The AM Forum

I have posted this elsewhere over the last few weeks but I'm not "getting" the answer.

I have a Hallicrafters HT 37 I am trying to use with a Hammarlund Receiver on AM.  I have both the Reciever and the transmitter wired through a Johnson T/R switch.  This whole thing works.  The transmitter keys and the Receiver switched to silent mode....  But the speaker gives me horendous feedback.  SO..  I realize that I need to mute the speaker when I talk.  And I have a mute conection on the receiver.  What exactly do I do? I don't know what to hook it to.  I had the same problem on my Valiant.  So there is a simple step that I am missing.  These are my first transmitter/receiver combos and I have never even seen one hooked up so I am on my own and looking for advice.  Please help me out so I can actually use this thing;)

Look at your HT-37 manual. Figures 2, 3, and 4 give you all the info you need to access the correct relay connections in the HT-37 to mute your receiver. It would also be wise to check the receiver's manual explanation of what the mute connections require (when going from receive to transmit and vice versa) for open or close relay activity.

Pete was giving you good dope......

Yer 140 has a jak on the bak fer rcvr muting. Go hre fer a manual.

http://www.hammarlund.org/files/HQ-140-X.pdf

klc

Pete nailed what you need to do but I would add to this unless you are also planning on using the setup for full break-in on CW a regular electromechanical relay is a simpler and less expensive alternative to an electronic switch (like the Johnson T/R box).    Keep this in mind as you expand your vintage collection.

For low to medium power rigs, one of the standard "cube" style relays with a 120 volt AC coil will inexpensively take care of your relay needs.   I think these are even still available from Radio Shack and are certainly plentiful elsewhere.  The coil voltage is controlled by the switched 120 volt AC output provided by most vintage transmitters.  One set of relay contacts handles antenna switching and a second set handles receiver muting.  I have Johnson Viking 1 and Viking 2 transmitters with the VFO-122 and I use a 4PDT coil with these and use one set of contacts to key the VFO which provides chirp free CW (I don't use full break-in with these rigs). 

For the higher power rigs (Desk KW, Viking 500) I use good quality vacuum relays but the little cube relays easily handle rigs through the Valiant power level.  The Dow key relays are convenient but realize that most of the hamfest/ebay finds are quite old at this point and are likely to be showing signs of age and the price they command along with the possibility of failure from age make them undesirable to me.

Thank you all.  As I said I am new to this and it's all new to me.  I did look at the manual and understand how ( I think) to wire it.  My questions now are:

What is the name of the conector that plugs in to the rig? I assume I need one of those then wire it like the manual shows to the receiver?  I would like the correct name so I don't sound like an idiot trying to explain what it looks like to some teenager in an electronics store.

I was given the T/R switch.  If I wire the transmitter and receiver together from the back, will I still have a use for yhe T/R switch?  I am planning on voice not CW at the moment.  I will still need some comon point for the antenna to be connected to both units.

Thank you all for your patience.  I know my questions seem simple to you but I am learning from them.

I believe the HT-37 has an 8 pin socket with a center hole that has a keyway in it.  Thar's called an "Octal socket".  You need an "octal plug" that fits into the socket and you wire up your switched 110 VAC to the appropriate pins as found on your transmitter schematic.

As for the home made transmit-receive switch, Here's how I have made several in the past.  Get the following items from Newark, Digikey, Mouser, or your favorite electronics retailer (if any still exist)

aluminum mini-box, maybe 3" by 4" by 5"

3 pole double pole relay with a 110 VAC coil and 10 amp contacts

SO-239 sockets (the kind that a PL-259 plugs into)  Get 3 of them

6 or 8 terminal screw type barrier strip to connect wires (110 VAC, receiver mute)

Mount SO-239 in aluminum box, mount relay so that contacts face SO-239's

Wire up as follows:  

Center of one SO-239 (transmitter)  to normally open contact of relay

Center of another SO-239 (receiver) to normally closed contact of relay

Center of 3rd SO-239 (antenna or tuner)  to common contact on relay

(use stiff wire for these, maybe #14, and make them as short as possible)

Do the same for another set of relay contacts, but label them NO, NC, Common.  These can be used to mute your receiver.  You can use smaller wire, maybe lamp cord.  These can go to the barrier strip terminals on the outside of your mini box.

Wire the coil of the relay through the barrier strip terminals to the 110 VAC from HT-37.

Label the SO-239's and barrier strip connections.  You'll have to check the schematic of your receiver to see which set of contacts (NO or NC) will mute it during transmit.

Take a picture of your first homebrew project for posterity!

Please excuse the crude schematic...

To start with, the HT-37 has an 11 pin socket so you need an 11 pin mate. The relay in the HT-37 is a 4-pole type and there are enough relay contracts available to control receiver muting and probably several other things. You don't need to outboard any additional relay box. Look at Figures 2, 3, and 4.

Johnson T/R switch is ready to go, as is, as an antenna "switching" device. Look at the attached picture below and see Figure 1. All the detail you need to connect antenna, receiver, and transmitter. In simple terms, when not transmitting, antenna is connected to receiver; when transmitting, receiver connection is blocked and antenna is connected to transmitter. No other antenna relay stuff is necessary. Make sure you plug in the AC cord.

Guess you didn't like the same answer I gave you regarding the aux. relay contacts
on the rear panel on the other forum?  ;D  

The eleven-pin plugs and matching caps can be ordered from RadioDaze.com.  I'm not sure what size plug is used on the Hammarlund, but radiodaze has a good assortment. You won't find them at the local supply house.

I'd suggest you verify that the HT-37 isn't producing white noise in the receiver; the TR switch manual is very specific about certain transmitters having that problem, and the HT-32 and HT-37 are likely candidates for being white noise generators. They may raise you noise floor.

Pete

I used a Johnson T/R switch with a HT-32A and Hammarlund HQ-170A combo years ago. No white noise detected from the HT-32A, but the T/R switch has gain (see first paragraph below), so the receiver noise floor was raised when it was in line.

It may have some power gain, and it definitely uses the PA tank as the input tuning for the
antenna switch. I just checked my HT-32 and SX-101A combo, and the transmitter raises
the RX noise floor to a S4 reading on 75 meters.  That was connecting the HT-32A output
(TX in standby) directly to the SX-101A antenna jack.  I don't have my TR Switch restored, but I will try it and see the combo will work well enough to be useable.


 Pete k1zjh

I had some time so I put new filter caps in the Johnson TR Switch.
The receiver S Meter raises by about three S units when the HT-32A is powered up in standby. The plate tuning provides the expected peak when the tank is tuned to the RX frequency; but the TX noise is definitely degrading the receiver's noise floor by quite a few dB (tested 80 and 40 meters) when the transmitter is powered up, even
in standby. It will work, but the RX is compromised.

Pete K1ZJH

My HT-32A is long gone so no way to verify what I heard/saw years ago. I still have at least two of those T/R switches floating around here somewhere. Don't remember what the response was when I used the Apache in place of the HT-32A. I've moved on to more smug rigs.

LOL! You'll have to define what a "smug rig" is for me :)  IIRC, you bought a Flex 5000?
The Hallicrafters were fun to restore and a diversion for casual operation.

Pete

I've been enjoying "smugness" with the 5000 for several years now. Had an SDR-1000 prior to that and "enjoyed" a combination of semi-smugness, occasional anguish, and periodic hair thinning.

The HT-32A I had was already refurbished. It came in a package deal with a set of Drake 4C twins. It worked great except the owner's cat periodically had urinated in it. No outward signs; I washed it down with Lysol and several other cleaners before first putting it on the air. After transmitter warmed up, aroma was hard to fathom although a good lit Italian cigar made it tolerable. Wife was not too happy so I got rid of it. One has to know their limitations.  :)

"Wife was not too happy so I got rid of it"

My wife was very happy when I quit smoking too.

klc