The link takes me to a page showing a unit with no display and no tuning
knob, needing a computer to run it. I needed to follow a link on that
page to find the self-contained unit.
http://afedri-sdr.com/index.php/lan-iq-sdr
http://afedri-sdr.com/index.php/ordering-information
I agree that the LAN-IQ-SDR looks really slick for DF work. Thanks for
posting!
73, Jim K9YC
On 2/24/2021 12:54 PM, kolson@rcn.com wrote:
I have read some negative info on the Malahit (the EBAY clones especially, the
Russian originals seem better) but it might be OK for RFI investigations. N9EWO
Review : Russian Malachite / Malahit DSP SDR (qsl.net)
But I can recommend this: LAN-IQ SDR (Stand-alone SDR) (afedri-sdr.com)
This is about $400 with tuning knob encoder but is a small, slick and fairly
serious receiver with a 12 bit Direct Sampling receiver on HF (the Icom 7300 is
a 14 bit Direct Sampler) and covers from 30 kHz to 1700 gHz with built in
Spectrum Display and Waterfall. It runs on USB power (I use a Power Bank that
folks use to recharge up their phones). It probably is overkill for just
occasional RFI expeditions, but if you like the idea of having a portable wide
range RX when not on the RFI hunt), it is well worth it.
No connection to the seller (4Z5LB in Israel). He shipped mine promptly, I was
surprised how soon it arrived!
73, Kevin K3OX
----- Original Message -----
From: Don Kirk <wd8dsb@gmail.com>
To: David Raymond <daraymond@iowatelecom.net>
Cc: topband <topband@contesting.com>
Sent: Wed, 24 Feb 2021 14:23:17 -0500 (EST)
Subject: Re: Topband: The WD8DSB mini-flag antenna
Hi Dave,
I hate to recommend anything and others have given you some good
recommendations, nevertheless I will make a few comments.
My workhorse radio for direction finding is the good old Realistic DX-440
(also sold as a Sangen ATS-803A) and you can still find nice clean used
ones on E-Bay for less than $100 (I suspect I drove the price of them up).
It is a very old and large radio, but I love this radio for numerous
reasons. It has an external antenna jack as well as an excellent
continuously adjustable RF gain control that really comes in handy. It
also has a BFO for receiving CW which sometimes is very helpful depending
on the signal you are tracking. It uses 6 D cells and has excellent
battery life. I use the radio in AM mode for tracking down power line
noise, but sometimes I need to use the BFO for signals that are just a
carrier as it helps to hear the signal (no need to look at a meter, etc).
I also use a laptop based SDR receiver which is just a cheap RTL-SDR dongle
along with a ham it up converter (both from NooElec) and I have both of
these stuck to the back of my laptop screen so I can go portable with it,
and this is a very handy tool especially if the signal is wandering all
over the place or if I am in a heavily populated area with lots of
different sources of RFI present. If you go this route make sure you pay
the few extra bucks for a TCXO in both of them.
The IC-705 is also a radio that likely would work well, especially since it
has waterfall displays for both the RF and Audio Spectrum, and it also has
an Audio Oscilloscope and I'm anxious to see how helpful that might be.
I see there is now a very small handheld HF SDR receiver called the Malahit
(looks like the size of nanoVNAs), but I don't know how good they really
work. If they become a trusted device I certainly will be interested in
using one for DFing.
73 my friend,
Don (wd8dsb)
On Tue, Feb 23, 2021 at 9:18 PM David Raymond <daraymond@iowatelecom.net>
wrote:
Don. . .thank you for the very nice loop article in QST. And, thank
you for your generosity of not taking compensation to help make it
affordable. The loop antenna would be a very useful tool to have in the
arsenal for DFing interference sources of all kinds which continue to
proliferate (even out in the country where I live). I am currently
experiencing an interference problem on 160m that is about 10-15 KHz
broad with a couple of modest peaks. It often parks in the 1825-1835 KHz
window on 160m. The frequency range it occupies wanders some and varies
inversely with the outside temperature. I have DFd it fairly close with
the HI-Z 8 circle array and know the direction of the source but need
something portable to home in on it. Do you or anyone here any
suggestions for a reasonably good portable receiver with an external
antenna jack (might be hard to find?) that will cover the 160m band . .
.and maybe up to 30 MHz?
Thanks and 73. . . Dave, W0FLS
On 2/23/2021 5:37 PM, John Kaufmann via Topband wrote:
As a follow-up to my original post, here are a few additional comments.
Don, you mention that you designed the mini-flag for a deep null off the
back at low elevation angles, which is entirely understandable. As I
said
in my earlier post, the null is very pronounced in the AM BCB on local
groundwave signals. However, I also see pretty significant nulls on
higher-angle signals, too. Just a short time ago, I was listening to
W1AW
on the low end of 160. They are located only ~100 miles from me. Their
signal has to be arriving at a pretty high angle, but the null is still
quite pronounced.
My homebrew preamp, that I mentioned in my post, uses a cascade of UTO
511
and UTO 533 mini-amplifier modules. I used this preamp, not necessarily
because it's optimal, but because I already happened to have it on hand.
The gain of the 511 is given as 16 dB typical while the 533 is 17 dB,
which
should yield a net gain of ~33 dB for the cascade of the two. The noise
figure on the 511 that serves as the input amplifier is specified as 2.3
dB,
but its spec sheet gives an operational frequency range of 5-500 MHz, so
I
can't be sure the noise figure (or the gain) holds up at lower
frequencies.
Nonetheless I can hear the ambient noise in my receiver increase on 160m
when I connect the mini-flag to the preamp, which suggests the noise
figure
for this preamp is at least adequate at my location. I use a Yaesu
FT-817ND
"backpack" radio as a portable radio with this antenna.
In EZNEC I calculate the RDF of this mini-flag as 7.4 dB on 160m at a 20
degree elevation angle. That's essentially the same as the K9AY loop or
other similar pennant/flag antennas. For use as a receiving antenna, the
important thing is the noise figure of the preamp. The DX Engineering
Web
site does not give the noise figure of their preamp. Don, perhaps you
know?
The other thing that might degrade the antenna is common-mode signal
pickup,
which can be a problem for very low gain antennas where you are working
with
very small signals. However, based on what I observe in terms of antenna
pattern for this mini-flag, I can't say that I see any pattern effects
that
might be attributable to common mode degradation. Don, maybe you can
comment here as well on this aspect of the antenna.
As I also mentioned in my earlier post, the dimensions of the DXE
implementation are somewhat smaller than what's given in the QST article.
For me, that works out well because the width of the DXE mini-flag just
manages to fit inside the trunk of my mid-size sedan. A wider flag would
not fit.
73, John W1FV
-----Original Message-----
From: Topband
[mailto:topband-bounces+john.kaufmann=verizon.net@contesting.com] On
Behalf
Of Don Kirk
Sent: Tuesday, February 23, 2021 5:22 PM
To: wb6rse1@mac.com
Cc: Top Band List List
Subject: Re: Topband: The WD8DSB mini-flag antenna
HI Steve,
Thanks for the nice implementation comment.
The portable flag front to back ratio is highly related to the elevation
angle and frequency of operation (just like any terminated loop), and
therefore I did not want to overstate the front to back ratio in my
portable flag article. I designed the portable flag for direction
finding
local RFI (ground wave based signals) and therefore made sure I selected
an
appropriate termination resistor to provide a very deep null at low
elevation angles on 160, 80 and 40 meters where I often deal with RFI
(the
portable flag has a very high front to back ratio at low elevation
angles),
and because of this it also has exceptional front to back ratio at low
elevation angles down in the AM Broadcast Band. Very small flags have
just
as good front to back ratio and RDF as a full size flag as long as the
appropriate termination resistor is used. The problem is when the flag
becomes too large for the frequency of operation which causes the
directional properties to degrade. You can see some front to back ratio
vs. elevation plots for my portable flag on my simple portable flag
website
and here is the URL to that site:
https://sites.google.com/site/portableflagantenna/home
Problem with very small flags is that the noise figure of the preamp
becomes a critical parameter, and because of this I don't recommend
attenuators be placed before the preamp as this causes degradation in the
signal to noise ratio. I stumbled upon this issue when doing field tests
on one of the DX Engineering prototype preamps, and had them change the
design so the attenuators now come after the actual amplifier stage which
solved the problem.
Everything I said above about the performance of very small terminated
loops assumes no interaction with surrounding objects, and ignores issues
related with feedlines since the feedline is very short on the portable
flag.
P.S. I make no money from DX Engineering as I agreed to not be paid in
order to keep the price of the portable flag as low as possible.
73,
Don (wd8dsb)
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