When I was carrying out tests on 40MHz ISM I always had a attenuator inline which reduced the receive capabilities too. My first attenuator which I'm ashamed to admit used 1/2watt resistors but it was all I had at the time, I placed an ordered for 2watt rated ones but due to Royal mail strikes the post was delay and I wanted to get on with the local range tests.
Quickly thrown together attenator : ( |
This morning the post arrived and in the bag of components I ordered were the 2 watt rated 100ohm resistors and I was able to rebuild and update the attenuator to a switchable one.
I had bought three old "non working" microwave modules converters mainly for the enclosures off ebay for £5 with the plans to repurpose them for other projects. New boxes this size are around £3-4 plus they had BNC's, other hardware and trimmers/parts that can be reused too.
I wanted the 20dB attenuator to only be inline when in transmit and bypass it on receive so decided I could use the the "TX GND" and "13.8v" pins from the ACC socket of the FT817.
Parts I used were:
MM Enclosure,
5v relay from the junk,
6 x 100 ohm resistors (2 Watt rated),
1 x 100 ohm resistor (1/2 Watt ratedfor 5v relay),
1 x 1N4001 diode,
2 x BNC connectors,
Pieces of wire,
FT-817 ACC mini din,
Copper clad board
The New 20dB attenuator with relay |
All connected to the power meter/dummy load |
Meter on 1000mW scale showing 10mW out with 1W in from FT817 |
So far the old microwave modules enclosures are getting used and this will allow me to monitor the without having to keep removing the fixed attenuator.
Update: 1452hrs
I decided to add a TX LED on the attenuator just so I know power is getting to the unit and it's changing over the relay.
Back in the loft, I can remote control it from the shack via VNC
Update: 1459hrs
Thought I would leave it beaconing on WSPR for part of the day. Hoping to do a longer range test tomorrow (weather permitting).
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