eHam

eHam Forums => Misc => Topic started by: AK4YA on August 28, 2012, 07:27:44 AM



Title: Tx/Rx switch/relay options
Post by: AK4YA on August 28, 2012, 07:27:44 AM
Are there any other ones out there besides the Ameritron arf-1000?  Its fairly limited on power output.


Title: RE: Tx/Rx switch/relay options
Post by: K8AXW on August 28, 2012, 09:24:49 AM
Please rephrase your question so that simpletons like me can understand what your problem is. 


Title: RE: Tx/Rx switch/relay options
Post by: AK4YA on August 28, 2012, 09:52:02 AM
sorry - I need a transmit/receive switch/relay in order to use a FDX setup of a separate receiver and transmitter with a single antenna.  MFJ has the MFJ-1708 but it is limited on its power handling capabilities.

Sorry I was the simpleton - I screwed up - it wasnt an ameritron arf-1000


Title: RE: Tx/Rx switch/relay options
Post by: K0RS on August 28, 2012, 10:30:00 AM
I should think a classic Dow-Key relay, such as the DK-1, would do the job.  Granted they are no longer manufactured, but neither are the rigs that they are commonly used with.  That said, they aren't difficult to find on swap lists or eBay.  Just don't pay an arm and a leg.  They are available with a host of relay voltages, from 6v DC all the way up to 240v AC.  The most common ones have either a 117v AC or 12v DC coil.  If you purchase one, make sure the coil voltage is appropriate for your application. Many vintage transmitters have a tap on the rear to provide voltage on transmit expressly for operation of T/R relays.  Many Dow-Keys have an external pair of contacts for operating a linear, muting, or any other function that's convenient when transmitting.

EF Johnson made a T/R relay similar in function to the MFJ model, but much larger and capable of 4KW.  It was tube-type.  These are rare and expensive.  The model # was 250-39.  See a picture here: http://antiqueradios.com/forums/viewtopic.php?f=5&t=170170 (http://antiqueradios.com/forums/viewtopic.php?f=5&t=170170)

See a nice collection of Dow-Keys here:  http://www.n4mw.com/gdowkey.htm (http://www.n4mw.com/gdowkey.htm)


Title: RE: Tx/Rx switch/relay options
Post by: WB2WIK on August 28, 2012, 11:51:10 AM
These coaxial RF transfer relays work fine.  They're the "modern day" replacements for the old Dow Key series: http://www.rfparts.com/coaxial.html



Title: RE: Tx/Rx switch/relay options
Post by: AK4YA on August 28, 2012, 12:18:13 PM
thanks a ton everyone


Title: RE: Tx/Rx switch/relay options
Post by: W5DQ on August 28, 2012, 02:38:09 PM
If you mean "Full Duplex" by using the term "FDX", then you're not going to need a TX/RX relay but rather a method to allow transmitting and receiving SIMUTANEOUSLY on the same antenna in the way you describe it. I don't know of any method to do that on HF but on VHF and higher, duplexers are used. Full duplex usually means transmit and receive at the same time hence why I understood FDX to mean that???

If you want to simply share an antenna on seperate TX and RX units, then a DOW key replay or similar should work. HOWEVER you should ENSURE that the relay has switched and is settled before applying TX power to the feed line. Likewise ensure the transmitter is unkeyed and RF has dropped to 0 watts before switching to RX. Transmitters do not like to be 'hot switched' and they will suffer if you do it. The higher the power, the more they suffer!!

Gene W5DQ