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 Post subject: Probably Dumb Antenna Question
PostPosted: Jun Wed 19, 2019 5:27 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 233
My 35 some-odd years studying ham gear assures me that I possess quite a knowledge in the field. That said, I post my dumb questions on basic things that slipped by. For instance, I've never figured out antenna switching. When using the xmitter antenna as the receiving antenna, I've never figured how to switch and antenna that is 50 ohms on the transmitter and 300 ohms which is the only coupling on most vintage receivers. And for the coupling to be done on either Homebrew or flea market grade antenna switching boxes.


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Wed 19, 2019 5:46 am 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 3493
Location: Lincoln City, OR
Greetings to Henry and the Forum:

The short answer is that it doesn't make any real difference to the receiver. So just feed it with the 50 ohm line. I have a Hammarlund HQ-129-X which has three screw terminals for the antenna. Two are for balanced feed; the third is a ground terminal. For unbalanced feed, ground the adjacent balanced screw terminal and connect coax shield to the pair of screws. Connect the coax center to the remaining screw.

Signal and noise levels are so far above the receiver internal noise on HF that there is no need to worry about impedance match. As I recall, most vintage receivers had antenna connections similar to the Hammarlund and were connected to in the same way.

Regards,

_________________
Jim T.
KB6GM


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Wed 19, 2019 3:32 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 343
Location: Limington, Me
I've heard of winding a wideband 4 to 1 transformer on a binocular core for better matching to
the receiver input. I don't know if it makes any difference for most cases.


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Wed 19, 2019 3:52 pm 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 233
So let me get this straight. For doing cw on my Knightkit xmitter, and using my HQ-I70 receiver, I'll be throwing 3 switches if I set up in the most basic way.
A knife switch for the antenna, the send/receive switch on the Hammarlund, and the function switch on the T60. So that means no monitoring of my code because the receiver will be blanked out, as it will be in "send" position while I'm transmitting. 3 switches to keep up with.


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Thu 20, 2019 1:02 am 
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Joined: Nov Mon 02, 2009 7:01 am
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Location: Lincoln City, OR
Greetings to Henry and the Forum:

I don't know how your T-60 is configured. I use a Johnson Ranger with my HQ-129 and its function switch energizes a socket on the rear panel with 117 volts AC when it is switched to transmit. I use the 117 VAC to switch two relays... a coaxial antenna relay which is SPDT to handle the antenna changeover function and a second small relay which shorts a pair of wires connected to the J1 "Relay" jack on the back of the receiver when not energized. The "Send-Rec." switch is permanently in the "Send" position. In this case, only the function switch on the transmitter needs to be manipulated to go from transmit to receive.

Back in the early 1960's when I was a novice, I used a knife switch also as I couldn't afford a coaxial relay. The knife switch was a double pole double throw switch. All of the coax shields were tied together; one side of the knife switch connected the antenna to either the receiver or the transmitter by switching the center conductors of the coax cables. The other side of the knife switch was connected to the "J1 - Relay" jack on the back of my HQ-129. When the knife switch was in the receive position, the other side shorted the "Relay" jack on the receiver. When the switch was thrown so as to connect the antenna to the transmitter, the "Relay" jack was no longer shorted, removing B+ from the receiver and muting it. The transmitter function switch was left in the "CW" position, which enabled the transmitter. However, with the key up, the transmitter did not transmit, so the knife switch sufficed to handle all the TR switching.

Do be careful as the receiver B+ appears on the knife switch with this method. Also be careful not to hit the key accidentally when receiving as the transmitter will have no load connected to it.

If you need diagrams, let me know and I will endeavor to draw some up.

In answer to your other question, there will be no side tone unless you use a keyer or a separate side tone generator to key the T-60. (Unless, of course, the T-60 has a side tone generator built in... don't know, as I am not familiar with that transmitter.)

Regards,

_________________
Jim T.
KB6GM


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Thu 20, 2019 1:49 am 
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Joined: Jul Sat 28, 2012 9:32 pm
Posts: 233
Diagrams would be great if it isn't too much trouble. The T60 does have an accessory socket, probably much like the others. And I'll be mostly using my Hammarlund HQ 170.


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Thu 20, 2019 9:20 am 
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Joined: Nov Mon 02, 2009 7:01 am
Posts: 3493
Location: Lincoln City, OR
Greetings to Henry and the Forum:

Please find two quick diagrams that I made up. One for the connection using a knife switch and the other is essentially what I am currently using on my novice nostalgia station, which consists of a Hammarlund HQ-129-X and a Johnson Ranger, just as I had in 1962.

In 1962, I used a knife switch. I don't recall whether I used the muting scheme shown in the diagram or threw 2 switches.... 1962 was a long time ago. :D

Attachment:
Antenna Changeover Schemes.pdf [89.06 KiB]
Downloaded 19 times


The second diagram is what I have now. My particular coaxial relay has no accessory contacts on it and requires 170 VDC to operate. Bridging the 120 VAC that comes out of the Ranger control jack and adding a filter cap gets me this voltage nicely. I am also using a separate lower voltage DC relay to mute the Hammarlund. This power is just dropped with a resistor from the 170 VDC for the coaxial relay.

Attachment:
Antenna Changeover Scheme Relay.pdf [73.12 KiB]
Downloaded 16 times


Since your junk box is unlikely to contain this exact combination of relays, I did not draw in that portion of the circuit. You will have to decide how to get relay control out of your T-60. It may be that you will end up with an external switch like a push-to-talk switch to control everything. The T-60 may or may not supply suitable power for your relay(s).... if not, then an external power supply or two may be necessary.

The diagrams should get you started, however.

Regards,

_________________
Jim T.
KB6GM


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Thu 20, 2019 10:59 pm 
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Joined: Nov Sat 07, 2009 11:37 pm
Posts: 2116
Location: Sayreville, NJ 08872
Back when I was a Novice, I used a HQ-170 receiver and a homebrew 75 watt transmitter that I bought from a local ham for $20.
Since I wanted and liked monitoring myself when transmitting, diddling with the "Mute" contacts/wiring/ etc. in the receiver wasn't important or necessary. At first, I did use a knife switch to switch antenna between receiver and transmitter. Then I found a simple TR switch in some magazine that I built into the transmitter. I derived the B+ and filament voltages directly from the transmitter so the power supply stuff in the schematic are not necessary. Current drain was not a concern.
Since I didn't really want to drill or mount another tube socket in the transmitter (it looked pretty and it was my first transmitter) I made a small "L" bracket, mounted the tube socket under the chassis , and mounted all the necessary parts there. Rather then drilling a hole for a jack to go to the receiver, I just snaked the coax to the receiver through a small unused hole in the back panel. The TR switch was simple and worked very well on all the Novice CW bands. As an added receiver protection, I added a #47 lamp in series with the receiver lead. Under non-lighted situation, lamp resistance is very low.


Attachments:
trswitch-simple.jpg
trswitch-simple.jpg [ 65.11 KiB | Viewed 308 times ]

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Pete, WA2CWA - "A cluttered desk is a sign of genius"
http://www.classicradiomanuals.com
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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Thu 20, 2019 11:07 pm 
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Joined: Nov Sat 07, 2009 11:37 pm
Posts: 2116
Location: Sayreville, NJ 08872
And, if you have money burning a hole in your pocket, you could always try to secure of these TR electronic switches. Not only does it switch, but also provides some receiver gain from 0 db to roughly 6 or 8 db depending on frequency.

Image

_________________
Pete, WA2CWA - "A cluttered desk is a sign of genius"
http://www.classicradiomanuals.com


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jun Sun 23, 2019 2:07 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 221
Location: Green Bay, Wi
For the 300 ohm input of the receiver just place a twin lead to 75 ohm TV matching transformer on the receiver terminals. The 300 ohm side is even nice enough to have spade terminals on it to screw onto the receiver and the 75 ohm end has an F connector on it that I am sure you can find in the junk box to go to your antenna. The mismatch between the 75 ohm transformer and your 52 ohm antenna will not be noticed but your receiver will come to life.


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 Post subject: Re: Probably Dumb Antenna Question
PostPosted: Jul Mon 01, 2019 5:58 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1267
Location: Champaign IL 61822
TV transformers don't work well for SW. You need a proper SW transformer to get from 50 or 75 ohms
to the 300 or more most vintage sw radios like. High end boatanchors like 50 to 100 ohms
and no transformer is needed.

The proper transformers are these:

https://www.ebay.com/itm/MINI-CIRCUITS- ... 0005.m1851

https://www.ebay.com/itm/Lot-of-10-OEM- ... SwgbhaPA80

or search ebay for T4-1-KK RF MINI-CIRCUITS

The main reason to use a transformer is to get a higher voltage for insensitive older
"home" radios with no RF stage, or just plain low gain. For these, a transformer helps.

I use these and they work nicely. In the range of SW radio they are low insertion loss.


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