The RFzero™ comes ready for use. The five LEDs, headers, LCD jumper and the ground wire are also supplied for individual mounting and fitting. A pair of test wires are included too.

The items included when you buy a RFzero™.

The price for the RFzero™ is

  • 499 DKK incl. VAT
  • 400 DKK excl. VAT for customers outside the EU. Local import taxes may apply

Money transfer (4,7% PayPal surcharge) and shipping cost applies.

Please use the contact form to send your purchase inquiry.

To release the full potential of your RFzero you must connect it to a GPS antenna. If you don’t have a GPS antenna already you may find inspiration in the third party accessories section further down on this page.

RFzero accessories

The RFzero accessories are also designed by one or more of the designers behind the RFzero itself.

Low and high pass filters

For the RFzero but also for general use a high/low/band pass filter PCB has been developed. The PCB fits into a 37 mm x 37 mm x 30 mm metal sheet box (Weissblechgehäuse) for best RF performance and shielding. You can design your very own filter that match the topology of the PCB e.g. using the free Elsie by Tonne Software Jim, W4ENE. The PCB is designed for 0805 SMD components. High Q capacitors, NP0 or better, and inductors should be used for best performance especially as frequency increases and/or for best stop-band attenuation.

The generic filter topology where each Z# is replaced with either a C or L or shorted.

The value and type of each Z# depends on the design criteria, e.g. for a low pass filter Z1, Z3, Z5 and Z7 are capacitors and Z8, Z9 and Z10 are inductors and if Z2, Z4 and Z6 are used they are capacitors and Z12 and Z13 are shorted. Not all Z# have to be used. If so they can be omitted or shorted whichever applies.

The filter PCB and a populated PCB.

Below are series of possible low pass filter designs where the second harmonic is attenuated at least 10 dB and the third harmonic is attenuated at least 55 dB by the low pass filter itself. When used in combination with a RFzero the harmonics will then be attenuated at least 60 dBc. Remember to short Z12 and Z13.

f minf maxZ1Z2Z3Z4Z5Z6Z7Z8Z9Z10
1,6 MHz3 MHz1 nF120 pF1,5 nF560 pF1,5 nF470 pF820 pF3,9 µH2,7 µH2,7 µH
2,9 MHz5,1 MHz680 pF68 pF1 pF360 pF820 pF220 pF470 pF1,8 µH1,5 µH1,5 µH
5 MHz9,3 MHz390 pF56 pF560 pF220 pF470 pF150 pF330 pF1 µH820 nH820 nH
9,1 MHz16,4 MHz220 pF39 pF270 pF120 pF220 pF82 pF120 pF560 nH470 nH470 nH
16 MHz30 MHz100 pF12 pF180 pF56 pF150 pF39 pF56 pF330 nH270 nH270 nH
30 MHz56 MHz47 pF2,2 pF100 pF12 pF100 pF8,2 pF47 pF180 nH180 nH180 nH
54 MHz72 MHz33 pF2,2 pF68 pF15 pF82 pF10 pF47 pF150 nH120 nH120 nH
100 MHz150 MHz15 pF1 pF33 pF3,9 pF33 pF3,3 pF12 pF68 nH68 nH68 nH

Attenuation at f max is typically 1 dB. The above values take into account the additional capacitance in the filter PCB.

Filter characteristics of a 52 MHz low pass filter from 1 MHz to 400 MHz. The insertion loss is 0,7 dB at 52 MHz. Red is transfer function (10 dB/div), blue is input return loss (10 dB/div) and green is input SWR (At 1 MHz it is 1:1).

Below is a possible high pass filter design that can be used to extract third and higher harmonic above 400 MHz, e.g. to get a 432 MHz signal. Remember to short Z12 and Z13.

f minZ1Z2Z3Z4Z5Z6Z7Z8Z9Z10
400 MHz6,8 nH130 nH6,8 nH27 nH6,8 nH39 nH8,2 nH10 pF12 pF12 pF

The Elsie filter design files can be downloaded here.

The price for filter PCB itself is

  • 20 DKK incl. VAT
  • 16 DKK excl. VAT for customers outside the EU. Import taxes may apply

Money transfer (4,7% PayPal surcharge) and shipping cost applies.

A 10% discount applies to five PCBs and 20% discount for ten PCBs.

Please use the contact form to send your purchase inquiry.

Download the filter design and assembly guide.

Third party accessories

Below are a number of typical accessories that can be used together with your RFzero. You may find them on flea markets, in electronics shops and online too. eBay and similar have most of the third party accessories but please look for the sellers with top customer ratings even if it means that you will have to pay a bit more. Especially when it comes to buying RF cables and connectors look for those who ONLY sell RF stuff. Avoid those who sell RF, beauty products and spark plugs from the same shop since they haven’t got a clue about RF and the specifications.


The GPS antenna must be made for the civilian frequency L1 at 1575,42 MHz. The cable should be fitted with a SMA male connector. Never use Reverse Polarity (RP) connectors! If there is a built-in pre-amplifier, i.e. active antenna, it must operate on 3,3 V and draw max 100 mA.

If your primary use of your RFzero is casual then a “hockey puck” antenna will do just fine. The eBay price level is ~5 USD. Please keep in mind that this kind of antenna is neither water- nor UV-proof. So you may have to put it into a proper box.

Example of a GPS hockey puck antenna with SMA male connector found on eBay.

If you plan to use your RFzero for regular or long term use a real outdoor antenna is recommended. Perhaps even a marine grade antenna if you live in a coastal environment. Outdoor antennas are not cheap but well worth the investment as they are UV proof too.


The physical size of the RFzero board is 79 mm x 99,5 mm thus it fits perfectly with a half Eurocard PCB. Thus there are a myriad of boxes, cabinets and enclosures available where the RFzero™ will slide in nicely.

Example of a cast alloy cabinet (150 mm x 105 mm x 55 mm) found on eBay.

Metal sheet boxes (Weissblechgehäuse)

For the very best RF performance the RFzero should be mounted inside a metal sheet box (Weissblechgehäuse) 102 mm x 82 mm x 30 mm. They are available from many RF specialist shops.

Metal sheet box (Weissblechgehäuse).

The filter PCB fits into a metal sheet box (Weissblechgehäuse) 37 mm x 37 mm x 30 mm.


If the level from the RFzero is not enough for your application you may boost the signal with an amplifier. There are really many amplifiers, both ready made, kits and designs, that can increase the 8 dBm to 13 dBm from the RFzero to whatever level you are looking for.

Example of an up to 3 W amplifier found on eBay. This amplifier has more gain than necessary. So remove the first stage device and its drain choke both marked with  yellow dots. Then short the input and output pads left by the removed device.


But you can also find amplifiers on eBay that we don’t recommend.

A NOT recommended amplifier found on eBay.

We don’t recommend buying amplifiers similar to the one above that can be found on eBay too. After three days of continuous operation the output device died.


Coaxial cables for the RFzero GPS and RF output must be fitted with SMA male type connectors.

SMA male connector.

If you will use a Hitachi HD44780 compatible LCD connected to JP12 two six wire jumper cables Single In Line (SIL) 1 module (2,54 mm) are needed.

Two six-wire cables found on eBay.


The RFzero is supplied with headers. But should you be in need for additional headers just remember to buy Single In Line (SIL) 1 module (2,54 mm) types. They are typically sold in a row with 40 male or female contacts.

A row of male SIL headers.

Level converter

3,3 V to/from 5 V level converters come in many shapes and forms. You can put it together yourself, buy a module or an IC.

Do-it-yourself level converter schematic. Most other N-channel FETs will work too. The number of level conversion channels can be expanded if required.

Example of a four bits level converter module found on eBay where LV goes to 3,3V and HV to the 5 V and the LV1 to the 3,3 V I/O pin and the HV1 to the 5 V I/O pin and so on.

Typical level converter ICs, also called bus transceivers, include the popular 74LVC245.

Liquid crystal displays

The RFzero LCD connector JP12 is designed for the Hitachi HD44780 compatible LCDs. They are typically available with 16 characters per line and two lines (16×2) and  20 characters per line and four lines (20×4) but other sizes also exist. The LCD can easily be connected using two six-wire jumper cables – please see above.

The RFzero is a 3,3 V board, however, it is possible to use a 5 V supplied LCD. BUT not all 5 V LCDs will work with 3,3 V digital logic signals. Therefore, it is highly recommended that you use a 3,3 V LCD and specifically ask the seller for such one. We have very positive experience with 3,3 V LCDs from To avoid having to twist the backlight wires you should only buy LCDs that have the anode on pin 15 and the cathode on pin 16, however, most do.

We have had very bad experience with the below eBay vendors who all say they sell 3,3 V LCDs. But on fortunately the LCDs from them don’t work properly on 3,3 V. In reality they need 5 V.

  • diybox
  • sensesmart
  • shieldfans
  • worldchips

You may also use other kinds of LCDs and graphical displays but integration is not as easy as the very common Hitachi HD44780 compatible LCDs.

Liquid crystal displays using I2C (Wire)

If you are short free pins but still want to connect a LCD then you can use the I2C bus together with a driver board, which is also a port expander like the SX1509 below, and use the default I2C bus on your board.

Example of a LCD I2C (Wire) driver board with a PCF8574 expander found on eBay.

Port expander

Even if the RFzero has a lot of digital I/Os available a situation might occur where you will need more I/O power. The MCP23008, MCP23S08, MCP23017, MCP23S17 and SX1509 chips are a brilliant and cost effective solutions that have eight or 16 I/Os and connect to either I2C/Wire or SPI at the other end thus requiring only two or three pins that can be found on the RFzero I2C User Bus or SPI bus.

Example of a SX1509 port expander module found on eBay.

Rotary encoders

There exists a huge variety of rotary encoders with and without a push button too but also in a very different price ranges. You know your own requirements. However, the fairly cheap rotary  encoders found on eBay will do the trick for most users.

T1 combiner

For T1 the RFzero is factory mounted with a Coilcraft PWB-2-BLB transformer. But if your main use is generating two-tone signals it is a good idea to change T1 to a combiner like the Mini-Circuits ADP-2-1W+ or equivalent.

The Mini-Circuits ADP-2-1W+ combiner.

U.FL connectors and cables

If you need to use your RFzero as an I/Q-generator you will need two U.FL connectors for PCB mount, e.g. from eBay and search for: U.FL PCB.

U.FL connectors seen from the bottom and top.

Two U.FL connectors mounted on the RFzero PCB and T1 removed.

Don’t forget to get some cables if you don’t have those with the right connectors already, e.g. U.FL in one end and SMA female bulk head at the other end.

Example of a cable with SMA female bulk head and U.FL connectors.