[ADXA] grounds and antenna 1 and 2 split ideas...

[Joel Harrison]

A good discussion and lots of advice as well. Thanks to all for jumping in.

Different radios obviously have different provisions and different levels
of protection. I have no real experience with Icom but do have experience
with Yaesu and in recent years with the Elecraft K3. Both of those brands
provided separate RX antenna inputs that would "open" the RX input signal
path on transmit. This "should" be adequate but one factor that must be
taken into account is the port isolation of the relay and why there has
been some issue with earlier Icom radios. Diode protection is also
important.

Here are a few basics to consider.

1. On a dBm scale 100 watts is 50 dBm. By comparison an S9 signal is -73
dBm, 123 dBm difference. Receiver damage usually will occur if there is
roughly 18 dBm of energy into the RX front end. Giving some thought to
this, if you're running 100 watts and your RX antenna is relatively close
to your xmit antenna you will need at least 32 dB of isolation to protect
your RX front end. The isolation between some RX antenna relay ports isn't
that good and has been identified here with some radios. If you're running
an amplifier the situation requires greater attention. 1500 Watts (62 dBm)
is 12 dBm stronger than the 100 watt signal at 50 dBm so greater isolation
is required. A simple test of your RX antenna ports isolation can easily
be measured. If you want to get down to that level contact me and I will
provide details and equipment required.

2. Larger separation between the RX antenna and XMIT antenna will also add
some level of isolation but not a great deal. Most of us are limited in
the separation distance we can achieve due to our property size. One of my
vertical RX arrays is only 250 from my XMIT antenna. The other is about
1,000 feet away but still has significant signal level on it during xmit
(obviously) to damage the RX front end.

If you're concerned about adequate isolation, or you have a radio that
does not provide a separate RX antenna input there are two options. One is
to purchase a device similar to the DX Engineering RTR-1A Receive Antenna
Interface. You can see this on their web site and also download the
documentation for review. The second option is to utilize a homebrew
version with an external relay switchable from your radio when you go from
RX to TX. This is very simply a homebrew project that is an external
version of what is in several radios today. If you use a small vacuum
relay you will have adequate port isolation and won't damage the RX. You
can purchase small vacuum relays on eBay or new for as little as $20 but
by all means measure the isolation.

This is a good topic to have a technical presentation on at a future
meeting. I also highly recommend "Managing Interstation Interference" by
George Cutsogeorge, W2VJN for your personal library. This is "the bible"
used by multi-op contest stations to address and eliminate strong signals
from adjacent transmitter harmonic energy. It deals primarily with stubs
and filters to reduce harmonics from other amateur bands but Chapters 1
and 2 are most informative and applicable to this topic. This is available
from Inrad at inrad.net

73 Joel W5ZN

p.s. I have no commercial connection or interest in DX Engineering or
Inrad, but I have blown up a good bit of various amateur radio devices
over the years and have experience with this topic, which only means I
will most likely blow up more stuff in the future!!! I could tell you all
some very funny (and embarrassing) stories!



> It appears the TS-590S RX antenna circuit is opened when the rig goes
into
> transmit, and also it has diode protection.   Since I don't currently
run
> high power on 160, and even if I did, I should be fine.   I do make sure
to disconnect everything if there is a chance of lightning, or I'll be
away from home.
> Thanks for all the help - some really good knowledge here!
> 73
> Dennis
>> On Jan 21, 2016, at 12:05 PM, hamop1 <k5yy1 at cox.net> wrote:
>> Dennis.
>>    Make sure you  have diode protection on the antenna receive inputs,
>> (1) the one in the main TR relay (for isolation impovement) , and (2)
if an RCA type phono antenna input for receiver (non coaxial) then it
usually hooks back into the coax receive side of the TR relay and can
couple into that via the ground portion, especially if no diode there
either. If you have, as Dave says, TWO Coax Ant outputs (ant 1 and ant 2)
on the back just program in Ant 1 for transmit in VFO 2 and antenna 2
programmed to VFO 2 for receive That way you have good TR isolation on
transmit, like for your normal receive line for TR relay function. Most
are diode protected, especially for lightning
>> protection.
>>     Despite this, I always unplug ALL coax cables or anything connected
>> to the equipment during a storm. Often I also unplug the AC line, as
years ago I had 20 equipment pieces fused/welded at the neutral of all the
AC plugs to the female wall neutral. That in itself produced other
internal PS and caps issues, not involving the receiving coax line.  If
I’m gone, always unplug ALL connections. The only thing I leave
attached is the Ground wire, and sometimes THAT ground is also an
entrance way to the radio for transmit antennas close to ground or
requiring a LOT of ground radials close by ..  RF does couple into the
ground radials ( that’s 1/2 the antenna ) and those ground currents do
spread a significant distance to the station and house ground at times.
Good to never ground a station ground to an
>> immediate ground radial system under the tower if that ever has to be
the situation. A 1/2 wave vertical is no problem since a ground is not
needed, only perhaps a short counterpoise system elevated a few feet to
coax integrity. The 1/2 wave vertical is a voltage feed, not current fed,
as I often used to forget.
>>    Good to have banter back and forth on these issues thru the adxa
>> site!
>> San YY
>> From: Dennis Schaefer
>> Sent: Thursday, January 21, 2016 11:26 AM
>> To: David Norris
>> Cc: hamop1 ; Joel Harrison ; adxa
>> Subject: Re: [ADXA] receive antenna port on back
>> Thanks to all - I'll be careful if I get an Icom rig but right now the
only Icoms I have are an IC-7000 for portable use and an IC-703 QRP rig.
>>  My main HF rig is a Kenwood TS-590S and it does have a separate
receive
>> antenna port.   That's the only one I'd use with a  receive antenna.
It
>> does have two antenna ports, and also an RCA Jack that is for the RX
ANT.   I don't think I can transmit on ANT 1 and receive on ANT 2  but
I'll look that up.
>> Of course, the main goal is something for quiet receive on 80 and 160
meters.    For starters, I'm thinking about a beverage on the ground with
a preamp.   I also have noise problems on the higher bands, mainly 12 and
17 meters because of where the WARC antenna is located.  I
haven't been able to isolate it yet, so a receive antenna out in the woods
for those bands would be helpful.
>> 73,
>> Dennis, W5RZ
>>> On Jan 21, 2016, at 10:49 AM, David Norris <k5uz at suddenlink.net>
wrote:
>>> Don't use the RXV ant jack on Icoms.  Use one of the other ant jacks.
You can set most of the newer radios to RCV on one jack and XMT on
another.  No chance of blown relays. This works fine on the 7700 and the
7800/7850.
>>> 73
>>> David A. Norris, K5UZ
>>> Director, Delta Division
>>> Sent from my iPhone
>>>> On Jan 21, 2016, at 8:39 AM, hamop1 <k5yy1 at cox.net> wrote:
>>>> Icom rigs have been known to blow thru the receive antenna only phono
jack input, getting RF THRU the internal TR relay for the main
antenna. Much is strict RF overload of that one ‘receive only’ line .....
I would disconnect any long wire close to the ground and
reconnect, perhaps an old “throw switch”?..  I have no problems if putting
a dipole in that “receive only” antenna input, for some reason. It should
overload too , if too close to the transmit
antenna...
>>>> 73
>>>> San
>>>> From: Dennis Schaefer
>>>> Sent: Thursday, January 21, 2016 8:05 AM
>>>> To: Joel Harrison
>>>> Cc: adxa
>>>> Subject: Re: [ADXA] VP8STI 160 Meters - A Wild Night!
>>>> Joel,
>>>> We appreciate the updates and it is good to see messages on the ADXA
list.
>>>> I don't work 160 much, but my 130 foot horizontal dipole works fairly
well for transmit when the feedline conductors are tied together and fed
against ground.   I need a receive antenna and my rig has a
receive antenna port.   I see receive antenna protectors, but I have not
really seen much about when one is needed.   If I am running 100 watts on
160, what are the possibilities that I will blow my receiver due to RF on
the receive antenna port?   I assume a relay or other circuit in the rig 
removes the antenna from the circuit when I am transmitting, but I'm not
sure.   I can ask the question on the
Kenwood TS-590S reflector, but I knew there was a lot of knowledge here also.
>>>> So - just for educational purposes - does using a separate receive
antenna increase chances of blowing the receiver front end at 100
watts?   At 1 kw?
>>>> 73,
>>>> Dennis, W5RZ
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