Skip to main content

January 26, 2025. So, OK you just bought 100 pieces of the J310 SMD type--What Now?

Bi-Directional IF Amplifier Stage from G4GXO


So, you just popped for 100 Pieces of the SMD version of the J310 for about $20 and that is when you discovered that China didn't pay the 10% tariff -- you did. About $2 extra to buy 100 pieces. Stupid decisions have consequences! A Tip of the Cap to you MAGA-O-Lytes.

Now what do you do with those 100 Pieces? With due recognition to Ron Taylor, G4GXO who designed this circuit which appeared in SPRAT #128 you build it. Yes, it is a bilateral circuit and signal reversal is done with Voltage switching. If you are a serious homebrewer, then you need to join the G-QRP club and purchase the SPRAT on a Stick!
 
In case you bought the SMD version of the J310 it has a max voltage of 10 Volts and this circuit should work at 10 VDC -- it might need some resistor tweaking but don't fret it will work OK.
 
This circuit simulates a Dual Gate MOSFET and does have an advantage of being able to adjust the gain by what is applied to Gate #2. In several of my transceivers where I used this circuit, a relay applies AGC to Gate #2 on Receive but switches in a fixed voltage on Transmit for max gain.

With a bit of twizzling in LT Spice you could make this a single J310 but lose the ability for AGC or ALC or Fixed Gain at Gate#2. Since the J310s are in cascade, the current flow (current draw) is less than for two separate devices. 

This circuit has seen service in my Tri-Band SS HW-100 and the KWM-4. You can see the SS HW-100 at https://www.jessystems.com

So, another piece to homebrewing a rig that has a low current draw with flexibility and bilateral. No, this is not a Bitx Topology although most likely a (TIA) termination insensitive array. The 820 Ohm resistors across the Toroid windings force a 16:1 match -- yes in/out is 50 Ohms.

BTW a really cool side benefit is that when you apply AGC to Gate #2 and have the level set just right -- the LED's Blink/Wink and show the AGC action. See the video at about 1min 20sec.

When you know you can make things go!

73's
Pete N6QW

 

Popular posts from this blog

March 31, 2024. Happy Easter to those who celebrate this day.

What a great day to Binge on Chocolate and experience the pain of that filling that has been leaking.  I would be in that category with the leaking filling(s) had I not just spent an amount equivalent to one of the fancy new uptown appliance box transceivers on two filling repairs. Well at least I can binge on the Chocolate bunnies without fear of pain. Regrettably everything appears to have jumped in price including the price of parts. Well not so much the parts as the shipping costs.  That notably is seen in the eBay treasures. I spotted a nice heathkit DX-20 for about $50 and the shipping was $65. Likely it is a twofer with part being a way to in effect charge a higher price by inflating the shipping and in part by increased shipping costs. Shipping with insurance across the US was about $150 for this jewel and that was three years ago. 6AM on the Left Coast ~ 20M Easter Sunday! My only hope is the cost of Chocolate Bunnies remains steady although a pound of See's Candies f...
Read more

January 26, 2024. A simple CW Transceiver/Transmitter

Cruise through the lower part of the ham bands bands and what do you hear? Well, FT-8 and CW. Often you will not hear any SSB stations yet go to the lower part of the bands, and it is a cacophony (I love that word) of bad sounding signals and some high-speed keying. Fast is not so much of the issue as is bad, run together and jerky keying. But none the less our hobby started there.    So, you could crank down your ICOM 7300 and watch the waterfall on CW or you could homebrew a radio. Actually, to do CW right you need more thought up front than you do with a SSB transceiver. Often, I will state that a CW Transceiver is much more difficult to build than a simple SSB rig. I published two articles in QRP Quarterly on CW transceivers and all I got was a yawn so maybe history will repeat itself.  Yawn!   30M CW Transceiver with RIT!   Of interest is that the LO is a Varactor tuned LC oscillator using a NE602. Look closely at the RIT circuit which is only activated on ...
Read more

August 30, 2024. A PNP 20M SSB Transceiver

Shown below is the Block Diagram for the 20M PNP SSB Transceiver steered in the  Transmit Mode . The components shown in the dotted block are relay steered so that the block module is single pass and amplifies in a single direction. The Block diagram show steered in Transmit.  Essentially the steering process works so that the IF Module input follows the Balanced Modulator on Transmit and then the input side follows the Receive Mixer on Receive. All done with some relays and a bit of RG174U coax. For those who count things in detail, this block diagram is not unlike what was used for the PSSST Transceiver which can be found on my website . Yes, a warmed over P3ST only using PNP devices. TYGNYBNT. 73's Pete N6QW
Read more