[Premium-Rx] Ten-Tec RX-340 ??
Clemens Paul
cpaul at gmx.net
Sun Sep 4 15:31:08 EDT 2005
Don,
Regarding the 756/proxx and its preamp you may want to re-read the specs.
There's NO specified sensitivity below 1,7 MHz for the 756/pro's/xx *with* preamp.
Maybe you can switch on the preamp below 1,7 MHz but it has no effect on sensitivity.
Seems you didn't notice this so far.
>and 0.5uV sensitivity compares very poorly with the WJ line (however maybe 0.5uV for MW
> is comparable to your EI? I am not familiar with the specs on the EI you mention).
Well,you may also want to re-read the specs of your say WJ8712B.
I've just downloaded the data sheet from
http://www.kongsfjord.no/
I see a noise figure of 14 dB.
The 7800's sensitivity on MW translates as I mentioned to a noise figure of 17dB.
Would you call this "a very poor comparison"?
This 3dB-difference in sensitivity is even more complete meaningless as according to CCIR curves
atmospheric noise even in rural areas is about >25-30 dB on MW !!
The WJ's IP3 is +25dBm (for 25kHz spacing),the 7800's with preamp on is +32dBm for
20kHz spacing on 1 MHz (ARRL).
So you get a 4dB better 3rd order dynamic range for the Icom.
Very poor comparison?
And here are real premium specs of the E1800:
Noise figure measured <12dB (no preamp), IP3 +40dBm
Don,listening with different receivers is one thing.
Nobody can exact duplicate you individual receiving situation.
Subjective impressions and may be some biasing due to enthusiasm for those premium rx's may
influence your findings.
But if we stick to objective and repeatable specs of those receivers I honestly
can hardly imagine that a IC7800 "can not hold a candle" to your WJ receivers.
And my own comparison of the 7800 to the E 1800,which is in its own class,confirms this.
73
Clemens
DL4RAJ
----- Original Message -----
From: AC7ZG
To: AC7ZG ; Clemens Paul
Cc: premium-rx at ml.skirrow.org
Sent: Sunday, September 04, 2005 2:14 PM
Subject: RE: [Premium-Rx] Ten-Tec RX-340 ??
correction below
-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org [mailto:premium-rx-bounces at ml.skirrow.org]On Behalf
Of AC7ZG
Sent: Sunday, September 04, 2005 5:12 AM
To: Clemens Paul
Cc: premium-rx at ml.skirrow.org
Subject: RE: [Premium-Rx] Ten-Tec RX-340 ??
Clemens
I never mentioned the preamp. (which you can also turn on in the ProXX for MW by the way),
And I was specificially talking about weak signal recovery in the Medium wave spectrum....
What I talk about is both obvious from usage (where the real receiver will shine or not)
and from the specs of the 7800:
Sensitivity of 7800 (from specs):
SSB,CW,RTTY(BW 2.4kHz 10dB S/N):
0.100-1.798MHz 0.5uv (w/preamp 1 ON)
1.8-29.99MHz 0.16uV(w/preamp 1 ON)
AM (BW 6kHz, 10d/B S/N):
0.1-1.799MHz 6.3uV(preamp 1 ON)
1.8-29.99MHz 2uV(preamp 1 ON)
This is the same ATTENUATOR CIRCUIT (not lack of Preamp on/off) that the proXX suffers from.
A cursory look at the schematics <look in your ICOM7800 looseleaf manual in section at end,
#2 schematic> shows that in the BPF Unit1, there is a resistor pair at the input of the "B0A"
enabled bandpass filter that isn't duplicated at the input of the other bandpass filters. The R1
value of 47K from input to ground plus the R3 of "0 ohms" is an attenuation pad circuit. Like
the Pro2/3, you'll have to remove the resistors and jumper R3(maybe not if it's just a wire
jumper across the location already at "0" ohms ) while leaving R1 "open" in order to remove the
attenuator and restore the Medium wave sensitivity. HOWEVER, likely in Europe you'll be
overloading the MW input. This does not happen in the weaker signal region of North America.
So, Clemens, from both specs and from usage, you cannot have the same medium wave
sensitivity as the higher bands, and 0.5uV sensitivity compares very poorly with the WJ line
(however maybe 0.5uV for MW is comparable to your EI? I am not familiar with the specs on the
EI you mention).
best regards
Don
-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org [mailto:premium-rx-bounces at ml.skirrow.org]On
Behalf Of Clemens Paul
Sent: Sunday, September 04, 2005 1:03 AM
To: AC7ZG
Cc: premium-rx at ml.skirrow.org
Subject: Re: [Premium-Rx] Ten-Tec RX-340 ??
Don,
contrary to the IC756proxx the IC-7800 can activate its preamp below 1,7 Mhz.
This results in a MDS of -123dBm or a noise figute of 17dB.
This is *very well* (about 10dB) below athmospheric noise on MW/LW during night.
So If your other receivers performed really better than the Icom on MW this isn't
definitely
a sensitivity issue.
My personal experience with my 7800 and Telefunken E1800,which is even more sensitive
below
1,7 MHz:
When receiving extremely weak ham cw signals on 137Khz *during daylight* (groundwave
propagation)
the E1800 gave a little better readibility due to its better sensitivity.
73
Clemens
----- Original Message -----
From: AC7ZG
To: Aidehua at aol.com ; premium-rx at ml.skirrow.org
Sent: Sunday, September 04, 2005 1:26 AM
Subject: RE: [Premium-Rx] Ten-Tec RX-340 ??
My icom7800 does not hold a candle to the wj8712p/wj8711a/hf1000a for TP medium wave
dxing, nor weak signal recovery on the shortwave bands.
I don't usually bring it with me to the coast of Washington for this reason. Like the
ICOM756pro2 and 3, the 7800 has an attenuator in circuit below 1700kHz to prevent overload by AM
stations. Guy Atkins has made some circuit changes to his pro3 to bring it into play as a weak
signal MW receiver, including removing the attenuation circuit and replacing the roofing filter
with one of the 6kHz versions from the 7800. (I've not similarly butchered my 7800 :-0
Don
AC7ZG
PS I've used one of my wj8711A's for receive (disabled during transmit) along with the
7800 to do some very weak signal ham radio qsos -- the 7800 could not keep up...
-----Original Message-----
From: premium-rx-bounces at ml.skirrow.org [mailto:premium-rx-bounces at ml.skirrow.org]On
Behalf Of Aidehua at aol.com
Sent: Saturday, September 03, 2005 1:02 PM
To: premium-rx at ml.skirrow.org
Subject: Re: [Premium-Rx] Ten-Tec RX-340 ??
Gosh, I love this group!! And here I was, feeling guilty for owning a retirement's
worth of receivers....I have never compared the HF-1000A with the 340, but have done so with my
Icom 7800. The 7800 is comparable on MW but the SAM on the WJ does supremely well and gives a
fullness the 7800 cannot hold a candle to.
I also agree the a retored/tweaked R390A (my EAC) really does a superior job on MW and
the Tropical Bands. For a serious night of DX listening, I always keep the R390 fired up,
especially since it's my last resort for specific targeting of stations (i.e., Africa on 60m).
Just wanted to chime in on how refreshing the group is here, considering not too many
hams appreciate this aspect of high end receivers.
73,
Ed NI6S
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