Charles,
The isolation transformer, for all intents and purposes, is like link coupling.
Keep in mind on the TX side I run QRP or LP, so it makes this a bit easier to
manage. Primary on the coax side and secondary on the antenna side.
The common mode choke is on the coax side and I used Jim, K9YC's RFI cookbook:
http://audiosystemsgroup.com/RFI-Ham.pdf
Specifically, the choke described in Chapter 7. I used 1/4" heliax for the TX
and RG58C/u on the RX. There was a noticeable improvement in F/B on my short
bi-directional beverage. On the TX side, it cleared up a RFI issue I was having
(the TX antenna is very close to the shack, the station is on the second floor,
my radial field is FAHHHHR from optimum).
So, it's actually easy to have both devices in-line at the same time. YMMV.
I must say that the work I've done improving my ground system has been worth
the effort. Since last year's strikes, I've added more short ground rods (I use
old copper pipe) and have almost encircled the shack, improved/cleaned
connections and shortened the run from the shack to the ground system. Things
work better on the lower bands, but did recently find I caused an issue on 17M,
I trip my monitor off when I transmit CW or RTTY. May be a shack cable routing
issue since I recently swapped desks and rerouted stuff. I'll find it hihi...
73,
Julius
Julius Fazekas
N2WN Tennessee Contest Group
http://k4tcg.org/
http://groups.google.com/group/tcg1?hl=en Tennessee QSO Party
http://www.tnqp.org/ Elecraft K2 #4455
Elecraft K3/100 #366
Elecraft K3/100 #
________________________________
From: Charles Moizeau <w2sh@msn.com>
To: phriendly1@yahoo.com; Topband <topband@contesting.com>; n4zr@contesting.com
Sent: Friday, January 27, 2012 5:48 PM
Subject: RE: Topband: Transformer isolation vs common mode choke was: Re: T
Vertical feed
Julius,
You say that to your system with its isolation transformer you ADDED a common
mode choke.
I can understand how you might have REPLACED the isolation transformer with the
common mode choke, but would you explain the interconnections you used in order
to have both of these elements work effectively together.
With thanks,
Charles, W2SH
> Date: Fri, 27 Jan 2012 12:19:34 -0800
> From: phriendly1@yahoo.com
> To: topband@contesting.com; n4zr@contesting.com
> Subject: Re: Topband: Transformer isolation vs common mode choke was: Re: T
> Vertical feed
>
> I had been using an isolation transformer with my system for a number of
> years. It is HB and works reasonably well. I had not been using a common mode
> choke.
>
> After reading Jim's document, and having the parts on hand, I constructed a
> choke and added it to the installation. It definitely was worth the effort.
>
> My coax/heliax feedlines are either on or under ground. The antennas in
> question are close to the house/shack (25' to 50').
>
> The common mode choke also cleared up some issues with the Tee transmitting
> antenna. It was easy enough to build and well worth the effort. I'd recommend
> it to anyone who may have a less than optimum antenna situation.
>
> 73,
> Julius
>
> Julius Fazekas
>
> N2WN
>
>
>
> Tennessee Contest Group
>
> http://k4tcg.org/
>
> http://groups.google.com/group/tcg1?hl=en
>
>
>
> Tennessee QSO Party
>
> http://www.tnqp.org/
>
>
>
> Elecraft K2 #4455
>
> Elecraft K3/100 #366
>
> Elecraft K3/100 #
>
> --- On Fri, 1/27/12, Pete Smith N4ZR <n4zr@contesting.com> wrote:
>
> From: Pete Smith N4ZR <n4zr@contesting.com>
> Subject: Topband: Transformer isolation vs common mode choke was: Re: T
> Vertical feed
> To: topband@contesting.com
> Date: Friday, January 27, 2012, 2:33 PM
>
> Someone recently commented in favor of using transformer isolation in
> lieu of a common mode choke in a receiving application. I presume this
> would be a 1:1 transformer using a binocular core, or at least
> completely separate primary and secondary windings. What are the pros
> and cons of this idea? Does capacitive coupling between primary and
> secondary, or some other factor, limit how much isolation can be
> achieved this way?
>
> 73, Pete N4ZR
> The World Contest Station Database, updated daily at www.conteststations.com
> The Reverse Beacon Network at http://reversebeacon.net, blog at
> reversebeacon.blogspot.com,
> spots at telnet.reversebeacon.net, port 7000 and
> arcluster.reversebeacon.net, port 7000
>
>
> On 1/27/2012 1:07 PM, Jim Brown wrote:
> > On 1/27/2012 8:40 AM, Charles Moizeau wrote:
> >> I am willing to insert a common-mode choke, but don't know what to measure
> >> beforehand to learn if one is needed.
> > There is NO DOWNSIDE to using a good common mode choke other than cost
> > and weight, and as W4TV has noted, there are downsides to NOT using one.
> >
> > As it turns out, there was a typo in the link I posted to my RFI
> > tutorial, which includes Cookbook guidelines for winding effective
> > ferrite chokes. The correct link is
> > http://audiosystemsgroup.com/RFI-Ham.pdf
> >
> > 73, Jim K9YC
> > _______________________________________________
> > UR RST IS ... ... ..9 QSB QSB - hw? BK
> >
> >
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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