Protecting RX-only Antenna from Nearby Transmit Antennas (

[@Roddy1965]

The inverse-square law only works in the far field of a finite sized radiator. Antennas radiating wavelengths at 10m, say, may not even begin to form far-field antenna pattern and inverse-square drop off for at least 100m-200m, so it might work on a farm, but not a suburban lot. It will be worse for longer wavelengths.

[@watthairston1483]

Thanks Dave, another great very informative video. The 1N4448 is the higher current version of the 1N914 also slight leakage current improvement; however, 1N914 is good in 99.9999% of the cases. Those A/D antennas are indeed "tanks" excellent store-bought antenna.... 73' de K4WRF

[@antoninyang7719]

Excellent idea, using a schottky diode can limit to 0.3 volts. I use same in audio cable out from my QCX, which has no AGC, as a limit to protect my ear.

[@davidsradioroom9678]

This is something I had never thought of before. thanks for sharing.

[@mikemcnamara4326]

Thanks for all you do Dave!

[@gussys]

It was a nice surprise to find this chanel . I’m a brand new tec just down the road in Montrose.

[@TFuzz58]

Excellent video. I was wondering how to do this when I do a loop. By the way, I put my DX Commander up in the back yard and got my first two HF contacts. First one was Fort Collins CO and the second was Redding CA. Noise floor isn’t as bad as I thought it would be. Cheers from Moose Jaw. Tim VE5THF

[@DAVIDGREGORYKERR]

What about a double pole double throw relay that can be turned on when transmitting and off when receiving in such a way the relay will disconnect the loop from the antenna preamp.

[@timmack2415]

Generally, the time delay in a traditional relay doesn't make it a good choice.

[@johnkiljan7441]

I have a Chinese MLA-30+ receiving loop with a bias-T powered pre-amp. I use it a lot for monitoring and it is right next to my transmitting antenna. Looking at the circuit diagram, I see that it already has back-to-back silicon signal diode protection built in. Plus, it is non-resonant, and that greatly reduces the amount of current going into the pre-amp. So I don't worry about it. For field day with multiple radios operating on different bands in a small field with resonant antennas, this can be a real danger to a transceiver's or receiver's front end, whether through a pre-amp or not. Like lightning strikes, these kinds of induced currents can burn out a coil or the first RF amplifier. One can buy RF overload protectors for receivers, but they are expensive. I think DX Engineering sells one for about $70. I built my own for my receiver just using parts from the junk box. I used the two back-to-back silicone signal diodes Dave mentions (I think the 1N914's are obsolete now, but anything similar will work), and then another pair of small power rectifier diodes (1N4007's) with that as well in case one of the small signal diodes opens up during an overload. In addition, as another commenter suggested, I wired in a small 0.2 amp penlight bulb in series to my circuit to act as a combination current limiter/fuse. One can find circuits for these kinds of protective devices online if you search for them. If you can't and want to build your own, just email me using my QRZ address and I'll send a circuit picture. -- John N0BUP

[@kosmasdorschel4936]

Thank you. I didn't know that. I will send you an email.

[@PapasDino]

Many modern radios include protected inputs for receive-only antennas which solves the problem. Even the IC-7300 has a inexpensive after-market modification to accept a receive only antenna and protects the front-end. Boatanchor transmitter/receiver combinations used relay based T/R switching which could also protect a separate receiver's front-end. 73 - Dino KLØS

[@francismcclaughry3794]

Dave I have a g5rv and I can use it all bands with a tuner.

[@peter360adventures9]

Ok my question is ok I can use this as a shunt on the sdr as my HF rig is in the same room would it be wise or not wise to transmit in CW.

[@g0fvt]

FWIW I have used back to back LEDs for the same purpose giving a higher threshold, but of course the front end of the receiver is subject to more signal before clipping occurs. It was an unusual situation sharing a roof with someone else running 100w on the same band as I was on. FWIW cross polarisation can also help reduce the levels at the receiver. Most CB radios use a combination of the back to back diodes and a small coupling capacitor in their receive circuitry to protect them from the transmitter, ham rigs tend to disconnect the receiver when on transmit. I suspect for your loop example the IN914s would be great solution but BEFORE any associated pre-amplifier. 3

[@CodeMasseur]

@Dcasler, suppose that we're not dealing with a RX-only loop antenna, but rather two EFHW antennas in close proximity. If one EFHW is transmitting and other EFHW is receiving, what is the technique to protect the RX EFHW? Do you insert a Diode directly into the feed line? Please advise, and 73 de W3DJS (Friend and supporter of your channel)

[@vironpayne3405]

Definitely worth the price of admission.

[@davidmeakins2915]

Can you transmit on an active antenna from Dave G4SCJ.

[@bobclarie]

Thanks Dave. I have two DX Engineering RF-PRO-1B receive only antennas. They are phased together with the DX Engineering NCC-2 receive antenna phasing controller. I use this system with my IC=7300. The bias-T for the RF=PRO 1B antenna has an RCA jack that allows you to connect it to the SEND jack on the IC-7300,or in my case, the NCC-2 which, on key down, will kill the power to the receive antennas pre amps. If you are using a receive only antenna with a pre amp that does not have a PTT/transmit to ground jack for power disconnect, one could build a simple interface relay to kill the power to any line powered receive only antenna. Thanks, '73 Bob

[@sphexes]

Good morning Dave. Thanks for the morning ham information with morning coffee. 73 W8XDX

[@daniell8387]

I picked up some of those diodes, I'm goign to try my 200' listening dipole again.

[@acestudioscouk-Ace-G0ACE]

Very useful! I'm sure a lot of people will find this simple solution very useful...Judging by the comments below this video, it may be worth a slightly more in depth video?

[@glenmartin2437]

Thank you, Dave. Have a great week. N0QFT

[@KuehncIncorporated]

Brilliant!

[@richardnalisnick462]

Great Idea! 73 W3SMT