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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of G8HUL
Sent: Tuesday, May 16, 2023 3:57 AM
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Low noise high reverse isolation low distortion RF Amplifier

In order to measure the IMD levels, unless the performance of the amplifier is terrible, it will have to be operated near it upper limit otherwise the IMD products will be so small as not to be visible on a spectrum analyser; so the signals concerned will not be that small, certainly in the range where very poor connector and cable non-linearities might play a part.

Regards
Jeff

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Brooke Clarke via groups.io
Sent: 15 May 2023 20:07
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Low noise high reverse isolation low distortion RF Amplifier

Hi Jeff:

The paper on Gore's web page is talking about high-power, multichannel systems.
The Langford paper is talking about the second order intercept of an active antenna and the feed line that comes after it, i.e. very low power levels. But details are missing, like what length of line and how the measurement was made.

--
Have Fun,

Brooke Clarke, N6GCE

axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.
-------- Original Message --------


I would disagree with Tom regarding " Properly functioning cables and connectors" not being non-linear. There is always some non-linearity, it just depends on the level. Even the slightest amount of contact resistance in the braid or at connector interface will cause unwanted products, perhaps at an extremely low level but they will be there.

There is a lot of info on the subject on the web, but here is one example:
< > <>

Regards
Jeff G8HUL

-----Original Message-----
From: [email protected] <mailto:[email protected]> <[email protected]> <mailto:[email protected]> On Behalf Of Tom Lee
Sent: 14 May 2023 12:28
To: [email protected] <mailto:[email protected]>
Subject: Re: [Test Equipment Design & Construction] Low noise high reverse isolation low distortion RF Amplifier

I agree with Jeff. Properly functioning cables and connectors are not nonlinear and thus cannot produce the effects that Lankford reports (assuming that he has achieved a proper match to eliminate the obvious length-dependent effects). A 20dB degradation in intercept sounds like the result of a tarnished connector to me.

-- Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070


On 5/14/2023 01:42, G8HUL wrote:

I think that the coax cables, and connectors, should be investigated in isolation, Non-linearities in cables and connectors are a well-known phenomenon.

73
Jeff G8HUL

-----Original Message-----
From: [email protected] <mailto:[email protected]>
<[email protected]> <mailto:[email protected]> On Behalf Of Jeff Green
Sent: 14 May 2023 01:19
To: [email protected] <mailto:[email protected]>
Subject: Re: [Test Equipment Design & Construction] Low noise high
reverse isolation low distortion RF Amplifier

The best I can do is to refer you to this web page PDF, Dr. Lankford's concept of best small antennas.


,%20LW,%20And%20SW%20rev%202.pdf

Here is some of the text"



"While studying active whip intercepts some time ago I discovered,
much to my amazement, that long coax (50 feet) lead often degrades 2nd
order intercepts of active whip antennas by 20dB