[Lowfer] Will an LF UpConverter Really be worth the effort, and expense

[Douglas D. Williams]

There is no commercially made LF converter that I am aware of that uses an
ovenized or temperature compensated oscillator. All the ones I've ever
seen, including the Palomar unit and some others, use tiny little 4 MHz
computer crystals. These might be fine for chasing NDBs, but will drift all
over the place with the slower QRSS modes.

The only LF converter that I have found to be adequate for QRSS work is the
one that Todd Roberts custom builds. It uses the AMRAD design, as published
in the April, 2002 edition of QST, but Todd has modified the circuit and
added a very large and stable ovenized 3.0 MHz oscillator. I use one in
front of my R-75, with very good results. Note that JD is correct and the
receiver itself needs to also be very stable. I have added the TCXO option
to my R-75 and have found through experience that my R-75/Todd Roberts
converter combo is easily stable enough for QRSS60 "slow". I don't know
whether or not Todd still builds these. He was kind enough to send me his
modification notes if anyone wants them. Note that you need a good low pass
filter in front of any LF converter.

Andy, frankly I find it hard to believe, judging by the quality of your
captures, that your TS-450 only has 4uV sensitivity below 500 kHz. That's
pretty deaf, yet you consistently are able to capture the same LF signals
that I do, at least in the Lowfer and 136 kHz bands. Have you done any
modifications to it? Some ham transceivers have an attenuator that kicks in
if you tune below 1.7 MHz, and this can often be disabled with a simple
mod. I remember doing this with my old TS-850.

D. KB4OER





On Fri, Dec 5, 2014 at 11:35 PM, N8OOU <n8oou at meekfarm.us> wrote:

> Andy, I have an older Palomar LF up-converter that I use with the
> ICOM-706. I have two observations to share about that combination.
>
> One is that the Palomar moves 0 - 500Kc to 3.5 - 4 Mhz. That is a good
> thing as the ICOM switches bandpass filters at 3.5 which makes  for good
> sensitivity.  It is also easy to mis-add the frequencies to get to the dial
> setting, compared to some converters outputting 4.0 Mhz.
>
> The second is the Palomar has a simple crystal oscillator which is very
> sensitive to temps. It reacts very quickly to a small temp change, and will
> put the signal out of the Argo window as JD has said.
>
> What I can hear with the Palomar/706 is about the same as my Kenwood
> TS-480 which the specs rate at 4 uV.
>
> I also have the "Ham-it-up" converter to put in front of an RTL-SDR
> dongle.  That converter is plagued with frequency drift, as well as the
> dongle itself. It has no input filtering so it is open to overload, and
> IM.  It's fun to play with but it's more a toy than a tool.
>
> I hope that helps a little.
>
> 73   de   N8OOU - Mike Meek
>
>
> On 12/05/2014 04:48 PM, KU4XR wrote:
>
>> Greetings all:
>>
>> I have nothing to compare the performance of my Kenwood TS450S to..
>> Factory Specs say
>> that the receiver sensitivity below 500 KHz is 4 µV, and above 1.7 MHz
>> is .2 µV ..
>> I'm sure that the radios own Noise Floor is quieter in the HF range
>> versus LF, But I think that
>> The radio has done a pretty good job receiving directly at LF.. It is
>> a Triple Conversion system..
>> SO... what are the experiences of those who have travelled this road
>> before ? I have a cheap
>> Jackson Harbor LF UpConverter, and I'm sure that it will leave a lot
>> to be desired in performance..
>> Is it " Worth " the expense to purchase a " good " converter ?? And.
>> what converter would that be ?
>> Will it be worth the effort to put a system together, for any Gain
>> over what I currently have ?
>> Thanks for sharing your thoughts, and experiences, I look forward to
>> reading them, and then
>> deciding whether, or not, an LF UpConverter will be an asset for me..
>>
>> 73 : Andy - KU4XR
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