Category: review

Broadcast Overload on Kiwi SDR

The Kiwi SDR and Wellbrook loop provide a very good single antenna solution for 0 to 30 MHz shortwave reception. The Kiwi is capable of displaying the complete band of 30 MHz, but the disadvantage is the very high power from some of the LW and MW stations can cause the receiver to overload in the evenings.

One approach would be to build a notch filter to attenuate just the one or two strongest signals, in my case this would have been 909 kHz Radio Five Live from Brookmans Park, and 1332 kHz Christian Radio. The problem I had was in the evening this would often change, and at times some of the continental AM stations would become an issue.

The alternative would be a bandstop filter, that would just attenuate the MW band. We also have two amateur allocations at 472 kHz and 1.9 MHz that I would like to receive, with the medium wave band in the middle. The solution would seem to be a bandstop produced by Nooelec. The units retail for around 11 dollars in the USA, you can get them from Amazon or eBay for around 16 GBP with free delivery.

They say on their website “We designed Distill:AM to provide sufficient attenuation for broadcast AM frequencies (>40dB typical) while ensuring adjacent bands, such as 160m, are minimally affected. The -3dB rolloff of the filter is 350kHz and 1900kHz. Minimal out-of-band insertion loss means the filter can stay in place for most any application, though we do recommend removing Distill:AM from your setup when not listening to HF frequencies. As a true bandstop filter, you are able to pass-through DC (bias power) when it is required.”

You can view the data sheet below.

I found 909 kHz reduced from around -20dBm to -50dBm so this helped reduce any signal overload.

You can read more or use the Kiwi receiver here.

The Welbrook look is an active broadband receiving loop antenna.

Nooelec have a range of products online.

ADS-B Reception using 5/8 wave 1090 MHz aerial.

I recently purchased a 5/8 wave antenna for 1090 ADS-B Reception from eBay. At the time the antenna are being sold by stranislavpalo130 in 2 versions from a 30cm 5/8 wave to 60cm 2x 5/8. The are priced between 20 to 25 pounds and are really well constructed.

1090 5-8 waveThe 30 cm 5/8 wave version is shown here, and comes complete with waterproof raydome and radials. The mounting bracket will take a standard small pole, although the antenna is so light its never going to present much of a load. I mounted mine for this test on a 12 m spiderbeam roach pole, and if its not too windy it can easily be mounted near the top.

I this time configured virtual radar to work with the Kinetic SBS-1. You can download the manual for the SBS-1 or visit their website for more information on their product range. If you havent see or used virtual radar I would suggest you review the setup information described earlier.

I compared the 5/8 wave with my home brew co-linear and the 5/8 wave won ! To be fair the co-linear I built was never vswr tested or even checked for a 50 OHM match as I have nothing that operated on that frequency. The home brew antenna worked out to a range of around 60 to 80 miles, the 5/8 is 80 to 100. The number of aircraft tracked (I know this varies by time / day) seemed to increased from 80 to over 100. The indications are the 5/8 wave represents an increase in range and number of aircraft received at anyone time.

Virtual Radar Screen

virtual radar map

Kinetic Base Station Radar

kinetic base station radar

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Comparing the Wellbrook Loop to a Doublet Antenna

This evening I decided to complete a test using two different HF setups in an effort to compare the receiver performance of my antennas.

Radio 1, Kenwood TS 990, doublet antenna 10m per leg @ 9m

Billy offers support.

Billy offers support.

Radio 2, Elad SDR, Wellbrook RX loop @ 3m

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I decide the best way to test on receive would be to leave both radios receiving on 7076 KHz for 90 minutes, using WSJT-X. Both receivers had been set to 3 KHz bandwidth, and over the course of the next 90 minutes they each collected over 600 measurement reports.

The test started at 1830 Hrs and continued to 2000 Hrs. The doublet collected 633 measurement reports, and the wellbrook 740. This was the first indication that the Elad coupled with the Wellbrook was out performing the Kenwood / doublet setup. The next stage was to look in detail at the reports, WSJT has an option to write all received data into a text file, this includes time, s/n and decoded text. I used this to select at random some calls that represented a selection of EU (and DX if possible) and compare the relative signals received at the very same time on both radio 1 and 2.

The following table shows a selection of data points

wellbrook v doublet

After reviewing the data it was clear the Wellbrook loop improved the quantity of stations decoded, and in many cases also improved the s/n received.

This is by no means a definitive test, but it does indicate the Wellbrook loop (as many others have reported) work well in somewhat noisy urban environments.  The wellbrook loop can be reviewed online at the Wellbrook communications website, the version I used for the tests was ALA1530  its 1m and designed for medium and shortwave 50 KHz to 30 MHz. Steve Nichols G0KYA completed a review in January 2012 Radcom You can see the Eznec plot as photo 3 in the review.

The other factor to consider is the loop antenna has some directivity, I didn’t rotate the antenna at any point during my tests. In many cases rotation will improve / reduce signals as the antenna has directional properties.

The Welbrook performed well on 7 MHz, I suspect it would be even better on 1.9 and 3.5 MHz… to be continued….

Dave M0TAZ

Hytera MD785G review and first impressions.

After my last article on the TYT MD380 I decided it would be nice to get a DMR radio for the home / car use. I read quite a lot online and decided to select a radio that would support roaming. The Hytera MD785G fitted the bill, and is available in both a high and low power UHF or VHF version. I selected the UHF 45w version, and purchased the programming software and lead. The ability to load codeplugs is essential, as DMR is still very much a moving target, new repeaters are coming on all the time.

The Hytera MD785G is a tier II DMR radio, UHF 400 to 470 MHz, with a 1024 channel capacity. It can be programmed with up to 64 zones (16 channels in each zone)

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Size 174 x 60 x 200 mm at 1.7 kg with colour LCD display.

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RF power is adjustable depending on model  from 5 to 45w (high power version) or 5 – 25w (low power version). The 785G supports GPS although the amateur DMR networks does not support GPS location data at this time.

The radio has a BNC connector on the rear for your aerial, and SMA for GPS. The resolved audio is loud, crisp and clear and the radio looks and feels solidly built.

 

 

I couldn’t find any good quality pictures of the top, front and rear online so I took some myself. Here you can see the BNC connector for your aerial, heatsink, power lead (detachable) and SMA for the active GPS antenna.

 

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UPDATE Jan 2016

The structure of the DMR network has changed substantially since I first wrote this article, and many of the codeplugs have become outdated. New codeplugs that reflect the FEB 16 structure can be found at GB7JG and GB7CL website.

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At the time of writing some previous sites have outdated codeplugs (although links retained as they may be updated) Codeplugs online are often outdated G0HWC site.  Other codeplugs are available from codeplugcentral and  GB7DD.

Hytera MD785 CPS software is available at GB7DD

You can monitor live UK traffic for DMR online, and clicking on a callsign / repeater  will filter activity just for that call / repeater.

A list of all the UK DMR repeaters is available on the UK repeaters website.

Ham radio now filmed W2XAB John giving a great talk available to watch below on DMR. He also produced a guide to DMR in PDF free to download.