[TenTec] receiver isolation

Thu Dec 7 21:34:32 EST 2017

I have been repairing an Icon IC-756 Pro 2. It is AMAZING what they went through to keep transmitted RF out of the receiver input.

They actually pick u[p on the TX 5 volt line and drive a transistor, which pulls a pair of series PIN diodes directly to ground (through a 0.1 uF capacitor). When this affair shorted out, the attenuation was over 90 dB!

It would be easy enough to do this for any radio with a separate receiver antenna input. The circuit only has about 8 parts.

Gary

> On Dec 7, 2017, at 8:06 AM, Carl Moreschi <n4py3 at earthlink.net> wrote:
> 
> I have a one wire mod that simply brings the sub receiver antenna connection out to the spare jack.  This works well for adding panadapters.  I have been using this for years.  It has to be protected enough to protect the sub-receiver antenna jack.  I see signals of about s9+20 on my panadapter when I transmit, even with an amplifier.  So this certainly is a good way to do this.
> 
> My N4PY software keep everything in sync.
> 
> Carl Moreschi N4PY
> 58 Hogwood Rd
> Louisburg, NC 27549
> www.n4py.com
> 
> On 12/7/2017 7:16 AM, Barry N1EU wrote:
>> The over-riding question is whether the Orion provides internal isolation
>> of the subrx antenna port.  The Orion schematics are somewhat challenging
>> to decipher without explanation of the complex control signals.  My
>> educated guess is that the subrx antenna port is disconnected via relay
>> during transmission and is therefore protected.  But I'm not 100% sure and
>> unless someone can authoritatively confirm my educated guess, the prudent
>> course of action is to add external protection.
>> 
>> Barry N1EU
>> 
>> On Thu, Dec 7, 2017 at 2:16 AM, Ken Brown<kenradiobrown at gmail.com>  wrote:
>> 
>>> It all depends on the coupling between the antennas. I should really say
>>> antenna systems, because there could be crosstalk between transmission
>>> lines or other equipment, and not just the coupling from transmit antenna
>>> to receive antenna. The "receiver Guard"recommendation is a good one. If
>>> the receive antenna is far from the transmit antenna, and an inefficient
>>> one such as a Beverage, and your feedlines have good shielding and are not
>>> all bundled together. Cross polarization between the transmit antenna and
>>> receive antenna is another way to reduce coupling, or if you prefer to
>>> increase isolation.
>>> 
>>> On Wed, Dec 6, 2017 at 12:05 PM, Kim Elmore<cw_de_n5op at sbcglobal.net>
>>> wrote:
>>> 
>>>> I use the DX Engineering Receiver Guard for jut this purpose. I have K9AY
>>>> receive loops about 60-70 ft from my F12 Sigma 80 OCF vertical dipole. So
>>>> far, everything has been fine.
>>>> 
>>>> Kim N5OP
>>>> 
>>>> "People that make music together cannot be enemies, at least as long as
>>>> the music lasts." -- Paul Hindemith
>>>> 
>>>>> On Dec 6, 2017, at 14:11, Barry N1EU<barry.n1eu at gmail.com>  wrote:
>>>>> 
>>>>> I interpreted the question to mean that he is transmitting legal limit
>>>> into
>>>>> his tx antenna, he has a receive antenna feeding the subreceiver
>>> through
>>>>> the rx antenna jack on the rear, and he wants to know if he needs to
>>> add
>>>>> external isolation/protection of the rx antenna during transmit.
>>>>> 
>>>>> It's a good question that's come up before but I confess to not
>>>>> knowing/remembering the authoritative answer.  Conventional wisdom is
>>> to
>>>>> add external isolation/protection.
>>>>> 
>>>>> 73, Barry N1EU
>>>>> 
>>>>>> On Wed, Dec 6, 2017 at 7:24 PM, Ken Brown<kenradiobrown at gmail.com>
>>>> wrote:
>>>>>> 
>>>>>> There should never be "legal limit" power level on any transceiver
>>>> antenna
>>>>>> port. The maximum power level should be the transceiver's transmit
>>>> power,
>>>>>> and it should only be on the tx/rx port when transmitting. The
>>> internal
>>>>>> switching in the transceiver will keep that transmit power out of the
>>>>>> receiver front end. There should never be any RF power other than
>>>> receive
>>>>>> signal levels from the antenna feeding into any antenna port on a
>>>>>> transceiver.
>>>>>> 
>>>>>> Perhaps I am misunderstanding your question. How/why would you ever
>>> have
>>>>>> legal limit RF power going IN to your transceiver?
>>>>>> 
>>>>>> DE N6KB
>>>>>> 
>>>>>> On Wed, Dec 6, 2017 at 7:05 AM, Sandor Wetsel<kg4fet at bellsouth.net>
>>>>>> wrote:
>>>>>> 
>>>>>>> 
>>>>>>> I have blown front ends on radios before so for me this is a concern.
>>>> Is
>>>>>>> the isolation of the Sub receiver good enough to protect it from a
>>>> legal
>>>>>>> limit transmission on the Main? This would be using either antenna
>>> port
>>>>>> for
>>>>>>> the SUB RX antenna. I did not want to assume now that I am into this
>>>>>> (565)
>>>>>>> rig a week now.
>>>>>>> 
>>>>>>> Thanks es Merry Cristmas
>>>>>>> 
>>>>>>> Sandor KG4FET
>>>>>>> 
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