Voltage drop measured on transmit -- normal?

VE7ATJ_Don

Good morning all

I have an older Astron VS-35M power supply (with both variable voltage and current) and using FRStack to monitor voltage, I've adjusted it for 13.9 to 14V when receiving.

Is it normal for FRStack to show a drop to 13.2V on transmit (100W)? I would have thought a 'regulated' power supply would be able to maintain the measured voltage within tighter limits. Or am I expecting too much?

I haven't taken the covers off the Astron, but as I say, it's pretty old..

Thanks.

Al_NN4ZZ

Hi Don,

It is normal to see about a .6 - .8 volt drop between the voltage measured at the power pole connector on the back of radio and what is measured internally on the radio side of the fuse on TRANSMIT.

I also use an Astron AS-35M supply and have found that my radio works best when it is set to 15 volts. More details on that as well as the readings and testing on my web page. Also what I found to be the fix when the drop is too high.

http://www.nn4zz.com/Flex6600.htm#Astron_Power_Supply

http://www.nn4zz.com/Flex6600.htm#Astron_Power_Supply

Regards, Al / NN4ZZ

al (at) nn4zz (dot) com

6600 Win10 Pro V2004 -- SSDR V3.3.33

KD0RC

Hi Don, that is not normal. My Astron RS-70M is set for 14.2 V and does not dip at all when transmitting a 100 W CW carrier. I am using the K9DUR SDRMonitor app to measure it. When I first moved the voltage from 13.4 (it was a little low) to 14.2 V, I measured it with a Brymen 869S voltmeter and saw no drop at that time either.

I wonder if you need to set the current limit up a bit. I don't know if you are at the limit and things are starting to fold back or if there is a problem with your supply.

Al_NN4ZZ

Hi Len & Don,

In my note above I am referring to the drop between the back of the radio measured with a Fluke meter to the voltage measured internally (I also use SDRMonitor). The voltage on the Astron meter does not change. I do measure a slight 0.1 volt drop between the supply and the back of the radio related to the power supply cable.

Al / NN4ZZ

Mike-VA3MW

That can happen. If you want to be sure, use a quality meter and measure the voltage on the back of the power supply and then on the back of the radio while in 100% Full TX (full load). FM works.

At 20+ amps it does not take much resistance to drop 1 vDC. Ohms law is your friend here. :)

KD0RC

Hi Al, our posts crossed in the mail...

I agree, a little higher voltage to overcome any cable and connector losses is a good thing, and is what I did with mine. Once I moved mine to 14.2 V, I got full power out on all bands. Prior to that, my slightly low voltage (13.4 V) gave me somewhere around 90 - 95 watts out depending on the band.

The RS-70M is a really stiff supply and I don't seem to have any noticeable ohmic losses in my cables/connectors, so I don't see any drop in voltage at the radio.

Every now and again I unplug and re-plug all of my Anderson PowerPole connectors just to get a little self-cleaning action. So far that practice seems to help.

Geoff AB6BT

A regulated power supply regulates the output voltage by comparing (sensing) the voltage on the output terminals to an internal reference. This voltage should not change with load within the limits of the specs of the power supply. (There are power supplies available that have remote sensing capabilities)

If you are measuring the voltage anywhere other than the output terminals then there will be voltage drop between the output terminals and your measuring point.

R=E/I. So lets say the voltage drop is 13.9V-13.2V =0.7V. If I = 20A, then R=0.035 Ohms.

It is certainly possible to have that amount of resistance considering wire, Power Pole connectors, internal fuse connections, etc

Seems reasonable to me.

Al_NN4ZZ

I recently changed radios from a 6700 to a 6600. This thread prompted me to re-check all the voltage measurements. There is a big difference with the 6600. The internal drop is very low on the 6600 as measured internally by SDRMonitor for TX at 100W. The total drop is only about 1/3 of what it was on the 6700.

Here are the new measurements for RX and TX at 100W. The voltage supplied to the radio is measured with a Fluke 177 meter at the power supply and at the powerpoles on the back of the radio while they are plugged into the radio. The internal voltage is reported by the SDRMonitor app.

RX readings

-----------------

The voltage at the power supply is 15.13 volts

There is 15.10 volts at the power poles on the radio. A drop of 0.03 due to the power cable resistance.

There is 15.0 volts measured internally by SDRMonitor - an additional drop of 0.1 volts internally ( radio fuse, wiring, etc)

TX readings, key down 100W

-----------------------------------------

The voltage at the power supply drops very slightly to 15.11 volts, a drop of 0.02 volts

There is a measurement of 14.77 volts at the power poles on the radio - this is a drop of 0.34 volts at the power pole due to the resistance of the power cable from the supply to the radio when supplying about 15 amps

There is a measurement of 14.74 volts internally by SDRMonitor - this is an additional drop of ONLY 0.03 volts internally ( radio fuse, etc) for a total of 0.26 volts. The big difference is the very low internal drop on the 6600.

I'm not sure why the 6600 is so much better, I could make some guesses but will take it. I'll be updating my web page with this info on the 6600.

Meter and pin setup to measure the voltage at the power poles. The pins slide in the connector without disconnecting it from the radio.

Regards, Al / NN4ZZ

al (at) nn4zz (dot) com

6600 Win10 Pro V2004 -- SSDR V3.3.33

VE7ATJ_Don

Hi all... many thanks for your comments, but to be clear -- all voltage measurements are the values supplied through the meters provided in FRStack. So whatever voltage it is measuring is what I'm comparing during receive and transmit.

Len... the 'current limiting' on the Astron is essentially turned off (knob is fully clockwise).

KD0RC

Al and Don, one potential source of resistance besides the connectors and wires is the fuse socket. You might want to put it in and out of its socket a few times to see if that makes a difference. I have not had that problem with my Flex, but did have it bad with a mobile ICOM rig a few years ago. Once I cleaned up the fuse contacts, the rig returned to normal.

Al_NN4ZZ

Len Wrote:

"one potential source of resistance besides the connectors and wires is the fuse socket." 

Agree, on my 6700 when I was having low voltage issues I found the fuse legs were a little corroded and cleaning them and the holder made a big improvement and stopped the lockup. Note from my web page on the lockup issue:

• Cleaning the fuse was probably the main issue. Adding conductive grease and adjusting up the power supply up from 13.8V to 14.4V and eventually to 15.0V also seems to help although it worked fine at 13.8V for years.  

http://www.nn4zz.com/Flex6700.htm#Low_Voltage_Lockup

Bumping the power supply up to 15 Volts also helped and I never had any more issues.

Regards, Al / NN4ZZ

al (at) nn4zz (dot) com

6600 Win10 Pro V2004 -- SSDR V3.3.33

Al_NN4ZZ

Don wrote:

"Hi all... many thanks for your comments, but to be clear -- all voltage measurements are the values supplied through the meters provided in FRStack. So whatever voltage it is measuring is what I'm comparing during receive and transmit."

Got it, so you are seeing a drop of about 0.8V between RX and TX internally on the radio. If you put a meter on the power supply I expect you will see almost no drop there ( if it is functioning correctly) when you go from RX to TX. On my 6700 when I was having the lockups the internal radio drop for TX was at 1.0 volts. The problems were resolved when I reduced the drop to about 0.6 volts. This was accomplished by cleaning the fuse in the 6700 and increasing the power supply to 15 volts.

From what I have heard a drop of .6 to .8 was expected on the 6700. And that amount was what I saw and it worked fine.

On my 6600 the internal TX drop is much lower at about 0.26 volts.

What radio model you have and how old is it? .

Regards, Al / NN4ZZ

al (at) nn4zz (dot) com

6600 Win10 Pro V2004 -- SSDR V3.3.33

VE7ATJ_Don

Hi Al... it's a 6500 which is at least 6 years old (I got it second hand in 2016).

Al_NN4ZZ

Don wrote:

"Hi Al... it's a 6500 which is at least 6 years old (I got it second hand in 2016)."

Don, so that is the same basic design/layout as my 6700. If you get a chance or if you have any problems like lower power out or lockups you might want to try cleaning the fuse to see if that makes a measurable difference in the TX drop. My 6700 was about 6 years old when the drop increased enough that it started causing problems.

It would be interesting if some other owners who also use a program to monitor the internal radio voltage could make these various voltage measurements and post the results here along with the radio model number. I'm just curious to see if there is a difference with the newer design (6400, 6600) compared to the 6300, 6500, and 6700. I was surprised to see how much lower the drop was on my 6600 and wonder it it just a one-off or something else.

Regards, Al / NN4ZZ

al (at) nn4zz (dot) com

6600 Win10 Pro V2004 -- SSDR V3.3.33

John KB4DU

Flex hardware manual states voltage 13.8 +/- 15%. So, I adjust the voltage at the power supply to provide 14.8 on transmit as measured by FRstack. This gives 15.2 on receive, within max of 15.8.

VE7ATJ_Don

Thanks Al.. I will pull the covers off (haven't done that yet :-)) and take a look at the fuse.

John... thanks for the info. Further Info... I've turned the voltage knob on the Astron fully clockwise (full voltage) and the FRStack is still only showing 14.3V internal. Time to get out the meter and see what's coming out the back of the power supply!

David Decoons, wo2x

Also worth noting, there are two internal voltage meters in the 6000 series radios that are accessible via the API. One is 12 volts at the fuse holder (not sure which side of the fuse) and other is 12 volts at the power amplifier. I believe the first is before the fuse holder.

I use Node Red to monitor both internal meters and recently replaced an old power cable to the radio (was not the one supplied with my Flex). I was seeing a significant voltage drop, so I pulled the power cable that came with the radio out of the box. I solder the rings lugs on the bare wire end and connect direct to the studs on the power supply. I do not run the radio power cables through a Rig Runner.

The quality of the “Power Pole” connectors (metal contacts inside) can over time cause a significant enough voltage drop that when operating the radio in FT8 at 100 watts can cause heating of the Power Pole connectors. The knock off Power Pole style connectors can develop high resistance over time.

73

Dave wo2x

Al_NN4ZZ

Hi Dave,

i use SDRMonitor to report on the internal voltage. On my 6700 it showed a significant improvement in reducing the TX voltage drop after cleaning the fuse. So it must monitor after the fuse on the 6700. And the SDRMonitor documentation says it monitors the “power supply voltage.”

On my 6600, it is interesting that the voltage drop is so much less when it switches to transmitting compared to the 6700. Perhaps the internal monitoring connection is at a different spot and before the fuse on the new models. Or perhaps it is still after the fuse holder but the board traces that carry the power are bigger (i.e. lower resistance). Or maybe something else. It would be interesting to hear if Steve Hicks or an engineer at Flex has any comment.

BTW, I also have the power cable connected directly to my supply.

Al / NN4ZZ

VE7ATJ_Don

Just an update for everyone:

a) Took the lid off the 6500 and dusted it out (I suspect it hadn't been opened since it was built!). And yes, the 30A fuse by the powerpoles was quite dirty. I had to use contact cleaner and an emery board to clean off the contacts.

b) Took the lid off the Astron as well. Also needed a thorough cleaning. Measured the max voltage at the terminals and it varied between 4.5V and 14.9V -- within specs.

c) Put everything back together and now find that with the Astron turned up all the way, FlexStack shows an internal voltage of 14.4V on receive and 14.1V on transmit. So, things are good.

Thanks again to all with their great suggestions. Merry Christmas guys.

Geoff AB6BT

Back to the original post...

The difference between 13.2V and 14V is only slightly more than -0.5dB.

So, in actual operation I doubt there would be any loss in ability to make a contact.

Merry Christmas all.

Al_NN4ZZ

Don,

Thanks for the update and looks like cleaning the fuse did the job for you also. Reducing the drop between RX and TX should help avoid any low voltage problems.

73, Al / NN4ZZ

WX7Y

It is ALWAYS a great Idea to clean off Oxidation from the Fuse contacts and holder and use a slight amount of no-ox mainly because if the Voltage is dropping more then Specs say it is being disapeted as Heat somewhere else as the current rises and the Fuse holder is the weekest point after probabely the PowerPole connectors and speeds up oxidation until it totaly fails and the socket must be replaced, It's nice with the FLEX radio we can identify were this problem is by the 3rd party programs and be pretty certain if it's the PowerPoles or the ATC Fuse Holder using a DVM externaly.

The amount of RF power is NOT really the issue.

Flex is NOT the only radios that have this issue, the little older ICOM's and maybe others that have the inline ATC type fuses fuse holder had to be replaced because of the Oxidation and Heat in the fuse socket ruined the spring tension of the socket.

ATC type fuse's even in higher current circuits in automobils have this issue UNLESS they have the Silicon greese or a tiny bit of NO-OX on them to keep the oxidation and moisture at bay.

have a great Holiday seasion

David Decoons, wo2x

Another thing to consider when adjusting your voltage (after cleaning). The radio’s TX IMD is less at a higher voltage. I run mine at 14.7 volts at Power Poles on RX. Coupled with the PG XL in AAB mode on SSB (4 amps bias) and I get very good reports as far as signal cleanliness. Not adaptive predistortion clean but MUCH cleaner than a Yaesu FT-3000 and ALS1300 amp.

73

Dave wo2x

Geoff AB6BT

Per Don,

"FlexStack shows an internal voltage of 14.4V on receive and 14.1V on transmit"

This does not show the difference from the Power Pole connectors on the rear of the radio and the FRstack measurement.

I may be mistaken but isn't that what we need to measure???

Not sure how this has anything to do with the fuse connections.

Al_NN4ZZ

Geoff,

Yes the key measurement is the difference (i.e. drop) between the voltage measured at the input to the radio power poles and what is seen internally. Even with a dirty fuse the drop on receive is pretty low since the current on RX is low. With a dirty fuse the drop is more significant on TX. So a big difference between the drop seen on RX and TX is a relative indicator. Originally the difference Don measured was 0.7 volts. After cleaning the fuse it was 0.3 volts.

Agree it is ideal to have accurate measurements of the voltage at the supply, at the power poles on the radio, and internally to get a complete picture of the drops at each step of the way. Measuring all 3 on both RX and TX will also identify if there are problems in the power supply, in the power cable, or the power poles as well as on the fuse / internally. By the way the voltage measurement shown on the power supply meter, at least on my Astron is not as accurate as measured with my Fluke.

In my measurements above for my new 6600, I listed all 3 for both RX and TX.

73, Al / NN4ZZ

Geoff AB6BT

Bret & AL,

Well we have control of three things. The wire gauge and connection to the power supply, The PowerPole connectors, and the fuse socket contacts. The sum of the resistances of these three is what accounts for the various voltage drops. Clearly, reducing the resistance in any one or combination of the three will reduce the voltage drop as measured internally.

As Al mentioned, it is a good idea to measure the voltage at the PowerPole connectors on the rear of the radio to get a good picture of where the voltage drops occur.

I use DeOxit spray frequently in my day job to help eliminate oxidation on electrical contacts. I also use it on PowerPole contacts. Caig also makes a couple greases meant to protect contacts from oxidation and to seal mating surfaces from the environment. I don't believe any of the greases thay make is conductive. They used to make a grease with copper particles but I'm not sure if that still exists.

I have never used NO-OX.

Can anyone comment on the pros and cons of NO-OX verses the Caig products?

Thanks.

Al_NN4ZZ

Geoff,

Here is the silver grease I used on my 6700. I got it from Amazon. It supposed to provide good conductivity. My 6600 is new but if I eventually need to open it, I'll use the grease on the fuse holder.

Al / NN4ZZ

Geoff AB6BT

Did you ever measure the conductivity of the grease?

Al_NN4ZZ

Geoff,

Just did a test. I made a short line of grease about a 1/4 inch long.

If the test leads of my meter are very close, maybe 1/32 of an inch apart the meter reads about 20 ohms.

As I get closer the reading drops,. It is hard to get the leads much closer without touching them together. But the resistance continues to drop as I do and when the leads touch it is almost zero as expected.

If I move the leads farther apart the reading goes up to several thousands of ohms. It reads tens of thousands of ohms at about 1/4 inch of grease.

So it appears to be low resistance and conductive when in close contact.

Regards, Al / NN4ZZ

al (at) nn4zz (dot) com

6600 Win10 Pro V2004 -- SSDR V3.3.33

Geoff AB6BT

Al,

That's interesting, So depending on how small the silver particles it might actually help reduce resistance betweem the mating surfaces of two contacts.

It would be worth testing with say an ATC fuse and the spade type connector it plugs in to both "dry" and with the grease. I don't know the style of fuse socket in the radio but some of the ATC holders I have use just common spade slide-on connectors.

WX7Y

YES the ATC holder in the FLex is just the 1/4" spande connectors

I also use the silver greese that Al uses on PowerPole contacts and 1/4" plugs and Sockets like the ATC Fuse in the FLEX, I WOULD NEVER USE De-Oxit spray in or close to a Flex radio on the fuse holder or the Radio's Power Poles or anywhere else because the overspray is UNCONTROLABLE, Basically Deoxit is the same as WD40 spray and has terrible over spray which is why I don't use it on Higher current/ Voltage connections in a radio even though it does have a adjustable spray nozel because of Over Spray and Dirt acumilation, This is why the Enginer that designed and built the Tube type amps for Ameritron does not recomend it for band switchs or anywhere else in the AMP.

For Electrical connections I would use Silver Paist or NO-OX as they are specificaly made to use on HIGH current and HIGH Voltage Electrical connections and won't go ANYWHERE else in the Radio IF it is used in very very small amounts, A very very small amout goes a very long ways

HOW EVER never use a conductive greese on RF Connectors, We should use a Silicon Greese, but most of us Hams are kinda cheep and it doesn't come with PL-259's or other cheep Mobile or Basestation Antennas like Comet or Diamond so we don't use it and think tapeing is going to keep the Water out, personaly if I don't have any silicon greese then I don't tape it so it can dry out and remind me that is a potantial problem area to fix when I get more Greese, why: the Tape make a place for the Water to puttle close to the connector and won't let it dry out and NO the Silicon tape is not a replacement.

I have been a RF Engineer in the Comercial Microwave, Two way and HI-Power TV transmitter install and repair industry for over 45 years and have seen these problems crop up with Microwave cavity filters, Motorola Micor and Mitrex, GE Master 2 and Master 3 Basestaions as well as High Power RF tunning cavities on the High power TV transmitters Tubes.

But to each there own, I personaly certainly wouldn't purchase a radio from ANYBODY that sprayed DE-Oxit / WD40 in the Radio thats just asking for trouble as dirt acumilates.