[HomeBrew] HOMEBREWED Antenna Changeover relay.

Sun Jul 4 11:38:10 EDT 2004

Hey Phil, Way to go.  I have some small bud cabinets, and octal relays
in both 12VDC and 120VAC.  I built one T/R relay for my DX-60B.

Now I've gotten a E.F. Johnson amplified TR-Switch.  Has a take off for
sampling the signal.

Being amplified has an advantage for the receivers.  I have enough
output - 400W on key up, so getting those with "smaller" stations, I can
still pull them out!

Bob - N0DGN

Philip B Atchley wrote:

>** Please do NOT cross-post messages in the TO: or CC: field of the e-mail message. **
>
>Hi All,
>In preparing to interface the Viking Ranger (picking it up early next
>week) and Hallicrafters SX-71 receiver I decided to build my own TX/RX
>interface unit (I'm an old hand at homebrewing). When I used the Ranger
>and Hammarlund HQ-110 before, I used a borrowed Dowkey "clone" antenna
>relay (at least I presume it was a clone, it didn't say Dow). I found it
>rather clumsy to work with as the owner has it mounted on a foot high
>piece of wood and jury rigged connectors for the Ranger etc. Nor did it
>short the receive antenna connection during transmit without doing a
>lash-up with the external contacts. 
>In the "true" spirit of ham radio I decided to build my own antenna
>changeover relay, preferably at no or little cost. The goals I came up
>with were:
>1. Switch antenna from RX to TX (naturally).
>2. Short the receiver antenna connection during TX (no need for full
>QSK).
>3. Be able to handle at least 100 Watts (Ranger runs 40W AM).
>4. Automatic operation, I.E. change over without having to flip an
>additional switch.
>5. Have additional relay contacts for receiver muting.
>6. Have internal control for Auxillary receiver RF gain control.
>7. Be housed in a compact, sturdy, well shielded enclosure.
>8. Be "universal" in operation. I.E. Operate on 120 VAC (Ranger) or 12
>VDC (other rigs) without extensive modification.
>At first thought the last item was expected to be the toughest, not so!
>Here's what I came up with. As it turned out, I was able to build it
>entirely with parts from the junk box at no monetary outlay whatsoever.
>1. Housing: I used the heavy gauge aluminum housing of a scrapped LPF (it
>had a cutoff of about 15MHz). At 6 x 2.25 x 2.25 inches with a SO-239 on
>each end it was ideal! 
>2. Relay: I used a 4P2T relay (Gold Contacts) with a 12 Volt coil. This
>provided all the contacts I needed for the various functions.
>3. Relay Power supply: A very small 19V Center tapped transformer
>(9.5/9.5VAC) with attached circuit board/rectifier provided 12 Volts to
>the relay when filtered with a small capacitor. The transformer was from
>a scrapped "boom box", I keep those kind of items. This allows 120VAC use
>with the Ranger, wires easily swapped for direct 12 VDC operation of the
>relay, OR, plug the unit into the wall and break the 12 Volt line with an
>outboard switch for rigs with no relay control.
>4. Connectors: I used the two original SO-239 connectors for Transmitter
>and Antenna connections and mounted a small Chassis Mount RCA jack for
>the Receiver connection. A Terminal strip with 6 pairs of screws allow
>connections for receiver muting/RF Gain Control.
>5. RF Gain Control: A 5K wirewound pot was mounted in the box for
>Auxillary Receiver Gain Control for monitoring the sent CW.
>6. Power connection to TX (Ranger). A wire was run directly from the PC
>board on the Transformer out a grommet in the box. The case of a scrapped
>Xtal was fitted to this wire to plug into the Relay Socket (A ceramic
>Xtal Socket) of the Ranger.
>How does it work? Well, I don't have the Ranger here yet, but testing
>with 120VAC all the functions switch OK. I don't anticipate any problems
>using this unit and it will easily mount under the overhead shelf of the
>operating table allowing easy access to the Receiver auxiliary RF gain
>control.
>This just shows that one doesn't need to spend BIG BUX to make simple (or
>not so simple) interface units. I often wonder how MFJ and others make so
>much money on relatively simple devices (Like a TNC/Mic switch box etc)??
>
>
>73 from the "Beaconeers Lair", 
>Phil, KO6BB   Merced, Central California.
>
>All Real Radios "Glow In The Dark".
>RECEIVER: Hallicrafters SX-71, Grundig YB-300
>
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>  
>

-- 
<                      Bob Bethman - N0DGN
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| N0DGN AMRadio Manassas, VA    |    REAL Tube Radio and AM        |
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