[Lowfer] FT-991, IC-R75, IC-7300 receiving on LF

[Michael Sapp]

Dex: You might try the FT-991 with and without an LF/MF low pass filter that 
has good pass band return loss (Butterworth LPF, etc)

and see if there is a difference in receive performance. You might try it 
with the IPO off vs on.

I found my FT-817 requires two conditions to be present to hear reasonably 
well at MF and upper LF as long as the IPO preamp is off.  First, it 
requires the receiver front end not to be overloaded from AM BC energy ( use 
an LPF). Secondly the receiver requires a reasonable impedance match to work 
reasonably well at MF and upper LF.  It does the same thing at 160 meters. 
The FT-817 receiver acts like it is deaf on 160m or even the AM band on 
receiver unless it has a well-matched antenna input condition.  I wonder if 
a similar design philosophy is used with the FT-991.

 From WSPR2 testing, if I add a simple broadband preamp with gain of 100 
along with well-matched LF filtering ahead of it, the FT-817 is only a 5~6 
dB down in overall sensitivity on 137 kHz versus my optimized 
filter>preamp>double-balanced mixer converter.  It works surprisingly well 
on 185~ 190 kHz with a well matched  LPF and broadband preamp combination 
(2N3904, 470 ohm Rc, 4.7 ohm ohm Re = gain 100).  I'm fairly certain it 
would work even better on 630m with a good LPF and 10 to 13 dB of external 
preamp gain.
 But it works surprisingly well in 630m wspr2 with only an LPF.

I had a Kenwood 430 years ago that had a discrete component diode quad mixer 
and no preamp in the factory design rf front end. It was a fairly good 
receiver on LF.  I'm sure the R-75 would beat it tho...I kind of miss that 
Kenwood 430 radio....

I should do some TH hunting some evening....

73, Mike wa3tts

----- Original Message ----- 
From: "Dexter McIntyre W4DEX" <dexter.mc at gmail.com>
To: "Discussion of the Lowfer (US, European,& UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Sent: Friday, March 16, 2018 9:02 AM
Subject: [Lowfer] FT-991, IC-R75, IC-7300 receiving on LF


> I've found the Yaesu FT-991 to be an excellent LF receiver possibly as 
> good
> as the R-75.
>
> Results of a comparison this morning on Carl's TH 189.360 KHz beacon:
>
> R-75:
>
>    https://www.dropbox.com/s/k9f465fdq6s9hip/R-75.m4a?dl=0
>
> FT-991:
>
>    https://www.dropbox.com/s/l9oxa6aksywzcgj/FT-991.m4a?dl=0
>
> IC-7300:
>
>    (No signal detected)
>
> The IC-7300 will receive LF but does not come close to the performance of
> the other two.
>
> My FT-991 is the early version which I've had for close to three years.  I
> haven't compared it to the R-75 at 137 KHz but know it works well for LFBC
> down to 153 KHz.
>
> Distance to TH beacon is 99 miles.  Active antenna used for the test is 
> two
> hundred feet from the house.
>
> Dex
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