Best post this year.
Mark Bitterlich
WA3JPY
p.s. Of course I am sure many will disagree.
----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Wednesday, December 28, 2016 9:41 PM
Subject: [Amps] FCC Denies Expert Linears' Request for Waiver of
Date: Wed, 28 Dec 2016 16:55:39 -0800
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Subject: Re: [Amps] FCC Denies Expert Linears' Request for Waiver of
15 dBRule
On Wed,12/28/2016 4:26 PM, qrv@kd4e.com wrote:
just the freedom to buy what you want to use?
It has NOTHING to do with freedom. One of the FCC's functions is to
establish the rules of the road for radio and other communications
mediums, and their function is much like establishing rules of the road
for our highways. Speed limits and no passing zones are not restrictions
on our freedoms, they are practical rules that make it safer for citizens.
The 15 dB rule was established at the height of the CB radio boom, and
was part of an attempt to deal with illegal operation using ham gear. It
may have outlived its usefulness, and it the petition to change it is
timely. But ALL amplifier manufacturers have been subject to it and
designed their products to conform. SPE chose to ignore it, and those
who have sold these amps in the US are in violation of Federal law.
My personal opinion is that the ham community would be better served by
allowing commercially made amplifiers to have more gain _IF_ FCC Rules
were also amended to tighten IMD and keying bandwidth limits on
transmitted signals and enforced on manufacturers who sell rigs that
don't meet those Rules. 20 dB would allow a 10W radio like a KX3 or ANAN
10e to drive a 1kW amp to full power. 21 dB gets it to 1.25 kW, less
than 1 dB below legal limit.
73, Jim K9YC
## Whoa. I thought the 15 db rule was only for the 12 + 10m bands ???
IE: > 24 mhz. Below 24 mhz, I was sure that was no gain limit.
## spe et all, would just have to switch in a pad on the 12+ 10m bands
to meet
fcc compliance.... or increase NFB.
## as for the TX IMD situation, its a mess. The Z match that the amp
makers has chosen, is done
so the eff is max, like typ 50%.... but only when the devices are run
flat out.... whereby the amp then
becomes an IMD garbage truck. If you back off on the PO of the amp, its
imd improves, BUT the eff
goes to hell, like down to 30-35% when run at half rated power. The fix
for the eff...is to use less vdc, when
using lower power levels, but then the IMD goes to hell. Lower vdc typ
makes the imd worse.
## to really do it right would mean to use devices rated for 3-4-5 kw,
then operate them at 1.5 kw pep out, then
design the Z match based on 1.5 kw out. Then use a power supply, that
will handle the 1.5 kw output. Ditto
with 1.5 kw LP filters. No rocket science here folks, for low imd, and
1.5 kw pep out on ssb, you either require
bigger devices, or more devices ....or both. Typ you will also get a 1
db redux in IMD for every 1 db in NFB.
Problem is, with more NFB, drive requirements increase. 3db of NFB on a
Drake L4B means you now require 200
watts to drive the amp. 6db means u require 400w of drive. So the NFB
works... provided the device has loads of gain
to begin with. IMD can also be reduced a bit by tweaking the bias....
like increasing idle current. But you can only go so far
with that method.
## Dishtronics 2.5 kw output amp, when run at 1.5 kw pep out, still has a
lousy -30 db pep IMD. If you look at the spec sheets
for these various devices, esp the IMD vs PO graphs, you will soon see
that they have to be severely re-rated to achieve what I would
call reasonable IMD.... -40db pep.... or –34 db below one tone of a 2
tone signal.
## problem is, no countries regs that I can see, regulate IMD for amateur
use, its a non regulated free for all. Even if it was regulated,
which committee will pick the numbers ? All the existing gear would be
grandfathered. Its the higher order IMD that causes the real issues,
like IMD- 9-11-13-15-17-19 etc.
## You would require 2 x sets of regs, one for the xcvrs..and another
for the amps. Dirty xcvr driving a clean amp = bad imd. Clean xcvr
driving a dirt amp = bad imd. They both have to be clean.
## Too bad the ARRL etc, cant call a spade a spade, when doing
equipment reviews... esp regarding spectral purity. yes, nice piece of
gear for a ham amp / xcvr... BUT we cant recommend it due to its lack of
spectral purity.....then dont accept their magazine advertising either,
until said gear meets ARRL etc, min specs for IMD etc.
## Ok say no regs. How about voluntary guidelines. How about some
leadership for a change. If ICOM / Kenwood / Yaesu can build
FCC compliant marine gear, that meets ITU / FCC specs... they could
easily do the same for amateur gear.
Jim VE7RF
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