From: Steve Dove <dsp@hifidelity.com>
To: rsgb_lf_group@blacksheep.org
Date: Tue, 13 Jul 2004 21:23:06 -0000
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Subject: Re: LF: Receivers
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Hi Mike,

Icom R-75:

'Consumer Reports' and 'Which?' magazine four-star best buy.

As has been mentioned, the R-75 works very well out of the box at LF, and has 
become a fave amongst 'Lowfers' over here.  I have a couple and they're 
mainstays for the 'Grabulators'.

Further to other remarks, under software control the AGC can be made 'Very 
Fast', intended for use during scanning as a poor man's spectrum analyser.  But 
it is quite useful as an alternative to turning the AGC off and letting the receiver 
clip/saturate on static crashes  -  'Argo' seems to make nicer plots under 'Very 
Fast'.

The receiver uses a single lowpass filter for 1.6MHz and below  -  no transition at 
500kHz-ish.  There is a fixed attenuator in this path of nominally 3dB, presumably 
just to secure a sane source impedance for the filter.  However, its removal 
makes considerably more difference than that with highly reactive and hi-Z LF-ey 
antennas -  the input impedance of the first mixer is probably quite a bit higher 
than 50R.  No obvious nasty side-effects from the attenuator's removal and is so 
considered a plus.

Inrad's 125Hz filter makes for a well worthwhile 'microscope';   for most 
circumstances if the radio is in a house the TCXO is not worth it;  the DSP option 
is useless for LF;  the noise blanker is amazing - allowing plots to be made under 
lighting-dimmer noise if need be.


Kenwood TS-440:

Has a discrete front-end filter-set for 500kHz and below, with no fixed attenuator 
and is very sensitive even down to 100kHz.  Optional filter (500Hz or 270Hz 
Kenwood,  400Hz or 250Hz Inrad) a must.  Ho-hum noise blanker.  
Recommended  -  circuitry and performance almost identical to the highly-
regarded TS-850.


Kenwood TS-140:

A real surprise for an 'entry-level' radio.  Very lively down to 200kHz, sensitivity 
dropping off towards 100kHz but still adequately sensitive at 136kHz  -  in fact 
this one here has been sitting collecting dust plotting DCF-39 for however long 
now.

Same front-end filter as 1.6MHz and below, but below 500kHz the fixed 
attenuator is switched out  -  thank you Kenwood!  There is tons of room to 
kluge in a <500kHz filter in that position.


IC-781:

Very good at LF.  Just a bit too much radio for the job!


IC-751a:

Very sensitive at LF, but  d r i f t s  way too much for QRSS, and so can't be 
recommended except for a band-cruiser.

Hope this is helpful.

        Cheers,

                Steve


07/12/04 16:49:57, "Mike Dennison" <mike.dennison@ntlworld.com> wrote:

>I am compiling a list of receivers and transceivers suitable 
>for 136kHz.