Entries from May 2015 ↓

Solar Power

I have had a small 50 watt solar system up and running for about two years. It keeps a single 12 volt automotive 24F class battery charged. The system provides power to light and run a modest 2 meter ham station located in my bedroom closet. The station is on all the time monitoring the local repeater.

Recently I have been considering adding a more capable solar system to compliment the 1KW emergency gas generator in the generator hut.

My interest in solar was raised when I discovered 100 watt solar panels priced at under $150.

The solar panel is not the only thing you need to build a solar power system but at $1.50 a watt, it becomes competative with gas powered generators.

So I bought a single 100 watt solar panel. It has been cloudy for the last two days since the panel arrived but even with light overcas the panel produces 20volts open circuit and 2.5 amps lighting the large filament of an automobile brake light.

The final system will have four 100 watt panels connected in series to produce up to 80 volts. Provision will be made to route the 80 volts to a 1000 watt sine wave inverter. The inverter costs $100 and will provide over 300 watts of 120vac 60 cycle power when the sun shines.

Antenna Switches

Over time I have used a number of tower based antenna switches. They all worked but were never able to select between morew than four antennas.

These switches were controlled through the coax feedline by using chokes and capacitors to isolate the control voltages from the RF energy. This seemed to work even at high transmitter power levels but the additional components required to do this would certainly have an adverse effect on reliability over time. I did not need another toy to repair at some future date so I decided to run a separate control line to power the relays used in my antenna switch.

By using a tower mounted antenna switch I need only one coax feedline from the shack to the tower and I have relatively short feedlines runs from the switch to the five antennas. Otherwise I would need five long feedlines into the shack, one for each antenna. The antenna switch more than pays for itself in money saved buying coax. The main downside is that you can only use one antenna at a time.

So if you own more than one ham rig, you can’t use that other ham rig on the antennas connected to the antenna switch when they are in use by the main rig. That is actually a good thing. Two rigs in close proximity and running power could easily blow each others front ends.

There is one valid reason for running more than one feedline to the shack, diversity reception. That is using two receivers one one a vertical and the other on a horizontally polarized antenna to enhance reception.

My antenna switch uses three 12 volt 30 amp SPST relays and a four conductor control line. Two of the relays have thier coils wired in prallel to act like a DPDT relay. They are wired just like the Heathkit four position antenna switch but use an additional SPDT relay. The extra relay takes the normally #4 antenna selection and translates it into #4 and #5.

The control cable is an old landline phone line. It has red, green, yellow, and black conductors and is dirt cheap. Power to the relays is 14 volts provided through diodes and a rotary switch at the operating position. The diodes isolate the five selections needed to provide proper sequencing of the relays.

Key Line Isolation

Interfacing the keying line to an amplifier used to be very simple in the old days when transceivers used a spare set of contacts in their TR relays to do that job.

Today modern transceivers use solid state switching to key external amps. The solid state switching is quieter making QSK operation much more pleasent. Solid state switching is also less capable of handling the higher keying voltages found in older amplifiers.

There is no shortage of interface circuits to solve the problem. You can build your own or purchase ready made devices available at under $100.

We do not like spending our money on ready made devices when we can build them ourselves. We also dislike external boxes with their wire leads cluttering the operating area. So we build our own and install the circuit into the transceiver if at all possible. We feel the keying problem is caused by inadequate transceiver keying ability, not excessive amplifier keying requirements. Besides, if you have more than one old amp and you don’t want to build more than one higher voltage keying circuit, the circuit needs to go into the transceiver.

Most decent interface circuits use fets, transistors, and diodes. The diodes isolate the amp from the transceiver, the fets switch the higher amp keying voltage, and the transistors control the switching fet. All this circuitry can be replaced with one small relay. The relay provides superb isolation but introduces time delays that might effect QSK operation.

The circuit we employ uses opto isolators which provide the superior isolation while preserving high speed keying.

A 4N35 is energized from the transceiver keying line. As the keying line goes to ground, it takes the cathode of the opto LED to ground causing the LED to illuminate the opto output transistor. The output transistor collector goes to ground taking the positive bias off the PNP fet driving transistor. As the base of the PNP transistor goes to ground, it conducts and allows a positive voltage to arrive at the gate of the fet. The fet turns on and keys the amp.