8-Band RF Board

This is the latest RF Board, that has 8 Band Modules. With this Board you can cover the whole Shortwave Band MINUS 1 Band, that you need to sacrifice.

It uses a single FET in SOT23 Package as PA. This can be various Types but I had best Results with IRLML2060.

Like the 5-Band Board it is configured as “Serial resonance class E”, which means high efficiency (usually 80-90%) and per Band only 2 Coils are needed. Ther serial resonance circuit also helps in pre-selection for the receiver by attenuating anything outside the selected (active) Band.

Let´s start with the Gerber Files (in case you want to order PCB´s). In case you need PCB´s just upload the zip File to JLC-PCB (tested). In case you have another PCB-Source, that´s up to you. I will not support you on that.

Next is the interactive BOM, that tells you which component goes where, and makes it easy to keep track of your progress.

Next is the Schematic, including the Values and additional Inforation for the Band-Dependend Filters:

This mouser shopping List for the 8-Band Board was created/provided by Alain (K1FM).

https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=b2a08bf77b

Notes:

Capacitors:

EVERY Capacitor on this Board is in Size 0805, and every capacitor on this board (Exept C80, C81, C82) needs to be

NP0 or C0G Type, rated at least for 100V !!!!

It is almost impossible to debug problems, caused by wrong or bad capacitors. They all look the same…. So I suggest to really use only the right ones.

Best Source (I could find) for the caps is mouser, as they have the biggest selection available.

C80, C81, C82 are 100nF, they can be X7R Type and rated for 16V or higher is OK.

Toroids/Inductors

The Toroids can be bought here: FT37-43 and T37-2 and T37-6

Use only Original Micrometals or Amidon Toroids. Don´t use Toroids from unknown sources, or you will run into problems with efficiency !

The Toroids should be wound with 0,4mm Diameter Copper Enamel Wire (or bigger)

Relays

Relays are 5V Latching Relays. This means, there is no current consumption other then in the 30ms while they are beeing switched.

Relay Footprints are for THT Relays (eg this), but they are more expensive compared to same sized SMT Relays.

I used the SMT Relays, and bent the “Gull wing” Legs straight down. They will fit perfectly the footprint for THT. The Legs will be a little short, but if you´re soldering carefully this will not cause problems.

Rest

Q1 can be IRLML2060 or anything else in SOT23, that has the same Pin Configuration. For example I´ve tested this one, which is not SOT23, but close and has the same Pin-Out. This created same Power and efficiency on the lower Bands, but could not hold up on the higher Bands.

R1 is a simple 10k Resistor in 0805 Size. Just a Pull-Up, no special requirements.

U1 is TCA9555PWR in TSSOP24 Package or anything similar.

J2 and J3 are FEMALE Jumper Headers in 2,54mm Spacing

J4 is the SMA Jack, for example this but they can be found cheaper on ebay. Just search for “SMA PCB Female” and you´ll get a lot of offers.

Assembly

Everything starts with soldering in U1.

You see the I-BOM in the Background…. Use it ! It´s very practical. Especially for what´s coming next…..

Some SMT soldering help can be found in this Video:

Capacitor Orgy !!!

It is extremely important, to have only the capacitpors on the Workbench, that you are about to solder in next. If you place the wrong capacitor on the wrong spot, you have virtually no chance to find that Error later. They all look the same. So I can only put emphasis on the need to keep track of you work. Use the iBOM for that…..

For example: 100nF Caps placed and checked !

Place all Capacitors (only one Value at a time) and the Resisitor first, then solder in the PA Fet (Q1).

In case you do not have the exact Value of the required Capacitor (or the BOM says for example 620p//330p), then you need to solder 2 SMT Capacitors in Parallel. This can be done very easily, by stacking them on top of each other. I just repeat it: Both need to be NP0 or C0G Type, rated for at least 100V !

All small Parts placed…..

Then continue with the Relays. In case you want to use the cheaper SMT Relays (IM43GR), then you need to bend the feet:

Before
After
Left: Original, Middle: partially bent, Right: All straightened
After all Relays are soldered in Place, it´s time to start with the Toroids. I´m using 0,4mm copper Enamel Wire. This provides low resistance = Low Loss.
After WInding / Before Placing: I try to make the spacing between turns equally around the complete circumference.
After I´ve wound a coil, I place it, and twist the ends. This way they are already in place and can be soldered at once. You really need to make sure to burn the enamel coating while soldering. If a coil has no contact, this equals a mismatch = high SWR, and the PA Fet will smoke within seconds !
After all Toroids have been wound, placed and soldered, all that´s left is the SMA Connector and the Inter PCB Connectors (here female).

CAUTION !!!

Since this Board is using a single SOT23 FET, it cannot handle bad SWR very well.

The additional Power dissapation, caused by reflection of Bad SWR will very easily add up to a level, that is out of specs for that tiny FET (usually max allowed power disappation between 0,8W and 1,2W – depending on type of FET and temperature)

Everything is fine – even for hours- up to SWR 1:1,5 even without Heat Sink. (Because we´re in the 80% and up Range of Efficiency) However, a few seconds Transmitting into SWR 1:3 or worse will destroy it immediately.

So use only perfectly matched Antenna (SWR 1:1,5 or better !)

The good News is: One SOT23 FET is easier to replace then 3x TO92 (=BS170) FETs and they are cheap…. 😉

RESULTS

With the Values published in the Schematic, one single FET IRLML2060 and 200µH Drain Inductor, Setting PA BIAS MAX at 110 (!!!), I get the following Numbers:

Serial Multi BandI RxI TXCalc PWR INVppCalc PWR OUTEfficiency
80m0,060,475,7345,605,2090,77
60m0,060,435,1542,804,5888,97
40m0,060,394,6241,204,2491,79
30m0,060,435,1342,404,4987,55
20m0,060,404,6440,804,1689,75
17m0,060,465,4945,205,1192,99
15m0,060,455,3443,204,6787,36
10m0,060,374,2640,004,0093,80
I in Amps, PWR in Watts, Vpp in Volts, Efficiency in %, All Values measured @13,8V