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No RCV Port? No Problem – DXE RTR-1A
8 January 2026 | by The Sweetness of Noise Free Copy
I have been using my Receive only Loop on Ground antenna at my station for the past few weeks. It was connected to my SDR through my receiver protection switch from OK1RP . That switch protects my SDR from overcurrent during transmit. I built this receiver protection switch from a kit nearly 8 years ago to protect my SDR when using it as the panadapter display for my Ten-Tec Eagle. Back then I didn't use the audio from the SDRPlay RSP1 for listening because it was connected to the noisy antenna in my attic so audio from it sounded worse than my outdoor antenna but the signal was sufficient to use as input to the panadapter.
But now, with the low noise, outdoor receive antenna at my station I can use the SDR as a receiver for listening during a QSO or just monitoring.
How you can use a receive antenna on a radio without a RCV port but with an outboard SDR?
For those of us that have radios lacking a dedicated antenna receive (RCV) port we need something able to listen to that the receive antenna that stays in sync with our transceiver. Software Defined Radios (SDRs) have become very common in our hobby and entry level, dongle style SDRs are quite affordable. They are receivers that connect to your PC via USB and generally offer wide receiver coverage. In the case of the SDRPlay RSP1 that I use, it makes an excellent outboard receiver. By syncing the SDR with the transceiver via OmniRig it tracks the frequency changes you are making from your radio. Additionally it can sync the radio frequency and mode when you work with the SDR software running on your PC.
The receiver needs protection
I had the FT-DX10's antenna port connected to my transmit antenna switch. That 2 position switch connected either my attic Doublet or the 80m OCF. The transceiver was not connected to the receive only antenna in any way in that configuration.
I listened to stations coming through the LoG Receive antenna through PC speakers generated by SDRPlay's SDRUno software rather than through the transceiver because the receive only antenna offered a greater signal to noise ratio. I turned down the AF volume on the FT-DX10 coming from the transmit antenna in order to hear only the receive antenna during QSOs. The sidetone volume is separate from the AF volume so having it down on the transceiver during a QSO was not an issue. Again, the transceiver was not connected to the LoG receive antenna so I couldn't use the radio controls during receive for filtering. SDRUno obviously did not offer the same features for shaping and adjusting the received signal as a dedicated amateur radio. It provided choices for bandwidth, NR and CW-Peak.
Switching from SDRUno to HDSDR
This is somewhat of an aside but I think it is worth mentioning. I have been using SDRUno with my SDRPlay RSP1 SDR for the past few years to "listen" to the SDR as a receiver. It works well enough but it has issues when I want to take the IQ output from it to software like CWSkimmer to provide a cluster server for stations I am hearing. When I set SDRUno to output IQ it offers a number of bandwidths but they are not consistent across the ham bands. For instance, 80, 40 and 20 offer 192 kHz as an available output bandwidth but 30, 17, 15 do not. If I need to change bandwidths it requires modifying the Virtual Audio Cable or configuring different VAC's for the different bands, etc. If I try using just 48 kHz for all bands that doesn't seem to work with CWSkimmer even though it has the option. So I have switched to use HDSDR since it supports the 192 kHz bandwidth IQ output for all bands. It also doesn't seem to lose it's mind when the computer goes to sleep like SDRUno. YMMV.
Anyway, let's get to the point
This setup has worked pretty well, but I really wanted to hear the Receive antenna directly through the transceiver to make use of all the additional filtering and controls it brings to the table. Also, listening to the receive audio from the PC when I'm working a station just feels a bit disconnected from the normal process of using the transceiver. I also wanted to continue to feed the SDR in parallel with the transceiver to have the panadapter and local cluster server functionality. I couldn't do that whilst using the SDR as an audio receiver. I needed more stuff.
The DX-Engineering RTR-1A
There was a new-in-box DX-Engineering RTR-1A available on a famous auction site. This is the discontinued version of what is now sold as the RTR-2A. I actually prefer the connections offered on the older switch plus it was far less than the cost of a new RTR-2A. These switches don't come up used very often so beggars sometimes can't be choosers, although I'm sure something will pop-up for a steal now that I've purchased one.
The RTR-1A is a switch designed to allow a transceiver such as the FT-DX10 that only has a single antenna connection to make use of a Receive Only antenna. It offers additional protection that a traditional transceiver with Receive Antenna ports does not have, because most transceivers simply ground the Receive antenna but don't offer any additional current protection coming in that port during receive. The RTR devices not only switch out the RCV port during operation they also offer active front end protection on the RX ANT IN port while sending the signal to the transceiver antenna input.
For convenience it has a choice of 2 types of RX ANT IN connections, not for using both at once.
The two RX ANT IN ports are in parallel
This is important to note. I initially thought that the 2 RX ANT IN ports were isolated from one another so that I could run the RCV antenna in one port and feed my SDR from the other RX ANT IN port. But if I'd simply read the label "literally" it would have been clear even without reading the manual. Those are both RX ANT IN, not OUT. They are in parallel. If you run a connector to the SDR antenna input from the RX ANT IN port you will be loading the input and significantly reducing the sensitivity of the receive antenna. Additionally, the SDR is not protected from transmit currents if you connect it in parallel with the receive antenna. Whatever is received on the RCV antenna entering that port will be passed straight through to the other connector. Since there's no protection, your SDR becomes a Red Shirt.
Because of this I can't feed my SDR with the receive antenna while using the RTR-1A without using a RF-splitter. Instead, I am using MAIN ANT OUT to route signals to the SDR for panadapter and skimmer logging only. I lose the nice receive functionality directly on the SDR with this configuration.
I could purchase or build an RF Splitter to use ahead of the RX ANT IN to split the output to the SDR. If I did I would need to also use my OK1RP antenna relay protection switch to disconnect the SDR. That would mean more than double the wiring, plus I would lose a minimum of another 3 dB on receive due to the splitter, and unless I buy a high quality HF $plitter from mini-circuits or DXE the lack of isolation would likely cause even greater losses due to loading across the circuits. I researched making a 1.6 MHz to 60 MHz HF splitter with 30+ dB separation and it involves building a very tight circuit. Even a couple extra mm of wire change the circuit inductance. I just don't think I'm up to that. Maybe I'll get a good splitter for my birthday, but for now I'll just use the TX ANT OUT to route to the SDR for panadapter use. I love our hobby but it seems I always am one part shy of my optimal solution. One thing I will say is that I learned a lot about RF splitting while researching the topic. It's a heck of a lot more than building a Y-cable.
Connecting the RTR
Let's get this wired up. More cables and wires at the station. Who doesn't love more things to connect and get tangled up? Even better, who doesn't love having to connect things with dissimilar connections? I'm fairly confident that I have over 25 adapters for RF and DC connector types yet I still have to order more adapters for every new project. I never have just the right single adapter and end up having to connect 3 - 4 adapters in series to get the combination I need. But I digress.
Connections on the RTR-1A switch
- The main TX antenna goes to the connector helpfully labeled MAIN ANT IN. It's a PL259 to help insure that you are connecting a real antenna there, especially if you are trying to connect things in the blind (not advisable).
- The Receive Only antenna goes to either of the RX ANT IN ports. One is a female F-Type connector commonly used for TV / cable coax. That is the one I am using with the coax coming in from the LoG antenna. Additionally I have a quick disconnect F-Type on the end of the coax so I can pull it free when I'm not at the station.
- I run a cable from the MAIN ANT OUT port to my SDR, in-line with a passive diode based front-end protector. The switch is supposed to offer protection for the SDR on disconnect, but I'm paranoid. That ends up being a RCA male to male phono cable to the front-end protector, which outputs to a male to BNC female adapter, which connects to a male BNC to male sma cable to the SDR (whew!)
- The next port connects the switch to your transceiver and is helpfully labeled RADIO. Connect the ANT port on your transceiver to this connector using a male to male PL259. Since it is also PL259 that helps you avoid connecting non-radiating bits to radiating bits.
- The last connection is labeled TRANSMIT GROUND. This connection is what tells the switch to switch from RX ant to TX antenna. It uses a RCA plug style connector to ground the center pin to shield when the radio goes into transmit. It can ONLY work with a connector that goes to ground, no positive voltage keying. My Ten-Tec Eagle had a TX GND RCA female connector built right into the back of the radio but as I mentioned above you will need to take the appropriate wires from the SCU-28 port on the Yaesu FT-DX10 (pin 2 to ground) for which I built a break out box from the SCU-28 with the appropriate connectors.
- Lastly the switch needs 12v DC power to operate. You could take that from the radio's SCU-28 cable or from an external supply assuming you have a common DC ground. If the switch is not powered it defaults connecting the MAIN ANT IN port to the RADIO port and grounds the RX ANT IN and MAIN ANT OUT ports, thus saving your SDR. If the switch is unpowered nothing goes out the MAIN ANT OUT port so my SDR sees nothing.
Okay that was simple right? The transmit and radio cables are using PL259, the switch is using RCA, F-Type and PL259 (and a barrel for power), the receive antenna has a F-Type and the SDR has a female SMA. If I add a splitter; well I'm not even going to go into all the additional connection adapters and cables I'd need.
All this so that we can participate in a hobby that communicates wirelessly
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| Connections |
In operation
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| Noise free reception |
My LoG receive antenna is about 9 -12 dB down on receive compared to the 80m OCF. So in most cases you want at least the first preamp on and sometimes the second preamp engaged although PRE-1 is usually sufficient. There is so little noise on the LoG that all you are really bringing up is the signal when you turn up AF. However when switching back to the main antenna you will be hit with a wall of sound and the waterfall will just turn white with the preamps engaged on lower bands.
I wish there was a dedicated button for the preamp on the DX10. It requires leaving the EXTEND menu up and touching the screen to change preamp settings. I have to touch it twice, once to get the IPO menu and the next to choose the setting. I may look into getting a LNA to run prior to the RTR for convenience of not having to mess with the IPO menu. I searched but I see no CAT command that I can send that will change the IPO setting from the computer.
Many signals from the LoG are so clean that they are completely copyable without budging the S-meter. I had lengthy ragchews with 3 stations today on 30m using my attic antenna (my only efficient antenna for 30) that were completely buried in the noise of my attic antenna. I was receiving 549 to 579 reports from these invisible stations. The Doublet in my attic is good for transmit but blinded by noise on receive, so the LoG is a complete game changer for me on WARC bands. It's also far less impacted by static crashes on 80m than the OCF.
Similarly, this evening I worked 6 WWA stations (II3WWA, CR6WWA, VE9WWA, YO0WWA, SN4WWA, EG1WWA) on 40m in quick succession where I couldn't reliably copy 3 of them on my 80m OCF but could hear them on the LoG. I'm flabbergasted at how much this changes home station operation.
So lower your power and power your radio with receive antenna switch
72/73 AA4OO
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