Topband: Transformer isolation vs common mode choke was: Re: T Vertical feed

[Guy Olinger K2AV]

I may have missed it somewhere, but where physically is the choke on the
entire run of the coax from the antenna/isolation transformer back to the
transmitter?  Some commentary appears to assume you have it placed right
next to the isolation transformer.  Is that true?

73, Guy

On Fri, Jan 27, 2012 at 9:55 PM, Julius Fazekas <phriendly1 at yahoo.com>wrote:

> 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 at msn.com>
> To: phriendly1 at yahoo.com; Topband <topband at contesting.com>;
> n4zr at 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 at yahoo.com
> > To: topband at contesting.com; n4zr at 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 at contesting.com> wrote:
> >
> > From: Pete Smith N4ZR <n4zr at contesting.com>
> > Subject: Topband: Transformer isolation vs common mode choke was: Re: T
> Vertical feed
> > To: topband at 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
>