Promoting Diversity (reception) - you and your TS-930/940

[N8YX]

The TS-930 and TS-940 series rigs arguably are the finest HF transceivers which use through-hole, rather than SMT construction that Kenwood ever built.

They'll do almost everything one could ask for...except receive two frequencies at once, a la the '950 or FT-1000D, and at the same time be computer-controllable.

Here's the beginning of a mod series which will rectify that.

First, we're going to need a method by which to share the antenna connection - as the TR7/R7 and TS-820S/R-820 can do. As delivered from Kenwood, the '940 has an RCA connector on its rear panel titled "External Receiver". A switch allows routing the main station antenna to the '940's internal receiver or to an external unit. But not both at once.

Looking at the layout of the rig and its rear panel with the bottom cover off, one finds a 'Remote/Internal' switch and miniature coax leads running to the common and rightmost connections, and a wire running from the RCA jack next to it to the third switch terminal.

To make the External Receiver connection "always active", one needs to unsolder the larger of the two coax cables which connect to the switch and move it to the rightmost switch connection - tied to the other coax cable. The wire to the RCA connector is then tied to the center terminal of the switch. The switch itself can be used to turn the connection to the external receiver "off" if ever desired.

The best approach to feeding both internal and external receivers would be via the inclusion of one of the following Mini-Circuits power splitters, as they would minimize impedance losses caused by connecting both receivers together with no form of matching network:





These offer 30dB isolation between ports and are usable from 0.004 to 60MHz.

I'm going to order one for each of my '940s. When I install one I'll post pics and details.

One person on the TS-930S Yahoo group indicated this was also a viable mod for the '930, so the instructions I've presented above may be adapted as necessary. I'm not sure how its rear panel is laid out.

[N8YX]

Next, we need a way to mute the companion receiver on transmit.

We can take the "Easy" or the "Hard" way out. The hard way assumes that you won't be using an external power amplifier and involves constructing a cable which will run between the external receiver and the TS-940's "Remote" control jack - which is a 7-pin DIN. For purposes of discussion I've slaved an R-5000 to my '940, so one could build a 7-pin to 7-pin cable and use the '940's amplifier control relay to accomplish the mute function. Refer to the '940s and R-5000 owner's manuals for details on which pins on the connectors at each cable end are used.

The "Easy" way - also for those who want to use an amplifier with the setup - is to buy one of these:



Ameritron offers a 'plug and play' cable for the '940 which runs right from the '940's Remote jack to the unit's "Multi Port" connector. You then make up a muting cable for the R-5000 which has an RCA male connector on one end and a 7-pin male DIN on the other. the cable center conductor runs to the corresponding 'mute' terminal as identified in the R-5000 owner's manual. Plug the RCA connector into the 'Radio' connection of the '704 and the DIN connector into the R-5000's "remote". An RCA-to-PL-259 equippec cable will let you bring the antenna feed from the '940's External Receiver jack into the '5000's Ant1 connector.

When you PTT...instant mute.

Using a scope, I've looked at the residual signal which is present on the Remote switch during 100w-out TX and found the amplitude to be very low. Most of it comes from leakage around and through RL4, the main T/R relay. Even when connected directly to a companion, unmuted receiver, the outputted signal isn't enough to deflect the rig's s-meter past 20/S-9. It's in the millivolt region, if that. Adding the Mini-Circuits mixer should further reduce it.

If one wishes to connect and use an amplifier with this setup, just apply 12VDC to the -704's power port...run an RCA-to-whatever cable from the -704's "Amp" and "ALC" jacks to the corresponding connections on your amplifier.

In subsequent parts we'll look at installing the splitter then get around to discussing how to computer-control the combination.

[N8YX]

Part III - DSP:

Another bit which both the TS-940S and R-5000 lack is DSP filtering. While retrofitting a '940 with an IF-based unit is possible, it would require a redesign of the entire IF board. I don't feel like messing with that at the moment. In addition, there's not much room to work with in the '5000...so an audio-based solution is required.

But which one? There are several companies producing capable DSP units, and the reviews of such equipment tend to be a little canted (IMHO).

One of the obvious requirements is for dual-channel operation. That is, the ability to feed the outputs of two rigs into the DSP unit and route the processed audio to two different output channels. The only unit currently offering these capabilities is the Timewave DSP-599zx:



The -599 won't process both channels at once, but I'm using mine as follows: 'Pass-through mode' on Channel A (the '940) and 'Process mode' on Channel B (the '5000). The '940's noise blanker and filtering system are a bit better than that of the '5000, and the Timewave unit closes the gap.

It also offers a CW pitch shift feature, which is functionally equivalent to the '940's Pitch control.

Timewave advises the user to make use of the '599's "PTT Input" for muting purposes when operating the unit in conjunction with a transceiver. I've currently got it connected to the 'Amp' connection of the ARB-704 (see previous post for details). Were I to add an amplifier to the shack, I would have to redo the cabling scheme to accommodate its switching control. Thus, a cable from the 'Remote' connector on the '940 will be run to the 'Radio A' (8-pin DIN) connector on the Timewave, and its 'PTT Input' connector (which is actually in parallel with the PTT input pin on the Radio A DIN) will be used to control the '704 via another custom-built cable.

Performance-wise, the '599 knocks out darn near all of the hash n' mash which pollutes the airwaves in my locale. Careful adjustment is the key, but when you finally get the 'right' combination figured out, you can store your settings in one of the unit's 6 memories. You can also set the unit so it will power up with your custom profile.

[N4VGB]

"Dual receive capability" and "diversity reception" are completely different topics. Just thought I'd mention it.

Now don't confuse the two again.

[N8YX]

"Dual receive capability" and "diversity reception" are completely different topics. Just thought I'd mention it.

Ahhh...no...not when you run the products of two separate receivers/antennas through a combiner/filter and utilize the recovered audio as a countermeasure against propagational fading.

The '5000 has an antenna selector which is also remote-controllable via software commands. Thus, I can switch between a shared antenna or one of several slopers manually - or let software handle it. One can also query the rigs' S-meter reading via software, so a 'voter' arrangement using Kenwood's CAT commands is possible.

[N4VGB]

"Dual receive capability" and "diversity reception" are completely different topics. Just thought I'd mention it.

Ahhh...no...not when you run the products of two separate receivers/antennas through a combiner/filter and utilize the recovered audio as a countermeasure against propagational fading.

The '5000 has an antenna selector which is also remote-controllable via software commands. Thus, I can switch between a shared antenna or one of several slopers manually - or let software handle it. One can also query the rigs' S-meter reading via software, so a 'voter' arrangement using Kenwood's CAT commands is possible.

Even true diversity can have it's problems. The phase of recovered audio depends on the phase of the RF at the detector stage, true diversity reception can produce it's own fade problem when the phase of the RF at the two separate detctors aren't in perfect sync. ;)

[N8YX]

Even true diversity can have it's problems. The phase of recovered audio depends on the phase of the RF at the detector stage, true diversity reception can produce it's own fade problem when the phase of the RF at the two separate detectors aren't in perfect sync. ;)

True, but there are a couple of ways to sync-lock the signals via phase-shifting or DSP techniques. The syncro-fade problem is less aggravating on voice modes as it is with data, and I've some ideas which should minimize THAT.

All that's necessary at this point is to construct the communications interfaces...write the code...and test the thing out.

[AF6LJ]

Fun Project :)
I am carious to know how the power divider works out.
I have a new (to me) project radio on it's way (R-599), if this works out I will give serious consideration to modding my TS-820.

[N4VGB]

True, but there are a couple of ways to sync-lock the signals via phase-shifting or DSP techniques. The syncro-fade problem is less aggravating on voice modes as it is with data, and I've some ideas which should minimize THAT.

Good luck, we just covered that topic in regards to the mil R-1247 on the R-390 email reflector group. The R-1247 is a modified R-390A done by Manson Labs and used in the AN/GRC-129, which also featured a T-368 with the modulator removed and a SSB generator in it's place. The R-1247 shows up on eBay regularly and brings high prices because of the completely false belief that it was a special order item used by NASA only. NASA did use them for data recovery in remote locations around the world, but it wasn't a strictly NASA piece of gear.

The R-1247 featured external oscillators that were supposedly of extremely high precision, but keeping them adjusted proved an endless task. It indeed came up in the email exchanges that we hams should be able to home brew some little DDS based oscillators and actually make the R-1247 perform to it's original goals. But none of us could think of a single reason to do it! :rofl:

I now several hams who use true diversity receivers and antenna setups, it will help you most of the time to dig the weak ones out for DX work. Some who have the antenna voting system instead, claim it works better? I dunno, since I have neither.

[N8YX]

Latest score:

A pair of (hopefully good) filters from a TS-930S.

The stock Kenwood SSB RX and TX filters as used in the '940 are 2.4KHz. The '930's are 2.7 and 3.0khz, respectively. A simple swap should widen things out just enough on transmit to get good SSB reports and give the rig a little more high-end response on AM RX when the "narrow" filter selection is engaged. When receiving SSB I can always use the rig's Slope Tune controls to tighten things down if necessary.