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LF: Re: RE: On Air Testing

To: [email protected]
Subject: LF: Re: RE: On Air Testing
From: "Hugh" <[email protected]>
Date: Fri, 7 Nov 2003 22:52:51 -0000
References: <[email protected]>
Reply-to: [email protected]
Sender: <[email protected]>
Hi Gary,
Jim beat me to it, I was going to suggest using the Vishay film resistors.
Photo attached of a dummy load I made using two 100 ohm RCH50 resistors in
parallel.
I think I got them from Farnell.
It seems to work fine on all HF bands and will take 100W for longer than
I've ever tried it !
The heatsink was bought cheaply at a radio rally.
73
Hugh
----- Original Message -----
From: James Moritz <[email protected]>
To: <[email protected]>
Sent: Friday, November 07, 2003 12:27 PM
Subject: LF: RE: On Air Testing


Whilst on the subject of dummy loads, are Metal Oxide resistors suitable
for
dummy loads ? because much higher ratings (5 watts) are available for
same
physical size as the 2 watt carbon film resistors in my home brew dummy
load.

73

Gary - G4WGT


Dear Gary, LF Group,

The metal oxide types would be fine, as are metal film, etc. In fact,
even some types of wirewound resistors are reasonably non-reactive at
136kHz. Several people have resorted to electric heating elements like
toasters and fan heaters to make satisfactory LF dummy loads. But
obviously, it is a safer bet to stick to known low inductance types like
carbon, metal oxide and metal film unless you have the equipment to
evaluate the actual RF impedance.

The Vishay RCH50 50W film resistors sold by RS components are pretty
good value at about 2-3 pounds each, and work OK up to HF - but
obviously you need a hefty heatsink as well as the resistors.

Cheers, Jim Moritz
73 de M0BMU



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