Pages: 1 [2] 3   Go Down

Author Topic: Receive disappears when connecting shell of coax connector  (Read 919 times)

KL7AM

  • Member
  • Posts: 103
Re: Receive disappears when connecting shell of coax connector
« Reply #15 on: October 11, 2022, 05:48:31 PM »

That is correct Mark
Logged

N7EKU

  • Member
  • Posts: 1471
Re: Receive disappears when connecting shell of coax connector
« Reply #16 on: October 11, 2022, 06:26:11 PM »

You've given almost no details that would help anyone try to figure out the problem,

What make and model is your transceiver?  How is it powered?  What is your antenna configuration?  Do you have an external ground hooked up, and if so how?  What have you tried so far to determine the problem?  Do you have any test equipment?  Have you tried the antenna on other radios?

Logged
Mark -- N7EKU/VE3

N4ATS

  • Member
  • Posts: 1416
Re: Receive disappears when connecting shell of coax connector
« Reply #17 on: October 12, 2022, 03:56:27 AM »

I have one question, is the center pin of the PL-259 actually "tight" when putting it into the SO-239? I.E. is it rubbing nice and tight? I have seen this in the past where the prongs are spread on the SO-239 and when the PL-259 is pushed in , the pin never contacts the prongs and the back shell of the PL-259 keeps it right smack in the center so RX will go away. 
Logged

N7EKU

  • Member
  • Posts: 1471
Re: Receive disappears when connecting shell of coax connector
« Reply #18 on: October 12, 2022, 06:12:20 AM »

I have one question, is the center pin of the PL-259 actually "tight" when putting it into the SO-239? I.E. is it rubbing nice and tight? I have seen this in the past where the prongs are spread on the SO-239 and when the PL-259 is pushed in , the pin never contacts the prongs and the back shell of the PL-259 keeps it right smack in the center so RX will go away.

I was going to suggest that too,

But thought the OM might have checked it already.  With the coax just hanging from the center pin it will make good contact, but if the leaves are spread they can lose contact when the shell is screwed on and the pin is centered.

73.
Logged
Mark -- N7EKU/VE3

W1VT

  • Member
  • Posts: 6071
Re: Receive disappears when connecting shell of coax connector
« Reply #19 on: October 12, 2022, 06:32:47 AM »

This can be an issue with soldered PL-259 center pins.  Excess solder can make the pins thicker.
Logged

KL7AM

  • Member
  • Posts: 103
Re: Receive disappears when connecting shell of coax connector
« Reply #20 on: October 12, 2022, 07:41:21 AM »

The receiver is a Drake SPR-4 which is a solid state older receiver.
I have lots of test equipment and service ham gear on a regular basis. It is a strange problem that sounds very simple and I mistakenly thought it would be an easy fix. I believe I have covered the simple possibilities already. Other receivers work fine with the same connection etc.
Access to make measurements is very difficult in the front end stages of this receiver so I thought I might get lucky and find someone that had a similar experience. I am thinking there is a possibility of a shorted cap in a tuned transformer in the front end or something similar. The receiver has circuit boards in the bottom of the chassis mounted vertically and in the case of the input circuits they are mounted so close together I can't safely get a probe in there safely. I suppose I will have to do some disassembly and see what I can find. I do have another SPR-4 and perhaps I can do some a/b comparisons for resistances or voltages that may help. It does act like the center pin is shorting to ground though...
Logged

W1VT

  • Member
  • Posts: 6071
Re: Receive disappears when connecting shell of coax connector
« Reply #21 on: October 12, 2022, 07:55:03 AM »

Another possibility is the other end of the wire that connects to the SO-239.

I had brick amplifier that I thought had a bad power connector.  Turned out the connection between the wire and the circuit board was bad.
I've fixed a lot of stuff with a good visual inspection.  Of course, a lot of that was done when I was a lot younger and  had better vision!
Logged

W9WQA

  • Member
  • Posts: 990
Re: Receive disappears when connecting shell of coax connector
« Reply #22 on: October 12, 2022, 07:55:33 AM »

sounds like a job for an,

OHM METER
Logged

AC2EU

  • Member
  • Posts: 2793
    • McVey Electronics
Re: Receive disappears when connecting shell of coax connector
« Reply #23 on: October 12, 2022, 09:46:49 AM »

Quote
Other receivers work fine with the same connection etc.

To be clear, is it the EXACT same connection? As in remove the radio and put the SPR4 in it's SAME connections or is it through a switch, patch panel or even a different coax used?
Something is DIFFERENT.

You say that you service ham gear. What then, do you suppose could be in the front end circuitry that would cause this? If it's receiving with just the center conductor, the front end must be active-right?
I too, have experienced the "spread center" syndrome, which about the only radio related problem it could be.
Otherwise it's most likely external to the radio.

AI5BC

  • Posts: 456
    • HomeURL
Re: Receive disappears when connecting shell of coax connector
« Reply #24 on: October 14, 2022, 08:37:17 AM »

If it was something that easy I wouldn't be posting here.
BS it is stupid simple to fix.
Logged

KL7AM

  • Member
  • Posts: 103
Re: Receive disappears when connecting shell of coax connector
« Reply #25 on: October 14, 2022, 12:03:55 PM »

It is the EXACT same connection.

And Mr. Wonderful AI5BC What is the "stupid simple to fix" Solution?
Logged

KA4WJA

  • Posts: 1601
    • HomeURL
Re: Receive disappears when connecting shell of coax connector
« Reply #26 on: October 14, 2022, 08:53:37 PM »

Hello to all,
1)  Of course, my first thoughts here was as others mentioned (a shorted piece of coax, shorted connector, blown balun, bad antenna switch, blown grounding block / lightning arrestor, etc. etc.)....but, then Allen actually tells us the radio in question is an old Drake SPR-4....and, my mind wonders who has worked on this radio before, 'cuz an SO-239 isn't supposed to be there.  :)

Without getting into the middle of the "argument"....has it not occurred to anyone that the Drake SPR-4 didn't come from the boys in Miamisburg with an SO-239?

It came from the factory with what was de rigueur in those days, an RCA jack / phono jack for the "antenna connector".





So, while someone may have done a good job modifying it, by professionally changing out the RCA jack with a SO-239....it is also possible there is an issue with this connector....

And, of course it is also possible that something else is amiss inside this receiver, as it is obvious that someone has done at least one modification to it.  And, there could be other mods done, other "repairs" attempted, etc., and/or plenty of things that need looking at and measuring.

Looks like a job for an ohm meter, to me too!  :)

And, Allen forgive me, but if I came up with this in less than 10 seconds, I assumed that you already realized the SO-239 is not "factory"....but, now I'm wondering? 

The receiver is a Drake SPR-4 which is a solid state older receiver.
I have lots of test equipment and service ham gear on a regular basis. It is a strange problem that sounds very simple and I mistakenly thought it would be an easy fix. I believe I have covered the simple possibilities already.

2)  Then, as I started to write the above answer, I had another thought...
Some of these older receivers also had various inputs...some low-imp (~ 50-ohm) and some hi-z....and, I wondered if the SPR-4 was one of these....
Now, I am a Drake guy, but even I wasn't sure, so I spent another 5 seconds downloading the SPR-4 manual.....and then spent about 60 seconds scanning the doc...and, what-da-ya-know, it is... :)

Perhaps Allen, KL7AM, needs to have a more detailed look at the SPR-4's manual?

www.wb4hfn.com/DRAKE/DrakeManuals/PDFDOCS/SPR-4_Manual.pdf

'Cuz, when I took just a quick look at it, it mentions that while for best single-band performance a 50-ohm coax-fed 1/2-wave dipole is good, it also mentions that "Bands A and  B require a long wire antenna."....

So, who knows what "bands" Allen has selected when he is testing this radio...

Quote
For optimum performance the SPR-4 should be used with a good antenna. For general broadcast and
short wave listening, a long wire antenna from 50to 100feet long will give good results. An antenna kit (Model AN-5) is available.

For best single band performance, a half wave dipole or other resonant antenna, fed with unbalanced
50 ohm coaxial cable, maybe used.

How­ ever, Bands A and  B require a long wire antenna.

For directional reception on 150 kHz to 1600 kHz, the accessory AL-4 shielded loop antenna may be
used. All antennas other than the AL-4 loop antenna, connect to the Ant. jack on the rear of the
chassis.


So...
So, in addition to picking up the ohm meter probes, maybe a better read of the manual, switching a switch, etc. will find the "issue" in short order?  :)

Hey, I could be all wrong on this....but, as I wrote, this was just my first thought....and, I thought I'd spend a few minutes pecking away on the keyboard to see if this helps. 



I do hope this helps?

73,
John,  KA4WJA

P.S.  I was recently accused of "talking down" to a fellow ham here, who was asking for advice / recommendations....when all was actually doing was attempting to pull some further info FROM him, attain more details, that was needed in order to better answer him in anything but generalities...

And, here in this thread, I see the same issue....there is little detail to make accurate recommendations / give detailed advice....so, I'd usually ask for more...
But, because of this recent episode, I decided to actually do some of the work for the questioner.....
This is, of course, not the best way to teach....but, it seems that these days it isn't acceptable to most to actually question them....so...
So....


« Last Edit: October 14, 2022, 09:09:05 PM by KA4WJA »
Logged

KA4WJA

  • Posts: 1601
    • HomeURL
Re: Receive disappears when connecting shell of coax connector
« Reply #27 on: October 14, 2022, 09:43:45 PM »

Opppss, missed the deadline to edit my above post...I was handling a family matter.  :(


Perhaps I'm going over-board in my zeal to make sure nobody misunderstands what I'm writing? 
But, whatever...


What I wished to be more clear on is....it just might be that there isn't anything majorly wrong with this SPR-4....it just may need to be operated properly / as per manual.

Sure, it could be a connector issue, it could be a old modification or repair gone awry, it could be the "wrong type" of antenna is being used on the "bands" selected, etc. etc....
Or, it could also just be that the operator needs to read the manual more carefully?



Again, I do hope this helps....and, that nobody takes offense.

73,
John,  KA4WJA
Logged

W1RKW

  • Member
  • Posts: 219
Re: Receive disappears when connecting shell of coax connector
« Reply #28 on: October 15, 2022, 04:34:19 AM »

I'd be curious to know how this behaves with a signal generator.


« Last Edit: October 15, 2022, 04:36:43 AM by W1RKW »
Logged

KL7AM

  • Member
  • Posts: 103
Re: Receive disappears when connecting shell of coax connector
« Reply #29 on: October 15, 2022, 10:54:00 AM »

I am tied up with other things for a bit. So, for those who have tried to help I will add more info. I have two of these receivers and so A/B comparisons are easy to make and when one is 40 db down from the other with the exact same test setup.
I don't know that I mentioned a SO-239 or PL-259 but if I did that isn't accurate but doesn't change
the issue. It does have the stock RCA connector.

I will be back when I have a little more time
Logged
Pages: 1 [2] 3   Go Up