Topband: The WD8DSB mini-flag antenna

Wed Feb 24 17:55:45 EST 2021

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 at 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 at gmail.com>
> To: David Raymond <daraymond at iowatelecom.net>
> Cc: topband <topband at 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 at 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 at contesting.com] On
>> Behalf
>>> Of Don Kirk
>>> Sent: Tuesday, February 23, 2021 5:22 PM
>>> To: wb6rse1 at 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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