Power point & antenna question

[budman67]

Just a quick 2 questions for the guru's,I have heard of the
D plug for the battery,is there a way to test it with a
regular home style meter.I want to know if it is a 25or
a 77.I thought the prc-77 just had a positive and negative
post?
I want to make sure I order the right DC cord and batt.
pack from prc.68.com

I have looked in my manuals,but I find them confusing.
Which of the three small post and one large centre one
is positive and negative?


Also, I am trying to figure out the long folding stick antenna,
it threads into the long brass piece,but not the top of the radio.
Do I need to thread it into the top of the flex end of the
tape antenna,it doesn't support the weight,also,do I need
to use the brass part?
Thanks

 

[tennmogger]

Do you have a battery to look at? Many of the batteries have the pinout and voltages printed on them.

If not, and you are looking at the pins on the bottom of the radio, they are set up like this:

- The big "D" pin is only for orientation, no connections to it.

- The pin following the "D", as if it were the letter "O" in the word "DO", is common connection for both the filament voltage (A-) and the high voltage (B-)

- The pin "above" the D (at about 1200 noon position) is the positive 14.5 volts, A+

- The pin above but behind the "D" (at about 1100 o'clock) is the filament voltage positive, A+.

The pins are the same whether it's a PRC-25 or a PRC-77. The '77 just doesn't use the filament tap. Your radio should say on the tag if it's a '25 or a 77. If it doesn't, then you have to look inside to know. I don't have a '25 so can't tell you where the tube is.

As for the antenna, I don't know what brass part you are referring to. Can you tell us the model number of the long multi-section antenna you have?

The short tape antenna screws into it's flex section, then into the radio. The antenna is the AT-892, the flex section typically says P/O AT-892 (part of AT-892). No, the flex section won't hold up the long whip.

The long whip you have might be the AT-271. It has an adapter on the bottom that fits the radio, or fits the spring. Is that thread adapter what you are calling the brass part? With the adapter it should screw into the radio, but should be used with it's spring section.

[edit: there is another adapter made for the AT-271 that is 3/8-24, not the 5/16x24 of the radio. Bet that's what's going on]

One other thing to know: The radio has to 'know' which antenna is screwed in, either the short one or the long one. It 'knows' that by how far the antenna screws into the radio. There's a switch down in the bottom of the threaded hole that gets pushed down by the long antenna so the transmitter output gets proper matching. So, the screw threads of the long antenna have to be longer, or there will be a skinny probe sticking out of the bottom of the threads on the long antenna to push the switch.

BTW, the newer AB-1036 antenna has a sliding switch device on it to tell the radio how long it is, and can be used either long or short by collapsing the telescoping sections.

There's good info on PRC68.com describing the different threads, 5/16 x 24 tpi, or 3/8" x 24 tpi.

Bob WB4ETT

Just a quick 2 questions for the guru's,I have heard of the
D plug for the battery,is there a way to test it with a
regular home style meter.I want to know if it is a 25or
a 77.I thought the prc-77 just had a positive and negative
post?
I want to make sure I order the right DC cord and batt.
pack from prc.68.com

I have looked in my manuals,but I find them confusing.
Which of the three small post and one large centre one
is positive and negative?


Also, I am trying to figure out the long folding stick antenna,
it threads into the long brass piece,but not the top of the radio.
Do I need to thread it into the top of the flex end of the
tape antenna,it doesn't support the weight,also,do I need
to use the brass part?
Thanks

 

[budman67]

Sorry,I should have thought to add the antenna # it is AT-271A
with a brass section AB-591A. The 591 has the probe nub you
stated,but the thread is to small to thread into the radio.
here is the picture of what I have,tape antenna on radios.

I don't have a spring part for the AT-271A,the picture in the
manual didn't show me a spring part.But you can see in the picture
that they are different sizes.But the manual states it is correct?

And just to make sure I under stand the plug,12 o clock is pos+,
3 oclock is neg-,and the 11 0 clock 3V+?

Thanks for taking the time to help me out.

 

[budman67]

Well,after some trial and error,I noticed that one of the AB-591a
has very worn threads,and it will only thread into one of the radios.
So I have solved the antenna problem.

As for the plug,it is marked A,B,C. PRC-68 was saying to measure
across A and L? Must be the front plug,as soon as I know which
is pos and neg,I'll try a jumper wires to try and power the radio
temporally.

 

[budman67]

I found a TM 11-5829-677-35 D S , G S , A N D D E P O T M A I N T E N A N C E
MANUAL R A D I O S E T A N / P R C - 7 7,going through the diagrams,I found
one with the J4 plug.
I was able to hook it and listen not much in the basement but it worked.

 

[OPCOM]

If you do order from PRC-68.com, you won't be disappointed. The pack should be the one with glass epoxy circuit board material, uses "D" cells, and should be usable in both 77 and 25 radios. I ran a '77 on ten "C" cells for over a day using several C holders from Radio Shack that I had cobbled up and placed in the battery box. I used a connector from a discarded battery kindly provided by Steve Haney of Haney Electronics TC0654@mesh.net.

You will note by comparing the RF output of a 77 and a 25 that the 25 takes about 1/2 second to build up RF output due to the tube heating time requirement. Therefore you must delay your speech by that amount when using a 25. I realize that may not help but it is the laziest way to figure out which radio you have if you have a known one to compare with.

 

[budman67]

I am quite certain I have the I have the 77,I managed to to pick up
Global tv,it was fading in and out,some channels were quiet then
rush then quiet again.Tomorrow I''l hook up the AT-271A on the
deck and try and hear something.

Thanks guys for the help

 

[budman67]

I am guessing that the RC-292 antenna is also a no go for getting across
to Canada from the US?

I have the room to set one up,but I haven't yet seen one for sale yet.

I have been reading up on this antenna TM 11-5820-348-15 that I
found on prc-68.com,might pick up some good skip on it.

 

[tennmogger]

The RC-292 is just a single omni-directional radiator that's installed higher than the similar antenna on a vehicle. It has low gain in any one direction because it tries to look in all directions at once.

If you want to communicate in a particular direction, you need a directional antenna. There are many beam type antennas made for use on the 6 meter amateur radio band, and those are not too expensive. If you can get one of those up in the air you'll have the best opportunity to talk across the border.

Keep in mind that the normal propagation mode of a 6 meter signal is basically line of sight (plus a little) and therefore depends on antenna height to determine how far it stays close enough to the earth to be heard.

Lucky for us, occasionally the ionosphere gets in a 'reflective' mood and bounces the signal back to earth at some distance away, or even multiple bounces.

With a good antenna you can make use of those bounces when they happen. That's why there's a chance of success to talk to someone even if there's no one within ground wave distance of your home.

The way you orient the beam (Yagi) antenna matters too. For FM, normal orientation is vertical. For modes like SSB and CW, normal mode is horizontal. As waves propagate they tend to convert to horizontal so horizontal is better.

So, there's a little challenge here. To hear nearby FM stations you would mount your antenna vertical, but for best distance you would want it horizontal. What to do? I'd mount it horizontal anyway. A local FM station would be weaker because it will be cross-pole, but being closer it will have a stronger signal. Distant stations will be weaker but the antenna will be oriented to get best signal from the distance.

If you are striving for long distance 'skip' signals then height is not that important. Just get it as high as is convenient, in the clear of reflecting objects, and enjoy listening.

By the way, some of the European tactical FM radios will tune below 30 MHz and therefore can be used on the 10 meter ham band.

Bob WB4ETT

I am guessing that the RC-292 antenna is also a no go for getting across
to Canada from the US?

I have the room to set one up,but I haven't yet seen one for sale yet.

I have been reading up on this antenna TM 11-5820-348-15 that I
found on prc-68.com,might pick up some good skip on it.