The Ham Radio Series 39 - My Station

In last weekend's update on the tower work, commenter Fladave posted: 

Being the curious type, might I ask what goodies are in the shack -Might you write a short article perhaps ? Wondering what radios your running, and so forth

One of the disadvantages of sitting on my side of the screen is that while I don’t remember everything I’ve posted about, it’s pretty sure that I remember more than anybody else.  I’ve never done a real thorough description of the shack, and since weekends tend to be slow news, this is as good a time as any.

My station actually has four transceivers in it; practically, only one is on at a time.  My main station rig, that I operate almost exclusively is an Icom IC-7610.  The ‘7610 is the successor to their very successful IC-7600 that held that spot for the 10 years before I switched to the ‘7610, and very, very strangely, is the second IC-7610 I’ve owned.  As I explained in my New Year's '23 post : 

I won the grand prize from a ham radio contest.  The ironic part was that it was the same exact model I bought with the insurance payout from our lightning strike, two years before, so I replaced that two year old radio with a brand new version of the same model.  Of course, since it's my "lucky radio" nothing I do with it will ever fail, nothing will ever be wrong or go bad, right?

The ‘7610 is a fairly high end station, so why that radio?  I spent over 20 years as a designer on various radio systems, and while I think it’s true that “Software Defined Radio” has taken on some of the air of being a magical, wonderful, thing as Artificial Intelligence has in that domain, the SDR has some attributes that definitely improve receiver performance.

Radio hobbyists have long been taught that “sensitivity and selectivity” are what they should look for, but in pretty much the entire radio hobby, and especially in ham radio, you need to add in consideration of dynamic range or strong-signal handling.  Dynamic range, is often described in terms of IMD or intermodulation distortion, or the Output 3rd order Intercept Point (OIP₃).  IMD is a function of linearity in the signal chain.  That is, when you amplify, switch or handle an RF signal in any way, you don’t want to add distortion of any kind.  Signals can be made bigger in amplifiers, or smaller in filters or in a gain-control system, but you never want to add signals, which comes from distortion or nonlinearity.  There’s only one component in a receiver that’s intentionally nonlinear and that’s a mixer which is actually an analog multiplier – and most analog (not SDR) radios have more than one; two or three mixers are the norm.  If you have no nonlinearity, you get no IMD.  

The IC-7610 is a band sampling radio; that means the spectrum is filtered into bands for the receiver (there are two receivers and two such circuits in the box) and each of those bands is converted to digital format in a high-speed Analog to Digital converter.  The incoming signal goes through no mixers, only one amplifier and to get high linearity out of an amplifier all you have to do is make sure to run it with a high enough current to ensure that the signals it’s handling are small in comparison to the bias conditions.   Once the signals are in the digital domain, they’re mathematically perfect, meaning demodulation and any audio processing is done with pure numbers.  You’re not going to hear two high-power stations creating gobbledygook on a frequency they’re not using because of IMD.

Icom marketing literature source. 

All that said, why the IC-7610 instead of another of the many radios with a similar approach?  Part of it is general familiarity with Icom and their way of doing things.  Like I said, the ‘7610 in 2020 replaced the ‘7600 from 10 years before and in the 20 years before 2010 there were other Icom radios.  I’ve also had a couple of Kenwood radios, Heathkits and classic radios from Collins.  I spent the most time comparing the ‘7610 to the Flex Radio 6400, and as I recall it now, I thought the Flex was comparable but to get it set up equivalently to the IC-7610 would cost quite a bit more.  

The other radios?  On the operating desk next to the ‘7610 is a mid ‘00s-era Icom IC-7000, which covers HF, 6m, 2m, and 70cm – all modes on all bands.  It is not as good a receiver, especially on HF, but it’s only in the worst conditions that it becomes an issue.  Both radios interface to the computer over a serial port so that the software I run my station with (Ham Radio Deluxe) can control both, and I can run the digital modes that have become so popular, based on WSJT-X: FT8, FT4, and many more.  When I set the station up, my idea was to make switching from the ‘7610 to the ‘7000 to be as simple as possible so I could get access to the VHF/UHF bands.  I switch one cable, change the address of the radio HRD controls so I can switch from 6m to 2m in under a minute.  

Those digital modes require a digital interface from the computer, and while the ‘7610 can interface to the computer with a USB cable to create the audio tones those modes need, the ‘7000 requires an external modem.  I use a Signalink USB and swap the cable to/from the radio.  With a ‘7610 by itself, that complication goes away and the Signalink is not needed.

On the shelves near the station, I have a 1960s vintage Collins KWM-2.  While it was a dream radio to me decades ago, it’s kind of a “Sunday Drive” radio.  It’s a nice radio, it does everything an SSB radio needs to do (it doesn’t have a narrow, CW filter).  It’s just that the newer radios have operating conveniences and features that run rings around the older radios like that (often called boatanchors, although this one isn’t particularly heavy).  Sitting here, I don’t recall the last time I had it on, which probably means it’s time to carefully cycle power to it. 

A high point in life was meeting the Project Engineer on the KWM-2; a fellow by the name of Ed Andrade.  He was a friend of a friend, a nearby neighbor over on the beach side.  Both of them have unfortunately passed away since.  

Sitting on the table top closer to the ‘7610 is an Icom IC-703 a backpacker’s, low-power (QRP) rig.  I wrote about this back when I found it at the local hamfest.  The '703 isn't currently in production, but I consider it a good SHTF radio, and it frequently gets mentioned in places like Arfcom.  It covers the HF ham bands from 1.8 to 30 MHz and the 50 MHz or 6 meter band.  On a 12V battery, like my emergency backup hurricane battery, it will deliver 10W output, which is a pretty decent level.  Like the KWM-2, I couldn’t tell you the last time I used it. 

That’s the indoors.  Outside I have three antennas which cover 3.5 to 55 MHz (HF and 6m).  The 80/40/30 antenna is actually only designed for 80 and 40, a Cushcraft MA8040 vertical, but adding a simple little L-network to the coax gets it on 30m without messing up the other bands (or, at least, not messing them up too badly). 

This raises the question of how to go about connecting three antennas to four radios.  I use two four position Alpha Delta switches (their Delta 4B).  One selects the antenna and the other selects the radio it goes to.  Both switches are fully manual, and while the computer or the ‘7610 could drive a switch with some sort of control link, these don’t have a computer interface.  That's on my "one of these days" list.

The radio select switch at the bottom has a port that’s pretty much a spare at this point, labeled IC-7000 V/U (VHF/UHF).  It has a coax jumper on it that I connect to test equipment like my NanoVNA for antenna testing, but the IC-703 or anything that I want to connect to an outside antenna can go there.