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K2DEN · 2010-08-11 13:49:17

Hi,
I am new here. I have been following AK2B's progress on his receivers and transmitters. I put one together (just a 20m receiver) my self but I ran into some problems i can not figure out.
On the hycac agc IF board when monitoring the agc line voltage, you can hear the receiver only when the gain pot is turned up all the way and the voltage is 3-5 volts. Then the agc does not work because the rf gain is pushing the line voltage up. I was thinking that I did not have enough gain before the crystal filter. I am using a universal rf amp from Diz before a crystal filter. The crystal filter is matched with a L network from 50 to 500 ohms and then back down to 50 ohms for the input of the hycas board. The IF is 9mhz.

The receiver is a lowpass then a bandpass, into a rf preamp that is turned way down. Then a minicircuits ADE-1 mixer, to a universal toolkits amp, then to a crystal filter, then to the hycas, after that it goes to a ADE-1 mixer acting as the product detector with a 8.998.5khz bfo. Then to a lm386 amp.
Here is a picture, sorry its not that great.

http://www.k2den.com/photo.html

You can not see the bfo or the af amp they are on the bottom.

Thank you,
Denver

BTW sorry if this should not be in this forum.

Last edited by K2DEN (2010-08-11 13:50:01)

ak2b · 2010-08-11 19:30:22

Hi Denver,

If you look at the slope here you will see that the agc voltage is max (5-7 volts) on the pin marked agc out when the signal is the weakest (remove the antenna). So, what you are seeing may not be wrong - with the IF gain at max. I see 6.11 volts with no signal on one board and slightly more on another with no signal. With an S9 signal I see about 3.3 volts on the AGC line.
What you've described in the way you built your receiver is pretty much boiler plate for the way that I've built mine except I haven't used an rf preamp yet. I've found with every receiver I've built that they all sound pretty bad right off the bat without some tweaking

K2DEN wrote:
BTW sorry if this should not be in this forum.

This is the perfect place. The receiver looks great, by the way.
Keep us posted.

Tom, ak2b

ak2b · 2010-08-11 23:11:42

Hi Denver,

After thinking a little more about your question, I have a few of my own.
What are using for a local oscillator? Do you have any type of signal generator that you can put a 9MHz signal into the HYCAS and then back up through the crystal filter and then the RF amp? The RF amp has a 20dbm gain so if you fed +7dbm from your LO into it you should see about 27dbm out (about 14V p-p) You should have the overall gain you need with the setup you have. It's just a matter of finding out where you are losing it. If you supply 12 volts to the HYCAS 'OFF' pin you should have about 60db of gain on that board alone.

Tom, ak2b

K2DEN · 2010-08-11 23:18:42

Hi Ak2B,
I have followed your posts, they were my inspiration for this project. I think I do not have enough gain before the IF board, because the gain has to be all the way up to hear anything, so adding some gain before hand will help me lower the gain and allow me to use more of the AGC. In your video Ak2B you can turn the gain all the way down and still hear the station, when I start turning it down I get to a point and it drops off.

I will be making the transmitter next week.

Denver

KitsAndParts.Com Forum

#1 2010-08-11 13:49:17

Receiver Project from K2DEN

#2 2010-08-11 19:30:22

Re: Receiver Project from K2DEN

K2DEN wrote:

#3 2010-08-11 23:11:42

Re: Receiver Project from K2DEN

#4 2010-08-11 23:18:42

Re: Receiver Project from K2DEN

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