How-To 2m and 70cm DEMI Transverters on a 6700 & Questions

EA4GLI

I have researched the forum for Transverter installation options/ideas and there are several threads floating around with information. It is a bit scattered so I thought that I would put my findings and decisions on a new thread that might be helpful to others.

The goal for me is to add the 2m and 70cm capability that I get out of my TS2000 to the Flex 6700. I want to have an all mode HF, VHF, UHF rig capable of working repeaters, SSB DX and SAT (even EME).  

After talking to FRS (Thanks Dudley) and DEMI (Thanks Sandra for your help) I have a better idea on how to proceed. But I would like suggestions or comments if you guys find holes in my current configuration idea.

The 2m part will be covered with the Amp-Preamp DEM 2MLDPA. In my case I went for the 60w version.

http://www.downeastmicrowave.com/product-p/2mldpa-60.htm



I added the following options:

• LDREM-OPT for remote ON/OFF
• LD-HP Common RF for a single connection to antenna
• XVRT IN and XVRT OUT ports (Default)

For the 70cm part I selected the L432-28HP which is the fully assembled 28Mhz IF 60w output 440 Transverter.

http://www.downeastmicrowave.com/product-p/l432-28hp.htm





The image above doesn't have the TX IF and 10 Mhz ref input BNCs.

I wanted to be able to use it with the 6700 and the Flex 1500.
I added the following options:

• Split IF configuration (this is important for Full Duplex)
• IF Drive 0 - 100mW
• HP Common RF Configuration (Single antenna)
• DUAL LO OPTION: Allows the use of either the internal clock or external 10Mhz source.
• Optional filters to be able to work at both ends of the band for SAT work and Repeater work.
• I also went with the larger heatsink. 

I also added a 10Mhz reference HUB. The DEMI 10-4:

http://www.downeastmicrowave.com/product-p/10-4.htm



This is a very interesting device if you happen to have the GPSDO option in your 6700/6500. It allows you to use the 10Mhz reference from the Flex radio and input that into 4 devices. In my case I will use it to send a 10MHz ref to the 70cm transverter, the Flex 1500 and the Kenwood TS2000 with this TXCO replacement (http://www.vk3hz.net/XRef/XRef_Home.html).

Remember to add BNC 50 Ohm 1w  to the unused ports.



Now on to the schematic for the connection with the Flex 6700.



Which finally brings me to my questions and concerns:

1. I have to share the XVTR port for both 2m and 70cm so, how do I tell from the 6700 to engage TX2 or TX3 based on the panadapter that is TX in SmartSDR? Those are the blue lines on the schematic.
2. I see how if I TX in 2m I can RX in 70cm because I will TX out of XVTR and RX on RXB on the Flex (green line). But what about TXing in 70cm and receiving in 2m? Do I need another port in the DEMI 2m Amp to send the receive preamped signal into RXA? And if I do that? Where do I put a Magnetic Loop for RX?
3. Am I missing anything in my configuration? Is this doable? 
4. I have tested with dummy loads and I can move both the TX and RX frequency in 2m and 70cm while I transmit which should allow me to move to compensate for doppler effect when working SATs, but I can't move both panadapters at the same time... I can't find a way to sync them to move them simultaneously. I guess orbitron/sat32/hrd sat will have to take care of that. 

len

Good luck trying to get the amp. I have had one on order since April 22, 2015.

Steve - K5FR

Same for me...

Roy Laufer

Trying to re-invent the wheel<HIHI>?

I am confused by some of your choices, unless they are more about the other radios you would like to use these DEMI parts with?????

The LDPA's IN and OUT ports are not the same as the split ports of a transverter - the OUT port passes the IN signal out of the LDPA IF YOU POWER DOWN THE LDPA. With the LDPA powered, the OUT port has no signal.

I don't see the need to split your IF TX & RX (I can easily duplex with combined IF connections), and I don't think your choice of wiring the LDPA's XVTR OUT to your L432's IF TX is such a good idea (it will only bypass the signal when you turn the LDPA OFF). The 10 MHz hub only becomes important if you simultaneously connect your other equipment - in your simplified diagram it is superfluous.

The 6700's limitation is that TX1, TX2, TX3 must be manually enabled, until the software allows this to be automated with the selection of the appropriate band's transmission controls.

I am very pleased with the use of my transfer switch to swap transmission bands "on the fly" and for $50 it seemed like a bargain.

Perhaps I am missing something in your design?

Good luck!
Roy AC2GS

dlwarnberg

Salvador... I want to follow this thread closely as I am proceeding down this path as well accept I elected to build my own transverters with the elecraft kits.. 432 mHz kit sitting on bench now, I will also add the thumbDV for local DSTAR repeaters when I get there..

Just an FYI on number 4, from my testing and playing with my ICOM 9100 (sold) your best best will be SAT32 or Orbitron, HRD does NOT handle frequency control for linear inverting SATS correctly as they say it will..

Thanks

David

EA4GLI

Well, thanks for the critique Roy, now, if you would be so kind as to add content to your statements....

How do you work Full Duplex SATs on VHF uplink UHF downlink out of one transverter port on the Flex 6700? Care to explain how I can do that without separate IFs? That was exactly the point of this post, to add clarity to this subject. I am not familiar how this can be done, I gathered some info, displayed it to the best of my abilities and asked for advice.

The 10Mhz hub is there to feed a Flex 1500 a TS2000 and other equipment that will take a 10 Mhz ref. signal. I thought that was clear in the text... didn't see the need to draw it in the schematic but if makes you happier imagine a TS2000 and a Flex 1500 connected to the other ports.

The LDPA's IN and OUT ports are not the same as the split ports of a transverter - the OUT port passes the IN signal out of the LDPA IF YOU POWER DOWN THE LDPA. With the LDPA powered, the OUT port has no signal.

Does your statement mean then that you cannot transmit on 70cm and receive on 2m?

Thanks for any clarification on this matter.

EA4GLI

I think the Maestro might make it easier to do, if you can move 2m with one knob and 70cm with the other. Thanks for the Orbitron/Sat32 advice.

We can only dream that we could add a feature in SmartSDR to SYNC two Slices, right?

Roy Laufer

Mea culpa, mea maxima culpa...

I did not mean to offend in any manner. It was just "tongue in cheek" (noticed the <HI HI>?)

I was just suggesting that for the sake of this discussion eliminating the extraneous bits would better allow everyone to focus upon the "logic" involved in the required connections. I have pondered these variables often lately (as you can see by my comments on the forum) and I thought I could help. Nothing more...

You can't do Duplex "out of one XVTR port" as far as I am aware.

What I do is take the RCVR B antenna port and the XVTR port and connect them to a transfer switch. The LDPA and L432-28 transverter's combined IF connection is then connected to the other two ports of the transfer switch. When the transfer switch's relay is not energized I have the LDPA connected to the XVTR and the L432-28 transverter connected to RCVR B - I can transmit on 2 meters and listen on 70cm. If I energized the transfer switch's relay I can do the exact opposite!

The transfer switch that I used can be found at http://www.ebay.com/itm/261533377382?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

... and here are a few links where I discussed my choices, and how they worked out.

https://getsatisfaction.com/flexradio/topics/is-it-possible-to-listen-to-4-2-meter-frequencies-and-4...
https://getsatisfaction.com/flexradio/topics/two-transverters-at-once

https://getsatisfaction.com/flexradio/topics/demi-432-28-transverter-with-fm-mod-preliminary-report


I am sorry if you misconstrued my poor attempt at levity.

Vy 73,
Roy AC2GS

EA4GLI

Thanks for that Roy. I edited-removed a rant I had on the post... I guess I was too sensitive to the post as well... it is tough sometimes to understand the "tone" inferred in a thread post. Sorry if i was quick to react as well.

Also, very informative, I will add those to my list. So your advice then is to keep the IF combined in the transverter and take it to the outside transfer switch, correct?

Roy Laufer

Yes, that would be my advice. Unfortunately, I don't work satellites so I have no practical experience with that aspect, but this configuration, that I put together seems to be the simplest and least expensive option I have come across that does everything that I need.

If I wanted to be REALLY fancy I would have acquired a TTL latching transfer switch and do the swapping via a piece of computer software...

I don't think that DEMI can build a transverter that will work well throughout ALL of 70cm (they tried to do that for me and failed terribly). Unless they have rethought the problem, you can have the weak signal SSB end OR the FM Repeater end of the band, but not both.

As for the other thing, thanks. This hobby is meant for enjoyment and lowering our blood pressure, not for raising it<HI HI>!

EA4GLI

That last part was one I discussed with DEMI, they mentioned the possibility to have different filters to allow me to have UHF at both sides of the spectrum.

The idea is to also be able to use the Flex 1500 with the transverter which will allow me to have full Duplex without a problem. I thought that the separate IF made sense and it is possible to connect the 1500 that way.

Roy Laufer

Well, I am glad that DEMI is continuing to improve their product. Just be sure that the filter option is easily switched in and out.

Their first attempt at my special transverter was to "loosen" the filtering so that I could use it at the high end. Its pre-amp was useless at that end and I had to throw all of the 6700 30dB pre-amp at the signal and it still wasn't great. The transmitter was supposedly rated at 60 watts nominal, but on the Repeater bands the best it could squeeze out were a few watts.

DEMI took it back and built another transverter from scratch with special order filters for  the FM Repeater high band, and this unit works beautifully! It took them 9 months to get it right, but they did get it right in the end.

I don't have any practical experience with the Flex 1500. It might require a separate IF in/out, I dunno.

Separate IF IN/OUT might complicate the 6700 connections though...

If you have two RCVR inputs free on your 6700 that wouldn't be a problem, but I think, like me, you have a mag loop on one of the RCVR inputs???

EA4GLI

Based on my conversations with them I think they "learnt" from your experience. They are the ones that pointed out the need for different filters to work either SSB or FM Repeaters.

As far as the 1500, I can work with just the one IF if I chose to (see http://kc.flexradio.com/Print50496.aspx), so maybe the combined IF will be the way to go. It will also make it usable with other radios.

Roy Laufer

I am glad that I motivated DEMI to improve their design (I wish I could have taken advantage of it, but "c'est la vie").

I think many local Hams don't quite understand my motivations. They may consider it a terminal case of "over-engineering" for the Repeater bands, where most people either use $40 Baofengs, 20+ year old Radio Shack junk, or a prized transceiver from the 1980's to discuss what they had for dinner the previous night and intend to have that night, not to mention the ongoing prostate problems... 

I call those "**** recitals"...

EA4GLI

True, and in all fairness, my all mode Kenwood TS-2000 with 100W VHF and 50W in UHF might be a better "weapon" if I add a couple of preamps to the VHF-UHF yagis than investing on the Flex 6700 and the DEMI gear.

At the very least though, I think that the 2m AMP is a great addition to the 6700 even if I have to "give up" on working SATs with the Flex.

Mike_WB8CXO

That gives me a lot of hope. Amp on order since August!

EA4GLI

So I am not getting the one I order 2 days ago before Xmas???
 

Roy Laufer

I would never "give up" my 6700's Panadapter's view of all 10MHz of the 70cm Repeater band. I tried to explain this to a much much more experienced Ham and Electrical Engineer, but I  was not sure if he thought I was delusional or ill informed. It was his opinion that such a piece of silicon would not operate without industrial refrigeration units and enough of an investment that usually goes to government gadgets. I offered to let him test "fly" my 6700 (I believe the line I used was "mi 6700 es su 6700"), but he was not that curious.

I have a perfectly serviceable Icom IC-7100, but when my 6700 was "in the shop", I could never bring myself to reconnect it and use it as a "primary" radio.

I guess that I am thoroughly spoiled by "the state of the art" when it comes to legacy radios.

I will never quite understand our brethren who will ONLY use radios made before the 1960's. I do not see this as a healthy trend for a progressing technology based hobby (perhaps a hobby of Etruscan pottery, but not radio electronics).

len

They keep pushing the date out. My current ship date is November. We only have 5 days left, so I hold out hope.

EA4GLI

Hey Roy,

Does this make sense?



The green dotted line it's supposed to represent voltage going to the RF Switch to energize it but I am not sure that will be coming from the Flex.

Roy Laufer

With the exception of the green line, this is the exact implementation that I am using successfully!

The green line won't work - it is the 6700's PTT input, not an output. Different transfer switch relays  are rated for different voltages. I have found 12VDC the easiest to deal with in my shack, and I believe it is the lowest voltage usually sold. The 6700's PTT only supplies a 3.3VDC voltage and the transfer switch's relay will be interpreted by your 6700 as you perpetually keying down to transmit. If it is simply a matter of supplying the power to energize the relay, I would suggest pulling some of your 12VDC (or 13.8VDC) from your shack's power supply with an inexpensive inline rocker switch (a latching foot switch could be used for handless switching if you would prefer this). Since you will probably need to flip your inputs from RCVR B to XVTR and vice versa, I think that the rocker is the simplest and least complicated method of dealing with the energize/de-energize control. 

You could use the spare TX1 as a simple output relay and apply an external voltage to actuate the transfer switch's relay (TX1 is rated for a maximum of 40 VDC at 140mA), but I would discourage this excessive degree of switching. To me, it's a just as much a  time consuming effort to enable/disable TX1 control versus actuating a small inline power switch to energize the relay when I want to transmit on the 70cm band. I do not foresee a time when I will need to alternately transmit on 70cm then 2 meters with each push to talk.

You could leave the inputs (RCVR B & XVTR) unchanged and have both panadapters set to transmit on XVTR and switch "on the fly" with the TX1 pin, but you would not be able to fully  Duplex in both 2M out/70cm in & 70cm out/2M in with that configuration.

All these configurations are like complicated logic puzzles. I triple checked my theoretical configuration before buying the parts, but still wasn't absolutely sure of it until I put it together and tried it out.

If I have confused you at any point, with my meanderings, feel free to ask whatever you would like.

EA4GLI

I understand. I normally need to draw something to totally understand it. I need to get some bnc to sma patch cables. Thanks for the help. I am sure it will be useful to others as well.

pa0bie

DDUtil can do band selection with a USB-8 relay card or with a LPT->16 relay interface. The band selection will follow the TX enable on one of the two slices at 2m or 70 cm.

Mike_WB8CXO

I finally received an email reply from DEMI a few days ago informing me they expect to ship my amp in Feb. THINKING ELECRAFT. Can easily sell them when the DEMI amp arrives.

Roy Laufer

I think of placing an order with DEMI as a "Zen exercise"...

Good luck with your order!

EA4GLI

Any progress on this guys? Any of you received the Demi gear?

Roy Laufer

Well, my 2 Meter DEMI LDPA and "modified" 70cm DEMI transverter, as well as my transfer switch are "alive" and well - no problems here. I am happy with my purchases. I just wish it had a few less "bumps in the road" and delays.

I'm looking forward to reading if anyone else has followed my transverter path and how it worked out for them.

len

I must be on the S*** list. Still waiting for the Amp. Ordered April 2015....No news.

K6OZY

This configuration seems to read like we can RX 70CM while 2M TX, but not RX 2M while 70CM TX. Do you think there is anyway to have it both ways?

Roy Laufer

With the transfer switch in place you can select to do UHF Tx/ VHF Rx or VHF Tx/UHF Rx!

I have it at my QTH and works very nicely!

Mike_WB8CXO

Latest promise from DEMI was this February so I have two weeks to go. Fingers crossed.