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This receiver was chosen over several others for the following reasons: Cost - At $500 direct from the vendor SSB Electronics USA during the Dayton Hamfest '99 it was quite a bit cheaper than a full communications receiver such as a R-7000. It doesn't have quite the coverage (1500 MHz upper end verse 2000 mHz) but it covers the 20 or so mHz of the water hole that I intend to study. Programming - The receiver comes with a Software Development Kit (SDK) and a Dynamic Linked Library (DLL) to control it. I will be able to integrate it into the system with direct calls from my SETI user interface to the DLLs. This will be faster and more reliable, than calls to an external receiver controlled via RS-232. Delphi - WiNRADiO uses the Delphi programming language for most of its applications and this is the language that the SETI system is being constructed with. Delphi is Borland's object Pascal and is, in my humble opinion, is superior to C or C++. The code is as tight (fast) as C or C++ and doesn't require any more memory. When ever I have to code in C its like I have suddenly developed a lisp. I can't express myself the way I can in Delphi. WiNRADiO versa FT-757 - The original SETI Search system used a Yeasu FT-757 H.F. receiver which was tuned via an RS-232 link. This had the disadvantage of requiring the development of a very stable Local Oscillator (LO) and mixer for down conversion from 1.4 Ghz to the 30 MHz range of the receiver. Although I did build a phase locked LO for the first system I was never very happy with its performance. Receiver Specifications (from WiNRADiO)
The WiNRADiO 1500 is designed for typical communications not SETI and it, like all other communications receivers has its Automatic Gain Control always on. This serves to limit front end overloading in congested bands but in SETI, where the bands are quite, this is undesirable. I have modified my radio to disable the AGC. You may follow these instructions but remember this will void your warrantee. 1. Remove the radio from the computer. I always work on an anti-static mat.
2. Remove the cover from the radio - You do know that this will invalidate the warrantee - right? Step 2 - Cut trace on top layer between pin 7 or U5 and test point TP21
Cut complete
Step 3 - Back into computer Step 1 - Remove the receiver lid.
Step 2 - Unsolder the antenna BNC connector lead. Careful not to melt the co-ax. Test it with an ohmmeter after removal to make sure its still OK. Step 3 - Remove the corner nuts and bolts holding the board AND the
nut and bolt holding the voltage regulator (five in all).
Step 4 - Remove the board. The only thing holding it is the 32-pin connector on the right (just under the antenna connection). You need to remove it very carefully and not bend the connector pins. They are high-quality connectors, but they do break easily if bent too far. To remove the board, push it up very gently using a small screwdriver as a lever, inserted from under the board where the antenna lead was connected, and also, alternately, into the round hole at the bottom of the ISA backplane ( close to the connector). Step 5 - The baseband output for SSB is at the end of chip resistor R74, which is located on the reverse side of the board, close to the bottom edge (if you are looking at the reverse side of the board, with the connector on the left), horizontally approximately in the middle. (Look at the lowest component - it is capacitor C126, and R74 is just next to it.)
Step 6 - Then make a 'thiny' shielded cable connection to the end of R74 which is closer to C126 (the "bottom" end). To ground the cable braid, you can use the "top" end of C111 which is just above R74, and is connected to a via which goes to the ground plane. Careful not to cause a short here with the braid. I used the cable from one of those cheap computer microphones.
Step 7 - Finally, before pushing the board back onto the backplane, make sure all the connector pins are straight. If needed, straighten them very gently before inserting to the backplane. A broken pin is very hard to replace (read "impossible"). Step 8 - Drill a hole in the ISA bracket and mount a small phone jack. Route the cable through a hole in the case and out to the phone jack for the baseband out.
Audio Bandwidth Improvement - The standard WiNRADiO 1500i receiver comes equipped to produce audio up to 3 KHz. This is not a good match for SETI scanning where there is so much area to look through and where the hardware and software is capable of much higher scan windows. The last modification brought out the baseband audio and increased the bandwidth to 5 KHz. This change will remove a filter and increase the bandwidth to 20 KHz.
Step 1 Remove top cover. Cut the warrantee sticker and then use
a flat blade screwdriver inserted into the slots to gently pry it open.
Step 2 Remove five screws. Refer to the picture to see which
screws to remove. The ones that come with the receiver are a security type
and are difficult to loosen unless you happen to have the proper
tool. I used a hex cutter to bite into the screw to get them
started. Once removed they should be discarded and replaced with
simple Phillips head #8 screws.
Remove only the five screws identified in the picture. The number 3 screw holds the three terminal regulator in place. Make sure to not remove the screw marked "Do not remove". Step 3 Unsolder Antenna - Unsolder the center conductor from the
receiver board using a lightweight soldering iron. I set my soldering
station to approximately 25 watt. Use a heaver iron, I used a 140 watt
soldering gun, to remove the outside braid from both the board and the edge of
the can.
Lift the receiver out of the can. The only thing holding it is the 32-pin connector on the right (just under the antenna connection). You need to remove it very carefully and not bend the connector pins. They are high-quality connectors, but they do break easily if bent too far. Push up very gently using a small screwdriver as a lever, inserted from under the board where the antenna lead was connected, and also, alternately, into the round hole at the bottom of the ISA backplane. Step 4 Unsolder Filter - Locate the black filter on the bottom left of
the PCB. Mine was marked CQ 33-455IT this is what will be removed.
Determine the filter pins to unsolder on the bottom of the board. Refer to the next picture to make sure you only unsolder those pins.
I use a solder sucker to clear the holes but solder wick works as well. Be careful. Step 5 Install the SETI Filter - Jumper pins 1 and 5 on the top side using small wire. I used 30 gauge solid.
Step 5 Reassemble - That completes the installation. Put the receiver back in the can making sure that the blind mate header pins are not bent.
Re-solder the braid to the board and the can. Use an ohm meter to verify that you have not melted the braid to the inner conductor then re-solder the inner conductor to the board. Put the cover back on and reinstall the receiver in you computer. Step 6 Initialization File Changes - Use Word Pad or some other text based editor to open your C:\Windows\WiNRADiO.Ini file. Add the following lines near the top of the file.
Notice the minus signs in the second and fourth lines and don't use a word processor, like MS Word to make the change because it will add a whole clump of formatting characters in the file. The WRAPI constants define the overlap of two bandpass filters which intersect to define the SSB IF bandwidth. When you change the constants as indicated, you will also change the tuning of the local oscillators in such way that the intersection point moves and the resulting bandwidth is extended to the maximum. This has an adverse effect for the suppression of the opposite side band. However, this should not matter in a SETI search. Testing - With the changes in place you will notice that the AM and FM settings no longer work and that the CW setting is very poor. This is normal since all SETI search work will be done in the lower SSB setting. With all changes in place I get over 20 KHz bandwidth. Phase Noise Testing: The phase noise of the WiNRADiO needed to be tested to quantify the receivers ability as a SETI receiver.
Testing was performed as outlined in the ARRL Handbook 1999 page 14.9. It consists of 6 steps:
Setup - Expand the thumbnail below for a picture of the equipment used.
The Weak Signal Source (WSS) produces -3 dBm at 1420.399 mHz as measured by the H/P power meter and the OptoElectronics 2210 counter. Attenuator String - A transfer switch was setup to switch in or out a single 3 dB attenuator. This was necessary because the other variable attenuators in the string were both 10 - 70 dB. A 30 dB fixed attenuator completed the string. The first attenuator is an automatic model so a control box had to be fashioned for it. The second is strictly manual. The string can give between 30 and 173 dB of attenuation. The ARRL manual warned against poor shielding and this was found to be true. Before I completely shut off the signal with the attenuators I had to go back and rework the seal on the WSS case. I also had to use hardline between all components except from the 30 dB attenuator and the receiver input. This was a 20 foot run of of RG-8 co-ax. Audio Measurement - The audio output of the 1500 was routed to a simple 8 ohm speaker to give a constant load and the voltmeter. I could have used one of the shack AC DMM's but since it was close to Christmas I decided give SETI Net a present and buy a true RMS voltmeter. A true RMS meter is preferable because it can give correct readings on sine waves and noise. This one came from a surplus store for $25 dollars. The bandwidth data was collected using the equipment setup above and plotted that using Excel. This shows a bandwidth of 1.7 kHz
Shut off the Weak Signal Source and note the noise floor (50 mVolts) then turn on the WSS and adjust the attenuator sting to give 3 dB higher than the noise floor (50 X 1.41 = 70.5 mVolts). At this point the noise power and the test signal power at the AF output are equal and is the MDS. Record the frequency at the peak (Fo), the attenuator setting (Ao) and the audio output (Vo). Fo = 1420,392,200 Ao = 73 dB Vo = 94 mV Tune the receiver up-band by 1kHz and adjust the attenuator to get as close as possible to Vo. Record the attenuation new audio out. Repeat additional offset frequencies.
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