Receiver: It's Alive

[NZ0I]

The Receiver board has been partially populated: the power supply, port expander, and receiver mixer (SA605) have been installed and shown to function. Receiver sensitivity is lacking at this point, but that shouldn't be too surprising. I'll be spending some time getting a test bench set up to investigate sensitivity issues. Visit the website for more details: http://openardf.org

@Jerry - I may be asking you some questions about your SA605 experience and test setup - feel free to comment on the plans described on the web site.

[Gerald Boyd]

I will make a block diagram markup in another email tonight.

 

The VHF signal generator I have is in a double shielded enclosure with an waveguide beyond cutoff attenuator. The inner enclosure and attenuator assembly are silver plated with EMI gaskets.

This  prevents RF leakage from the generator bypassing the attenuator and making low signal measurements difficult.

 

You may want to check to see if there is a ham in your area that has a communications test set. One brand that’s on the surplus market is Cushman communications monitor.

You can get down to sub microvolts with one. Was common in radio test shop in the 70’s for testing land mobile FM. Just turn off the modulation to get CW.

 

I wonder if it’s possible to rent a generator from a test equipment outfit? When I was helped a locale communications company DF some 5Ghz interference they rented a spectrum analyzer for my use.

 

To test your current VHF RF generator setup set the attenuator at high setting and connect it to a dummy load. Then check to see if a nearby 2 meter HT picks up the signal?

I can set my Kenwood next to my signal generator / cables and there is no leaked signal. The shielding is amazing.

 

For monitoring the audio output You may be able to use your PC or iPhone as an OSCOPE to monitor the audio level?

I have an audio spectrum analyzer application and a VU meter app for my iphone. You may be able to use something like that to look at the audio level to see the demodulated signal. Attached are some screen shots from that app.

 

For monitoring the IF yes a shortwave receiver will work but you may want to couple it in such a way that you don’t load down the IF circuits of the receiver under test. Maybe a loop sniffer coil ahead of the attenuator and place near the crystal filter circuit. Making a direct connection with another low Z system  may upset the IF under test. A wide band opamp set for unity gain to provide a hi z input may work as a probe to isolate the test receiver used for IF sniffing?

 

Back in the car transmitter hunt  days I modified a 2 meter FM mobile to bring out the IF so that I could do CW to DF weak signal FM fox transmitters. Added a buffer amp to isolate the remote receiver.

Will look at the recent schematic to see how it may be done with our setup.

 

Jerry

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[NZ0I]

@Jerry

In your test setup, when you were testing the SA605 on the IF Board, what were you using to generate the VFO and BFO clocks? Were you using an Si5351, or a test bench signal generator? If a test bench signal generator, what were the VFO and BFO signal levels you were providing to pins 4 and 10 of the SA605?

Thanks! And thank you for the suggestions for test equipment for receiver testing and characterization!

-Charles

[Gerald Boyd]

See attached word doc

Jerry

 

From: receiver-devel...@googlegroups.com [mailto:receiver-devel...@googlegroups.com] On Behalf Of NZ0I

Sent: Saturday, April 22, 2017 8:00 PM
To: Receiver Development Platform <receiver-devel...@googlegroups.com>

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