[AMRadio] Sorta OT but just wondering about RF termination resistors.

[Randy Berry]

Thanks to all that replied. I wasn't even thinking about
series-parallel resistors to get the desired resistance. I looked
right over that. I have an MFJ oil can. It works great for HF pretty
close to 1:1 SWR up to 30 MHz but for VHF and UHF the SWR is not so
good. UHF is the worst. It's almost 2:1 on 440. I ordered all the
parts I need for the dummy load I want to build. Including 4 150 watt
50 ohm resistors to run in series-parallel for 600 watts pep total. I
just need to think about it and figure out how I am going to mount
flange resistors designed to bolt right to the heatsink in series.
Mounting them in parallel is no problem. It will be in a vented box
with a 90mm fan for forced air cooling. I've got a heatsink that will
do perfectly inside the box I ordered. I seriously doubt I'll ever go
beyond 50 watts on 2 meters or 440, but the headroom is nice to have
just in case I do decide to buy a VHF/UHF amp. Plus these resistors
are good from DC to 2 GHz. It cost $75 shipped for all the parts. I
have a few of the parts in the junk drawer like heatsinks already. The
biggest problem is I had to order things I'll probably use once. Like
a 90mm hole saw. Unfortunately Harbor Fright doesn't have any 3.5" (90
mm) hole saws. I don't get QST, I won't even start that fire fight
here.

  Thanks again,
Randy, N3LRX

On Tue, Feb 26, 2019 at 11:08 PM <donroden at hiwaay.net> wrote:
>
> Look a month or so back.... a 100 watt mineral-oil dummy load … the
> one with the digital wattmeter.
>
> don W4DNR
>
> Quoting Rob Atkinson <ranchorobbo at gmail.com>:
>
> > hey don,
> > if it's the one I saw it's a few dozen teeny SMT resistors on a pc
> > card to get a DL that can handle around 5 watts.  First thing in my
> > mind was shoot, I'd go downstairs to a bag of 2 W 200 ohm carbons, and
> > fish out four, drill holes in that kit pc card, solder 'em up  and
> > call it good and done.  screw that SMT %^&*.
> >
> > rob
> > k5uj
> >
> > On Tue, Feb 26, 2019 at 7:01 PM <donroden at hiwaay.net> wrote:
> >>
> >> QST has a building a dummy load article in the last couple of months.
> >>
> >> something like 12 600 ohm thin-film resistors @ 50 cents each
> >>
> >> and two 50 ohm resistors in parallel = 25 ohms
> >>
> >> two 25 ohm pairs is series gets you back to 25+25=50 ohms
> >>
> >> Don W4DNR
> >>
--
tnx es 73 de Randy, N3LRX/8
https://n3lrx.com