Can someone explain

[jazzboypro]

Hello all,

Weird thing happening here (at least it's weird to me) I have an R8600 connected to a discone antenna. The radio is listening to 51.449 Mhz FM (Monitoring 6 meter band). I also have my 7610 doing ft8 on 20 meter. The 7610 is connected to an EFHW antenna.

When the 7610 transmits, i hear someone talking in the 8600 and when the 7610 stops transmitting the voice stops also. The person speaking is a male speaking french and by his accent he is likely located in my province (Quebec). The signal is strong and i can hear him very well. It is not amateur radio talk. It sounds like a commercial radio or TV broadcast but i am not aware of any radio station using this frequency. Any idea what might be causing that ?

Many Thanks
73 de VA2FCS

 

[nd5y]

Intermod.

 

[kudzu_kid]

Possible 2nd harmonic of 102.898 (102.9 MHz) - is there an FM station around that freq?

 

[jazzboypro]

Possible 2nd harmonic of 102.898 (102.9 MHz) - is there an FM station around that freq?

There is actually a radio station at 102.9.

 

[vagrant]

With each Icom 8600 there is a man living inside of it. This also explains the above average cost of the R8600. Anyways, he is probably working his part time job when you aren't using the 8600.

 

[jazzboypro]

Any chances of damaging the 8600 when i transmit with the 7610 ?

 

[vagrant]

Indeed there are chances of damaging it. I use a Hewlett Packard limiter. Please note that it handles 0-1.8GHz. Here is a link to one on eBay and that price is fair. ( I use them with all my SDR/receivers/scanners and especially with my mobile receivers due to the proximity of my transmitting antennas. )

HP / Agilent 5086-7284 1.8GHz Limiter | eBay

Find many great new & used options and get the best deals for HP / Agilent 5086-7284 1.8GHz Limiter at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[jazzboypro]

Indeed there are chances of damaging it. I use a Hewlett Packard limiter. Please note that it handles 0-1.8GHz. Here is a link to one on eBay and that price is fair. ( I use them with all my SDR/receivers/scanners and especially with my mobile receivers due to the proximity of my transmitting antennas. )

HP / Agilent 5086-7284 1.8GHz Limiter | eBay

Find many great new & used options and get the best deals for HP / Agilent 5086-7284 1.8GHz Limiter at the best online prices at eBay! Free shipping for many products!

www.ebay.com

Thanks for the info. Just bought a few

 

[dlwtrunked]

Possible 2nd harmonic of 102.898 (102.9 MHz) - is there an FM station around that freq?

No. 2nd harrmonic is always twice the frequency. And lower harmonics are a myth. (There are times when when a transmitter uses a doubler and you might receive the pre-doubled frequency but those are so rare that it should not really be considered) What he descirbed is clearly intermodutlation ("intermod") where two signal have mixed to provide another frequency. This can originate in the receiver due to overload, in one of the transmitters (yes, the transmitting antenna can sometimes receive a strong signal and mix it with its own frequency...I saw that once in CT and they knew about it), and finally, it can even occur with loose metal connections, not part of that equipment, but receiving both signals and then being a non-linear conduction, add and subtract them. Find the other signal, then add or subtract multiples of it and his signal and you will find one of the results matches the frequency where is hearing hearing this happen. Chance are, he will not be able to stop this other that receiving and transmitting at the same time other than by adding a filter to the receiver to block hist transmitting signal to get that back down to a reasonable level. The limiter is a good idea but it only stops very strong levels that might damage the receiver but will not stop strong signal less than that which can cause other reception problem like intermod.

 

[jazzboypro]

No. 2nd harrmonic is always twice the frequency. And lower harmonics are a myth. (There are times when when a transmitter uses a doubler and you might receive the pre-doubled frequency but those are so rare that it should not really be considered) What he descirbed is clearly intermodutlation ("intermod") where two signal have mixed to provide another frequency. This can originate in the receiver due to overload, in one of the transmitters (yes, the transmitting antenna can sometimes receive a strong signal and mix it with its own frequency...I saw that once in CT and they knew about it), and finally, it can even occur with loose metal connections, not part of that equipment, but receiving both signals and then being a non-linear conduction, add and subtract them. Find the other signal, then add or subtract multiples of it and his signal and you will find one of the results matches the frequency where is hearing hearing this happen. Chance are, he will not be able to stop this other that receiving and transmitting at the same time other than by adding a filter to the receiver to block hist transmitting signal to get that back down to a reasonable level. The limiter is a good idea but it only stops very strong levels that might damage the receiver but will not stop strong signal less than that which can cause other reception problem like intermod.

Thanks for the explanation. I understand that this might be tough to avoid. My main goal is to protect the front end of my radios without having to disconnect antennas and/or turn off the radios all the time

 

[RFI-EMI-GUY]

Hello all,

Weird thing happening here (at least it's weird to me) I have an R8600 connected to a discone antenna. The radio is listening to 51.449 Mhz FM (Monitoring 6 meter band). I also have my 7610 doing ft8 on 20 meter. The 7610 is connected to an EFHW antenna.

When the 7610 transmits, i hear someone talking in the 8600 and when the 7610 stops transmitting the voice stops also. The person speaking is a male speaking french and by his accent he is likely located in my province (Quebec). The signal is strong and i can hear him very well. It is not amateur radio talk. It sounds like a commercial radio or TV broadcast but i am not aware of any radio station using this frequency. Any idea what might be causing that ?

Many Thanks
73 de VA2FCS

If you vary the frequency of your 20 meter transmission does the interference change or go away? If so it is intermodulation. You should be able to put a filter on the 8600 to reject 20 meters. However if the mix is occurring in the 20 meter transmitter, a filter will be needed there to reject whatever it is mixing with. IM mixes can be predicted mathematically with software if you know the signal frequencies .

 

[jazzboypro]

If you vary the frequency of your 20 meter transmission does the interference change or go away? If so it is intermodulation. You should be able to put a filter on the 8600 to reject 20 meters. However if the mix is occurring in the 20 meter transmitter, a filter will be needed there to reject whatever it is mixing with. IM mixes can be predicted mathematically with software if you know the signal frequencies .

I did not check what happens if i change the transmitter frequency. It should be fairly easy to reproduce this behavior and see what happens when i change the frequency

 

[jazzboypro]

Well i just got a refund for the HP/agilent limiter. The guy is out of stock....any other place to source them ?

 

[krokus]

I did not check what happens if i change the transmitter frequency. It should be fairly easy to reproduce this behavior and see what happens when i change the frequency

Any results from this test?

 

[jazzboypro]

Any results from this test?

Actually yes. The problem disappeared when changing frequency. It was a radio station north of my QTH.

 

[krokus]

Actually yes. The problem disappeared when changing frequency. It was a radio station north of my QTH.

Gotta love IMI. Glad you resolved the issue.