Topband: Receiver protectors.

[Dave Cuthbert]

Jim,

Good data.

It looks like the RG-5000 consists of two back-to-back diodes (in IC1) with
the other components not contributing. Do you have a part number for IC1?

GDT/ES1A diodes
The GDT (gas discharge tube) doesn't appear to help. By the time it
conducts at 90 volts the diode string current is 160 amps and the diodes
will have failed. During a fast rising pulse (<1us) the GDT voltage can
rise to 1000 volts before conducting and the diodes will fail from
excessive current. When the GDT does conduct it may clamp around 15 volts.


ES1A/IC1
IC1 appears to contain two back-to-back diodes. The output limiting voltage
is that of a single diode, preventing the ES1A diode string from
conducting. Fed by a 10 watt, 50 ohm source the average current thru IC1 is
900 mA.

Multistage clamping protector circuits require limiting impedance between
each stage. For the RG-5000 circuit the diodes do all the clamping until
the GDT conducts. For the case where the GDT takes 1 us to conduct with a
1000 volt pulse (lightning) the current thru a diode should be limited to
10 amps. Small signal diodes I've used in clamps survive 10 amps for 1 us.
The limiting impedance between the GDT and the diode clamp needs to be 100
ohms. As 100 ohms impacts insertion loss the diode clamp requires parallel
diodes so that a smaller resistor value can be used. If we make the
resistor between the GDT and the diode clamp 10 ohms we need to parallel 10
diode strings. The capacitance will be somewhere around 20 pF which is okay
past 30 MHz. A limiting impedance must also be placed between the ES1A
string and IC1. Instead of this I would simply use 20 ES1A diodes with 10
paralleled to clamp negative and 10 paralleled to clamp positive. The
circuit is then:

GDT -->10 ohms --> diode clamp

The resistor must take 1000 volts for 1 us and an Ohmite OX series resistor
will do.

If a clamp voltage greater than one diode is desired I use steering two
diodes to a zener diode clamp instead of series-connected diodes. The
zener/capacitor can be biased with a small DC current so that the RF signal
doesn't have to charge the zener/cap.

QST RG-5000 review
https://static.dxengineering.com/global/images/technicalarticles/dxe-rg-5000_sn.pdf


    Dave KH6AQ

On Tue, Mar 17, 2020 at 5:27 PM <jim at w8wts.radio> wrote:

> In a thread back in January, 2020 on connecting receive antennas for top
> band, a few fellows mentioned a review that I wrote in 2014, where I
> compared the DEO RG‐2000M and DXE RG‐5000 Receiver Protectors.
>
>
>
> I have updated my review with new measurements, additional theory of
> operation, more details and some bug fixes.  If anyone is interested, it is
> at https://www.w8wts.radio/RXProtectorsREV03-2020.pdf.  I hope that people
> find it interesting.
>
>
>
> Be safe everyone - stay home and get on the air.
>
>
>
> 73,
>
>
>
> Jim, W8WTS
>
>
>
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>