Filters, filters and more filters

Exact, stable frequency is very important in ham radio. Especially if you intend to use digital modes, such as WSJT. I have built a GPS disciplined oscillator to generate 10MHz reference signal and used it in my 1296MHz transverter. It worked nicely ... until the moment when I connected a 40W power amplifier. Wow ... I intend to run 1500W for EME some day, so my GPS should withstand much more than 40W!

What is a solution? A filter, of course. The 23cm band uses 1296MHz while GPS uses 1575MHz. Should be easy to separate.

I have found an eBay seller named "iseeabluewhale" who sends packages signed "GPIO Labs" from Ontario, Canada. This seller offers reasonably cheap filters. One of them is a bandpass for 1575MHz (GPS frequency L1):

 

I have measured the frequency response. Looks quite good, 1296MHz suppressed nearly 60dB:

Time to test the GPSDO with this filter again. I will post the results later.

Second filter that I needed was 432MHz bandpass between my new 10GHz and 24GHz transverters and IF radio. One of them will output IF on- and below 432MHz, the other above 432MHz. Luckily, GPIO Labs make both filters, see the pictures:

Nice filters! It would be nice to find something like that for the 1296MHz frequency. There was one in their eBay listing, but the bandwidth is too narrow for the weak signal portion of the 23cm band:

 

What can we do? Obviously - get a filter elsewhere. Maybe make it ourself! For example using this design from W6PQL. I have made one of these filters (very easy to build) and here is the result:

 

Yes, this filter is quite good. Definitely cheap and easy to make. And the suppression of unwanted signals goes below 80dB!

I have recently used that filter to suppress unwanted spurious signals from ADF4351 synthesizer in the posting below. Quite a game changer there!

73 Herbert
AF4JF

Synthesizer with ADF4351

I have discovered interesting synthesizer modules on eBay:

I have also found an interesting project from Alain, F1CJN on the Internet.

This synthesizer can easily be controlled by Arduino Uno and a Shield with LCD Display:

Final result is here. A synthesizer that can be programmed for many stored frequencies. Following picture shows one of them:

I will upload more about this wonderful synthesizer shortly. Hoping to use it for a small local beacon for 23cm.

73 Herbert

UPDATE 2016-06-07:

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Nothing is perfect. Not even synthesizers. There is a serious problem with spectrum purity when used for frequencies above ~ 1.1GHz. See following pictures.

We need 960MHz reference signal for a Microsource YIG that generates 23GHz. Spectrum around 960MHz seems to be OK:

However, 1296MHz seems to have a problem with spurious signal only 25MHz away and only 39dB suppressed:

Workable solution seems to be to generate the beacon signal on 1/2 frequency and double it. That would require 648MHz. Following picture shows reasonably clean spectrum for that. You can see the 2nd harmonic on the spectrum analyzer already:

Looks like I have to work on frequency locking in my lab - frequencies shown on my RIGOL analyzer are little off the frequencies shown on the Arduino. Luckily, this synthesizer allows (wonder of all wonders) locking to a 10MHz reference!

(to be continued)

73 Herbert

AF4JF

UPDATE 2016-06-10:

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I have retrieved my old 23cm filter that I built long time ago with the idea of using Flex 1500 with IF between 28 and 50MHz in mind. This filter was made per W6PQL description and is described incl. pictures and frequency response in my other posting here.

Wonder of all wonders, it fixed the problem! The 1296MHz signal is a little weaker (6-7dBm) but all unwanted peaks seem to be suppressed more than 55dB:

In fact, I can't identify them in the noise floor anymore. Definitely good enough for a small local beacon! I will follow that idea soon ...

73 Herbert
AF4JF

Microwave Activity Day - May 7th, 2016

This posting comes after long, long period of doing nothing .. I mean nothing for my ham radio hobby. Looks like the overload from my job is finally over and some weekends not spent on job sites are in line now.

We (WA0CNS, N5MU and myself - AF4JF) went to our local hilltop in EM48rq with open view towards West and tested our 24GHz equipment.

Results were not perfect, but promising. My transverter copied 24GHz signal from Harry WA0CNS quite nicely, but Harry didn't hear mine. My station was only a mixer, no PA used today.

It was very interesting to watch how narrow the signal beam from dish antenna on 24GHz actually is. We need to work on aiming system, probably make contact on 10GHz first and then switch to 24GHz. Some more testing still needed.

73 Herbert

AF4JF

MUD 2016

Microwave Update 2016 will take place in St. Louis this year. Click on this link to find more info.

73 Herbert
AF4JF

Another Synthesizer Issue

I have published my findings with a MICROSOURCE synthesizer here some time ago. That synthesizer is working fine, along with several  other ELCOM LCDFSL-1201 units in my shack. I thought that ELCOM interface is pretty transparent - until I decided to use LCDFSL-1101 programmed for 10.8GHz (10.368 + 432 = 10.8). Well, it isn't.

I have browsed Internet for a while and discovered that many others would like to know how to program that unit. There even is a new controller board for it on a web site in Australia. Hmm .. maybe later, perhaps in winter time. For now, I have found easier solution. Use ELCOM DFS-1101 instead.

The DFS-1101 does not have connector for external reference. There is an internal Xtal used (I believe 100MHz) instead. This unit uses funny frequency calculation: you have to divide the wanted frequency by 5 and add 1024 to the result. In my case (need 10.800GHz):

10 800 / 5 = 2160

2160 + 1024 =  3184 ..... 31 84 00 is the code the interface needs to generate 10.800GHz

I will keep looking for a solution compatible with my LCDFSL-1101 unit. Until found, this cheap DFS-1101 will do the job.

 DFS-1101 unit (left) with my test board with PIC (WW2R design)

Frequency ~ 10.800GHz, voltage 14.7V (before stabilizers), current 646mA.

Unit works with +6V (some ELCOMs require 8V)

My Microwave Activity

I wasn't very active since my last posting on this blog ... in fact, I wasn't active at all. Only made several dozens of QSOs on 160m during winter months. My job keeps me busy and often out of town for weeks without end.

Looks like this is about to change soon. I should be able to return to my hobby and work on all my delayed ham radio projects (along with house maintenance, of course). Here are some of them:

• 24GHz transverter
• New 10GHz station with 3ft antenna and TWT amplifier
• Beacon for 23cm

I have obtained two TWT amplifiers. One for my home QTH, another for my portable station. Pictures will be here on my blog site soon.

73 Herbert

MAD (Microwave Activity Day) on 7/6/2013

The SLAMS group participated on another Microwave Activity Day (MAD) on Saturday July 6th, 2013. I went to my usual location, YMCA parking lot in EM48sq, together with Mel K0PFX and Armand, KD0PXF:

I was set up for 10GHz (dish on the left side), 23cm and 70cm - mostly because this was a first test on few 15el. Comet antenna. It worked well and, even better, this antenna is easy to assemble/disassemble in field. I am going to replace my 12el. Cushcraft with this one and use the Cushcraft at my house for Packet Radio 9600Bd.

Detail of my 23cm gear laid out on a table:

I have experienced the same problem with my transverter - it was overheated even when taken out of the car! Direct sunshine  is able to heat the box to high enough temperature to trip the PA thermal protection. I will have to do something about that before next contest ...

73!