Saturday, June 17, 2023

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.


  1. Nice setup, SiG, comparable to what I had set up back in Long Beach. I had a Flex 5000 and a Kenwood TS-950SDX on HF, and a Yaesu FT-847 for Satellites. I used a Kenwood TS-790 for terrestrial VHF/UHF, and I round it out with my Elecraft K2/100 and a Kenwood TM-D710 for Get Outta Dodge radios. It's changed quite a bit since moving here, and I suppose I should do a "My Current Shack" post.

    1. Antennas are a weak spot right now. I'd like a taller tower and a 2m beam, but that just opens up a whole swamp full of questions that I'm uncomfortable with. The easier option is a pushup pole to hold the 2m beam that's only up when I want to use it.

      I have this strange interest in trying 2m moonbounce. For that, the antenna doesn't need to be high. Being low, but being able to position it in alt-az might even be better than being high because of ground reflections. Changing over to the 6m yagi from the old 6m LPDA I was using improved my signal on 6, but the LPDA was better than a wet noodle on 2m and yagi isn't.

    2. I'm waiting for SLW do decide what she wants for a patio cover/pergola/whatever. Then I'll put my 33' vertical, SGC tuner, and 4 elevated radials, which is what I had in Long Beach, up on it. 1/4 on 40, 1/2 on 20, and 5/8 on 17. It worked extremely well. And I've got a 6M 5/8 vertical NIB waiting to go up. When I was planning on a tower I was going to have an M2 2M9 Yagi with an SSB preamp at the antenna. Have 150' of 1/2" Heliax I was going to use.

  2. Thanks for the description OM. As Q&A leads to follow up Q’s, I am wondering how your lighting protection and grounding schemes have improved since you took the hit a few yrs back ? Few of us have installations that meet all current electrical codes, ( mine doesnt ) although we do follow tower and feedline grounding, with coaxial surge arrestors, however I lack a full perimeter ground.
    Its summertime in Florida and its a lightning fest down south in Ft Lauderdale.


    1. My bonding and grounding scheme had one major change, adding lightning protection to my rotator controller cable. That was posted here.

      Overall, I thought my lightning bonding and grounding scheme worked out worked well. No radio was damaged over its antenna port. The only radio that was damaged was my IC-7600, and the damage was having its USB bus transceiver blown. That was attached to the computer's USB port, and the computer's was blown by the lightning over the rotator controller's wiring.

      The computer, a many-year-old hand me down, had its power supply blown by the same induced lightning voltage on the rotator controller's wiring.

      The worst damage I had was to the most expensive item in the shack. I used to have a linear amplifier that did full legal power. I had an electrician run 220 back to the shack and the powerline had enough induced onto it to take out the amplifier's power supply. My ham insurance (the policy that ARRL sells) totaled it and paid for the replacement. It wasn't damaged over any of its RF paths either.

      There are three copper ground pipes, 8' long. There's one where all the coaxes enter and leave the house, and two on the base that the tower is mounted to. Some of that is discussed here>. The 4" aluminum pipe that holds the hardware to crank over the tower is part of the ground system, too, making it four ground rods. Inside the shack, all the equipment grounds are tied to each other over an aluminum ground bus, grounded to a Steelcase office desk (a surplus sale in town), trying to make one massive ground as much as possible. That ground is tied to the first ground rod, right outside the shack, but it's still around six feet of wire, meaning it's useless as an RF ground above the middle of the HF spectrum. A generally used estimate is 1/20 wave can be sufficiently far enough from ground to say things aren't grounded. To find 1/20 wave at some frequency, take that old antenna quarter wave formula (234/f in MHz for Length in feet) and divide that by 5. It's still quite useful as a lightning ground.