This article is to provide some useful information about the original brown paint Ten Tec (model 546) OMNI and Ten Tec (model 560 Corsair I and II).

There is often confusion about the OMNI D. This designator was used for the OMNI series A to units that had a digital display instead of the slide rule dial similar to the one in the external VFO. The analog dial series A are relatively rare.

The series A was the first version. It had some bugs, but was a good offering for its contemporaries. It covered all the legacy ham bands. You may find some units that have a cover plate on the filter selection area. This is an upgrade to an A to bring it up nearly to a factory produced B model.

The series B has a 6 position switch for the filters, provision for 1.8 KC phone and 500 cycle CW IF xtal filters. It also has an AUX position on the band switch, which I have never seen implemented successfully. It was put there to imply that the OMNI could be upgraded for WARC bands added during its production years. You could add 10 MC transmit successfully on the WWV receive only position with the right components. Ten Tec has no record of the values of the necessary components. If I ever work on one that has them installed, I will try to post them for reference. I do NOT recommend any other than factory installed bands of 10 MHz and possibly 24.5 MHz. There are terrible transmitter spurs using the OMNI mixing scheme on 18 MHz. There were other significant improvements.

The series C was the final issue of the OMNI series. (There was no 546 D version, the "D" referred to an optional digital dial in the series A.) The 546 C had separate toggle switches for the IF and audio filters. The standard 2.4 KC phone and 1.8 KC phone filters worked well. The 250 and 500 cycle filters had insertion loss and group phase delay which resulted in an annoying thump on the first character of a received CW signal. Some online postings blamed the audio derived AGC for the problem. With the series C, you could use either a 500 cycle IF filter AND/OR the audio filter. You did not have this range of selection on the rotary switch in the B version. In my experience, I found my rig worked better on CW with QRM with the 1.8 KC IF filter plus an audio filter, and did not exhibit the AGC thump at all. Also, kits or factory installed WARC band coverage was available for 10 MHz, 18 MHz (do not use, see below) and 24.5 MHz.

The OMNI has ultra fast CW break in and wonderful natural sounding SSB audio. I loved this rig a lot. Other than the deficiency described below, I could find little fault with its design. The external VFO had a blend control that allowed true dual receiver split frequency operation that was great for 40 meter SSB DX operation. It was a break through feature way ahead of its time.

KNOWN SPURIOUS OUTPUTS OF TEN TEC Model 546 OMNI A, B, C, D:

Band	Frequency	Notes
160 Meters	1.950 MHz	adjustment in service manual, cannot be fully eliminated but tolerable.
15 Meters	21.320 MHz	adjustment in service manual, cannot be fully eliminated but tolerable.
17 Meters	18.000 MHz	(OMNI series C only) - Extremely bad, shows on sensitive wattmeter, possibly out of FCC spec for acceptable spurious emission. Adjustment in service manual, drifts and even when perfectly tuned, cannot be eliminated. Can hear it in receiver when tuned to 18.000 MHz, but worse yet, transmitter leaks 18.0 MHz in output regardless of VFO dial setting. Caused by mixing scheme. Elimated this problem in Corsair.
10 Meters (Position B)	28.98 MHz	Very bad. There is no way to fully eliminate. Use 29 MHz (10 meter band switch position C) and tune down. See service manual and specs from Ten Tec. If this meets FCC spurious emission specs, it just squeaks by.

There were modifications from Ten Tec OMNI 546 that added the WARC bands once they were legal. The 10 MC and 24.5 MC bands worked OK. However, the 9 MC IF plus the 9 MC pre-mix signal resulted in a significant spurious signal at the second harmonic of 9 MC, which was 18 MC on the 17 meter band. I strongly recommend that you do not transmit on 17 meters if you have this band installed. Use a sensitive power meter and try to adjust the transmit mixer for best balance, but I did not find it completely eliminated the spur. Use a separate receiver or spectrum analyzer and see that what I am telling you is true. Read the eham reviews and find the one comment that tipped me off. In its defense, the OMNI was never designed to cover the WARC bands. They tried to add them, and it was a stretch.

Align the receiver so that on 80 and 160 the coil slug is all the way down in the coil, not matching the dial markings. This gives better circuit Q and more sensitivity on 160, which can be a problem. The Ten Tec manual for the 546 is quite comprehensive, and if you follow it carefully, it will allow you to adjust everything the way the factory used to.

TEN TEC MODEL 546 OMNI A, B, C, D ACCESSORIES:

Model 243 - Remote VFO

Model 248 - Noise blanker

Model 252MO - AC power supply with meter

Model 645 - keyer

Various IF filters: 1.8 KHz, 500 Hz, 250 Hz

The 248 accessory noise blanker in the OMNI does not work. Period. I did see one blanker that had a two pole xtal filter that worked, but was never able to find a schematic or any information on it. It may have come from another Ten Tec rig. But the OMNI blankers with no xtal filter in them just plain do not work.

The diodes in the SWR and POWER detection circuit can fail. This commonly disables the ALC control circuit. If it fails, look at the diodes first. The T/R relay will cause weak or intermittent receive when it fails. Both these problems are a relatively easy repair. The VFO grease can set up; a kit is available from Ten Tec to rebuild the VFO. This is not an easy repair unless you are patient. If you find the VFO tuning knob is stiffer, dismantle it and apply new grease BEFORE you chew up the unobtainium drive parts. If your radio VFO is already damaged due to bad grease, you can buy an N3ZI VFO kit for a reasonable price; inject it at the external VFO jack, using the buffer amplifier he supplies. You will get more stability than the original VFO, and still use the OMNI digital frequency read out. This preserves all the fine features of this radio. However, the unique "blend" function in both the OMNI and Corsair for dual frequency receive will be lost by going to an external digital VFO. This feature is very handy for working split, and way ahead of its time.

Eventually the band switch contacts will fail. You may still be able to buy replacement wafers from Ten Tec. Once they are gone, you are up an unsanitary river with no means of propulsion. Before you assume problems with these, check the phenolic shaft coupler for stripped set screws. Also check the grounding of shield panels on the final compartment. Check the nuts holding the wafers in the final area, so that they do not allow slop as the switch is moved. Sometimes a previous repair to the SWR diodes did not include proper tightness.

The Model 560 Ten Tec Corsair was a fresh design that solved all the electronic problems with the WARC band spurs, the xtal filter problems, the noise blanker problems, and it came with a much better power supply that contained a crowbar circuit. The 160 meter sensitivity is no longer a problem. The Corsair has better metering. It has an audio speech processor which works very well. It has passband tuning that is excellent. All the mixer circuits are really upgraded to active mixers instead of diode rings that do not suppress spurs properly. The WARC bands work due to better mixing schemes. But 17 meters requires you to use "reverse" sideband to match the accepted convention; not a big inconvenience to get rid of the spur. This was the rig of choice for serious Dxrs for years, and still weighs in well on the Sherwood receive site, an impressive accomplishment for a rig of this era. Check the Sherwood ratings (http://www.sherweng.com/table.html). This radio ranks next to the legendary Collins R390 and the much newer Yaesu FT-950!

The repair comments on the VFO, T/R relay, SWR and POWER diodes apply to the OMNI and the Corsair one and two.

The Corsair two added a keyer and an even better noise blanker with selectable time constant. These changes, along with a gray paint job instead of brown are the most significant changes. A more detailed discussion is at: http://corsair.wikidot.com/corsair-c1c2

The Paragon was the first synthesized radio from Ten Tec. I see a lot of them sold as parts since the synthesizer circuit is hard to repair due to intermittents. If you want a vintage Ten Tec, I suggest the Corsair two is a better choice. If you want stability, use an outboard N3ZI VFO.

Any negative comments here should not be taken as hard criticism of Ten Tec 's ground breaking engineering accomplishment in producing these amazing radios. I have gotten a lot of enjoyment from operating this gear.