• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:
    https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html

Antennae in close proximity

superdeez

Member
Joined
Jun 3, 2017
Messages
10
Hello, all. I have a question regarding my home and mobile setups, which are similar in nature.

In both home and mobile, I have both a 2m and an 11m (CB) radio setup. In the car, the 2m and CB antennas are aboue 2.5 feet from each other and at the house they're about 6' apart. If I have a QSO on 2m, I turn the RF Gain on the CB radio down to zero in an attempt to mitigate high levels of RF coming into the radio, but I recently noticed that the CB's meter was rising to a 1 when I keyed up the 2m radio.

Do I still have to worry about cooking the front end of the CB running my 2m rigs at 10W? The antennas in questiion are correct for their respectrive bands. Additionally when mobile, I have a third radio that I just use as a receiver via another 2m antenna, but I have attempted to shield it from high RF levels by placing an RF limiter designed for SDR radios in the coax.

I'm just curious everyone's thoughts if I could be causing equipment damage or anything better I could do. Will putting the RF Gain to zero actually reduce the RF that is reaching the front end of the CB?
 

Golay

Member
Joined
Apr 28, 2016
Messages
330
Location
Nankin Township, Michigan
I think (at the house anyway) that antennas are far enough apart so that won't be an issue. I'm pondering if your issue isn't the antenna, but two feedlines next to each other, one inducing the other. Of course, the simplest situation is to only have one radio on at a time.
 

W5lz

Member
Joined
Feb 28, 2019
Messages
332
What you say is happening is about as 'normal' as it gets and I just don't think you have anything to worry about.
 

jwt873

Member
Premium Subscriber
Joined
Dec 1, 2015
Messages
862
Location
Woodlands, MB
I have my 2M/70CM vertical mounted about 2 feet above my HF beam.. (It's just above the driven element). I've run up to 600 Watts on 10M HF and up to 100 Watts on 2M. There hasn't been any interaction between them.antennas.jpg
 

Hit_Factor

Member
Premium Subscriber
Joined
Mar 6, 2010
Messages
940
Location
Saint Joseph, MI
I run a kilowatt on HF antenna about 6 feet above my VHF antenna. On my truck my two antennas are 3 feet from each other, running upto 100w.
 

superdeez

Member
Joined
Jun 3, 2017
Messages
10
Thank you for the replies. I take it that it shouldn't be an issue if the power is kept low?
 

W5lz

Member
Joined
Feb 28, 2019
Messages
332
I'm not sure low power is the best preventive for one interfering with another until the distance between them get's to be very large. The 'other' antenna is going to have some power put into it. Until it makes a noticeable difference, I don't think you really have anything to worry about.
 

mmckenna

I ♥ Ø
Joined
Jul 27, 2005
Messages
10,789
Location
SNCZCA01DS0
I've run a 50 watt VHF radio in my old truck with a 1/4 wave antenna in the center of the roof. 2 feet behind it was a CB antenna. Ran that way for many years, no issue.
I doubt you'll have any problem.

As said, turning down the RF gain won't protect the radio if it was going to be an issue.

But, there are variables. Power, antenna gain, coupling between antennas, feed line losses, durability of the receivers, etc. There really isn't a "right" answer without doing some actual hands on testing.
 

ab3a

Member
Joined
Oct 8, 2007
Messages
319
Location
Lisbon MD
The front end of some transceivers often have switching diodes, where one diode goes in to conduction for transmitting while the other goes in to blocking to keep the signal from damaging the receiver. These switching diodes may be getting forced in to conduction by a powerful nearby signal. You won't notice much, but you may be reradiating harmonics because of it. So for example, if the two meter radio goes key down and you see some meter movement on the CB, that CB radio may have the switching diode getting forced in and out of conduction by the nearby signal. This could cause you to radiate harmonics on higher bands such as 292 MHz or 438 MHz.

The only way you'd know this was happening is to look for the extraneous signals. If you know someone with a half decent SDR such as an Airspy or a spectrum analyzer you can look for the two meter signal from a distance to see if it meets specification (I think spurious signals are required to be at least 40 dB down from the main signal). You can then disconnect the CB radio from it's antenna and try it again. If you see those spurs disappear you'll know that this is likely a problem.

Most of the antenna systems cited above have horizontal polarization on one antenna and vertical polarization on the other. If they're both horizontal or both vertical, you are likely to get more coupling between the antennas.

This is something that may be so intermittent that nobody notices what's happening. However, if it is happening, it is incumbent upon you to remedy the situation with filters, grounding switches or some solution.

73,
 

superdeez

Member
Joined
Jun 3, 2017
Messages
10
In an effort to protect the CB, I've bought a low pass filter. Since I put this 23 channel unit in I've been getting some minor interference on 2m, so perhaps this will remedy that also. Still waiting for the filter in the mail.
 
Top