Is a coax switch adequate?

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rcase
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Joined: Tue Jan 02, 2018 5:32 am

Is a coax switch adequate?

Post by rcase » Tue Jan 02, 2018 6:02 am

Hi
I just purchased the SDR RSP2 and would like to use it as a second receiver for my Kenwood TS2000s.

I plan to use the same antenna for RX and TX and manually switch between the RSP2 and my Kenwood with a coax switch. My antenna is a skywire loop in my backyard. I plan to leave the RSP2 on when I transmit, but the coax will be switched over to my Kenwood. Will this setup damage the front end of my RSP2? If so, what other measures should I take?

Thanks in advance for any advice.
73,
Rod
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Recordable
Posts: 16
Joined: Tue Jan 02, 2018 10:05 am

Re: Is a coax switch adequate?

Post by Recordable » Tue Jan 02, 2018 10:40 am

Hi,
I do not know if it is adecuate. I´ll try it.
I bought some coaxial switches from electronic trash shop to make a switching box.
I plan to switch my new (two days old ) SDRPLAY dsr1a
I am in the process of adding a IF tap to my Kenwood TS-480 SAT to use it like a panadapter.
The coaxial switches only switch two positions so I ´ll put two of them to switch to three devices.
I plan to switch the antenna or two transceiver or receivers IF tap.
The switches are good quality because are from broadcast satellite modules.
some work on 12 volts some on 24 volts. all are SMA connector fitted.
Time will tell... I suppose we can see the losses directly by comparison after/ before the switch is in line.
Happy New Year...¡¡¡¡¡
I realyze you are going to share the antenna during transmision, so beware of damage..¡¡¡¡ you need a different solution than mine...¡¡¡
Last edited by Recordable on Tue Jan 02, 2018 11:15 am, edited 1 time in total.

Recordable
Posts: 16
Joined: Tue Jan 02, 2018 10:05 am

Re: Is a coax switch adequate?

Post by Recordable » Tue Jan 02, 2018 11:08 am

I realize you are going to use it during transmision and not by a IF tap.
In the case of sharing the antenna (during transmission) using a manual switch, check the antenna switch shorts the SDR section.
Not all the switch does.
(This can be problematic with the transceiver if shorting the transceiver section during transmision).
this is the minimun I shuld check.
I shuld add a static dischage device like a small neon lamp in the SDR entrance.
Some transceivers have a separate recepcion antenna input. in that case is not risky to share the SDR using a different antenna.
There are switching devices controlled like the ELAD switching box that do the job of switching protecting the receiver. you shuld check them.
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Recordable
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Re: Is a coax switch adequate?

Post by Recordable » Tue Jan 02, 2018 11:19 am

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Roger
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Re: Is a coax switch adequate?

Post by Roger » Tue Jan 02, 2018 9:26 pm

Your transmitter has a max power output of 100W or 50 dBm

The RSP2 has a maximum input of 0 dBm continuous or 10 dBm over a short period on all the ports.

So to be safe your switch needs 50-0= 50 dB of isolation. I have a quality Daiwa switch which shorts the unused inputs to ground and it claims to have 70 dB of isolation. I measured it and found it close to that value so it works OK.
Other switches may be better or worse and some like MFJ may not spec the switch at all.

If you are building your own switch or buying one I would do the following test. I would run your TS2000, using the switch, at the lowest possible power level (1 watt?) and measure the signal level using SDRUno and your RSP. With 1 watt out of the TS2000 you have a 30 dBm signal and with the minimum 50 dB isolation you should read no more than -20 dbM which is 53 dB over S9. If you get more than that the switch is not acceptable at 100W.

One other note. When you finish transmitting it will take some time for the AGC circuits in SDRuno to recover if you quickly switch back to receive. A more elegant solution is to use a relay switch which is activated by the send output on your 2000 and to setup a CAT control link between the 2000 and SDRUno so that you can automatically switch back to the SDR after transmitting. There are commercial products from several vendors that do the job nicely. This has been discussed extensively on the SDRPlay and SDRuno Facebook groups and there may be some posts here on the SDRPlay forum.
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Recordable
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Re: Is a coax switch adequate?

Post by Recordable » Tue Jan 02, 2018 10:53 pm

Here is demo of a commercial devicefor safe switching:

https://www.youtube.com/watch?v=eoDgQECGhsE
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rcase
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Re: Is a coax switch adequate?

Post by rcase » Wed Jan 03, 2018 6:20 am

Thank you everyone for the very helpful advice. I think that I will get the switch from Dx engineering rather than risking it with my coax switch.

Best,
Rod
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