[1000mp] RX ANT response (long, detailed)

Tod - ID tod at k0to.us
Fri Feb 24 11:59:07 EST 2006 

Zoli:

I assure you that I have absolutely no interest in promoting (marketing is a
different activity but I don't have an interest in doing that either)
anyone's "box".

Perhaps it is an simply an honest mistake on my part, but  I did examine the
schematic some time ago and concluded that the RX input on the rear of the
radio was not directly grounded when the radio was transmitting. Still, I am
not known for being mistake-free so as I drafted this message I got out the
schematics for my MP and looked again. Let me describe, in some detail, what
I found.

If we start with the sheet labeled "Circuit Diagram" in the lower right
corner we can get a quick idea of where the RX Ant IN signal and the Ant-A
and Ant-B signals go inside the radio. The two coax antenna inputs are shown
in the upper left corner of the sheet. The board they are on is called the
"ANT Unit". From that board the path goes through the "LPF Unit" and the
"HPF unit" and arrives at the "RF Unit" as the only line input on the left
side of that board as shown in the block diagram. There are two jacks just
above that line and they are labeled "RX Ant IN" and "RX Ant OUT" . These
are the RCA jacks in the lower middle area on the back of the FT1000MP.All
three of these lines feed into the box labeled RL1001 [you may need a
magnifying glass to read the labels].

Now lets look at the detail of the "ANT Unit" schematic. It is on a
different sheet. The "CNTL Unit" detail is in the upper left and the "ANT
Unit" detail is on the lower right side. That schematic shows that the
unused antenna connected to coax jacks A and B  is grounded. The selected
antenna goes to the jack on the left side of the diagram labeled "ANT". This
jack will connect by small coax cables to the "LPF Unit" and from there to
the "HPF Unit" so we can pick up the routing as it enters and exits from
those Units. If you follow that path you will see that there is no relay
grounding of the line between the departure from the "ANT Unit" and the
departure from the "HPF Unit". When the RX line from either coax A or coax B
leaves the "HPF Unit"  as "RX RF" it goes to the "RF Unit" which is detailed
on the third large schematic sheet. 

In the upper left corner of the "RF Unit" diagram we see the "RX Ant IN"
entry; the "RX Ant OUT" exit and the "RX RF" entry. There is a pair of
relays there which select whether the "RX RF" line will connect to the front
end of the receiver or the "RX Ant IN" line will connect to the front end. 

*****  As a point of interest, unless the RX button on the front of the
radio has been pushed to select the RX IN antenna instead of ANT-A or ANT-B
as the choice for receiving, "RX OUT" will be floating and not have a signal
output from the A or B antennas. If RX has been pushed, "RX OUT" will
connect to A or B during receive. This is of interest if you wish to use
that signal as the sense antenna for one of the noise cancellation boxes.
*****

When the RX button on the front of the radio has been pushed to select a
separate RX antenna, "RX Ant IN" connects to receiver front end instead of
"RX RF" from one of the coax inputs. On my schematic that line is shunted to
ground through a 1uH choke and a 100 ohm resistor and then it continues and
goes through the two attenuation resistors <R1039,R1040>  or not depending
on whether or not you have selected the attenuation from the front panel.
>From that point the RX signal heads off to T1008 on its way to the RX band
input filters.

At this point I have not found any relay contact to ground either transmit
or receive. There is a ground path through the tiny L1030 (1uH) and the low
power R1045 (100 ohms). After that there is a path to ground through the
combination C1071-L1041-R1057(100 ohms).

I guess this is what caused me to think that it might be smart to provide an
absolutely sure path to ground for the "RX Ant IN" line whenever I am
transmitting. Since I have just painstakingly followed the RX Antenna path
into the front end of the receiver and found the same thing I did as the
last time I looked at this, I think I will continue to use the 'box' of my
choice to provide that safety.

Tod, KØTO

 

> -----Original Message-----
> From: 1000mp-bounces at mailman.qth.net 
> [mailto:1000mp-bounces at mailman.qth.net] On Behalf Of Pitman, 
> Zoltan, VF-NL
> Sent: Friday, February 24, 2006 6:12 AM
> To: All about Yaesu 1000mp
> Subject: RE: [1000mp] RX ANT
> 
> Read the schematics and it can be easily seen that it is 
> absolutely unnecessary for the FT1000MP-series as the radio 
> takes care of it inside.
> 
> There are always some people here who jump on this hype and 
> spam us with some marketing for this box. 
> 
> Zoli HA1AG
> 
> 
> 
> 
> 
> 
> 
> 
> > -----Original Message-----
> > From: 1000mp-bounces at mailman.qth.net
> > [mailto:1000mp-bounces at mailman.qth.net] On Behalf Of George
> > (K8GG) & Marijke Guerin
> > Sent: Friday, February 24, 2006 14:03 PM
> > To: Yuri; All about Yaesu 1000mp
> > Subject: Re: [1000mp] RX ANT
> > 
> > 
> > Yuri, et. al.,
> > 
> > Theoretically the RX Antenna jack is disconnected when 
> transmitting, 
> > but some FT1000D and FT1000MP transceivers, etc., and some Icoms do 
> > get RF feedback from their RX antennas and have blown out 
> part of the 
> > front end of the receiver section.
> > 
> > It is best to get a Front End Saver - FES - either build 
> one or go to 
> > Gary, KD9SV or via Craig at the Ham Radio Bookstore.
> > 
> > 73        George    K8GG
> > 
> > 
> > >
> > > Tod, KØTO wrote:
> > >
> > > If you do choose to have a separate RX antenna be 
> absolutely certain 
> > > to provide RF voltage protection for the RX in line so 
> that you do 
> > > not damage the front end of the FT1000X. The best system is to 
> > > ground it when transmitting. Many past reflector messages have 
> > > commented on this  and provided information.
> > >
> > > Hi Tod,
> > > Doesn't RX jack get grounded inside the radio while transmitting?
> > >
> > > Thanks.
> > > Yuri  VE3DZ
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