Whenever I am perusing through e-bay or walking the isles of a hamfest, I am always drawn to the "Twins", whatever the make and model. So it is no surprise that I would end up with a few of these beauties. 

So what defines twins? They are “separates” (separate transmitter and receiver) manufactured by the same company with the intent of working together and looking alike. They often have the capability of operating in a “transceive” mode (one unit having frequency control of both units). They are often referred to as a “line” like the Collins “S” line. Not only were the transmitter and receiver designed to look the same, but a whole host of matching accessories (amplifiers, speakers, antenna tuners, station consoles, etc.) was manufactured to go with them (great marketing scheme).

Twins had a relatively short golden age. Prior to WWII, most hams home brewed their own transmitters. Manufactures felt lucky getting hams to spend their money on commercial receivers. There could be no twins in this environment (unless someone home brewed a transmitter to match a receiver – humm – I wonder if that was ever done?).

Twins started showing up in the mid 1950s. Back then big was beautiful daddy-o! Big cars with rocket fins, homes in the suburbs with yards for towers, big expectations. Naturally, a ham radio needed to be an impressive sight! This was the age of the “Boat Anchor” (a term given decades later to these wonderful radios because they were heavy enough to keep a boat anchored). There are a few twins from this era.

Next came the reign of the “Low Boys”. This started around the mid-1960s and went through the mid-1970s. These radios had slimmed-down from the Boat Anchor (BA) days. They were about half as high, wide and deep (1/8^th the volume) of the BA rigs and took up much less space on the operating table (and looked sleek too – far out man!). These were the hay-days of the twins.

Transceivers started showing up about this same time. They were focused on squeezing the most radio into a single box. They were trying to break into the mobile scene. On the plus side, they offered a single frequency-tuning knob that made the receiver and transmitter track. On the minus side, they only offered a single frequency-tuning knob that made the receiver and transmitter track. Soon after, receiver incremental tuning (RIT) was invented and the circle of life was completed.

Transceivers were (back then) a compromise in performance versus size. To reduce the size and power consumption of the radio, they shared stages (tubes) for both transmit and receive. Neither function getting the optimum performance one could hope for. Twins on the other hand could also work in “transceive” mode (one unit having frequency control of both units) or as separates. They used optimized circuit designs in both the transmitter and the receiver. Although none were marketed as QSK capable, they can readily be adapted to QSK service. Transceivers of this era can never operate QSK.

As radios became solid state, a lot of the compromises inherent in transceivers were corrected. Ultimately, the transceivers won the day and the twins were gone forever (sigh).

Twins came in a few combinations:

Identical Twins have the same exterior dimensions. Their panels are laid out with knobs, dials, switches, and meters all in the same locations. The functions of the controls are different of course, but take one step back and it’s hard to tell them apart. Some examples of identical twins are:

1. Drake 4 line (R-4C / T-4XC, R-4B / T-4XB, etc.)
2. Collins S line (75S3 / 32S3, 75S1 / 32S1, etc.) 
3. Hallicrafters (SX-117 / HT-44) 
4. Heathkit (RX-1 / TX-1, HR-1680 / HX-1681)
5. Yaesu (FR-101 / FL-101)
6. Kenwood (R-599D / T-599D)

Mirror Image Twins have the same exterior dimensions. Their panels are symmetrically laid out with the same number of knobs, dials, switches, and meters. The placement of these controls is a mirror image of their twin. For example one would have the meter in the upper left corner while the other would have the meter in the upper right corner. Some examples of mirror image twins are:

1. Hallicrafters (SX-146 / HT-46)
2. Heathkit “Green” line (SB-301 / SB-401, etc.)

Fraternal Twins have the same exterior dimensions. Their panels are styled the same but are neither identical or mirror images. They often do not operate in the transceive mode. There can be a difference in the number of knobs or meters. Some examples of fraternal twins are:

1. Collins “Gold Dust” twins (75A4 / KWS-1, 75A3 / 32V3, etc.)
2. Heathkit (RX-1 / HX-10, SB-303 / SB-401)
3. Yaesu (FRdx-400 / FLdx-400)

Kissing Cousins are manufactured by the same company, have the same general styling and were intended to be “paired-up”, but are not the same size or layout.  They do not operate in the transceive mode, only separate. I personally don’t consider these to be “twins”. Some examples of kissing cousins are:

1. Hallicrafters (SX-115 / SX-101 / HT-32, SX-111 / HT-37, SX-140 / HT-40)
2. Hammarlund (HQ-170 / HX-50)
3. Heathkit (DX-60B / HG-10B / HR-10B)

I guess there can be great debate as to what category some rigs fall into, but I think I have given a fairly accurate accounting.

Now you can look through my “twins” pages and know what you are looking at.

Have fun.