Multiple frequencies go active when mic is keyed

[ih784]

Good morning,

I the majority of vhf frequencies set as channels and am listening to them. However, If I key up a handheld roughly 300 feet away, numerous channels will break squelch, go active and remain active unless I manually adjust the squelch. I assume its bleed over of some sort? Is there any way to correct this?

 

[WA0CBW]

What radios and what frequencies?

 

[boatbod]

Your local transmission is overloading the front end of the sdr device causing intermod.

 

[G7RUX]

Your local transmission is overloading the front end of the sdr device causing intermod.

^this^

 

[ih784]

What radios and what frequencies?

Marine radio frequencies

 

[ih784]

Your local transmission is overloading the front end of the sdr device causing intermod.

Is there a way to remedy this?

 

[ecps92]

Is there a way to remedy this?

Don't key up so close to the Radios, or even lower the power or both

 

[ih784]

I understand. However, I am using 25 kHz bandwidth and the problem occurs. When I used 12.5 kHz bandwidth, I had no issue. This is for marine frequencies. I wouldn’t have thought a handheld would or should cause problems.

 

[G7RUX]

I understand. However, I am using 25 kHz bandwidth and the problem occurs. When I used 12.5 kHz bandwidth, I had no issue. This is for marine frequencies. I wouldn’t have thought a handheld would or should cause problems.

It is more an issue with the receive system. If you are using a preamp then this can make matters much worse or may even be the source of the problem itself.

Pop a 10dB attenuator in front of the receiver and see how that looks; if it is the receiver generating the issues then you should see a decent reduction in the level of the problem generated signals.

 

[prcguy]

Is there a way to remedy this?

What type of receiver is having the problem?

 

[ih784]

What type of receiver is having the problem?

It is more an issue with the receive system. If you are using a preamp then this can make matters much worse or may even be the source of the problem itself.

Pop a 10dB attenuator in front of the receiver and see how that looks; if it is the receiver generating the issues then you should see a decent reduction in the level of the problem generated signals.

I believe its an issue with the receive side. I am using an RTL-SDR v3. using SDRT. I imported the frequencies from RR and created the aliases.

 

[boatbod]

Cheap sdr dongles are highly susceptible to overloading due to the very limited filtering in their front ends. (You can't filter marine vhf if your device is intended to easily receive 30Mhz-1Ghz). Best you can do is add shielding and external filtering to reject strong local signals at specific frequencies.

 

[prcguy]

I believe its an issue with the receive side. I am using an RTL-SDR v3. using SDRT. I imported the frequencies from RR and created the aliases.

RTL SDR dongles are the absolute bottom feeders of receivers and very susceptible to overload and internal IMD generation. There is no fix but you can run the gain way down and probably reduce the problem but reception will suffer.

 

[ih784]

I bought an airspy mini and used it for the first time today. That thing is so much better. If I can figure out the frequencies I need, I may just run those. But, in the meantime I’m trying to nail that down and will have to deal with it. Thanks guys!

 

[G7RUX]

If you don't want to tune around much or to receive marine VHF on the SDR then you can just use a simple filter to reduce the issue.

 

[ih784]

Is there any particular one you might recommend?

 

[G7RUX]

Not really, it depends what you want to receive, what you don't want to receive and what sort of attenuation you require to make the SDR behave.

 

[dlwtrunked]

I understand. However, I am using 25 kHz bandwidth and the problem occurs. When I used 12.5 kHz bandwidth, I had no issue. This is for marine frequencies. I wouldn’t have thought a handheld would or should cause problems.

Bandwidth has nothing to do with it. You are overloading your receiver. The only was to stop doing that is to use lower power, use a better receiver, get the receive or transmit antenna farther apart, or add an attenuator to the receive system (which will weaken all signals). And you may not be able to satisfactorily do that. Yes, a handheld is low power, put close enough to the receiver, it has definitely enough power. Putting a filter on the receiver only will work if the frequencies are a couple MHz apart unless you want to spend some real money and end up with something quite large.