Simple beacon for 1296 MHz - S53MV design

Not so many beacon articles can be found on the web where everything is well explained and documented regarding the home-brew beacon design for the microwave frequencies. One of the authors who really care about it is Matjaz Vidmar S53MV. All his projects are well described, proven in practice, and all assembled from the cheap and wide spread electronic parts. The most important, they are working !

Between all of his numerous design, the beacon for the 23 cm band is one of the simplest microwave project. The project was published years ago and can be found in the script "Beacon 99" (PDF format) on the following address: http://lea.hamradio.si/~s53mv/beacon.pdf .
The design is straight forward, 648 MHz oscillator and 1296 MHz multiplier with small amplifier. All beacon was assembled on only two 0.8mm FR4 PCB. The oscillator PCB is single side and the 1296 MHz doubler PCB is double side with one side used for the ground. If you strictly follow the design and instructions there should be no mistake. The 1296 MHz multiplier is a no-tune design, so plug and pray. The 648 MHz oscillator board consists of the chain of multipliers where each one should be tuned to the exact frequency to obtain the good signal on the output (10dbm).

The multiplier chain is simple :
Oscillator 27 MHz
x2 multiplier 54 MHz
x3 multiplier 162 MHz
x2 multiplier 324 MHz
x2 multiplier 648 MHz

As I already build the 648 MHz oscillator for the 1296 ZIF SSB TRX (in the same script) I decide to use this one for the beacon with the main crystal frequency on 18 MHz. The signal on 648 MHz was stable and the power was higher than 10 dBm. Frequency can be adjusted through the multi turn trimmer feeding the voltage to the varactor diode. With the cheap computer grade 18 MHz crystal the range 1295.900 - 1296.100 MHz was obtained with no problem and stable output power and frequency. Attention should be used when tuning the trimmer capacitors. Each multiplier stage, from the oscillator upward, should be tuned to the maximum power at the same time controlling the frequency of the multiplier stage that we are tuning. That way no mistake can be done and you should end with the correct output frequency.

The 1296 MHz multiplier board is a no tune, so after connecting the power you should have 23 dbm (200mW) output power. Also here, I did not follow the design because that time I did not have all parts ready. So I apply some modifications:
Instead of the 1st ATF35376 (multiplier) a MMIC SNA386 was used, modifying also the bias network. Both gate resistors are removed together with the LED diode with 330 ohm resistor and 10 ohms resistor was replaced with the 240 ohm. Standard MMIC multiplier configuration was used to double the frequency from the 648 to 1296 MHz. There was enough drive power to saturate SNA386 and to generate strong harmonic on 1296 MHz.

Straight after the 4 pole strip line filter the first amplifier ATF35376 was again replaced but now with MMIC ERA-2. Gate resistor was removed and MMIC bias was adapted for the 12 volt supply. 4V7 diode was removed together with 180 ohm resistor and 10 ohm bias resistors replaced with 220 ohm.

Of course, to complete the modification, the last amplifier BFP196 was replaced with the BFG540x transistor amplifying the signal to the +23dbm output with the power supply of 12 volts.

Just a two things to take care when building this multiplier, the grounding MMIC and the output transistor via are just 3.2 mm holes closed from the ground side by thin copper foil. Tho holes are then filled up with the hot melted tinol creating good contact with the copper foil. Four filter stubs are grounded using the 0.6mm silver wire (one wire from the RG-214 center conductor). Bend the wire creating the C shape to allow good connection (2mm) on he top and the ground side of the PCB. Tight the wire with the pliers and solder the wire both sides.

A short troubleshooting list if you run in the problems:
- BFX89 transistors should be mounted as close as possible to the PCB, not more than 1 mm above it
- BFX89 can be replaced with the BFY90 with better results
- BFR91 transistor is soldered directly from the copper side
- 22 nF blocking capacitors a very important, use the good quality ceramic capacitors
- keep all connecting leads as short as possible, a must for the capacitors
- the coils L4 and L5 are identical, pay attention on direction
- use only high quality trimmer capacitors in the multiplier chain
- up to now I build several oscillator boards for the frequencies of 576, 648, 720, 864 MHz and the only problem I had was the trimmer capacitor. After some time, the low quality trimmers are changing their value. The tuning point may be quite sharp on the second and the third stage, so this can cause that your oscillator after some time stop working, more often if your beacon is located outside, on the mast close to the antenna.

The proper shielding is required as per article instructions and the beacon can be mounted close to the antenna to avoid the loss in the coaxial cable. The keying is done by means of switching the power supply to the 648/1296 MHz stage. The oscillator board is always powered to achieve the better frequency stability.

I prefer to have the beacon not exposed to the atmospherics. The frequency stability is also less affected by the temperature if the beacon is held indoor. Of course, the loos in the coaxial cable have to be covered by extra amplifier to have the same power on the antenna. My beacon was built around standard 1H 17" rack together with the power supply and the IK0WRB beacon keyer. The keyed voltage is little bit lower than 12 volts. This result with the lower power output (100mW), but also the final transistor lower temperature. In the rack there is enough place for the extra amplifier and the inter-digital filter if required.

I was surprised with the final frequency stability and the shape/sound of the signal. On the video, you can notice the second harmonic frequency received on the FT-817d accompanied with the W1GHZ 23cm transverter (high side injection). Keyed signal can not be noticed due to 50 ohm termination, and the frequency stability is not affected by the keying of the final stage. At the same time notice the power output on the power meter. The beacon was left on the bench for a couple of days connected to the dummy load. No significant change of frequency was noted nor the lower output power.

After the initial beacon connected to the dummy load test, there was time to perform the "live" test running the beacon connected to the real antenna. The first antenna that I have handy and ready was the "Cheap WA5VJB" style yagi antenna. With some 10 dBi gain and indoor, connected to the beacon with a peace of RG-214 cable the antenna was pointed to the nearest mountain (1400 m ASL) from my home location. The idea was to use the already well known reflection point on the top of the mountain so the beacon can be heard in the near Italian provinces. The signal was good and stable, with no significant frequency drift. After several initial reports the beacon was switched off, ready to be mounted on the remote location.

The beacon is planned to be mounted indoor, so quite long run of the coaxial cable will result the low power on the antenna with just a little bit more than 100 mW of the beacon output power. For that reason I add another 10 db amplifier stage at the end easy producing more than 1 watt of output power. The amplifier was mounted in the robust CNC machined aluminum housing attached to the bottom of the rack.

The final result can be heard on the following video clip. Of course, 9A4QV/b signal is the strongest one between the two others.

W1GHZ 1296 MHz Hairpin filter

Building the Rover transverter for the 1296 MHz I experience the lower power output than expected, so I start looking what can cause this 10 dB lower output than predicted. Not only on the TX side, I notice the lower signal also on the RX side comparing the received signal with the other transverter design with the similar conversion gain. Among the all other parts affecting the signal loss, the filter is the only one that was designed and not fabricated. Paul, the author already made a good job with all relevant measurements on the filter, already published, but I wanted  some other verifications to get some more data to be able to use the same filter in some other projects.

The filter was duplicated from the W1GHZ 1296 MHz transverter (3 pole) on the standard 1.6mm FR-4 laminate. I prefer to use the "toner transfer" technique with my flat iron. Iron already became the standard tool on my workbench :-) A pair of SMA connectors are added to be able to measure and compare the filter more easily. Of course using the SMA connectors bring some additional losses to overall measurements, but I can live with that. The filter itself in the transverter configuration will have even lower I.L. 

IMPORTANT !!! The following measurements are done with the reference signal of -12.72 dBm !!!

So the reference signal was not 0 dBm, but -12.72 dBm and it is necessary to correct all the readings that you see on the following spectrum analyser screen shots. I start with the center frequency (C.F.) 1296 MHz, span 500 MHz to see quickly if my flat iron was successful or not :-) Quick look on the curve and everything looks as predicted. The filter is centered around the 1296 Mhz with the I.L of -4.53 dB (17.25dBm -12.72dBm). Looking the screen the BW - 3dB is 100 MHz.

The next step was to measure the filter response 144 MHz from the center frequency. At 1152 Mhz the signal was 40.28 dB down as per screen shot. I forget to measure the signal on 1440 MHz but we can see that the skirt is not so good as on the lower side, so the signal is only 23.28 dB down on the 1440 MHz. Of course "Right side up" mixing approach should work better than using the higher L.O. frequency in this case.

As I plan to use the same transverter but with the I.F. 432 MHz I measure the filter response on the 864  MHz with signal  62.28 dB down. The center frequency is 1296 MHz and the span is 900 MHz, 10dB/div. Despite the mixing products problem using the 432 MHz for the I.F. transverter is working quite good with this filter.

Using the same filter with the I.F. of 50 MHz to work on 1296 MHz is almost impossible. The signal on 1246 MHz is down only 11.28 dB. This measurement was just to compare this filter skirt with some other filters measured before. So here is the screenshot.

When measured the filter bandpass and the loss, I was still curious about the filter return loss / SWR so additional test was performed using the network analyser. This measurement gave me quite good idea about  the characteristics where the minimum obtained R.L. was 16.29 dB or the SWR of 1:1.36. This way I was quite sure that the mixer RF port is terminated with the impedance close to 50 ohms.

At the end, I tried to tune the filter for even better RL, what was possible but on the other side affecting the pass-band characteristic. This filter is designed as a no tune project and I was happy with the above presented results. They correlate much with all already published by Paul, W1GHZ. The small differences are result of  maybe different FR-4 used, slightly different dielectric constant, or the fact that my filter was not covered - galvanised. Non uniform Er can also affect the results where FR-4 has quite loss on microwave frequencies. Of course, the "Right side up" version of the transverter is using the 4-section hair pin filter with little bit different characteristics, but why not believing to Paul who already made all relevant measurements.

To summarise:

Freq:   1296   1152   1440   1246   864     MHz
Loss:   4.53   40.28   23.28  11.28  62.28  dB

3cm Waveguide double-slot antenna

Omnidirectional, horizontally polarised waveguide antenna for the 3cm band that can be used for ATV or beacon operation. This is not the beginners project as it requires some special machining tools, or CNC equipment . On the other side the software and calculations can be useful for the lower band antennas (23cm or 13cm) where hand-tool can be used to fabricate waveguide antenna.

All calculations are done using the HLSSA software running properly also in the DOS window. Using the  WR-75 size waveguide, 10 slot per side with the central frequency of 10.450 MHz, gain of 12 dBi was calculated.

Actual antenna dimensions are then modified to meet the calculated ones. The calculated distance Slot-Short (Lwg/4) was 11.29 mm, but I prefer to use 3 x Lwg/4 and adding the 2.3 mm length for the short-end cap give us a total length of 36.17 mm. If the short-end tuning is required, it is easy to insert the sliding short-end peace when you are using 3 x Lwg/4 length. With only Lwg/4 length, there is not so much room for tuning the antenna for the best RL.

For easy tuning and troubleshooting there is no coaxial to waveguide transition on the antenna. Instead, the WR-75 size flange was attached. To test or measure and tune the RL/SWR of the antenna the commercial or previously checked and measured coax to waveguide transition should be used not to affect the RL of  the antenna itself.

If you are planing to use the antenna indoor or on the location protected from the rain fall or snow than no radom is required. If you are planing to use the antenna positioned outside, on the mast, than good microwave radom should be used to protect the antenna from the watter but also from the bugs that just like to settle inside the waveguide. The radom should be at least 6cm in diameter not to degrade the basic antenna characteristics. Do not use the heat shrink tubing or similar ideas other then microwave radom. Anything in the near field region of the antenna can spoil the gain, diagram and overall characteristics. If you are constrained to use this kind of antenna protection, than insure that the same is inserted in the HLSSA program during the antenna designing.

The last attached photo can give you some idea how to install the antenna without radom. When installing the antenna, pay attention to position the antenna vertically. 3dB vertical beamwidth is quite narrow !! More slots will give you more gain but the vertical beamwidth will be narrower. If your antenna is positioned very high , on the hill comparing to the close stations, the close stations may suffer the narrow bandwith problem. If the antenna is slanted, this problem will affect some users even more.
Another fact is that the omnidirectional diagram is not the perfect, to be honest, far away from the perfect becoming more like cross diagram with the regions with the difference of 3dB comparing to the maximum antenna gain. So if you want to cover your preferred areas, turning the antenna can give you sometimes even 3 dB more gain. This problem can be solved by using the "wings" attached to the antenna, already published on the web.

3cm Waveguide to SMA transition

Not so easy to find now days and if new, sometimes quite expensive, the waveguide transition became the target of many home-brewers. So many different dimensions and designs are published with the same idea of making a good waveguide to coax transition.
If you have the possibility to measure the RL and SWR than almost any design can be tweaked for the best results, but if you can't measure it than you have to rely on the data provided by the author or constructor. The transition that I built, based on the Paul W1GHZ article was easy to copy, without any fancy tool and tuning equipment. I prefer to use his design because there are only two measures that you have to take care of while all others dimensions are defined by the standard waveguide size.

To build this transition we need a peace of WR-75 or WR-90 waveguide with the flange, SMA female connector, and a peace of the brass or copper sheet. Cut the peace of the required waveguide length, but not shorter than 1 lambda. Drill the hole for the SMA connector from the short end of the waveguide (distance C). Distance is measured from the end of the waveguide to the center of the pin hole. Hole should be 4,2 mm in diameter if you are using standard SMA connector with the teflon insulation. Find the female SMA connector with the longer pin/teflon insulation and put the same in the prepared hole on the waveguide. From the closer waveguide end cut the excess teflon inside the waveguide so only center pin will remain like on the picture below. The diameter of the center pin is 1,27 mm and the only thing you need to do is to cut the pin exactly according to the length D. This is the pin length in the waveguide!! Finally, cut the peace of the brass or copper sheet to form short end cover for the waveguide (AxB dimensions).

W/guide       A        B       C      D

WR-75     19,05  9,525  5,26  5,49

WR-90     22,86  10,16  5,46  5,89

(all measures in mm)

Now when we have all parts ready, it's time to put all this together. Of course, we will need to solder the short end peace to the waveguide and then the SMA connector in the previously prepared hole. This can be done by using the high power soldering iron or gas torch with not so tidy result. I prefer to use the iron, the same one I am using for tone transfer PCB. With the highest temperature set after 5 to 6 minutes the parts will be hot enough to work with them. Using the pliers, rotate the waveguide vertically with the flange sitting on the flatiron and with the other set of pliers position the short end on the waveguide end. Use the standard soldering iron to solder the short end. While the waveguide is still hot, position the SMA connector on the place and use the same technique to solder the SMA.

After the job is done, leave the waveguide to cool down for a few minutes. I make a several transitions using the same technique and the results are quite good. The RL obtained is -20dB (SWR 1:1.2) which is not bad for no-tune version. You may get lucky to get better results but if you are looking for lower SWR than you have to tune the transition. This can be done using different techniques: by changing the short end distance or even by adding some tuning screws. AD6IW give me a hint how to do this easy way. Making the hole for the SMA bigger (lonitudinally) we are able to change the distance from the pin to the short end by moving the SMA along the waveguide. Find the position where the SWR is lower and then solder the SMA. This will be good enough for all amateur applications.

After all, one hour job can give you a nice waveguide transition. To bulid or to buy, it's up to you...

Beacon keyer IK0WRB

http://web.tiscalinet.it/vcoletti/pic/keyer/beacon.html

If you ever build the beacon, or if you have the idea of building one, there is a part that every beacon needs, the keyer. Various beacon keyer designs are available on the internet but IK0WRB solution was the one that I prefer to use. Up to now I built a several keyers and all of them a working perfectly. As a matter of fact, the 144 MHz 9A0BVS beacon is running more that 3 years with this keyer where small reed relay !! is switching the power for the buffer stage. At the beginning nobody believed that the relay will last so long. It is still working.

As a spare solution, there is a keyer based on the transistor switch, where no mechanical parts are included. The schematic is standard IK0WRB keyer with a small modification where two transistors are used in a switch configuration. The first NPN transistor is used to key the input to the ground, and the second PNP transistor is used to switch the positive voltage. The jumper is used to chose beteween this two options, depending on the type of the beacon you are planing to use.

One of the things that make this project unique is the possibility to change the text and the format of the message on a very convenient way, just by tweaking the options in the windows based application written  by the author. The same application is generating at the end the HEX file to be programmed in the PIC 16F84. Of course, the message speed and the duration of the beacon carrier can be selected. Another nice feature is the possibility to use any convenient crystal frequency for this project. As I have a bunch of standard 3.579 MHz crystals, this is my favorite.

All the project can be done using the SMD technology where complete PCB can be really small. Between using the tiny SMD components and drilling the holes on the PCB for the standard components I prefer to use the SMD :-) . As this can be a beginner's project I made a PCB using the standard components with the socket for the micro-controller where the same can be easily reprogrammed with the new messages for a different beacons.

The keyer from the photo is a part of the 23cm beacon where positive voltage is keyed for the 648>1296 frequency doubler. The shape of the signal is looking good without any clicks or chirp. Simple keyer for all beacon builders....

W1GHZ rover transverter for 1296 MHz

http://www.w1ghz.org/MBT/multiband.htm 

The idea of building this project was how cheap and simple you can build the 23cm transverter that actually works, not just on the bench but also having you on the microwave bands making some contacts. So this project was one of the simplest to build not requiring much understanding and fancy lab equipment to tune. In this case simple means no tune, just solder assemble and run. There is really nothing to tune in this project if you follow the "For dummies" style instructions written by the author W1GHZ . AD6IW likes to say for this kind of project "Plug and pray" :-)  So this was simple.

What about cheap? How cheap you can go for the project like 23cm transverter? The most critical parts you can buy from the author, the rest you can buy on the e-bay or on the flea market, or even use some old microwave stock equipment. Wise guys will find almost all parts from the old SAT TV LNB converters. Let's check our shopping basket:

Local oscillator board + one Transverter board (1296 MHz)  $20

Relay board for SMD relay  $3

Mixer ADE-5 for 1296MHz $5

Relay G6Z-1F-A-DC12  $5

MMIC (8pcs)  $30

SMA female (5pcs) 5$

SMA male (5pcs)  5$

Rest of the parts (SMD components, Oscillator 80MHz) $7

At the end the total price will be around $80. Is this cheap or what? Just to compare, the good quality crystal for the microwave local oscillator will cost you in the Europe between EUR 20-25 ($30) !! Building complete transverter for $80 is really fair price, best buy price. So this was cheap.

Ordering the PCBs and mixers from the gentleman like Paul was an easy task, custom officers (Croatian) was another story. The rest of the parts I found in my "microwave scrap stock". Let's start.

This type of transverter is the earliest one using the Local Oscillator frequency of 720MHz. The latest model (Right side up) is using Local Oscillator working on the frequency of 576MHz. Assembling and soldering the Local oscillator PCB and the SMD components should not be difficult. Just follow the instructions and pay the attention to the MMIC bias resistor. Depending on the type of MMIC you are planing to use, calculate the value of the bias resistor. If you are not familiar with schematic and where to install the components check the following page http://4smicrowave.ae5k.us/w1ghz/place.html where all details are clearly seen and well documented.

Canned oscillator is mounted on the ground side of the PCB together with the output connector and few other components. 80Mhz canned oscillator should not be expensive, most probably the shipping will be much  higher then the value of oscillator. I found my on the old DX-80 PC motherboard, used as a clock. The 64Mhz canned oscillator can be found in some ADSL wireless routers. I prefer to use good quality SMA connectors instead of cheap F connectors.

First test was successful and 4 mW of output power was easily measured. No additional MMIC in the amplifier chain was required in my case. First downside of this project is the Local oscillator frequency. We can not expect high frequency accuracy from the cheap canned oscillator. After the multiplier chain I get the 10 kHz offset on the 720 MHz. After the final multiplying to 1440 MHz the offset is doubled. 20 Khz is the final offset from the required frequency. I can live with that, considering the price of  the complete oscillator. It is important just to know the offset, later you can calculate your band start and band stop IF frequency. Changing and looking for the other canned oscillator can help sometimes, but I was not so lucky. It is not worth spending time on this problem until you know what is your working frequency.

With a good working oscillator the next step was assembling the transverter board. I used all the parts that are listed in the author's article. The only change I made was the MMIC bias resistor to meet the maximum allowed current and the best MMIC performances. Find the MMIC datas heet and check for the Vd and Ibias where using the simple formula:

              Vcc - Vd
Rbias =  -----------
                 Ibias

bias resistor should be calculated. Use the next higher value then the one you get from the mentioned formula. Assembling was straightforward and the only thing to take care was soldering the components to the PCB ground where more heat should be applied to ensure good connection. The good practice is checking all the mounted parts before applying the power to the transverter. Once you have the white smoke out from the component it is not easy to bring the smoke back :-) , so be careful. The worst thing that can happen is loosing some MMICs. Apply the RX power to the terminal and measure the current where the value should not exceed the MMIC INA10386 bias current. After that connect the power to the 1440 MHz multiplier chain on the same PCB and measure the current using the same method. The total current consumption should be calculated according to all three MMIC bias current.

Now it is time to connect the local oscillator, 23cm antenna and the IF rig. Power up your IF radio first and then after applying the power to the transverter RX part you should notice the slightly higher noise on your IF radio which leads to conclusion that your RX part might work properly. Remember to use LSB on your 144 MHz radio where 143.900 MHz correspond to the 1296.100 MHz. If you have some local beacon in your area check for the signal, or just ask some local HAM to help you with some transmission test. There is nothing to tune except to check and measure the MMIC bias current.

The TX side of the transverter should be checked the same way. The maximum output power was 8 mW in my case. Changing the MMICs did not result with higher power despite the author article where he stated that 15 mw should be the achieved without any problem. I heard from some hams that they manage to get 15 + mW but with the Right side up version. I did not measure the filter pass band, but I suspect on the filter  loos. FR4 laminate have high loos on the microwave frequencies and the Er may vary between the various types of used laminates. Any how this is enough power to make some local qso or to drive some small amplifier. Do not forget to use the attenuator on the IF TX side. 1mW of the drive IF power is enough for this type of mixer. I prefer to use home-brew "sequencer" where attenuator and RX-TX voltage switching is controlled by "RF-cox" or PTT external signal.

Instead of the author PC board with relay i prefer to use a coaxial relay with SMA connectors. The one I use in this project was found on the flea market for a really good price. The truth is that the maximum usable frequency according to the data sheet is 2 GHz what is good enough for our needs. Moreover the coil power was 12V, so just a coil protection diode was required.

As this is intended to be a cheap project, the housing should be the same style. Old CD-ROM player was cannibalized for this purpose. A sheet of the FR-4 laminate was cut to fit inside the CD-ROM. All RF transverter PC boards are mounted on the top side while on the bottom side there is place for the sequencer board with the attenuator. For the moment no LNA or power amplifier is attached, but there is enough room  left on the bottom side to accommodate this as well. Front side was modified from the PC cover leftover. Two LEDs and a switch gives a finish touch to the project.

At the end you should have a nice rover transverter that can give you some extra points in the local microwave contest or you can give a chance to somebody to work some new squares. Both way you should have a lot of fun using this simple transverter. If you are lucky enough to live in the area where the hams are active in the microwave bands you will be able to make a lot of qsos. And remember: rover does not mean EME. This is a simple transverter and this kind of the design suffer from the facts that you should be aware of.

I already mention the canned oscillator frequency accuracy.
Sometimes tuning reverse side (LSB) can be confusing but sometimes this can help you, avoiding the big gun signals on the 144 MHz IF frequency working in the contest. Some of the older 2m radios can not tune below the band, some new radios can do that with some modifications but still they suffer from the lower sensitivity on this part of the band.
Roughly calculating, the conversion gain is low or none. Loos in the splitter 6dB, filter 7dB, mixer 6db, connectors 1 dB, coaxial switch 1 dB give us a total of 21dB. The only active amplifier on the receiving side is INA10386 delivering same or maybe a few dB higher gain on this frequency.

Knowing all this, I decide to build this rover transverter just to see how easy is to start with the microwaves not spending the big bucks.

13cm Pipe-cap filter

I needed a filter for my 13cm transverter project. What was the best buy option? Thinking and looking for the simple filter but with the characteristics that suits my needs, the answer was Pipe-cap. Simple enough, cheap, and easy to tune. After all, so many articles written about it (WA5VJB, W1GHZ, etc.) showing that this can actually work not losing so many time on mechanical design.

Check the local plumbing store for the pipe-caps used in the central heating plant. It should look like the ones on the photo. The one we need for the 13cm filter is 1" pipe-cap. Remember that the inner dia. is approx. 28-29 mm and the inner height is approx. 23-24 mm.

After choosing the right pipe-cap, a M5 brass screw with two brass nuts should be purchased as well. Beside this we need a two SMA connectors and a piece of double sided FR-4 laminate, 0.8mm will be fine.

Drill the 5mm hole in the center of the pipe-cap and solder the brass nut on top of it. Prepare the peace of FR-4 laminate where you etch the 50 ohms micro-strip lines where SMA connectors and probes should be soldered. The length of the probe is 10mm (length inside the pipe-cap) and the probe spacing is 18mm. For the probe use the wire (silvered center conductor rigid coaxial cable should work) or any coper 0.6-0.8mm dia. wire. Don't forget to solder the SMA ground to the PCB. Soldering 1" cooper pipe-cap might be tricky if using just the low power soldering tool. To avoid bad connections use the clothes iron to heat the pipe cap and then even with the low power solder you should not have a problem to solder properly cooper or brass. When finished, the pipe-cap filter should look like this.

Tuning the filter to the required frequency can be done with simple RF signal generator and a power meter. For this purpose I used the 13cm Comtech ATV transmitter controlled with the I2C protocol and a simple diode power meter made from SAT TV LNB mixer diode. Tune the generator to 2320 MHz. Ensure that the power meter sensitivity is set to range 10-30 mW center scale. The screw should be all the way down touching the bottom of the filter. Back the tuning screw out and after 4 to 5 turns you will notice the signal on the power meter. Gently tune to the maximum and that's it. This is the best what you can do just with this type of "tuning set". Use  the second nut to stop the tuning screw. After all, a drop of the paint or nail varnish can help to fix the screw and the nuts. If you can read the power, measure the power with and without the filter, the difference will give you a pretty good idea about the I.L. Changing the frequency and measuring the power with the help of the Excel spreadsheet and plotting the chart can give you an idea about the filter pass-band.

If you have the access to the network analyzer more accurate tuning and readings can be done. The one I made showing the filter characteristics based on the tune to the maximum method. The filter response is as expected with I.L. down to -2.85 dB and the stop band rejection down to -32 dB for 144 Mhz from the center frequency, not bad at all for such a simple filter. Playing with the size of the probes can give us more or less sharp skirts, higher or lower I.L., all affecting the stop band rejection.

Final notes:

* Tuning the filter with the screw is quite sensitive. Trying to stop the screw with the second brass nut may become tricky and not easy for everybody. Try to replace stop brass nut with the nylon one what will produce some tension to the tuning screw and prevent detuning due vibrations.

* Instead of using the micro-strip PCB lines, semi rigid coaxial cable can be used as well, extending the center conductor inside the pipe-cap and soldering the coaxial shield to the filter grounding.

* The same filter has been used in the home brew 2320/432 MHz transverter with very good results.