Category Archives: Ham Radio

Dan sheds light on various Hammarlund SP-600 models

Many thanks to SWLing Post contributor, Daniel Hawkins, who leaves the following comment in reply to our previous post about the Northern Radio SP-600 and discussion about diversity operation. Dan writes:

Diversity operation: two or more receivers and antennas used to copy CW or RTTY from one or more transmitters.

Most of the Hammarlund SP-600s were models built for diversity use including the well-known JX-17, the most common SP-600. Diversity models can be used as single receivers. In this eBay example Northern Radio has modified a SP-600 J-11 for diversity use.

SP-600 nomenclature: J means joint army/navy (JAN) mil-spec components. L means low frequency. X means crystal frequency control in addition to VFO. My SP-600 is a JX-21, which is not a diversity model. Higher model numbers do not necessarily mean later production dates. All SP-600s use the same serial number sequence regardless of model. Somewhere between serial numbers 15,000 and 17,000 (mid 1950’s) Hammarlund stopped using molded black beauty capacitors and switched to installing ceramic capacitors.

The two-digit model numbers indicate model types. JX-1, 7, 10 and 21 were similar non-diversity receivers. SP-600s built for military contracts will have an additional tag showing the military model number(s).

Here is a great page showing Northern Radio modified SP-600s in action with accompanying Northern Radio RTTY gear.

Thanks for the primer, Dan! I believe I have one of the X models with crystal control, but I’ll need to verify once back home. Any other SP-600 owners out there in the Post readership?

Dan’s take on ADS-B with the Raspberry Pi B model

Many thanks to SWLing Post contributor, Dan Srebnick (K2DLS), who recently posted a detailed overview of his ADS-B installation on his blog:

Monitoring NextGen ATC (on the cheap!)

A key component of next generation air traffic control is Automatic Dependent Surveillance – Broadcast (ADS-B). The current FAA mandate is for all included aircraft to output ADB-B transmissions no later than January 1, 2020. But you don’t have to wait to receive and map ADS-B. There is a lot of air traffic to be seen.

[…]I decided to use a spare older RTL-SDR stick based on the RTL2832U and R820T chips. This USB device comes with a small antenna that I hoped would be good enough to get me started. It is not in any way optimized for the 1090 MHz signals that are used by ADS-B and is roughly 19 parts per million (ppm) off frequency. It cost a bit over $10 at a hamfest a couple of years ago. The designs have improved since the early models were offered. Newer models include a TCXO (thermally compensated crystal oscillator) for stability and accuracy.

I needed software to take signals from the RTL-SDR stick and plot them on a map. That software is “dump1090”, originally written by Salvatore Sanfilippo. I added an install stanza to the Makefile, along with a systemd service file, for a smooth system install. I also needed to install the RTL-SDR USB drivers. The complete installation runs “headless”, meaning no monitor, keyboard or mouse need be connected. Remote management can be done via ssh.[…]

Continue reading on Dan’s blog…

This is fantastic, Dan! Thank you for taking the time to share all of the code snippets you needed to do the installation on the Raspberry Pi B as well. Post Readers: if you have an older Raspberry Pi and RTL-SDR sitting on a shelf, use Dan’s guidance to turn them into an ADS-B feeder!

Click here to read my ADS-B feeder tutorial based on the Raspberry Pi 3.

Tony performs a quick LNA4ALL test

Many thanks to SWLing Post contributor, Tony Roper, who shares the following guest post which originally appeared on his blog, Planes and Stuff:

Quick LNA4ALL test

by Tony Roper

Despite the best efforts of the Royal Mail service, I have been able to get my hands on a Low Noise Amplifier created by Adam at LNA4ALL. The Royal Mail showed just how useless it is, when the parcel arrived here in the UK in just 11 hours from Croatia on February the 14th, but then not getting delivered to me until March the 14th – yes, one month! There is no surprise that courier companies such as DPD and Hermes are getting more business than the Royal Mail – they are bloody useless.

Anyway, the reason for the purchase is for a later review on an AIS dongle that I will be testing, but which has unfortunately been possibly damaged before getting to me.

So, as I had some time to spare I thought I’d run a quick test on how the LNA performs against the claims that is shown on the LNA4ALL website. For the test I used a quickly built 12v to 5v PSU that was connected to a Maplin bench PSU and also a Rigol DP711 Linear DC PSU where I could ensure a precise power input. As it was, it was good that I used the DP711 because my quick PSU was only chucking out 1.2v at connection to the LNA4ALL, despite an unconnected output of 5v – some work needed there I think.

Despite this lower power the LNA4ALL still worked with just the 1.2v input, though the results where not as good.

Other equipment used were a Rigol DSG815 Signal Generator and a Rigol DSA1030 Spectrum Analyser (no longer available), along with various Mini-Circuits shielded test cables. The Rigol equipment I purchased from Telonic Instruments Ltd last year.

Below then is a table that contains all the relevant data. As you’ll see the Gain claim is pretty much spot on with some being over. Just a couple of frequencies are below that which is claimed, especially at 28 MHz.

LNA4ALL Frequency data

A couple of things to note.

Firstly, somehow I managed to miss testing 1296 MHz. I obviously didn’t put it in the table in Excel before I started ? Also, the DSG815 only goes up to 1.5 GHz so I couldn’t test above that.

Secondly I ran a test for the AIS centre frequency of 162 MHz, for which there was no comparison to the LNA4ALL data. A gain of over 24dB though shows that the LNA would be perfect for those of you with AIS receivers that may want to get better reception. To prove the theory I compared the LNA reception against data without it connected to the NASA Engine AIS receiver that I currently use. In ShipPlotter I average a max range of around 15nm without the LNA, but with it connected this increased to around 22nm. The number of messages received also tripled as it was able to dig out the weaker signals.

The NASA Engine isn’t a bad receiver, but it is a frequency hopper rather than a dual monitor, and so it changes between the two AIS frequencies every 30 seconds (161.975 MHz and 162.025 MHz). I suspect a dual monitor would give better message numbers and range.

Below is a graph made using the excellent software by Neal Arundale – NMEA AIS Router. As you can see the message numbers (or sentences) for over an hour are pretty good – well, it is a vast improvement on what I used to get with my current “temporary” set-up, with 419 messages received in an hour. The software is available at his website, for free, along with various other programs that you can use with AIS. If you’d rather not use ShipPlotter he has created his own AIS Decoder which can be linked into Google Earth and such like. Visit his website for more information.

My antenna isn’t exactly top-notch. It is at a height of just 4 metres AGL in the extension loft, and it is made from galvanised steel angle bead used by plasterers to strengthen corners prior to skimming – this I cut down as a dipole for a target of 162 MHz. As usual with my trimming of antennas, I cut just too much off and ended up with it cut to 161.167 MHz. It gives a VSWR of 1.018 and Return loss of 40.82dB, with 162 MHz being approx. 30dB Return loss which equates to 1.075 VSWR – that will do.

Also, as I live right on the coast, about 50 metres from the sea, I’m practically at sea level, which doesn’t help much with range and signal reception either. Despite this the antenna produces great results, though it is just temporary until I can get a new homebuild up on the roof.

VSWR reading for the homebrew loft AIS Antenna

The LNA4ALL retails at various prices depending on what option you go for. I went for the aluminium box version so it was around £54 including the delivery. I had looked at a Mini-circuits equivalent, and when it looked like the LNA4ALL was lost I did actually order one. But this was nearly twice the price, and seeing as the LNA4ALL contains many components from Mini-Circuit I doubt it is any different really.

All in all the LNA4ALL is all you need to boost your weak signals – couldn’t get any more all’s in ?.

Many thanks for sharing your quick test of the LNA4ALL, Tony! Post Readers: if you’d like to read more of Tony’s work, check out his blog, Planes and Stuff.

More RadioShack store closing details including dates

Many thanks to SWLing Post contributor, Dave Zantow (N9EWO), who writes:

Here is a very interesting PDF legal document (via Prime Clerk) that not only has the “COMPLETE” RadioShack store list that are closing by early April (Tranche One and Two) but with important dates given.

Click here to download Docket 98-2 (PDF).

(more info:

Yes, sadly the store I worked in for over 8 years is closing by (before) April 6th when this store will become Sprint only. Being in a Mall , its funny it was not closed in the first bankruptcy ?? It’s been in that spot since late 1981.

Many thanks, Dave. As I mentioned in this previous post, poor RadioShack is all but dead for us hobbyists and Makers–one last chance to grab some closeout deals before the retail outlets become Sprint stores.

TX Factor Episode 15

Many thanks to SWLing Post contributor, Thomas Ally, who notes that TX Factor have just published their 15th episode.

Here’s the episode description via TX Factor:

Bob gives a relaxed overview of the RS-BA1 remote control software for the Icom IC-7300. We meet two youngsters with a passion for amateur radio. And Mike and Bob head off to Bristol to spend a day with some very enthusiastic members of the British Amateur Television Club to learn all about digital amateur television.

Click here to view on YouTube.