Safe distance between xmit and rx antenna on 6300?

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What is safe distance between xmit and rx antennas with a Flex6300 using Legal Limit power output? 

If I have a legal limit output on 1 antenna on ant1 output through an amplifier and ant2 port is a separate receive antenna, NOT in full duplex mode, is it safe to transmit 1kw+ while the rx antenna is in the near field. 

Example tx ant is a horizontal 900 foot loop with 1500 watt capability

rx antenna is a dipole for example with both the loop and dipole within 20 feet of each other. 

Are there any internal safety mechanism or relay activity that isolates the RX from the TX port during transmit operations? I am NOT in full duplex mode nor will I be while using amplified power. 

I just don't want to blow ant2 port in RX mode while TX on my amplified ant1 port. 

There are some nights on low bands where I rx better on a dedicated antenna other than the loop. 

Thanks! 
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Eric Owens

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Posted 3 years ago

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James Kennedy-WU5E

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DX Engineering sell a nice device I have on my FLEX 6500

DX Engineering Receiver Guard Electronic RF Limiters are the best limiter devices to choose when your receive antenna input could be subjected to high levels of RF. The DXE-RG-5000HD and DXE-RG-5000 are specifically designed to protect a sensitive receiver front-end against high levels of RF from nearby transmit signals. DX Engineering Receiver Guards are a must for multiple radio contesting stations and they provide low-cost front-end "insurance" in these common high-RF situations, among others:
- Receive antennas in very close proximity to transmit antennas
- Field-day operations with many transmitters in close range
- Multi-transmitter contesting sites
- Neighboring Amateur and CB operators
- Frequent high-power mobile encounters

Extensively tested and proven in real-world stations, now DX Engineering offers two Receiver Guards, to provide automatic protection for every receive equipment application:
- The new DXE-RG-5000HD works for all radios and offers the ultimate performance required by the upper tier of transceivers tested to have the best narrow-spaced third-order dynamic range or published RMDR (Reciprocal Mixing Dynamic Range). These transceivers include Elecraft K3 series, FlexRadio 6700, 5000A and 3000, Icom IC-7851, Kenwood TS-990S and 590S(G), TenTec Orion series, Yaesu FTdx-5000 series, and other radios with similar performance.
- The original DXE-RG-5000 offers excellent dynamic range and performance characteristics to cover the capabilities of all other transceivers and receivers.

At the heart of each Receiver Guard is a highly effective electronic RF limiter covering 500 kHz to 150 MHz with an insertion loss under 0.15 dB at 50 MHz and under 0.3 dB to 150 MHz. Their multi-stage design includes a gas discharge tube for maximum pulse energy protection. These are passive electronic limiters, not filters, so competitive contesting stations still use separate band filters. For example Receiver Guard limiter model DXE-RG-5000HD can reject 10 watts of catastrophic receive antenna feedline RF while passing a signal of about 87 dB over S-9, which is only 25 mw! That level is well under the point of front end damage. When there are high levels of RF on your receive antennas, DX Engineering's Receiver Guards generate far less harmonic noise than other limiters on the market, which allows your station to continue to operate safely and competitively. At normal HF signal levels Receiver Guard operates continuously with no effect on the performance of your station while providing the best possible protection for your radio.

Here are Receiver Guard features:
* Keeps stray high levels of RF from damaging your receiver input
* Ideal for separate 160 and/or 80 meter receive systems with large pulse and RF energy capture area
* Uses state of the art components for maximum protection of receivers
* Under 6 ns response time
* Multi-Stage protectio


it sells for about 85 plus shipping


I have my mine hooked up and working great


Jim

WU5E


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Mike Aust

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Got both the DXE Receiver Guard Limiter & DXE RTR-1, works great
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Mike Aust

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There one from Texas Dealer that uses a Mini-Circuits 180degree balun's
with diodes, but seems to generate IM's when near 50Kw AM broadcast stations.

The DXE unit is better 
(Edited)
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Mike va3mw

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Let Tim respond, but I believe the ports can take a pretty good signal before doing any damage.  This was discussed in the Alpha Group.  

The DX Engineering RTR-1 is a great addition, but not required.

If I remember correctly, it would be hard to blow it up.

Mike va3mw
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HCampbell WB4IVF

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(Edited)
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Eric Owens

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Thank you so far for the great replies. 

I just want to maximize my RX by having alternative options during high noise environments. 
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km9r.mike

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Official Response
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Tim - W4TME, Customer Experience Manager

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This is the right way to calculate the RF energy being processed by the ADC.
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Bob - W7KWS -

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Tim,

What levels invoke receiver protection?
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Tim - W4TME, Customer Experience Manager

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The ADC overload is +9 dBm.  The damage level is above that value at ~ +20 dBm.  The protection relay will engage before the signal levels reach the damage level.
(Edited)
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Bob - W7KWS -

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My ham neighbor & I had identical 5-band, 2-element quads for a total of around 12dB gain between them (6dB forward gain each). They were around 150 Ft. apart. We aimed them at each other & he transmitted a 1500 Watt carrier on 20-meters. On my end I connected my quad through a Bird 43 Watt meter to a dummy load. His 1500 Watts induced 3-Watts into my system.

Think of a 10-Watt soldering iron to estimate the heat 3-Watts might generate in a 50-Ohm load (your receiver).
(Edited)
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Eric Owens

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I'm not sure if you are implying that 3 watts is a lot or a little when talking about the flex. I honeatly can't remember how much heat a 10w iron generates. I assume not a whole lot.
(Edited)
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Mike Aust

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That's not ideal, I would have Rx limiters on the Rx side on all the time
so no damage.Maybe an old tube Rx front end could take that 3Watts. 
The DXE Rx Guard Engineering limiter's are great.
(Edited)
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Bob - W7KWS -

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A ten Watt iron will melt solder & burn you. If it's spread out over a large piece of metal it won't. If 3-Watts is disipated in a small component it will likley let the smoke out.

Most Japanese transceivers have some fairly stout back to back diodes across the receive signal path. These components are designed to clamp dangerous antenna currents. I can't recall their specs but I suspect that 3-Watts would heat them up quickly. Heat usually results in premature failure.

As a question seperate from ADC overload, I asked Tim, above, for information on when a Flex 6xxx protects itself from potentially damaging antenna currents. I assume that their radio, being well designed, includes some sort of protection.
(Edited)
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Gerald - K5SDR, Employee

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Reverse power protection kicks in at +20 dBm plus or minus a few dB based on the band. This will normally protect the expensive components like the A/D converter but will not protect the cheap components like the ESD diodes themselves. They wil sacrifice themselves to protect the expensive stuff. No guarantees but those things usually help prevent more extensive damage. If you transmit back into the receiver or get a lightning ESD hit, the radio may need to come home
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Eric Owens

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Thanks awesome replies. 

I am going to be more than likely purchasing a DX Engineer Receive Guard ... 

https://www.dxengineering.com/parts/dxe-rg5000hd
(Edited)