Auto switching between TX and Rx antenna
I have a Yaesu FT450 which has only one antenna port.
On the 30m band I have an inverted L as my TX antenna and a homebrew magnetic loop as my RX antenna. The magnetic loop works much better for receiving and eliminates most of the noise the inverted L picks up.
However its a pain manually switching my coax switch every time.
Can anyone recommend an off the shelf automatic switch or a homebrew solution.
Might look at this. You still need a relay, but this would switch the relay for you:
Here's one that does that job exactly:
Of course you could homebrew an equivalent, or modify the transceiver to add a separate RX antenna port.
MFJ sells a switch that will let you plug in your two antennas:
I've never used it so I don't know how good it is.
Originally Posted by WB2WIK
This is what I use, works just fine.
Even cheaper & simpler is an SPDT relay, driven by the rig's amplifier relay output. At 100W on HF, K1 can be a small relay like this one (coil = 12VDC@33mA). Drive it with your FT-450's amplifier relay output (50V@400mA max) to the "RIG PTT" input shown. D1 (1N4001, etc) prevents back-EMF from exceeding 12V. Run your rig's antenna through the relay contacts. When the contacts close, you're connected to one antenna and when they open, you're connected to the other antenna. Use an SPST switch (S1) to enable or disable it. Mount it all in a metal enclosure with short leads to/from the relay contacts or short bits of coax.
You can't use RF sensing or the relay will hot switch on leading edges. The relay has to be actuated from the PTT line or the amplifier keying line, otherwise it will switch while RF is present.
Originally Posted by KF5FEI
Many thanks for all the replies.
I'll probably go with the DX engineering RTR box which will have to be switched from the TX ground out on the linear port of the FT450.
Here is another approch.
Using an Ameritron 8 port remote switch; I am just now completeing an add-on box to enable the use of the high half of the ports 5 to 8 to be used for special receive with auto switching.
The circuit allows any of 16 combinations of transmit/ receive to be dialed in and used with auto switching as well as a way to give the other station a signal report off either antenna on a ''momentary switch' basis.
This box uses 3 bit binary control referenced to ground of the remote relays such that my add-on box wires as an intercept to the main box to use the same binary signals on the high ports 5 to 8 on a selector control basis plus main box selector 1 to 4, in combination.
No mods to the original control are needed and with the Aux box switched off the main control box is reverted back to with it's full 8 port manuel control.
It requires 3 dpdt relays, dp 6 port rotary switch and a diode copy of all the same diode matrix signal selections used by the main control box to address the port 5 to 8.
Do a chart of what signals appear on the terminals 1,2 and 3 to ground vs the selector position from one to 8 and build the same diode matrix of the ports you want to switch to, then for Xmit just release the relays to allow the pass-through of the signals for the selected Xmit port.
Of course you still have to supply 12 volts to operate the remote relays in either mode.
Auto switching is done with a port box used to key my other amplifiers that always provide "slaved" switch ground when the rig is keyed.
There is no RF in this type of control. It's all outside at the remote switch box.
My idea is still the simplest and by far the least expensive solution that will do what he wants.