EMRFD Message Archive 5822

Message Date From Subject
5822 2011-02-07 05:37:00 MAc hycas - resonant circuit
Hi all.
What do you think about using a hycas stage as RF amplifier with resonant circuit in output instead wideband? Did anybody try it?

Best 73
5823 2011-02-07 09:24:26 Tim Re: hycas - resonant circuit
My gut feeling is that it would be very similar to the classic 40673 tuned-input-tuned-output RF amp. i.e. stability can be achieved but might depend on careful construction.

Not sure if the AGC application to the RF stage is what you're interested in but I assume it is :-).

The common gate J310 circuit is very nicely stable in contrast, and WB9JPS has shown some very thorough measurements of the results of applying AGC control to that circuit: http://web.mac.com/gwj/Site/Test_Equipment_files/R2Pro_LNA_Performance_1.pdf
What I come away with is that third order intercept suffers for in-between AGC settings.

I would be surprised if the common-source hycas configuration and classic 40673 had IMD vs drain current curves much different than the ones WB9JPS shows. The last page of the December 2007 hycas article certainly calls out REALLY REALLY STRONGLY at optimal drain currents for IMD. But to tell you the truth I don't know if I can pull 40673 or similar curves off the web. Time for me to do something
5824 2011-02-07 12:48:24 MAc Re: hycas - resonant circuit
'...> Not sure if the AGC application to the RF stage is what you're interested in but I assume it is :-)...."


Of course. I,m looking for easy way to improve simple transceiver based on mc3362.


I'm reading it NOW :-) Thank you Tim.


The second way i think about is not to improve existing audio derived RF AGC but add a IF stage after xtal filter. It can be better.
5825 2011-02-07 13:52:42 wb8yyy_curt Re: hycas - resonant circuit
The input network is designed for impedance matching at the 9 MHz IF to 50 ohms (I think).

I can't imagine why someone would want this much gain in an RF stage, nor this level of complexity (I just homebrewed one for an IF application, and I can relate it takes a while to build one!)

I would go back to the book for RF stage ideas ...

73 curt

PS - I still need to add those matching components to get mine working at 4915 kHz with a Cohn xtal filter - I suspect I can try the same inductor and a bit more capacitance - and go from there.

5826 2011-02-07 14:28:12 kb1gmx Re: hycas - resonant circuit
5827 2011-02-08 07:02:11 davidpnewkirk Re: hycas - resonant circuit
5828 2011-02-08 11:41:07 kb1gmx Re: hycas - resonant circuit
5829 2011-02-08 14:54:11 ae5ew Re: hycas - resonant circuit
I still have my SX-190. I replaced the front end FETs with J310s.
Put some pots in the AGC line.
Significantly increased the 10m sensitivity. Actually got to the noise level. The pots helped to minimize possible instability.
Charles AE5EW

5837 2011-02-13 13:09:07 longjohn119 Re: hycas - resonant circuit
I have used a hycas and it's standard 2 FET brother for RF preamps. One had a varactor tuned DTC in front for a preselector with variable gain and tuned from 3 Mhz to 20-25 Mhz (It's been awhile and I gave it to a friend years ago so I don't remember the exact range)

I currently have a little AM radio for my fishing boat I'm making that uses a Sanyo LA1135 AM radio IC that I hacked out of an old car stereo. Take a look at the datasheet and you find a hycas circuit on the front end, in this case ahead of a varactor tuned DTC. Actually this is a pretty cool little IC with a lot of 'hackability'


I also used a 2 FET version in a preamp for a varactor tuned loop but that didn't really work out all that well due I believe to an impedance mismatch. Rather than working that out I went to a balanced/shielded coax pickup loop which also acts like a balun so I used a 50 ohm bipolar preamp with a pin diode to control the gain which was based