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Hairpin filter for Es'Hail 2 (AMSAT P4-A, QO-100)

My first experiments to set up an hairpin filter for the 13cm band (2.4GHz). The deal is to get the right passband and proper SWR - ideally w/o trimming. So I had to do some trial rounds to get the proper parameters for the PCB material my supplier is using.

I think I hit it quite well, see yourself (S21/dB, S11/SWR).I set the frequency on purpose a bit "upwards" to get the maximum distance to the LO frequency to filter out. As shown, the filter can so ~25dB for a 2m LO setup and ~40dB for 70cm LO setup. So I will go for 70cm LO which will ensure I keep out-of-band bins on transmission 40dB below the in-band bin.

This measurements are w/o additional LNA mounted, next is to add ERA-2 amplifiers and biasing/12V supply to come to ~0dB attenuation in the passband region:

It will fit in a standard metal box for shielding (measurements in mm):

Hairpin filter for the 9cm band

For my 9cm transverter project I require a simple to use filter to extract the proper USB after mixing. So I re-used the data for the 2400GHz filter and scaled it properly. I ensured that a 2.4GHz and 3.4GHz filter is used on the very same PCB (and I separated it manually myself).

I have to say that the higher band is harder to design and to hit the right frequencies. At least the frequencies are a bit low, so I can cut the PCB traces a bit to tune it into the 3.4GHz region. The 9cm band is probably also the reasonable limit for using standard (but thinner) FR4 material...

This measurements are w/o additional LNA mounted:

The PCB size is the same as for the 2.4GHz filter above.

For development, I use my self-made Excel script to generate the structures for simulation and PCB layout (direct import as copper layers). Then I simulate everything in QUCS Studio.

Pipe end cap filter (cavity filter) for the 9cm band

Another way to implement filters is the use of 28mm copper caps used for plumbing. I found the work of Kent, WA5VJB about "cheap microwave filters" (PDF to external web page) and tried them myself.

The cap I used measures 30mm in diameter and 21mm in length (from outside). The screw and (counter) nut is made of brass, M4 x 30mm. I made the hole and the thread in the cap using my lathe, so it is perfectly in the middle. The most critical decision was the length of the two feeding rods (or just wires) inside the filter, as described by Kent.

I tried two variants (with the length of 8mm and 13mm) to see the impact on bandwidth and SWR versus insertion loss. The rods on the PCB are 19mm apart in the center of the cavity and connected with 50 Ohms striplines on the back of the PCB to standard SMA edge connectors.

Here are some pictures of my production of a pipecap filter (use the left/right button icons to scroll through):

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Here are my results(S21 and S11), first with 8mm feed rods:

This filter has quite a small pass band and requires a bit of patience to tune properly, as also the insertion loss is quite high. In the second filter I used 13mm feed rods:

As you can see, longer rods cause less insertion loss in the pass band, but a much wider bandwidth along with a somewhat wider usable SWR. Which means they are also a bit less critical to tune as they have a rather low Q factor.

I tried another version with 10mm feeds and made some more measurements. I figured out that the tunable range (31mm diameter x 21mm height cap) is between 2.5GHz and 8GHz. I also saw another resonance somewhere above 10GHz. Here is for completeness and comparison the filter tuned at 3.4GHz.

/ownpics/9cm_S11_S21_cal_3.4GHz_10mm.jpg

My experiments with microwave antennas from 1-24 GHz (mostly Vivaldi)

I did quite some design experiments with "Vivaldi antennas" (or correctly named tapered slot antennas - TSA).

Some are for large bandwidth, some are for power. I often use them for experimental setups as they are much leaner than parabolic dishes or yagi antennas and still provide a good SWR as load and at least "some" directivity.

My best variant "Vivaldi V5" for the 13/9/6/3cm ham radio bands

For the main bands it is obviously a λ/2 antenna with quite nice and flat SWR over a broad range.

As you can see it is also resonant on 23cm (presumably λ/4 only, and probably radiates quite "sideways"), but I didn't do further investigations there. The idea is to use it for the El Cuatro on short-range communication of some 10s of kilometres.

I have some antennas left, if you are interested pls. contact me.

My El Cuatro I got from Fred, OE8FNK

I bought an very early version of Freds multiband-transceiver, version EC2. It had quite low output power and no internal FM demodulator (so I used a cheap Baofeng for that).

I got it with some software I basically could not use. So I reverse-engineered the hardware (see PIC pinout functions below) and totally re-wrote it. Be aware, the new versions are much more powerful, anyhow I'd release my code here as it might be useful e.g. to control an MAX2871 PLL or the 16x2 i2c LCD display which is used in my EC2.

You can find a detailed description of the El Cuatro by Fred, OE8FNK in the DUBUS Technik XVII (external link to DUBUS web site).

The files here on this web page are provided "as is", without any warranty. You accept that you use them at your own risk and to use it for non-commercial purposes only. / Die Dateien werden "wie sie sind" angeboten, ohne jede Gewährleistung. Du akzeptierst sie auf eigenes Risiko und nur für nicht-kommerzielle Zwecke zu verwenden.

I accept / Ich akzeptiere:

Download is only allowed when accepting my conditions and disclaimer above.

3.4GHz / 9cm all-mode transverter

a compact 9cm transverter for all operating modes

ZF: 144MHz, 500mW (e.g. FT817)
RF: 3400MHz, ~100mW
LO: 3256MHz, ~13dBm (PLL module bought from from Dieter, DF9NP)
First prototype implementation using my transverter board and end cap filters for OE8PKR - still a lot of wiring, hi!