Ham Radio Help Desk

Continuing our discussion of Single Operator Two Radio (SO2R) station design brings us to the topic of antenna routing.

Previously we discussed SO2R gear arrangements which have two antennas connected to two radios, one antenna for each radio.

If all you have are two antennas for your two radios then there really is no point in putting in a matrix to allow either antenna to route to either radio.

However, let’s assume you do have a pressing need to multiplex the antennas and use this as an evolutionary step in our series of posts.
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Continuing our discussion about SO2R technical discussion brings a focus to the concerns of cross band interference between your two radios.

Having one transmitter spewing energy at full power while trying to listen on the other radio’s receiver is daunting. Unless you have an Elecraft K3, your radio’s ability to perform adequate band pass filtering is probably not sufficient for the 2nd and 3rd harmonics from the transmitter resulting in severe de-sense of the receiver signal chain.

Orienting the antennas to minimize their interaction will help. If you are lucky you may well achieve good isolation between at least some of the cross band combinations.

To help radios avoid this interaction, a few manufacturers have products which provide excellent band pass filtering.
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In my many years as a ham, I somehow missed the whole topic of the Single Operator Two Radio (SO2R) technique for amateur radio contesting. I pulled up a few YouTube videos showcasing the great operators using this technique and convinced myself SO2R is interesting enough to research.

The ability to add a bit more excitement to those late contest constant CQs with an additional radio looking for other contacts, especially new multipliers, is inviting.

There are many resources on the Internet about why to do SO2R. I invite the reader to explore these resources. We will review a couple key concepts on why to do SO2R and then dig in deep to some technical approaches.
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A friend is exploring antenna choices at his QTH and needs advice on some new antenna styles to try.

I stopped by for a visit to discover a very large yard with ample room for all kinds of wires antennas.

One issue my friend has it noise on his current antenna.

While his home is an excellent blank canvas waiting for lots of amateur radio antenna possibilities, I thought a full-wave loop might be a real good next-antenna to try.

Which full-wave loop to try first: 40 meter, 80 meter, 160 meter, more?

Google Earth comes to our aid with the excellent program.

Here is a view of my friend’s home…

Using the excellent tools in Google Earth I added two notional loop possiblities: a red line loop as large as the yard, and a 160 meter full wave loop in white. Isn’t this a nice big yard?

For the while loop I included the feed line as part of the total loop length to ensure a reasonable loading appears at the feed point in the house.

Using Google’s measuring tools I confirmed the white loop’s length to be around 525 feet or so including both sides of the transmission line. The red loop is about 680 feet total.

Simulations reveal the usual big lobes at higher frequencies and good behavior at low frequencies.

The big question is do we take full advantage of the yard and make the great big loop, or do we stick with a 160 meter full wave loop and live with that?

Anyone have any thoughts?

One thing I notice a lot during contests with my trusty Icom IC-746 (pre pro) is the splatter from power house stations nearby in frequency. I realize I can’t keep their splatter out if it falls within the passband of my receiver. However, I can at least try a more narrow filter to mitigate out of band energy.

The IC-746 comes with a 2.4 kHz wide filters for the first 9 MHz IF and for the second 455 kHz IF along with some wide options for AM and FM use.

I purchased this radio from a CW operator so it was no surprise what I found in the two 9 MHz optional slots: 350 and 250 kHz filters. They work real well for CW and, I suppose, the wider of the two would be good for RTTY work which I am just starting to use.

However, I do lots of SSB work and often get the AGC following the nearby signals rather than the one I want. So I really wanted to try out the 1.9 kHz Icom FL-223. It did not take long to find one on E-Bay from… Taiwan no less. In about a week I had my package.
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