RX-TX switch for SDRPlay

Post information or questions regarding SDRplay products here
KE2KB
Posts: 17
Joined: Fri Dec 02, 2016 1:11 am

RX-TX switch for SDRPlay

Postby KE2KB » Sat Mar 18, 2017 12:29 am

Hi;
i want to use my SDRPlay (RSP1) on the same antenna I will be using to transmit on. My rig is Heathkit HW-101 (vacuum tube) @ 100W PEP max.
I want to be 100% sure that the transmitter cannot be keyed while the SDR is connected to the antenna, and I want the SDR to be grounded while not connected to the antenna.

There are several methods I can use, but I would like to get some input here.

Thanks

Frank - KE2KB

Reason: No reason

dsalomon
Posts: 51
Joined: Sat Oct 10, 2015 1:50 pm

Re: RX-TX switch for SDRPlay

Postby dsalomon » Sat Mar 18, 2017 9:18 am

A manual coax switch is inexpensive. But you have to remember to switch it. A coax relay is a more expensive option, and will switch automatically. Another option are commercial devices made for ham radio that will automatically switch and ground. A few examples.

https://www.dxengineering.com/search/pr ... =Ascending

https://www.dxengineering.com/search/pr ... =Ascending

For any automated solution, you have to make sure the switching is fast. If the relay isn't faster than the RF energy, you have a problem. I use the DX Engineering RTR-1A (the predecessor to the current RTR-2). My transmit antenna is very close, i.e. within 20 feet, to my receiving antenna. I often run legal limit. It has never failed me. An added benefit to the DX Engineering model it that it also has a limiter built in. When the receiving antenna is connected, it caps the RF to safe levels, but not low enough to impact the incoming signal.

Good luck with your search.

73 - David, AG4F

Reason: No reason

KE2KB
Posts: 17
Joined: Fri Dec 02, 2016 1:11 am

Re: RX-TX switch for SDRPlay

Postby KE2KB » Wed Mar 22, 2017 9:22 pm

I have found several solutions online using a small relay. But as you said, the relay needs to switch out and ground the receiver before any RF from the transmitter reaches it.
I'm running an HW-101 with up to 100W output. I'm thinking I could use an inexpensive external relay to switch out and ground the receiver, and also switch the transmit relay using contacts in the same relay. I can introduce a short delay in the line to the transmit relay coil that would guarantee that the transmitter is not turned on before the receiver is off-line.

Is there any specific relay type I should use so that a 50 ohm impedance is maintained?

Reason: No reason

W2DLC
Posts: 13
Joined: Tue Apr 04, 2017 1:51 pm

Re: RX-TX switch for SDRPlay

Postby W2DLC » Thu Apr 06, 2017 1:58 pm

I'm using the K8IQY magic box. Unfortunately, the kit is discontinued, but you may be able to find one used for sale, or build one from the documentation. It makes any transmitter/receiver combination act like a transceiver.
http://www.4sqrp.com/MagicBox.php
Last edited by W2DLC on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
Reason: No reason

W2DLC
Posts: 13
Joined: Tue Apr 04, 2017 1:51 pm

Re: RX-TX switch for SDRPlay

Postby W2DLC » Tue Apr 11, 2017 12:32 am

I should mention that this Magic Box has worked well with my other communications receiver, but with the SDR, it still gets sufficiently overloaded that the audio section takes several seconds to recover. I still haven't solved this problem. It's too long a recovery time for CW. The Magic Box itself has full QSK and cuts the transmitter feedback by 80dB. The RF section of the SDR1 seems to recover instantly, but the audio section remains muted for 5-10 seconds.

Reason: No reason

W2DLC
Posts: 13
Joined: Tue Apr 04, 2017 1:51 pm

Re: RX-TX switch for SDRPlay

Postby W2DLC » Sat Apr 22, 2017 7:01 pm

The new API seem to have resolved the recovery time problem. It now recovers immediately after transmitting. I have also found that I can reduce the AGC a lot more and still have good sensitivity for CW reception. I leave the LNA at minimum.

Reason: No reason


Return to “SDRplay related”

Who is online

Users browsing this forum: No registered users and 1 guest