RX antenna port isolation in TX

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  • Updated 2 years ago
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Hi does the Flex 6000 series ground the RX antenna on TX, or do I need to use a front end saver device??

something along the lines of this ??

http://www.qsl.net/wy3a/Front-End-Saver.htm

Thanks
Trevor
EI2GLB 
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trevor dunne

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Posted 2 years ago

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N5BE

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Trevor

I have a separate Receive Antenna that feeds a MFJ 1026 noise cancelling comparator in-line with my 6300.. It's keyed by the PTT to disengage for protection; there is an adjustable delay as well. In the mode of "suspenders & belts" I have also installed a Array Solutions surge protector: 
https://www.arraysolutions.com/surge-and-rf-protection/as-rxfep . As someone who has blown out the front end of my K3 years ago I'm very sensitive to what you are asking. As an aside the MFJ 1026 is a big difference maker here in the DX wasteland of Texas. It allowed me the "hear" and work two good contacts, Algeria and South Pole! My receive antenna is in close proximity to my resonant 40 and 80 meter horse fence dipoles so I opted for layered protection.

Best regards,

Lee
N5BEG
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KY6LA - Howard, Elmer

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The 6700 is a FULL DUPLEX Radio with more than adequate port isolation without any additional equipment needed

I have been running my 6700 for years without anything extra and see no issues whatsoever
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Milen KG2C

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Howard, I'm guessing this assumes suitable distance between the antennas connected to the 7600 when you are running it in full duplex mode. If you connect rf watt meters on both ports, how much power do you see coming back from the receiving port when you transmit on another port?
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KY6LA - Howard, Elmer

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From my beam I run about 12KW ERP with the amp on.

No issues whatsoever on RX port on a plxel loop about 100' away about 30' below thebeqm or dipole on ANT2 65' below the beam and about 50' away

The 6700 is also designed for SO2R without any external devices

IiRC the antenna ports have protection at about 19(?) dBm.
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Paul - K6HR

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I once observed my 6300 go into a protection mode when I had exceeded the input threshold for the receiver. 6000 series radios monitor the antenna input and prevent overload from damaging the radio.
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HCampbell WB4IVF

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Here’s a good previous discussion on front end protection and devices, including comments from Flex:

https://community.flexradio.com/flexradio/topics/front_end_protection

Also, some interesting charts showing modeled coupling in watts between different types of antennas at various spacings, and 1KW transmitter power, courtesy of W8JI:

http://www.w8ji.com/antenna_coupling.htm

Front end protection devices may not be effective at some of higher levels, like 50+ dBm.

Howard
(Edited)
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Steve - N5AC, VP Engineering / CTO

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Official Response
In general there is 40-50dB isolation between ANT1 and ANT2 and >90dB between ANT1/2 and RX A, RX B or XVTR.  This is, then, added to the antenna isolation you have at your site.  If you have concerns about this, one of the good ways to test is to set your radio for 1W and then try combinations and measure what you see in the panadapter.  The radio is calibrated at 1W so you should be able to calculate isolation and extrapolate without any concerns.  There is also a worksheet to help you determine if you need more isolation here: FLEX-6000 FDX Power Calculation Worksheet
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Jim Bryce W5HFS

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See "Flex-6000 Signature Series  SmartSDR Software User Guide, Version 2.0.17" Section 32 "How to Operate In Full Duplex (FDX) Mode" (pp. 145 - 154) for details on isolation and protection and the 6000 series ability to operate full duplex, yet another forward looking design feature. Of course it's still a very good idea to have static discharge devices installed in your antenna feed-lines for EMF induced by lightening, other sources, or power line downed on you antenna.
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Trevor-EI2GLB

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Thanks for the replies, I have a 6500 so can't tx and listen at the same time, think I will use a front end saver to be safe,

See you on the low bands,

73
Trevor
EI2GLB
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Steve - N5AC, VP Engineering / CTO

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You do have full duplex on a 6500 also.  Click the FDX icon in the lower left of SmartSDR.  You must have the RX and TX antenna on separate ports of the radio.
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Trevor-EI2GLB

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That's interesting must have a look in the manual and see more about this,

Thanks
Trevor
EI2GLB
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Carl K5HK

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Steve,

I have a 6300 and want to use the Inlogis/DX Engineering broadband loop antenna for a low noise option?  Can I use antenna input 2 for RX and antenna input 1 TX safely.  I have about  100' seperation from the RX loop and the a Marconni T with elevated radials for 160m.

I also have a 6500 at my in town location and know it has Rx antenna function okay...maybe I need to switch that rig out here to my remote antenna farm location?

73,
Carl K5HK
Reno NV
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Tim - W4TME, Customer Experience Manager

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Use the power calculation worksheet to determine if you are OK.

http://www.flexradio.com/downloads/flex-6000-fdx-power-calculation-worksheet-pdf/