Monday, July 23, 2012

Possible Microwave Locations

We have taken a friend from Germany on a short "winery trip" last Sunday. Attached pictures show possible microwave locations that we have discovered along our way. They are all in EM48. First picture is from Hermann, MO viewing West, remaining two are from Grafton, IL viewing South-West and North-West. Wine was excellent.





Saturday, July 21, 2012

PTT output for IC251a

Friend of mine (Rich, N0PQU) owns IC251a. It is a nice reliable 144MHz all mode transceiver. Rich wants to use it as IF radio for his 10GHz transverter. Problem is that this radio doesn't have PTT output.

We have found nice article (by Scott N0EDV) about installing a sequencer inside this transceiver. However, his technical solution wasn't exactly what we needed, so we designed one of our own.

The IC251a has a RX-TX switch on its front panel. Our first idea was to use that. This switch has +9V on it in RX mode and 0V in TX .. apparently the 9V comes from a switching logic inside the radio and the RX-TX switch grounds that when transmitting. 

We needed something with high impedance and we also needed the logic reversed (switch relay in TX mode), so we designed following circuit:


First half of the OP-AMP, the "O1a", is basically a "unity gain amplifier" with very high input impedance and  the second half, the "O1b", is a voltage comparator. Should the input voltage on the PTT switch drop below ~8V (RX-TX is switched), then the comparator energizes its output, "LED1" comes ON and the optical insulator "OP1" switches its (galvanically isolated) output ON. Exactly what we needed.

HOWEVER

Connection between "PTT" input and the RX-TX switch must be made with a 100k resistor in series, otherwise the "unity gain" amplifier doesn't copy the "0" voltage when switched to TX. This is because of the way how this OP-AMP is connected to the power supply - no negative voltage applied. In the real world, the "-" (inverting) input always has a little lower voltage than the "+" (non-inverting) input, so if you ground the "+" input by PTT directly, the "-" input has nowhere to go and "O1a" goes to output >10V.

We have taken several pictures of the connection points inside the radio to share the idea:






Everything works well on a test bench. We will connect it to the transverter soon and update this Posting with results of that.

UPDATE 

This radio was successfully used for 10GHz contacts on 09/29/2012, details here.





Sunday, July 15, 2012

23 cm Beacon for St. Louis

I have returned to my delayed project of a 23cm beacon for St. Louis. It will be running 10W to 4x "wheel" antenna (by WA5VJB) on 1296.350 MHz and will be located in EM48ss next to the WB9PNU beacon for 3cm.

Here is a picture of the oscillator unit in a small box. The circuit board (by W6PQL) has an oscillator on one side and temperature-controlled oven on the other. This small box will be enclosed in Styrofoam inside bigger box:



Some pictures of the antenna:




I will update this posting with more details and pictures as soon as I have something new to share. It might take some time, but the goal here is to have the beacon operational by the end of this year (2012).




Saturday, July 7, 2012

MAD activity on a Hot 100F Day 07/07

We have tried to participate on MAD (stands for "Microwave Activity Day") activity today.
I have met with Jim N5MU at the YMCA parking lot in EM48sq again. Today's goals were:

  • work W9SZ on 10GHz in EN50rl ... didn't happen
  • work NG9R on 144/1296MHz in EN40na .. achieved
  • test "Eggbeater" antenna on 144MHz liaison frequency SSB ... worked well
  • test my "new" 30W/1296MHz amplifier ... worked very well

Would you believe that it takes almost half an hour to set up all this equipment?

AF4JF equipment for 144/1296/10368MHz used today

I have obtained a 23cm PA from KM5PO (on eBay) long time ago. It works very well, but requires 24V for the power FET and 16V for transfer relay. I have used a power inverter to generate these voltages from my 12V battery.

The 23cm PA, SBMS concept with Infineon PTF10021 FET, is the box with huge heatsink in the middle. The gray diecast box on its left is my 23cm DEMI transverter. Power inverter is on its right. You can also see two power supplies (24V and 16V) in the front of the picture, next the the Diamond SWR meter:

AF4JF gear

Detail on the 23cm PA and the MFJ Power Booster

12V Deep Cycle Marine Battery
(see Power Poles for the Booster and Clamps for Power Inverter)

Overall, a successful day. I will try to consolidate all that 23cm gear into one nice compact box with one power connector. Well, maybe two, but not 4 ... Some day.

73 de AF4JF
EM48sq

Sunday, July 1, 2012

Power Supply for DMC modules 24GHz

DMC modules used for 24GHz transverter (see my other post here) need (+8.4V) and (-5.0V) voltages, where the (-5V) must be applied first.

I have built a simple power supply that honors this requirement. Original idea came from another HAM's web site. I liked this simple solution with a Zenner Diode, so I adapted it for my needs:



First test results were good. Note that output voltage (+8.4V) can be adjusted by changing resistance of R3. In my case, I have used two resistors in parallel. PCB provides enough space for both of them.