Double Conversion Frequency Upconverter

The 100 MHz upconverter I've built seems to work VERY well.  I don't have any complaints as it is right now.

For the sake of experimenting, and trying to learn I've decided to try to increase the distance between the LO and the Pass Band.

In the 100 MHz upconverter there's only 9 MHz between the LO and the final pass band.  I want to try to increase that distance to have as much reduction of the LO in the final pass band as possible.  (I don't think this is required to be honest, which is why I already mentioned this is for the sake of experimenting).

I enjoy working with RF Filters so I thought this would be a chance to build two of my own (and spend some more money on an already completed project LOL).

So the idea I'm going to try looks something like this block diagram below including the filter designs to reduce the LO(s) as much as possible.

This is all subject to change, but I just wanted to post the idea I'm playing around with at this point.  I will also have available a MK-3 by mini-circuits which is a frequency (doubler) Multiplier.  I may play around with that, and then rework the filters again.  But that's just something I was kicking around with.  I could (I think) use it at the 19 MHz Mixer on the 10 MHz LO and end up with 29 MHz out of that mixer (I think), which would make it even easier to build the second LO BPF since there would then be 29 MHz from the 100 MHz second LO and the final pass band.  That's just something I've been toying with in the back of my mind.  Again I don't really thing any of this is needed at this point.  My 100 MHz upconverter is working great (so far) even in the face of some very strong signals.  I just want to learn more is the bottom line.  

Parts for this modification have already been ordered.  So this is the next revision based on my 100 MHz up-converter noted previous on this blog.

Building and Characterizing RF filters with simple and cheap tools

(UPDATED 2015-03-06)

SEE ALSO: 100 MHz upconverter, and Double Conversion upconverter

I have a need to build a steep skirted RF High Pass Filter.  The filter I'm going to try to build isn't maybe the best/perfect option, but I'm looking at it more as a test and learning experience.  So I can't claim thiis to be the perfect option.  

With that in mind, and wanting to do this as cheaply as possible here are some of the details about this little mini-project.  The FTDX-5000 has a fixed 9 MHz IF output.  It's pretty difficult to obtain or build a HP filter with a sharp enough skirt where we don't have a high insertion loss, or not enough reduction in gain in the unwanted Lower portion of the filter when I'm  using a 9 MHz input to the single-stage upconverter.

In order to attempt push the boundaries a bit, I'm thinking I will try to use a frequency doubler/multiplier on the 9 MHz IF OUTPUT from the FTDX-5000.  This will give me 18 MHz separation between the LO and the Pass Band, instead of only 9 MHz.

This comes at a cost of -11db on the resulting 18 MHz signal from the original 9 MHz.

•  9MHz x2 = 18 MHz using MK-3 http://www.minicircuits.com/pdfs/MK-3.pdf $60.00 shipped. I don't think this will work!  I'm pretty sure this requires a very high input level that the 9 MHz IF won't have.  
• It's probably better to think about doing a double up-conversion using a second OCXO like a 12.8 MHz = 9 MHz = 21.8 MHz instead!  These 12.8 MHz OCXO's are 2x the cost of the 100 MHz OCXO I already have.  But building the filters is much simpler since we have a larger band spread and things become a lot easier from a filter sharpness perspective.  
• The down side is that if we're not really careful with the filters we end up using we could actually be introducing MORE spurs, noise etc...

This also means I'll have to swap out the HF Band Pass filter I've *been using* (a Minicircuits ZX75-12+) - Probably another mini-project filter to do there too I guess.  By the time this whole thing is done I'll probably had to build all of my own filters instead of getting off the shelf stuff.  The only issue with doing that is that manufacturers and re-sellers these days are really pushing SMD/SMT parts.  The last batch of parts I got were no larger than a spec of pepper.  Literally, and I had to abandon that one and reorder larger inductor coils and ceramic disc caps.

The filter I'm wanting to build is intended to reduce the 100 MHz OCXO oscillator main carrier by 55-60 db below the 118 MHz+ Pass Band I want to make use of.  Since I don't need this 100 MHz carrier in the pass band that flows into the Nooelec 0.5ppm RTL SDR Dongle I'm trying to eliminate it from being passed into the Dongle as much as possible.  The idea being that I just don't want it to de-sense the receiver in the RTL Dongle.

Honestly I'll be pleasantly surprised if this has a noticeable positive impact on the 118 MHz+ Pass band desired.

The filter I've come up with reduces <= 104 MHz by at least -65db to -69db while only reducing 118 MHz+ by about -5.53db effectively 'insertion loss' at my desired frequency.  So the net effect should be (-65 - -5.53) = -59.47db.  That seems like a pretty good reduction of the LO showing up in the input to the RTL Dongle.  Currently it's about +5db above the 109 MHz+ desired pass band where I'm not using a frequency doubler.

The new HP filter I'm planning to build will have a -5.53db insertion loss at 118 MHz.  That's
the 100 MHz LO + the 18 MHz (9 MHz X2).  For a total loss of -16.63db.  I'm not too concerned about this at this point as I have an +22db LNA available for HF (LNA4HF).

(using Iowa Hills RF Filter Designer v2.2)

So what I'm hoping this might accomplish for the upconvertion process is to reduce spur images showing up in the Pass Band.  (not that there are many at all, in fact at this point I can't really see much of that going on)  So this is just a sort of research/test and development/learning process for me.  I have an idea, and I want to test if it helps or not, or doesn't do anything all, or makes things worse.

I've already added a 41db voltage variable attenuator.  So there should be plenty of options for optimizing the RX chain.

I'll post everything about this as begin this mini-project on THIS page.  I've already ordered the parts and I'll post the parts list here asap with design details on the filter etc.

This is a work in progress updates will be coming as I get them.

KEY POINTS

• Iron Hills Filter Designer (Freeware) & Notes [Download]
• Touchstone RF Analyzer (Free Version) [Download]
• Nooelec Ham-It-Up v1.2 w/Noise Source option installed [Buy Ham-it-up] & [Buy Noise Source Kit]
• Filter Parts List
• All Parts Numbers are from http://www.mouser.com except those notes as http://www.digikey.com
• ----------------------------------------------------------
• SMA EDGE MOUNT JACK (Female): 538-73251-1150 (INPUT)
• SMA EDGE MOUNT (Male) 712-CONSMA013.062 (OUTPUT)
• ----------------------------------------------------------
• Ceramic Disc Capacitors 5%
• 24 pf   $1.01 x1
• 120 pf  $0.90 x1
• 20 pf  $0.71 x2
• 33 pf  $0.19 x3
• 15 pf  $0.34 x1
• 27 pf  $0.31 x1
• Coil craft
• 1812SMS-56NJLB Air core RF inductor 56 nH
• 1812SMS-R12JLB Air core RF inductor 120 nH
• 1812SMS-R15JLB Air core RF inductor 150 nH
• 1812SMS-82NJLB Air core RF inductor 82 nH
• 
  
• Construction Photos & Notes
• Test Results (Touchstone RF Analyzer, and resulting spectrum differences at the RTL Dongle)

Related Testing (NW0W)

TEST SETUP WITHOUT LNA(s) - Using "HAM IT UP" Noise Source

SBP21.4+ (on the HF input from NS)

ZX75HP-44-S+ and Par Electronics VHF-FM Notch Filter on the output

TEST SETUP WITHOUT LNA(s) - Using "HAM IT UP" Noise Source

SBP21.4+ (on the HF input from NS)

ZX75HP-44-S+ and Strosberg Eng. FTL201A FM-Bcast Notch Filter on the output

Related Results using Touchstone RF Analyzer + RTL 

W2AEW use of the Ham-It-Up Noise Source

Inspired by (Adam Alicajic ~ 9A4QV)

9Mhz IF LO PASS FILTER (whew)

First time I've done this so I can't swear to how well I thought it through or really any aspects of the entire thing LOL.  I'm trusting the design at this point.  The results on-air seem impressive though.

I wanted to see if I could clean up the output RF from the 9 Mhz IF out of the FTDX-5000 which then goes into my new HF Upconverter to help reduce images, and noise, and misc trash in the spectrum prior to upconvertion.

I went to CoilCraft and downloaded their "Low Pass Filter Designer" software (free) and designed a 7 Pole (7th Order Low Pass Elliptic) filter.  I ordered their inductors from the design directly from CoilCraft.  Then ordered the required Caps from Mouser.

Below is a screen shot of the design.

Following are some photo's of the constructions.  This was VERY difficult for me since I don't have tools to work with SMT parts that are the size of 4 grains of pepper!  Literally.

BUT I did manage to get it built, and after retouching some bad solder joints it seems to be working very well.  I plan to include a real plot from a VNA setup I have eventually.  But that'll be a while as setup for that takes too much time at this point.  

This is a strip of sticky copper tape 1" wide top to bottom, turned upside down so I could hold the Inductors in place while I tacked them with solder. (not pretty, but like I said it's not easy either without the proper tools)

This is some double sided copper clad PCB.  I trimmed away the copper on in the middle on both sides so as not to effect the inductors.  Then cut slots for solder pads to match the layout of the inductors I tacked together in the above photo.

Top side completed.  With caps added.

Bottom Side with Caps added.

HF Upconverter - Assembly and Initial Testing

SUCCESS!

After a few days or working on my new HF Upconverter I got it working!  I'd been waiting for some Buck type DC-DC converters.  So I could connect the OCXO (3.3vdc) up to the 13.8vdc from my primary Astron RS-35M.  One of the Buck converters drops 13.8vdc to 12.0 vdc, then a second one drops it again from 12vdc to 3.3vdc.  They seem to be working fine.  The 12vdc is variable.  The 3.3vdc is not which is kind of a bummer, but it's at idle on my Fluke meter 3.29vdc. (probably close enough although if I'm going to the trouble of an OCXO I'd like the PS's to be adjustable).  I'll probably hunt around for a Buck DC-DC 12-3.3vdc that is adjustable.  These things are CHEAP on ebay.  Total spent on both was around $15.00 combined including shipping.  Which beats spending hours building them at this point.

I am running the OCXO HF upconverter right now as I type this, and it seems to be rock solid so far.  No FM Bcast interference (which I didn't think I'd have with all the shielding).

I have a fair amount of work to do yet on this.  However, the fact that the SBL-1+ Mixer and the OCXO work as expected is definitely encouraging.

I am listening right now to 14 Mhz Morse Code on the FTDX-5000 and also on SDR# at 109 Mhz.  (remember the FTDX-5000 uses a 9Mhz IF Output that I'm tapped into, so the actual VFO frequency is irrelevant since all signals are sent out in the 9 Mhz realm.

Anyway...I just wanted to post that as simple as this is right now and working as well as it is, I can't wait to add the Lo and Hi pass filters to my Homebrew HF Upconverter that is accurate to within 200ppb (that's parts per BILLION)!  NO DRIFTING has been noted in my testing thus far.

Tomorrow I'll start it up from cold, and see if there is any noticeable.  I'll also post some updated pictures of where the project is now.

Things are subject to change until I setting on a mixer.  While the SBL-1+ works fine I'm curious how well the the other two I ordered from Minicircuits will work.  The are supposed to be better, and certainly should be at 4-7x the cost of the SBL-1+ (which was only $9.95).

This is FUN STUFF!

100 Mhz OCXO 200ppb For Home Brew Upconverter

I still have some work to do on this.  The closest (bottom left) (pin 1) large pad get +1.15-2.15vdc via resistor network voltage divider that bridges over from the large pad behind it  (pin 14) that is the +3.3vdc Power Supply pin.

The SMA is the 100Mhz @ 200ppb output from the OCXO which comes off pin 8.

The resistor network I was talking about is a voltage divider in the standard configuration of R1 and R2 except that I've slightly modified it to include a 1-turn 1000 Ohm Potentiometer which should allow fine tuning the OCXO by as much as -500hz and +500hz.  Hopefully this won't be needed much as that the point of having the OCXO to start with, but it simplifies retouching tuning quite a bit and seemed simple enough to add (as long as my design holds up!).

There will be a KNOB on the front of this which allows easy access for tuning the OCXO to mate up with the signals on the 9 Mhz output of the FTDX-5000.  INSTEAD OF having to go into HDSDR software's option menu and extio menu to adjust things (WHICH DRIVES ME NUTS!).

I hadn't realized that I had to provide a Vcc for pin 1 initially, and at first when I discovered this I didn't really like the idea.  Still not sure I do frankly, BUT since it adds a feature I hadn't thought of to start with I figured why not make it something I can make use of, instead of simply setting pin 1's voltage to 1.65vdc which SHOULD place the OCXO at 0pmm/0hz offset from 100 Mhz.

This "feature" provides a much as 1 full Khz adjustment (I think, according to the doc's I've read).