A blog about homebrew projects for Ham Radio. I cover aerials, test equipment, transmitters, both QRP and QRO, receivers and transceivers. The emphasis is on design and building. Generally I have boards and parts available at a modest cost. If you need more details, like a board layout, or any questions please ask. I'm more than happy to help.
After an eternity I finally got a low noise amplifier inside a metal box that didn't oscillate! So, I quickly compared two regulators on my voltage regulator module:
Regulator Amplified Noise pp
78L08 200mV
TL431 15mV
78L08 + capacitance multiplier 4mV
These readings would need to scaled to match previous results. But for now I have confirmed, in my mind, how much better a TL431 is over a jellybean regulator.
73's
Richard
In my experience modifying ex-commercial radio gear for ham use is a mixed bag:
Mind you, the Icom and Yaseu mobile rigs I own have been sadly lacking.
So when I opened a Mororla GM300 I was pleasantly surprised to see a radio with shielding over every coil in the receiver front end and a diode mixer. This was a departure from the norm and worth investigation.
Alas, trying to reprogram the radio for 70cm use was fruitless. After a couple of hours trying every serial interface I had and several versions of the Motorala software I had no success.
Which got me thinking. It's a fairly standard PLL circuit. So I pulled the entire synthesizer/receiver/exciter board from the radio. Powered from the bench using STM8 eForth and a $1 minimal development board I quickly had the PLL loaded up.
Only problem was the oscillators would not lock up oin the required frequencies. Padding with a few surface mount caps was partially successful. The tuning range is only just wide enough.
At this point I have a proof of concept. Driving the LED display on the head looks straightforward. But I am hampered by only having a partial circuit of the radio. If you can help me it would be appreciated.
73's
I'm getting tired of the semiconductor supply disruptions which manifests itself as price increases and supply shortages. Even humble voltage regulation is being impacted.
As an example of the voltage regulation quandary consider the synthesizer board in my present project, a HF SSB transceiver based on the Weaver method. In the past I would have slapped a 7805 linear regulator on the chassis for heat-sinking and used wires to connect it to the PCB. But this project is being designed with modular PCB's sized 100mm x 33mm since this fits into a readily available extruded aluminium tube. So less wiring from the chassis to pcb's inside tubing is better.
An AD9850 based synthesizer with micro, mmic and switchable outputs draws some 150-180mA. Now I can use a 7805 type linear regulator in a TO-252 (DPak) package but I have run out and the replacement will cost around $1. It could have cost as little as $0.30 but the wholesaler is out of stock.
However, I could use 3 separate regulators on the board and that would cost around $0.15-$0.20. But my choices are much wider and the heat to be dissipated is spread over 3 regulators. My parts bin probably means I wont have to buy any regulators, a good thing, if I go down the distributed path.
Will normal ever return? After 12 months of the supply disruptions I am starting to wonder.
73's
Was glad to help a good friend, VK6UM Larry, with the repair of an IC-R8500 recently. After some digging around it was clear this was a later version than the schematics I could find online applied to. The fault was the blinking display, a characteristic of a PLL not locking up.
A few minutes with my ICQ7A used as a sniffer confirmed VCO_A had no output. A few voltage measurements and it appeared the special Icom chip, IC3, was not enabling the power to the VCO. Knowing that chip was likely to be unobtainable, and for thoroughness, I checked the main micro was sending instructions to the synthesizer board.
I was able to confirm both shift registers, 4094's, were receiving pulses. But the shift register feeding the special Icom chip had no signals on the output pins that drive pins labelled "CON0" through "CON3". It seemed a reasonable assumption that these pins mapped to the output pins enabling the VCO's. So a replacement shift register was obtained.
Upon installation there was no change. A closer examination showed the data pulse was too low in amplitude to be considered a logic high. It transpired, after a fair amount of thought and measurement, that the data line was being loaded by a 130 ohm resistance that should not have been there. The fault was traced to a capacitor array on the main board having broken down somehow. Once removed from the PCB no amount of cleaning the defective part could remove this unwanted resistance, though it did change in value.
A replacement part could not be found. So in desperation something was fabricated in-situ with 1206 22pF caps and fine wire. Partial success. The radio is now working within narrow segments of it's wideband coverage.