[ICOM] IC 746 (non-pro) Recieve antenna ?
Gary P. Fiber
gfiber at comcast.net
Thu Mar 13 11:04:22 EST 2008
Jim,
Usually there is a relay in series with the receive antenna line
internal to the rig.. RL4 on the CTRL unit of the IC-746 non pro is the
TR switch relay. It opens the receiver input during transmit. Depending
on where the mods.dk information places the new " IN" jack you could be
past that relay at the receiver front end. I downloaded a copy of the
746 service manual and looking at the schematic and reading the circuit
description came up with that answer.
On most Icom's with the RX antenna OUT to IN jacks the relay is between
the SO-239 and Receive antenna OUT jack.
That relay, usually a reed type, opens during Transmit removing the
receiver input from the antenna line. There are also pin diodes or other
types of switching diodes in that circuit too to protect the receiver
front end during transmit.
I hope some of this helps
Gary K8IZ
Jim Miller wrote:
> Sounds like good advice. I had figured I would have to switch the single
> antenna connection from the transmit to the receive and was concerned about
> not having the transmit antenna connected fast enough to prevent the
> transmit from going into thin air until the relay was closed.
>
> With this mod the transmit antenna will be connected at all times. But, how
> is that different than the way it comes from the factory? They must have a
> way of disconnecting the receive circuit during transmit since it is one
> antenna and would be feeding transmit power directly into the receive
> circuitry. Looks like the radio already has to deal with this situation.
>
> Using a external relay like is recommended for keying an amplifier to
> disconnect the receive antenna during transmit would be a simple fix and
> would be an easy solution.
>
> Tnx es 73, de Jim KG0KP
>
> ----- Original Message -----
> From: "Gary Fiber" <gfiber at comcast.net>
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Sent: Thursday, March 13, 2008 7:33 AM
> Subject: Re: [ICOM] IC 746 (non-pro) Recieve antenna ?
>
>
>
>> Looks like that mod may place the "IN" jack right into the receiver
>> front end. Older Icoms did that and it was after most TX/RX relays
>> and antenna switching.
>> I would still use some sort of relay to open the receive antenna
>> during transmit.
>> Otherwise you are likely dependant on switching diodes and may blow
>> the receiver front end when you transmit on the other antenna due to
>> RF energy absorbed by the receive antenna.
>>
>> Gary K8IZ
>>
>> At 10:52 PM 3/12/2008, you wrote:
>>
>>> Thanks. The mods.dk one looks to me like the best answer. Now if I can
>>> just get my 160 antenna back up.
>>>
>>> Thanks es 73, de Jim KG0KP
>>>
>>> ----- Original Message -----
>>> From: "Billy Cox" <aa4nu at ix.netcom.com>
>>> To: "ICOM Reflector" <icom at mailman.qth.net>
>>> Sent: Wednesday, March 12, 2008 10:14 PM
>>> Subject: Re: [ICOM] IC 746 (non-pro) Recieve antenna ?
>>>
>>>
>>>
>>>> Here's a few options ...
>>>>
>>>> http://www.radiobooks.com/products/svdxii.htm
>>>>
>>>> http://www.mods.dk/view.php?ArticleId=3765
>>>>
>>>> http://www.greenrover.demon.co.uk/746_rxmod.html
>>>>
>>>> http://www.ham.dmz.ro/icom/ic-746-separating-the-tx-and-rx-lines.php
>>>>
>>>> There might be others out on the web ...
>>>>
>>>> That help?
>>>>
>>>> 73 de Billy, AA4NU
>>>>
>>>>
>>>> ----- Original Message -----
>>>> From: "Jim Miller" <JimMiller at STL-OnLine.Net>
>>>> To: "ICOM Reflector" <icom at mailman.qth.net>
>>>> Sent: Wednesday, March 12, 2008 9:26 PM
>>>> Subject: [ICOM] IC 746 (non-pro) Recieve antenna ?
>>>>
>>>>
>>>>
>>>>> I have wondered about the Rx antenna also. My thought was to use the
>>>>>
> T/R
>
>>>>> relay output for the amplifier to control an antenna switch. Is
>>>>>
> there
>
>>> an
>>>
>>>>> (inexpensive) antenna switch that can be electrically controlled or
>>>>>
>>> would
>>>
>>>>> it
>>>>> be too slow?
>>>>>
>>>>> Tnx es 73, de Jim KG0KP
>>>>>
>>>>> ----- Original Message -----
>>>>> From: <Greenacres113 at aol.com>
>>>>> To: <icom at mailman.qth.net>
>>>>> Sent: Wednesday, March 12, 2008 2:12 PM
>>>>> Subject: [ICOM] ic 746 antenna switching
>>>>>
>>>>>
>>>>>
>>>>>> I have an Icom 746 non Pro. Just a plain IC 746. It's got ant.
>>>>>>
> ports
>
>>> on
>>>
>>>>> the
>>>>>
>>>>>> back but not an aux. ant. one.
>>>>>> ......
>>>>>> I just put up a 160m OCF dipole. I was thinking of building a
>>>>>>
>>>>> beverage/loop
>>>>>
>>>>>> to rx with.
>>>>>> .....
>>>>>> I thought of a sorta' crude way if it's possible. Use the split
>>>>>>
> freq
>
>>>>>> provision. Put the tx ant on vfo B [ ant1] & the beverage/loop
>>>>>>
> on
>
>>> vfo
>>>
>>>>> A. [ant 2]
>>>>>
>>>>>> Just as u wud work split chasing the TX5 or something. It would
>>>>>>
>>> require
>>>
>>>>>> matching the freq.s but I think it could be done.
>>>>>> ....
>>>>>> Is there a better way on the IC 746 ?
>>>>>>
>>>>>> k9il
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> **************It's Tax Time! Get tips, forms, and advice on AOL
>>>>>>
> Money &
>
>>>>>> Finance. (http://money.aol.com/tax?NCID=aolprf00030000000001)
>>>>>> ----
>>>>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>>>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>>>>> Icom FAQ: http://www.qsl.net/icom/
>>>>>>
>>>>> ----
>>>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>>>> Icom FAQ: http://www.qsl.net/icom/
>>>>>
>>>>>
>>>> ----
>>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>>> Icom FAQ: http://www.qsl.net/icom/
>>>>
>>>>
>>> ----
>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>> Icom FAQ: http://www.qsl.net/icom/
>>>
>>>
>>> --
>>> No virus found in this incoming message.
>>> Checked by AVG.
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>>> 3/12/2008 1:27 PM
>>>
>> Gary Fiber K8IZ
>> GROL PG-19-6691
>> Washington State Resident
>>
>>
>> ----
>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>>
>>
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
>
>
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