Building 10 MHz OCXO

As part of my experimenting with building a double conversion up-converter I'm working on building a 10 MHz OCXO for the first LO.  I'm using a 3.3vdc LDO voltage regulator to power the OCXO.  This regulator is really simple to setup.  And aside from the IC itself it just takes two small ceramic capacitors to be stable.  When built the little DC-DC converter takes up less space than a US quarter.  The downside of this device is HEAT.  If input to the IC is > 10vdc it gets pretty hot trying to bring it output down to 3.3v.  So I'm limiting the input to 10vdc.

I'll probably eventually require this using an LM117 as those can take up to 40vdc input and run output as low as 1.25vdc (+-).  The way I've used them in the past I added a potentiometer and some resistors and caps to create variable voltage output.  But these devices can also just run a static voltage output by using a fixed resistor and some caps.  

The trouble with just about any of these is disapation of heat.  The process of dropping 13.8vdc to 3.3vdc if not done properly can generate enough heat to burn your finger when touching the device or heatsink.  So there's a balance that needs to be made.

ANYWAY...Here's a photo of the 10 MHz OCXO with the LDO Regulator onboard. 

Here's a shot of the LM117 variable supply I'm using to drop 13.8vdc to 10vdc which then drops to 3.3vdc that feeds the OCXO.

This is not the final configuration, this is just a test setup to verify the Variable Frequency adjustment of the OCXO using a voltage divider resistor network.  See the adjustable 1k Ohm Pot for that.

Common Use Capacitance Chart

I find I'm looking these conversions up all the time these days.  Just posting this in one place so I don't have to hunt it down all the time.

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)

A SIMPLE Voltage Variable Power Supply

I'm planning to include a 41db voltage-variable-attenutator in my HF Upconverter.  So I needed to build a tiny voltage-variable supply capable of 17vdc max down to 1.2vdc.  I discovered that using an LM117 was a nice way to accomplish this.  Since I needed something more than a voltage divider and it needed to have a fairly large range. 1.2vdc-17vdc.  

Input to this supply will be around 18-20vdc (I need to test what I need before I'm sure exactly)  I think there's about a 1.2vdc drop with the LM117 (something like that) so in my test feeding it with 13.8vdc output around 12.4vdc (from memory I didn't actually log it), but when turning the poteniometer all the way it went all the way down to 1.2vdc. 

The LM117 can accept as MAX input +40vdc [datasheet]

I simply followed the Datasheet for part values as a default.  Seems to work well.

Minus a few minutes to read the Datasheet, and solder the parts up this took about 30 minutes to build.  And seems to work JUST LIKE I HOPED.

I liked this so much I built a stand-alone Variable Power supply

Below is the start of a 13.8vdc INPUT and 1.2-38vdc @1.5amp Variable Power supply I've started building.  It's super simple to build this.  Takes just a few minutes with the right parts.

2 caps, 1 fixed resistor, and a 5k variable pot plus the LM117 and a tiny DC-DC BOOST converter capable of up to 40vdc output.  Input to the DC-DC boost in my case is a 13.8vdc supply that is common to a lot of things I already use in the shack.  Although it could be just about anything < 40vdc (approximately).

The LM117 max output is only about 1.5amp but this is more than enough for testing simple stuff in most cases (that I would be using something like this for).  Usually I'm trying to test a LNA and the mass of LNA's I have range from 5vdc to 28vdc all of them draw very few mA's.  So this is more than enough to use as a simple test bench variable supply for this.

This is a picture of the beginnings of my stand-alone supply.  I have a LOT of options I could incorporate with something like this, and probably will eventually.  I haven't added the DC-DC Boost supply to this yet, I had to order a second one since I already used the first one I bought.  These supplies only cost < $8USD on ebay.  The few other parts listed about are also < $8.00 for the most part.

I took the above pix after I was done testing one of my 5vdc LNA's

Space to the LEFT will contain the DC-DC Boost converter.  the LM117 is to the right with the small heatsink attached.  In this configuration I just connected it directly to the 13.8vdc regulated supply I meantioned earlier.  After I add the DC-DC Boost Converter it will connect to the converter, and the converter will then connect to the 13.8 vdc supply.

I could add a rotary switch with preset resistance with a bypass switch to the variable pot for convenience.  Then I could perhaps have presets of 2.5vdc, 3.3vdc, 5vdc, 6vdc, 9vdc, 10vdc, 12vdc, 15vdc, 20vdc, 24vdc, and 28vdc for convenience.  Just a matter of adding the switches, and some resistors.

I'll post more pix as this little project moves forward.

Touchstone RF Spectrum Analyzer Software

(ALSO SEE)

I wanted to have a quick and simple view of a large bandwidth that's being sent into my RTL Dongle.  Basically I wanted to SEE how altering the various low pass, and high pass, and band pass filters in my 100 Mhz Upconverter affected the output being sent to the RTL Dongle.  I came across this video showing how Touchtone's "RF Spectrum Analyzer Software" (I used the FREE version) could be used with one of these dongles to get a sense of how a filter is functioning.

(this is NOT MY Video, but demonstrates what I wanted to do basically)

Seems to work well enough!  I can now see what I wanted to be able visualize.

This was BEFORE I added a FM Broadcast band NOTCH filter AFTER the Upconverter

and just in front of the RTL Dongle.  NOTE the spectrum shape just above 105 Mhz is similar to the Band Pass filter shape I have at the input to My Upconverter.  LO Freq of 100 Mhz is at -65 dbm

This was AFTER I added a FM Broadcast band NOTCH filter AFTER the Upconverter and just in front of the RTL Dongle.  Notice the dramatic different in spurs around the 100.0 Mhz LO frequency and also the LO is down around -89dbm  Also the very different shape of the pass band around 109-115 Mhz.

While this example didn't show me what I'd hoped for, it DID show me reality of how this filter affected the results.  SO the lesson learned here is that this is a FREE and USEFUL Tool if you are attempting to visualize the effects of filtering.

I think what I'm actually looking for is a NOTCH filter that stop hard around 102 Mhz, however, this sort of thing can be quite difficult to find.  I'm basically trying to minimize the LO as much as possible or at least get it to be lower than the pass band from 109-115 Mhz. 

Anyway, I just wanted to share this with folks in case anyone else is trying to visualize the effects of a filter.  Of course, the thing to do REALLY is to inject a wide band noise source into the filter, and measure the output using software like this.  By the way, the "Ham It Up" upconverter has a noise source built in (minus a few simple addon parts to activate it.  It's a cheap way to get a decent noise source however.

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.