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eHam Forums => Station Building => Topic started by: F4GFT on February 14, 2023, 02:27:58 PM

Title: Using Yaesu FAS-1-4R as a transceiver switch (rather than an antenna switch)
Post by: F4GFT on February 14, 2023, 02:27:58 PM

I am using an Yaesu FAS-1-4R as a remote antenna switch for many years, and am very happy with the unit. I have another one and wonder if I could use it to switch between two transceivers, with sufficient decoupling to not fry the receiver of the #1 transceiver while sending on #2. I cannot find specs for using this switch as a transceiver switch (rather than an antenna switch). Any experience? I do not run an amplifier, just the stock 100W. If the Yaesu FAS-1-4R is not suitable, what would you recommend for the task?

Andy F4GFT
Title: Re: Using Yaesu FAS-1-4R as a transceiver switch (rather than an antenna switch)
Post by: WA3SKN on February 14, 2023, 02:44:04 PM
ALL ports are shorted(grounded) until a relay operates... so only one radio could be used at a time.
Will that work with your plans?

-Mike.
Title: Re: Using Yaesu FAS-1-4R as a transceiver switch (rather than an antenna switch)
Post by: W3PX on February 14, 2023, 03:37:30 PM
If you had access to a Nano VNA or could purchase one, you could measure the port to port isolation and know for sure.
Title: Re: Using Yaesu FAS-1-4R as a transceiver switch (rather than an antenna switch)
Post by: F4GFT on February 15, 2023, 03:02:14 AM

>ALL ports are shorted(grounded) until a relay operates... so only one radio could be used at a time.
>Will that work with your plans?

Yes, I think so. I would like to be able to use the radio with the shorted port on its port#2 for 6m monitoring (the 6m antenna is some 35ft away from the HF antennas), but that's another story.

>If you had access to a Nano VNA or could purchase one, you could measure the port to port >isolation and know for sure.

I can get my hands on one; I did not know these things also measured isolation. Is it safe to assume that at least 60dB are required? One of the radios is a FT-950; I heard the FT-2000 had a somewhat fragile input stage. The other is a TS-930, no idea about the ruggedness of its receiver.

Andy F4GFT
Title: Re: Using Yaesu FAS-1-4R as a transceiver switch (rather than an antenna switch)
Post by: W3PX on February 15, 2023, 03:13:44 AM

I can get my hands on one; I did not know these things also measured isolation. Is it safe to assume that at least 60dB are required? One of the radios is a FT-950; I heard the FT-2000 had a somewhat fragile input stage. The other is a TS-930, no idea about the ruggedness of its receiver.

Andy F4GFT

To test the port-to-port isolation of your switch, you would use the Nano VNA to measure S21, transmission between the two test ports.

A 100W signal (+50 dBm) present at one port of the antenna switch, with a port to port isolation of 60 dB, would present a -10 dBm signal at the second port.

Check the receiver maximum input level spec for your radios to be sure.

73 Frank W3PX