Parts

RF

RTL-SDR

These were originally designed for DVB-T reception, but can be used as a generic RX front end for SDR. Use with your compute device and favorite SDR software for a ~25 to 1700 MHz RX. Quite fun for the money. Biggest drawback is no front end filter.

This page on the RTL-SDR Blog is a great place to find out more about this hardware. And they conveniently have produce an improved modified version that they sell. See HERE. Bonus: they've documented all sorts of fun things you can do with these nifty little RXs.

We have used the original, designed for TV, versions. (price check: ~$15 via Amazon spring 2022) Biggest drawback is the initial frequency error. I measured two samples at 52 ppm and 59 ppm error. (Initial frequency error means tuning dial error.) Usually easy to calibrate the error in SDR software. (I've used an ATSC broadcast TV pilot.)

These also come with a right angle MCX jack, a short MCX to Belling-Lee connector cable lead, and a simple whip antenna with the Belling-Lee on the end.

I successfully substituted a vertical SMA jack on the PCB of one, but the board design didn't make that the greatest or easiest rework.

We have moved on and are using the RTL-Blog V3 RTL-SDRs. (price check: $30 via Amazon spring 2022)

Use the cheap ones if you are on a tight budget, or for the learning experience. Otherwise, go for the RTL-SDR Blog ones.

LNBs

Satellite TV LNBs have a horn, an LNA, and will conveniently mix 10368 MHz amateur radio signals down to 618 MHz where an RTL-SDR can do the rest. The search phrase appears to be "universal Ku LNB".

We have used the Avenger LNB part number PLL321S-2. This looks like the current version. (price check: 2022-06-01 $18, similar units appear for around $10 to $20)

The downside is initial frequency error and stability. (Stability means having to chase signals around the band with the tuning knob.) (TODO: get some stability numbers)

This universal Ku band LNB works quite well at 10 GHz. It has a 9.75 GHz LO when powered at 12 or 13.8 V. It is V polarized by default. (Can be switched to H polarization by sending an extra low frequency control signal.)

An improved option today is the Bullseye LNB. (price check: 2022-06-01 $30 on ebay) These have better initial frequency error and stability. (TODO: get numbers) This LNB can be recalibrated. See notes here. N6IZW breadboarded one of these, and SDMG members brought their Bullseyes to recalibrate.

The Bullseye LNB has a second connector. This is an output with it's 25 MHz internal frequency reference. There may be interesting uses for this.

ADF4350 module

Originally, we used these with Aruinos for for an LO source for transverters. See our notes detailing the assembly HERE.

Needs to be driven by a microcontroller. Example software for transverter LO use or for our simple microwave TXs documented here may be found at adf4350-examples.

Search for "ADF4350" in the usual places. Same module appears to be sold by many vendors. (price check: 2022-06-01 $25 on Amazon)

1296 bandpass filters

These 23 cm filters per W6PQL look interesting.

N6IZW bought some Mini-Circuits LFCN-1525+ low pass filters from ebay seller caloutlet (CA) installed on a board with SMA jacks. (price check: $13 2022-05) (Search for Mini-Circuits LFCN/HFCN Filter Evaluation Board Assembly ~ You choose model PN. Select the appropriate Mini-Circuits model number.) Shown below.

Bias tees

A bias tee is used to inject or pick off DC power from a coaxial cable. Internally it consists of a DC blocking capacitor and an RF choke. Given how simple these are, probably best to pick one with the connectors you need. It is simple enough to DIY.

Searching for these can require interesting search terms like "power inserter".

We have used PCT Store's PCT-MPI-1G. (price check: 2022-01-06 $4 direct + shipping, $15 on Amazon, similar units starting at around $10)

We are trying to document reproducible builds. This is one item you might have already in your junkbox. I found an old VDSL splitter that passed frequencies greater than 10 MHz to one port and less than 10 MHz to another port. A quick check with a DMM found that it would work just fine as a bias tee for the frequencies of interest (~600 MHz).

Yes, the RTL-SDR has an internal bias tee that can be turned on to supply power to an LNA. Unfortunately, it's not suitable for the LNBs.

Coaxial adapters and miscellaneous

Here in San Diego, we have a fantastic local retailer We-Supply that carries many useful things including a surprising variety of coaxial adapters.

Coaxial adapters, gender changers, cable assemblies, and even coax to banana adapters can be found from many suppliers. If you are doing radio, you should have or should soon find your preferred supplier(s). Check with your local or the online microwave community if you need help finding a source. Sometimes your local community can supply you with extra bits and pieces.

Antennas

1296

The whip that comes with the TV versions of RTL-SDR work for RX.

A ground plane or dipole works.

For horizontal polarized omnidirectional antennas, W1GHZ describes a tuned turnstile antenna and WA5VJB sells PCB big wheel antennas.

The WA5VJB "cheap" yagi is excellent and an easy build. Provides a useful amount of gain. [TODO: look up my performance measurement notes.]

TODO: try the 3 element 1296 PCB yagi WA5VJB sells.

We've tried some PCB Vivaldi antennas.

This band is common enough to have a lot of commercial antenna offerings.

10 GHz

The satellite TV LNB has an antenna built in. Sufficient for anything less than DX. TODO: add a lens or dish to the satellite TV LNB for more gain. (I think N6IZW has done that before.)

For TX, a coax-to-waveguide transition is an open-ended waveguide antenna which is good for about 5 or 6 dBi.

A sheet metal horn can provide useful gain.

Dish antennas provide a lot of gain.

WA5VJB sells Vivaldi and log periodic PCB antennas.

Microcontrollers

Use what works. Tell us what you've tried.

Arduino

We started with Arduino, because it's easy for folks who are not experts in embedded systems. N6IZW found a nifty Arduino Uno clone that has a jumper to select 3.3 V in addition to the Uno's customary 5 V I/O. 3.3 V is perfect for the ADF4350 boards.

Originally, we used these with the ADF4350 module for an LO source for transverters.

N6IZW purchased Prototype PCB for Arduino UNO R3 Shield Board DIY Breadboard from eBay, item number 221937627684.

Pi Pico

$4 and in stock. 3.3 V I/O. N6IZW has tried it with a still-in-development Arduino IDE backend for Pi Pico. I intend to try it with native MicroPython.

Compute devices

Laptops.

Desktops.

TODO: look into tablets. Portability and price can be attractive.

N6IZW has used a 4th gen Kindle Fire HD 7" with the SDR Touch application with an OTG cable with an RTL-SDR.

Software

TODO: try out:

• fldigi
• wsjtx
• Hellscheiber
• GNU Radio

I've been using gqrx on linux. Included with distributions and easy to use.

N6IZW has been using SDR# on MS-Windows.