpg
Markup_SweepGenSetUp-L.jpg [ 96.12 KiB | Viewed 4236 times ]


Also, I attached a photo of my alignment bench - stuck in a closet in my office (spare bedroom). You'll notice a few minor differences in our commitment of bench space and equipment. :lol: :lol: :lol:
Attachment:
AlignBench.JPG
AlignBench.JPG [ 185.03 KiB | Viewed 4236 times ]


Another concern I have is how to implement a marker signal for 455KHz or 10.7MHz. For right now, I'm assuming this will require a separate RF generator signal. How would this separate marker be injected on your diagrams?

Thanks again for your help.

Tim


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 6:21 pm 
Member
User avatar

Joined: Aug Tue 28, 2018 9:22 pm
Posts: 2414
Location: Sanford Fla 32771 (USA)
I have played with the idea of adding varicaps to my Heathkit IG-102 to generate a limited sweep function. The varicaps would be driven by a programable pic chip with a built in DAC allowing ramp or modified ramp driving the variac. Keep in mind it is the "I wonder if" in me. Yes it would be simpler to buy, but for me that's not the fun. (of course my problem is I never finish a project once it is working in some sort of breadboard stage).
Paul

_________________
Paul of Florida ….I had my patience tested. I’m negative.
https://paulsironhorse.smugmug.com/


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 6:43 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
Hi Paul,

Funny you mention sweepkng the IG-102.

I did that on mine a few years back. I built up a small pc board with a 555 ramp circuit driving a varactor. I then connected this across the main tuning cap in the generator.

It worked fine but had little value as far as calibration or linearity. So it was a fun projects but thats about it. Im sure I've still got the little pc board, somewhere, if you'd like it let me know.

Tim


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Fri 04, 2019 6:50 pm 
Member
User avatar

Joined: Aug Tue 28, 2018 9:22 pm
Posts: 2414
Location: Sanford Fla 32771 (USA)
Quote:
did that on mine a few years back. I built up a small pc board with a 555 ramp circuit driving a varactor. I then connected this across the main tuning cap in the generator.

It worked fine but had little value as far as calibration or linearity.

Thanks, based on your early test I think I will proceed with my attempt. Freq calibration would be done with a freq counter. And since I would be programming the PIC DAc output I can adjust the sweep ramp to any shape I need. Thus sweep rate, sweep freq, sweep width.
I just ordered some varicaps, 3 to 33 pf range. Shot in the dark for the values..
.
Thanks for the offer on your board.
Paul

_________________
Paul of Florida ….I had my patience tested. I’m negative.
https://paulsironhorse.smugmug.com/


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Sat 05, 2019 4:34 am 
Member
User avatar

Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7167
Location: Liberty, Missouri
My sweep generator, an HP3336C requires the start and stop frequencies to set up a sweep. In the pic below, the start freq was set to 435KC and the stop was set to 475KC, a spread of 40KC. This puts 455KC at the center of the display, and each horizontal division across the screen is 4KC wide. No markers needed.

If your generator allows you to set the Start and Stop frequencies, or, if sweep is implemented by setting the center frequency and then entering the +/- deviation limits, you shouldn't have a need for markers either.

The resulting display below gives you all the frequency, and amplitude information needed.

Image

_________________
Pics, Bold & underlined text, are usually links.

https://mikeharrison.smugmug.com/

Mike


Last edited by Mikeinkcmo on Mar Fri 01, 2019 12:38 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Sat 05, 2019 7:47 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1426
Location: Jackson, TN
Good points, Mike.,

I set out to verify how the FM modulation feature actually produces a sweep.

Results:
Set ch2 to Ramp, with a reasonable sweep frequency, say 10 Hz.
Setting the modulation feature to FM will cause the ch1 frequency to repeatedly ramp from a minimum to a maximum value.
The minimum value is the ch1 frequency minus 1/2 of the modulation parameter value.
The maximum value is the ch1 frequency plus 1/2 of the modulation parameter value.

I verified this by setting ch1 to 10, 000 Hz, and ch2 to 0.01 Hz.
Modulation parameter was set to 1,000
Connected external frequency counter to ch1

With the very slow sweep rate (100 seconds) i could watch the output start at 9,500 and gradually climb to 10,500 Hz.

Conclusion:
FM modulation will sweep the signal with the center frequency being equal to ch1 setting.
Span of the frequency sweep is equal to the parameter setting on the modulation window.
Therefore, as suggested by Mike, no marker is needed since the ch1 frequency will be located right in the center of the sweep.

Also, I was pleased to see that the frequency counter agrees with the generator display within 1 count.

Overall, despite poor documentation, the FY6800 does a more than adequate job for my purposes.

Tim


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Jan Sat 05, 2019 10:06 pm 
Member
User avatar

Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7167
Location: Liberty, Missouri
Good deal, now THAT makes your setups a snap from here on out. As you now see, that is light years ahead of old sweep generators which needed markers to know where you were.

I suggest you build up a Log detector using the Analog Devices chip, It'll take RF frequencies up to 90MC, you simply connect it at the output of the last RF stage/transformer, and it'll take the RF and convert directly into a DC voltage you feed directly into the scope. Cant get any simpler, and the pictures will look just like those "in the book". :wink:

I suggest you use DC coupling on the scope inputs, and set up your scope X axis first, so the trace just reaches the left and right edges. Then, apply the "Y" with no signal and adjust the Vertical gain to get yourself 10dB per div., and write the settings down for next time.

_________________
Pics, Bold & underlined text, are usually links.

https://mikeharrison.smugmug.com/

Mike


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Feb Thu 28, 2019 7:17 pm 
New Member
User avatar

Joined: Feb Thu 28, 2019 7:02 pm
Posts: 14
Location: France
Hello

If it can be usefull, I used it as a wob here (in French unfortunately).

And this is the kind of picture I get

Unfortunately as a newcomer I have to wait tomorrow to give link and picture

See you
Jean Pierre


Attachments:
File comment: S curve with 010.6 marker
FY 106.jpg
FY 106.jpg [ 31.23 KiB | Viewed 3698 times ]
Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Feb Thu 28, 2019 8:57 pm 
Member

Joined: Sep Tue 12, 2017 3:04 am
Posts: 142
Location: 251 Moon Lane Spring City, TN
Jean, how did you get the marker on the resonance trace?


Top
 Profile  
 
 Post subject: Re: KKMoon FY-6800 DDS Signal Generator
PostPosted: Mar Fri 01, 2019 8:54 am 
New Member
User avatar

Joined: Feb Thu 28, 2019 7:02 pm
Posts: 14
Location: France
Here is the link

https://vintage-audio-heritage.fr/viewt ... 6&start=10

You will found all the details.

For the marker I use an other generator, for instance a DDS from an arduino, but any generator will do.
The secret is on the probe. I inject a small amout of the marker from DDS, just before the detector diode. Thus there is a beat between signal from the wob and the one from the generator.
Using a DDS allows to know accurately the marker fréquency and use any frequency as required .
See the details in the upper link

I also build a simple wob, includind markers

https://vintage-audio-heritage.fr/viewt ... =71&t=4445

On all the pictures, the yellow signal is the vobulating saw tooth who synchonises the scope, and knowing the frequency limits it gives a raw idee of the frequency on the curve

For simplicity here is the tricky probe I use

@Mike
Yes, of course if you have a professionnal sweep generator where you can set start and end frequency you don't need a marker.
But not everybody can afford such a generator.
If you have one you don't need the Chineese


Attachments:
probe.jpg
probe.jpg [ 45.99 KiB | Viewed 3622 times ]


Last edited by balvenie on Mar Sat 02, 2019 4:06 pm, edited 3 times in total.
Top
 Profile  
 
Post New Topic Post Reply  [ 24 posts ]  Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: keith49vj3, wdecho and 25 guests



Search for:
Jump to:  


































-->


Privacy Policy :: Powered by phpBB