THIS IS A VERY LONG EMAIL. If you are uninterested, delete now.
Bob is right, The situation with shortwave broadcast interference here has
indeed gotten much better in the past 5 years. However the problem has not
gone completely away.
Some History:
Besides many stations simply shutting down, all stations were compelled to
move outside of our 40m band, at the same time our Region-One 40m band which
used to be from 7.000 to 7.100 Mhz was expanded another 100 kHz to 7.200
MHz. We are still not allowed to operate between 7.2 and 7.3 MHz.
In the past, a multitude of SW BC stations were operating inside of the
Region One (EU) and Two (USA) 40m bands, which also meant "inside" the
bandpass filters of our receivers. Therefore they were not attenuated at
all. There was nothing blocking their 60 over 9 signals from hitting the
front end of our receivers.
The front end stages are overloaded, not just from one, but rather from the
summation of all the signals hitting them - whether inside or outside the
bandpass of the radio's BPF. They are especially sensitive to those
stations inside the bandpass filters. However the ones outside the BPF but
still close by were only attenuated by some 30 dB or so, and so their
voltage still added to the chaos.
The first line of defense is the receiver's attenuator, but this of course
attenuates the wanted signal.
Earlier radios (1970s) had tunable preselectors. Some were better than
others. Those in the early Argonauts and Omni's were superb. By tuning a
bit lower than the band, we were able to attenuate the signals broadcasting
above the band by quite a bit.
Preselectors were really "in" in Europe. They did a fairly good job
attenuating signals outside of the band. However a real good preselector
such as the Braun, cost about $600 and in the 1970s, that was a lot of
money. They still did nothing to attenuate SW BC stations inside the ham
bands.
Like several other contesters, I built my own 40m tunable preselector which
had a 6dB bandpass of just 30 kHz. So stations 30 or 40 kHz away were
attenuated by 20 dB or more, even though they were inside the ham band.
More important, it attenuated the entire wider spectrum by over 30 dB. This
really reduced the sum of voltage hitting the front end and left the
receiver clean as a whistle.
At my insistence and after sending Jack Burchfield audio tapes of the result
of using a preselector with a Jupiter, Jack promised to provision all radios
going forward for use with a preselector. Too late for the Orion, but the
Omni VII and Eagle both provision this.
I also wrote to Elecraft and showed them how much it improved their K2.
They acknowledged but made no further comment. However the K3 also
provisions for this. Dunno if it would have happened without my feedback or
not.
WHAT THE CHAOS WAS LIKE:
Keep in mind that at the same time the SW BC stations started shutting down
or QSYing, our radios took a quantum leap in IMD rejection, thanks to
Ten-Tec's example of roofing filters with the Orion.
On all previous radios, when used with a full size dipole on 40m at about
30ft. height or higher, all you could hear on 40m was an S7 to S9+ "roar"
across the entire band. You could only detect ham stations that were S9 or
better. THIS IS NOT EXAGERATED.
Using an attenuator works wonders. With old analog technology, inserting
10dB of attenuation resulted in reducing IMD by 30 dB. There was a 3:1
improvement ratio, so it really worked wonders. Most radios were clean with
20 dB of attenuation. But that also meant that weak DX stations that were
under S4, simply vanished. OK, it was still a lot better than before.
I am not really up to speed on the very latest digital technology but it is
my understanding that this 3:1 reduction ratio no longer exists. It is more
like 1:1.
80m was not nearly as bad as 40, but it was bad enough. The attenuation was
necessary there as well - better yet, a preselector.
Our pre-selectors had the advantage that they induced just 6dB of insertion
loss and gave us, depending on quality (and cost), 30 dB or much more IMD
rejection. Thus we lost only the stations that were S1. We could hear the
stations that were S2 or stronger.
ALL Japenese radios had this problem.
Interesting, the Omni's with their tunable preselector were not troubled so
much.
Nor were the Argonauts.
Neither was the Drake R4C, once fitted with Sherwood roofing filters.
I never used a Corsair in my life so I cannot comment on it.
I had an Argonaut II and was very disappointed.
I loved its look and feel and features, but it performed similar to the JA
radios.
Same for the Paragon.
YES, YOUR BELOVED PARAGON, just wasn't all that good on this side of the
pond.
Then a Miracle happened: OMNI V.
For some reason this radio seemed to work - though I still used my broadband
preselector (not the tunable one) with it.
Today most of us understand the reason the OMNI V was better than the JA
stuff. It was the result of the type of IF conversion used, coupled with
Xtal local oscillators (instead of PLL) and a VFO running at a high
frequency and divided down to reach 5 MHz - which significantly reduced
phase noise.
All things being equal, downward conversion is superior to upward conversion
in BDR3 (my take is, in general by about 20 dB). This is due to the
technology and cost difference between Xtal filters above 40 MHz and Xtal
filters 9 MHz or lower.
You "can" produce an upward conversion radio with excellent BDR3 but the
cost is atrocious (examples: Icom 7800 and Hilberling PT-8000). And you
can produce one with "good" BDR3 by paying special attention to the stage
gain in each of the front end stages (example: Omni VII).
The DL-QRP group tested the Argonaut V and it was pathetic. It was
seriously LOUSY over here.
That was about 2003 or so.
I haven't tried one in today's band condx.
Maybe it would be a lot better now that our bands have improved.
Almost all of the QRP radios we have been looking at for SOTA used NE-605 or
similar ICs for their mixers. These crunch, similar to the Argonaut V.
Last time I used one of these rigs here in EU was about 1989 and they were
still poor performers; nowhere near the performance of the Argonaut 505/09.
I know a lot of people on the other side of the pond think I am being too
fussy or too critical and I understand that. Without having actually been
here, seeing/hearing it, you can't possibly imagine how bad it was just 5 or
6 years ago.
I may be over-critical today, now that things have improved.
But I'm not going to buy a bunch of radios and try them, just to be
disapointed.
Can't afford it.
What I know: the Argonaut 6 and the KX3 have no trouble here under today's
condx.
What I know: their position on Rob Sherwood's RX performance list: Very
high.
In the meantime I have arranged to borrow a YouKit and an LNR LD-5.
I will soon KNOW and won't have to speculate.
Stay tuned . . .
73 - Rick, DJ0IP
(Nr. Frankfurt, Germany)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Bwana Bob
Sent: Thursday, March 17, 2016 3:13 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] SOTA RADIO
Rick:
Is there still that much SW broadcasting in Europe? I know that the BBC,
Swiss Radio International, Radio Netherlands, and the Voice of Russia (Radio
Moscow, when I was a kid) have all gone dark. Who is left? Deutsche Welle,
maybe?
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