Message-id: <1CA1911B969D4902AAD788A5E1DCEB67@MichaelSappPC>
From: "Michael Sapp" <wa3tts@verizon.net>
To: <rsgb_lf_group@blacksheep.org>
References: <158269908ce.marcocadeddu@tin.it>
 <3AE1A816B0CB402AB1E75C3CEF20FC47@StevePC>
In-reply-to: <3AE1A816B0CB402AB1E75C3CEF20FC47@StevePC>
Date: Wed, 02 Nov 2016 18:13:36 -0400
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Subject: Re: LF: Re: SWR Bridges
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Steve & All:  One weekend last winter I decided to play around with an 
Elecraft CP-1 dual directional coupler kit which has 25 and 250 watt power 
ratings depending on how you build it for 1-30MHz (20 and 30 dB coupling 
options.) I decided to try to modify the high power version designed for 1 
to 30 MHz that I previously built which has a 30dB coupling ratio.  It uses 
a pair of  FT50-61 cores with 31 turns as the coupling links. I simply 
changed the FT50-61 cores at 31turns each to FT50-75 cores with 31 turns 
each. The 30 dB coupling factor remained essentially unchanged from 50 kHz 
to 500kHz and the return loss into a matched load 50 ohm was > 30 dB.  This 
coupler kit has switchable 2W 5% 50 ohm load resistors as well as RF coupler 
outputs. I use the RF coupler port outputs and the best (surplus ebay) 
precision loads I had available to test it out.  I have not ran any LF/MF tx 
power through the modified CP-1 coupler but I use it regularly to check the 
match on my MF/LF EWE antennas, rx loop antenna projects, etc.  The pdf 
manual for the CP-1 is on the Elecraft web page to review the schematic.

What I learned from this exercise was that the coupling factor remained the 
same for a given number of turns on the coupling toroids in the CP-1 
coupler. Apparently one can change the core material to shift the frequency 
range according to one's needs.  One of these days I should run some tests 
with 77 and 43 cores and compare the results.  Anyway, the test results with 
the FT50-75 cores in the CP-1 coupler are in the dropbox link below...

https://www.dropbox.com/s/khtl9m4eoyc0cr9/ELCRCP1.jpg?dl=0


When I get around to building an LF/MF transmitter I will likely use the 
modified CP-1 and keep an eye on the core temperature with a contactless IR 
thermometer to determine the usable power limit....

73, Mike wa3tts


----- Original Message ----- 
From: "Steve" <VE7SL@shaw.ca>
To: <rsgb_lf_group@blacksheep.org>
Sent: Wednesday, November 02, 2016 5:36 PM
Subject: Re: LF: Re: SWR Bridges


> Tnx Pete and Marco...yes, I agree that using an RF ammeter to set 
> impedance match, once resonant, is a simple way for those that are without 
> a scopematch. For most LF/MFers however, it is only a matter of time 
> before they construct the scopematch!
>
> Steve  73
>
>
>
>>
>> Hi Steve,
>>
>> wish to add just one comment sharing with you my experience.
>> For routine tests or measures on antennas since almost a dozen of
>> years use an home made VNA (I realized the N2PK VNA and still works
>> fine!) this make available visual and numerical datas which very
>> important to understand what I'm doing. As everybody, of course, I like
>> to have an instrument in line while transmitting just to see is
>> everything is "normal" and under control. For this purpose I made a
>> small console which includes the low pass filter, an RF ammeter and an
>> SWR bridge is very easy to design and make yourself such instrument I
>> made mine covering from 137kHz to 160m and I guess it is reliable at
>> least as all "in line" meters.
>>
>> 73 de Marco IK1HSS
>>
>>
>> ----Messaggio originale----
>> Da: VE7SL@shaw.ca
>> Data: 2-nov-2016 19.12
>> A: <rsgb_lf_group@blacksheep.org>
>> Ogg: LF: Re: SWR Bridges
>>
>> Many thanks to all of those taking the time to reply to my inquiry. It
>> seems
>> that results vary depending upon what meter is being used but it sounds
>> as
>> though only a few are having reliable / accurate results. I normally
>> use the
>> scope match and call it the 'most valuable piece of gear in my shack'
>> but
>> was curious about suggesting the use of an HF SWR bridge for those that
>> do
>> not yet have such a thing, and if it would be a reliable method of
>> matching
>> an antenna. In some cases 'yes', but it seems, in most cases, may be
>> unreliable and only lead to confusion.
>>
>>
>> Steve  73
>>
>>
>>
>> WEB - "The VE7SL Radio Notebook":  http://members.shaw.ca/ve7sl
>> VE7SL BLOG - "Homebrewing and Operating Adventures From 2200m to
>> Nanowaves":
>> http://ve7sl.blogspot.ca/
>>
>>
>>
>>
>>
>>
>
>
> WEB - "The VE7SL Radio Notebook":  http://members.shaw.ca/ve7sl
>
> VE7SL BLOG - "Homebrewing and Operating Adventures From 2200m to 
> Nanowaves": http://ve7sl.blogspot.ca/
>