Minimum safe transmitting antenna distance

[DavidRParticipant]

Can someone confirm these numbers?

I wanted to get an idea of how far a transmitting antenna should be from a connected SDRPlay. Under the table are the resources I used to calculate these distances, which are approximations. Assumptions are rigs in general use, 100W HF sets, 10W QRP HF sets, 50W mobiles for 2M/70CM, and common walkie talkies at 5W.

Assuming this is correct, it would seem impractical to have the SDR connected while operating an HF without some device disconnecting the SDR antenna, such as the MFJ device I have seen. It would appear that operating a walkie talkie is practical outside the distances below, which isn’t difficult to achieve.

Band Power Minimum safe distance (meters)
160M 100W 1500
160M 10W 500
80M 100W 800
80M 10W 300
40M 100W 400
40M 10W 150
30M 100W 300
30M 10W 100
20M 100W 200
20M 10W 75
17M 100W 150
17M 10W 50
15M 100W 150
15M 10W 50
12M 100W 150
12M 10W 50
10M 100W 100
10M 10W 30
6M 100W 60
6M 10W 20
2M 50W 15
1.25M 50W 10
70CM 50W 5
MURS (151MHz) 5W 5
FRS/GMRS (462MHz) 5W 2

https://www.random-science-tools.com/electronics/friis.htm

http://www.sdrplay.com/community/viewtopic.php?t=1355&p=4389

https://www.rapidtables.com/convert/power/dBm_to_Watt.html

using flat dipole antenna gain as 1.64

http://www.arrl.org/files/file/Regulatory/Band%20Chart/Band%20Chart%20-%2011X17%20Color.pdf

[Andy2Participant]

I use an HP RF limiter type 5086-7248. It will limit the RF arriving at your RSP’s antenna connector to a few mW. They are quite old now and obsolete, but can sometimes be found on the net. I’ve had mine since the 1980’s!

[N7BYDParticipant]

Andy, when I check the 5086-7248 it comes back as a mixer. Would the HP / Agilent 5086-7261 be a good choice? The question I have is it is rated at 0 to 2.5 GHz, 10 W, I am assuming that 10W would be max power it was rated to handle as input can’t seem to find what their output would be.

Thanks

Tom

[fresnoboyParticipant]

Hi. I think he meant the 5086-7284, not 48.

I can’t tell the difference between the 7248 and the 7261. Does anyone know where a datasheet for these parts can be found?

The goal is to limit input power to 0db right? I am doing planning to put a set of antennas on my roof, and I need to protect a couple RSP2s from a nearby Diamond 2M/70cm antenna with a transceiver that can do 50W out.

[kq4avzParticipant]

Can this really be true?? With these distances, what’s to keep someone in your vicinity from keying up on their ham radio and killing all the SDRPlays around them?? Nothing malicious — there’s just no way they could know. And the above is calculated only at 100 watt max. Legal limit, at least in the US is 1,500 watt.

[Author]

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