That would be a good test and something that may be worth testing and measuring
for all transceivers as part of the full ARRL lab
reports.
As a practical matter, I often tune my Pegasus for Hi-Fi SSB FFT spectral
(SpectraPlus) testing using an open or dead short "dummy
load." While the intent is not to measure IM products, I haven't heard or seen
any detrimental effect while using an absurd load
like this.
I have seen an incredible amount of collector current occur with Ten-Tec
finals at full power under open/closed terminations and
(knock-on-wood) I have never replaced a Ten-Tec final component ever....across
a half-dozen different products in more than ten
years.
So where is all this power being absorbed when the antenna port is open? It's
absorbed as DC power within the final amplifier. The
RF component, never seeing a matched termination is completely reflected back
into the P.A. And, since the P.A. is a fixed 50-ohm
output, the reflected wave never has a chance to re-reflect as in the case of
the situtation where a Pi Network or ATU follows the
final amp. This is why the final block gets SO hot when transmitting into an
open circuit. In this case, more than 100-watts of
power IS being dissipated...though little of it is RF and efficiency drops
precipitously as a function of the degree of mismatch.
-Paul, W9AC
----- Original Message -----
From: "George, W5YR" <w5yr@att.net>
To: <wa3fiy@radioadv.com>
Cc: "Paul Christensen" <w9ac@arrl.net>; "tentec" <tentec@contesting.com>;
"N4PY" <n4py@qvssoftware.com>
Sent: Tuesday, August 13, 2002 4:46 PM
Subject: Re: [TenTec] No 6M on the Orion (WTB: Ten-Tec 526 6N2)
> I agree, Paul, and the issue is almost academic since most finals are
> operated at very nearly 1:1 SWR loads. What I am questioning is the broad
> claim that the Orion can deliver 100 watts to ANY SWR and not melt, without
> saying something about the quality of the signal.
>
> I don't doubt that the final devices can dissipate 100 watts - with that
> optional fan only?? - but if Joe Ham decides to operate with a 10:1 SWR on
> 40 SSB (using his 10-meter dipole) what will he sound like? After all, the
> specs say that he can operate into any SWR . . .
>
> I agree, Lee, that unless TT has done an exceptional design, unlike other
> 12-volt finals, the overall performance must be similar. However, there
> must be limits to the load mismatch for the distortion products to remain
> within limits.
>
> I have measured just about everything under the Sun on my Icom 756 PRO but
> I haven't looked at output distortion vs load mismatch. Guess that will be
> the next project . . .
>
> 73/72/oo, George W5YR - the Yellow Rose of Texas
> Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> Amateur Radio W5YR, in the 56th year and it just keeps getting better!
> QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
> Icom IC-756PRO #02121 Kachina 505 DSP #91900556 Icom IC-765 #02437
>
>
> WA3FIY wrote:
> >
> > I suspect George is referring to the third and fifth order IM
> > products of the final amplifier of the Orion, not the IP3 and IP
> > 5 intercept points of receiver.
> >
> > As far as what the IM products will be in the case of load
> > mismatch, I see no reason they would be much different than
> > other 100 watt 12 volt final amplifiers. Interesting question
> > though.
|