Topband: Hi Z amplifiers for 160m

[Lee STRAHAN]

Greetings all,
   George has some very pertinent points here and only on one point I will disagree. What a Hi-Z amplifier needs to do is dependent on your aspirations of the size and quantity of elements you decide to use. The combiner losses will dictate what you must do at the element end of an array for an amplifier. Let me clear one thing up. The YCCC amplifier is not a unity gain amplifier. It has a 6 dB loss due to its output impedance of around 75 ohms. Thus the evolution of what I called the +6 amps 6 or 7 years ago that indeed have unity gain and still have a 75 ohm output impedance. A significant reduction in the noise figure of an array with a lossy combiner.
   If ones aspirations are only to use a simple array like the YCCC then the operational amplifier versions seem to fill the bill, but don't expect then to apply the same amplifiers as you build arrays for higher and higher RDF. And, there are much better amplifiers available to replace the 8055 if I remember the YCCC part number correctly. The 8055 has like 4nV/root Hz noise while some of the new ones get down to 1 nV/root Hz noise a very significant improvement.
   I could bore you all to distraction with other fine points that Hi-Z amps need as specifications. It may not meet the eye but that is why performance comes at a price.

Lee   K7TJR
Hi-Z Antennas




Chris,
Assuming a trans-impedance amplifier, "unity gain" is enough (with reasonable size elements). Noise and IP3 are far more important. Lightning and surge immunity are also important. Also, isolate the amp from common mode noise travelling on the feed-line. Filter the power supply well. Use an F connector (a high quality one that can be torqued.) GL and 73, George, AA7JV/C6AGU

On Wed, 11 Mar 2020 11:33:34 +0000
  Chris Moulding <chrism at crosscountrywireless.net> wrote:
> As well as being a radio amateur (G4HYG) I also run a small business designing and making radio equipment (Cross Country Wireless).
>
> Recently I've been asked by a radio contest group to see if I can redesign the YCCC Hi Z amplifier using modern components and using similar mounting arrangements to our Loop Antenna Amplifier.
>
> The first prototype using surface mount components is working well.
>
> So far I've not build an array of antennas but that will come later when the production boards arrive.
>
> The prototype uses a unity voltage gain amplifier and a BNC connector.
>
> I've a couple of questions for others on the list with experience of running vertical receive arrays:
>
> Is a unity voltage gain amplifier OK or do you think it needs more gain for long coax runs?
>
> At present I'm using a BNC male connector for the output. Would an F type connector be more compatible with existing antenna arrays.
>
> 73, Chris G4HYG
>
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