[TenTec] OT: Holiday SDR Project

[Carl Moreschi]

The MFJ 1708 schematic shows the relay in the transmit position which is 
contrary to what it says in the diagram.  Without the jumper, in receive 
only the panadapter receiver would be connected to the antenna, not the 
transceiver.  Adding the jumper between the antenna and transceiver 
causes the transceiver to be always connected to the antenna which is 
exactly what you want.  In transmit, the relay still grounds the 
panadapter antenna and removes it from the antenna which again is 
exactly what you want.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 11/9/2014 9:56 AM, george fritkin via TenTec wrote:
> To whomever reads  this......using the jumper on the MFJ 1708 is not a good idea
>
> George, W6GF
>
>
> On Saturday, November 8, 2014 11:19 PM, Rick - DJ0IP / NJ0IP<Rick at DJ0IP.de>  wrote:
>
>
>
> On the topic of antenna switches for multiple receivers, there are such
> devices available.
> One such device is the DA-4 from RF Systems.
> See:  http://www.universal-radio.com/catalog/preamps/0601.html
> I've used this before but only with multiple receivers.
> I don't know how well it behaves around RF.
>
> The Eagle and Omni VII both have a mod which interrupts the RX antenna line
> and routes it to the back panel.  You could use the line out to drive a
> switch and have the line in be one of the outputs of this device.
>
> You would have to copy this mod for use with the OM6, which would be very
> easy to do since there is a lot of space inside the OM6.
>
> Or, do like I did and simply build your own 3-dB splitter.  Mine is a in a
> tiny square box about 2.5"x2.5"x1".
>
> If you don't want to make the splitter yourself, they are available
> commercially, such as the one from Mini Circuits, which claims only 0.3 dB
> insertion loss (though this is only possible with a broadband amp (I
> thought), yet I don't see any mention of an amp).
> http://www.minicircuits.com/pdfs/ZFSC-2-6+.pdf
>
> In the case of the Eagle, it inserts AFTER the RX-GND (protection) relay, so
> it is safe to use "as is" for this purpose.  I would have to look back at
> the OM7 circuit diagram to see if it has the same type of protection relay.
>
> If you d-i-y, you would need to add the protection relay yourself, just
> before splitting the RX ant out.
> This type of solution enables both receivers to work at the same time,
> though usually with 3dB loss, which most of the time is not even noticeable.
>
> 73 - Rick, DJ0IP
> (Nr. Frankfurt am Main)
>
>
> -----Original Message-----
> From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Don
> Rasmussen via TenTec
> Sent: Sunday, November 09, 2014 7:04 AM
> To: tentec at contesting.com
> Subject: Re: [TenTec] OT: Holiday SDR Project
>
> Great info Carl - thanks.
> Sounds like Corsair 2 has the best option for passing the receive but that
> is not a CAT radio for N4PY software so yes, some external antenna switching
> would be needed as you suggest. I prefer a universal solution so maybe the
> MFJ or a DX Engineering RTR-1A and using the amp control line to activate
> it.
>
> I was never a big one for panadapters but figured with a $66 SDR receiver
> there might be a simple/inexpensive solution for that - any way I look at it
> seems to be a couple hundred dollars - hi...
>
> =====================================================================
>
> What radio are you using? Many radios have an easy way to share antennas. If
> that's not an easy solution then the MFJ1708 can do the job. See below.
> The solution to share antennas is to add an MFJ-1708 T/R switch.  This unit
> will automatically sense RF from the transmitter and then remove the
> panadapter radio from the receive antenna connection.  But the MFJ switch
> will also remove the transceiver from the transmit connection while in
> receive.  So the MFJ switch needs a very simple mod.  You must solder a 14
> gauge wire between the transmit and antenna SO-239 connections.  This will
> then make the switch operate properly for this use.  Additionally, you can
> wire the relay to energize from your radio's amp key line for faster and
> safer switching. Carl Moreschi N4PY
> 58 Hogwood Rd
> Louisburg, NC 27549 www.n4py.com
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