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.
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.
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!
