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Homebrew projects - 23 cm.
Written by PH0V   
Saturday, 09 May 2009 15:56

Years ago I have, together with a few other HAMs from the area Noord Holland experimented with EME on a place close to Schiphol Airport. Earth-Moon-Earth many times is called Moon-bounce, I like to call this myself "Moon reflection".

Approximately 20 years ago I collected a 6m parabolic dish from a Dutch HAM in the middle of The Netherlands. This parabolic dish was build by him selve but unfortunately must be dismanteld because his new QTH did not have enough room to rebuild it there. After a few years of storage it has been rebuild on the site of the formal company  where Jaques PA0JCA worked. We were quite happy with this location because who has room enough in his garden for such a dish?

After buiding up, which took about a year, we have made some contacts with this dish. But soon after this the message came that Jacques had to leave the company. The company was taken over and the number of employees was reduced (reorganised). The dish with every bit and peace was collected by an other HAM from the south of The Netherlands (Limburg), unfortunately I forgotten his callsign. No sign of the dish ever was heard untill some recent rumor came that Hans PA0EHG is the new owner of this dish. 

The situation here in Sint-Pancras again put my mind on EME. Since building a reasonable high antenne tower has been rejected by the local authorities. So anything low on the ground cannot be any problem at all??? Knowing that EME now is achievable for small stations with small antenna's since computer programmes as WSJT JT65 combined with an PC and a audio board helps to achive several extra 10-s of dB's compared with CW.

In the mean time I have collected a 2,5 m parabolic dish. Several calculations has been made of the windload, so a decent fundamental construction could be made. Below here an impression of how big such a "small dish" is. 

To increase the power output with 3 - 4 dB to something between 200 and 300 W, more drive power was also needed. I need something in the range of 25 and 30W, hopefully something more to drive the 2 final power modules to the maximum output. After some modifications of my old 23 cm transverter I was able to measure approx. 25 W at the output of the transverter, this behind the coaxial relay.

Below here the inside of the transverter, based on a design of OE9PMJ. To get some better results of the receiver a pre-amp is build inside using a design with 4 glasstrimmers, 2 lechers in "free-air" and a MGF 1403 fet. The EME construction will be equiped with a pre-amp of G4DDK. Please find an article about this pre-amp also on this web-site.

The output power of the OE9PMJ module is about 100 mW, could be more, but then the signal is'nt "clear" anymore. This 100 mW then is amplified to just over 1 W by an 2 stage driver with a old BFR64 in the final and then amplified to this earlier noted 25W by an MGF 284, this as designed by Bert, PE1RKI. On the frontpage my old callsign PA3AGS is still visable as well as an special sticker (left under the mains switch) this was nessesary then for every amateur equipment at that time.

 

Fronvieuw of the transverter.

In the mean time the power ampifier has been finished as well. This PA is build with 4 MRF286 fets of Motorola. The power blocks has been build together with 2 switch-mode power supplies of Siemens in one big box. The power supplies are wired in parallel. Before this I measured the current from and to each power supply to find if there was no big current with this way of wiring in parallel. It seems not to exeed a few tens of milliamps so no problem. The 1296 Mhs input signal has been devided to 2 signals by an teflon PCB splitter and fed to the 2 PA blocks. Both the PA blocks are equipped with 2 MRF286 fets who are driven by an splitter also on this PCB. The amplified signal is been combined by a combiner also on this teflon PCB. After this the 2 signals from the 2  PA blocks then are combined by a seperate combiner. This combiner also has been made on an PFTE print. The complete amplifier consumes 22 Ampere at 28 Volt, this with a drive power of approx. 22W out of the above described. The output power I cannot measure exactly, but I hope te get from another HAM a Bird powermeter wth an plug-in for 1296 Mhz, then I know more. I have measured the loss of the splitter and combiner (connected to each other), this was less than 0,3 dB. 

Picture of the power amplifier without the top cover.

On the left the 2 switch-mode 24V 10A supplies,  wired in parallel. On the right rear panel the 2 couplers. Underneath the 2 big heathsincs the 2 PS blocks are mounted with 2 MRF286 fets on each PA. Below a picture of the PA.

 

The only thing to do is the construction of the aerial.......

 - to be continued-

Last Updated on Wednesday, 09 November 2011 22:33
 
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