[600MRG] Is this snake oil?

Sat Mar 25 13:08:38 EDT 2023

Tom,

Interesting topic (addressing the galvanic isolator, I presume).

My LFA feed 6m yagis use a balun that appears to be "just" coax with a 
whole bunch of ferrite beads along its length.

I have used this approach to minimize common mode on other antennas 
(usually placed near the antenna end of the coax run).

I did not use any on my 600m inverted-L that had base loading coil.

Coax tapped into the coil near the ground end (which went to a ground 
rod and had radials on the ground).  Coax shield connected to ground end 
of the coil.

My new "T" antenna will have similar configuration.  The vertical will 
be 300-ohm open wire feed to two dipoles with 4:1 balun at ground end 
for use on 80 or 40m.  The open wire feed will be disconnected from the 
balun and shorted together to act as a shortened vertical with dipoles 
acting as top hats and base connected to the same loading coil set up. 
Coax runs about 100-foot to my 630m transmitter (converted 100w NDB) and 
K3 transceiver in the shack.

See any need for common mode protection?  I can acquire ferrite beads 
that will fit over RG-213 (to be placed at the coil connection).  In the 
past my noise floor ran between -110 dBm and -90 dBm (as measured by my 
SDR-IQ).

73, Ed - KL7UW

On 3/25/2023 6:53 AM, Tom W8JI wrote:
> It is sad how little our community knows and understand the way common 
> mode is created, and how that common mode enters a system signal path. 
> It leave us open for all sort of odd devices and theories.
> 
> With a coaxial line, common mode can only enter the signal path at a 
> flaw or break in the shield. It works this way in everything from loop 
> antennas to our feed lines. A "shielded  magnetic loop" does not receive 
> signals from the wire inside the shield, for example.  The wire inside 
> the loop shield is just a transformer winding that couples to the shield 
> inside layer, and that layer couples to the shield outside at the shield 
> gap where the necessary electric field appears to drive the outside of 
> the shield. The outside layer of the shield is the only actual antenna 
> if the system is built properly. If it is improperly built, then the 
> feed line shield and everything connected to the feed line shield it is 
> involved.
> 
> This is even why a small e-probe antenna gets more sensitive when we 
> mount it higher, it has more feed line shield to pick up signal.
> 
> In ALL of these cases , the point of common mode ingress into the 
> receiver signal path is always at a discontinuity or break in the 
> shield.  In a shielded loop it is at the shield gap. In a e-probe it is 
> at the probe element, where the shield center is continued out past the 
> shield by the "probe".  This causes people to miss what is really going 
> on, and they make up a well intentioned but seriously flawed theory.
> 
> If the shield has good integrity to the receiver input any ingress at 
> the receiver would be negligible compared to ingress at the antenna or 
> an upstream gap or break. The meaningful leak-in point, unless there is 
> a flaw in the cable shielding, would be at the antenna.
> 
> Another thing often missed is the antenna (which by definition needs 
> common mode on it to function as an antenna) receives signals directly 
> from noise sources through local induction fields or long distance 
> electromagnetic radius fields. Even if the feed line shield has unwanted 
> common mode noise, the noise level on the shield has to exceed the 
> desired antenna's pickup of noise.
> 
> One of the very worse antennas for this is an E-field probe, because the 
> lack of a stable infinite ground means the shield is as much the antenna 
> as the probe is!! There is no way around this without an RF ground plane 
> (electrical mass) at the probe! This is why elevated probes become more 
> sensitive with more height...because the shield is the bulk of the antenna.
> 
> All of this is important to get our heads around to build better and 
> cleaner systems. To me, while this isolator has a possible function (I 
> designed one for DX Engineering 20 years ago so I obviously thought they 
> have a place) it would not be when it is placed at the receiver. It 
> would be when placed somewhere outside where the shield path should be 
> broken before the reaching the ingress point, which is usually at the 
> antenna. I sure wouldn't put one at my receiver or at my receiver 
> multiplexer panels.  A single proper bead would be way better in my 
> shack, if I need anything.
> 
> 73 Tom
> 
> 
> On 3/25/2023 12:26 AM, D.J.J. Ring, Jr. wrote:
>> https://www.bonito.net/hamradio/en/galvanic-antenna-isolator-gi1000/
>>
>> The Galvanic Antenna Isolator GI1000 suppresses noise reaching the 
>> ground connections on the receiver. The GI1000 covers a wide-band 
>> range of 50 kHz – 1 GHz (typ. 1,5dB insertion loss). This unit can be 
>> used in many receiving applications, It will also work with 
>> frequencies up to 1,25 GHz but above 1000 MHz insertion loss may 
>> increase by up to 3db. The unit also has integrated double 
>> over-voltage protection and input and output are blocked for DC voltage.
>>
>> The galvanic isolator GI1000 separates the path of the direct current 
>> between the outer shield of the coax cable and the shielding of the 
>> antenna feeding line in order to suppress interference caused by 
>> potential differences. This is achieved by using a small toroidal 
>> transformer. The inner conductor of the coax cable is insulated with 
>> capacitors providing coarse and fine voltage surge protection.
>>
>> Close connection please
>> The GI1000 should be connected to the receiver as closely as possible 
>> to avoid other interference. We offer short very adapter cables with 
>> different connectors.
>>
>> Galvanischer Antennen Isolator GI1000
>>
>> GI1000 & CCMC30 a great team
>> Even a cascaded use of the GI1000 directly at the receiver input and 
>> the CCMC30 following it directly after the coaxial power inserter can 
>> in some cases lead to an increased efficiency. Especially in the lower 
>> frequency range, surprising improvements can occur:
>>
>> CCMC30 mit G1000 kaskadiert
>>
>> Galvanic Antenna Isolator GI1000 Specifications:
>> Excellent protection against sheath waves and voltage surges.Double 
>> voltage surge protection. On the antenna side Gas Discharge tube with 
>> an ignition voltage of 90v. On the receiver side you will find an 
>> ESD-diode (30KV; max.pulse power 350W (8/20μs) Input and output has 
>> been blocked for direct currents of max. 50V.
>>
>> Tested by Clint Gouveia
>> The well known DXer Clint Gouveia (Oxford Shortwave Log) is using the 
>> GI300 (previous model) on nearly all his DX-Expeditions. He wrote a 
>> Test including Videos. Please ready his tests here: read the test
>>
>> 73
>>
>> DR
>> N1EA
>>
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