开云体育

Hi Matt,

It is advisable to measure the coil at its operational frequency of 7 MHz. We never get pure coils. First and foremost there is a winding capacitance does affect the effective inductance. If you measure L at 1 MHz, the effects of that capacitance are not strong. You may find that if you adjust your coil for the desired inductance value at 1 MHz, it may show a higher inductance at 7MHz. This is caused by the winding capacitance which is in parallel to the inductance forming a parallel tuned circuit. The resonance depends on the coil design and is usually much higher than the frequency of operation

73
Dieter

PS
I edited the first version of this reply.

Hi Dieter,

When designing a coil for a 40m trap, would it be advisable to set the frequency to 7MHz?

Or would it be better near 1MHz for instance?

Thanks!
73'
Matt -WA0V
?

Hi Johnny,
thanks for your suggestion. Unfortunately the EEPROM in the FA-VA 5 is filled to 99 %. There is no space left for any new features. Also, there are no plans to issue a new firmware for the FA-VA 5.
However, having a sweep generator is a good idea. I will put it on the list for any future developments.

73 Michael, DG5MK

I own the FA-VA5 from 4 years, this is my review and description:

I would suggest to Michael DG5MK a new feature, if is possible to add a sweep generator function, with these parameters:
- start/stop frequency
- number of points
- sweep time

I think it's not too much difficult to implement in the firmware, it is like an SWR sweep without RL measurement.

Val,
Did you get any responses to your request for help? I don't see any posted in the forum.

A new chat has been created:

Hi Michael

My e-mail to your t-online address bounces back. Tried a few times. Please advise.
thanks
Dieter, VK3FFB

By: Dieter VK3FFB (group owner) <dpelz@...>

View/Join This Chat

Do not reply to this message to post to the chat. You can participate in chats only through the group's website.

Dear FA-VA5 users,

We may not be the most active group, but we meet the purpose of this group. Questions coming in from time to time are answered and discussed promptly.

It is now my pleasure to inform you that we are soon reaching a member count of 200 (196 now). This will be a great milestone for the FA-VA5 user group.

Thanks to all members who posted questions in the past. Any unexplained observations with the FA-VA5 are worth a post. There are no dumb questions :)

I'd like to thank all members who responded to posted questions in the past and I encourage you to do so in the future.?

I also want to ask members to consider becoming a group editor. Just send me a message if you feel inclined to being a group editor.?

Please feel free to post suggestions for the improvement of the group service.?

thanks

Dieter, VK3FFB
Group Owner

If we consider the following:

The FA-VA5 measures impedance (Z) in a novel way devised by Michael, DG5MK. It then derives the VSWR via the reflection coefficient magnitude |rho|

VSWR = ( 1 + |rho| ) / ( 1 - |rho| )

however

|rho| = |( Z - Z0 ) / ( Z + Z0)|

and if I see this right, then this is where the calibration problem originates from. If Z has an error, VSWR can't be correct.

Z is the unknown impedance (antenna input) and is therefore complex ( Z_real + j x Z_imag ).

So, if we have an inaccurate impedance measurement resulting from SOL standards with limited quality, we also get an inaccurate VSWR value.

Maybe my old brain is missing something, but I think, this is the crux of the matter.

73
Dieter, VK3FFB

SWR is a scalar number. (It is by definition the ratio of two voltage magnitudes |Vmax|/|Vmin| on a transmission line.)

Thats my point. If you want to do a reliable vector smith chart analysis with the VA5, the self made calibration kit may be the bottleneck, even below 100MHz. But not for the SWR

No rush, Peer. Take your time. Jan already sent one pic.?

SWR is a scalar number. (It is by definition the ratio of two voltage magnitudes |Vmax|/|Vmin| on a transmission line.)

73
Dieter, VK3FFB

Hi Dieter,

Currently I'm on holiday. I will send the pictures as soon as I'm back home.?

For the SOL topic up to 100Mhz,? youre right. A bit polemic :) On the other hand, in my setup Im not using the V of the VA-5. No Smith,? only scalar SWR. And for that purpose even my self made SOL does the trick. Wether the SWR? dip has 1.3 oder 1.1, as long as the frequency indicates that my Antenna is inside the band and my TRX will be happy.?

Best 73,
Peer

Dieter VK3FFB (group owner) <dpelz@...> added the album FA-VA5 BNC connector soldering: This image was sent by Jan (SDR-KITS) to illustrate the required soldering of a critical BNC grounding pin.?

"I have seen this issue at least two or three times when FA-VA% Customers complained about poor quality measurements or VA5 locking up.

?

The problem was found by me after a customer return of a faulty FA-VA5.

?

This joint needs to be soldered from the top component side and needs a lot of heat, at least 60W iron with 3mm or 4mm wide solder bit.

?

A badly soldered joint can play up after time because of strain on the BNC connector after regular use.

Although the BNC connector may still show connected to GND? via the backplane, measurement accuracy may suffer if the BNC ground terminal is

not making good contact with the top copper."

click on "Photos" left to see the image.

?

Peer

Glad to hear you found the problem.?

For the benefit of other FA-VA5 owners, it would be helpful if you could provide images of the BNC connector ground solder points.?

Page 7 (... BNC socket) of the FA-VA5 manual (building instructions) already alerts to the need for ensuring proper soldering:

"... The two ground pins are to be soldered on the underside of the board with a 100W soldering iron to ensure the solder flows well in order to avoid cold solder joints. ..."

but it does not have an image of the solder points under the PCB.?

On the SOL calibration "up to 100 MHz" it is perhaps a little courageous to say "it is absolutely uncritical what type of SOL stuff you gonna use". :)

thanks & 73

Dieter, VK3FFB

I'll remember that in the future.

For quick readers, the solution is down below!

Hi Dieter, Wes,

don't get me wrong. I highly appreciate tips and tricks for all kind of things. But, speculating and explaining basics isn't that helpful.

I think Wes has already commented on the matter very well, so I am not going to repeat here.The SWR detection inside amateur radio transceivers is not using an impedance measurement technique. Instead, it uses a relatively simple SWR measurement circuit. Therefore, we cannot expect that "both values should align at least within some khz". Neither can we expect a high SWR measurement accuracy of such in-built devices. Their purpose is related to operational monitoring, especially the detection of antenna faults. We also have to be clear about the nature of the transceiver in-built measurements. Unlike with the FA-VA5, transceiver in-built SWR detection assumes a constant source impedance of 50 Ohms. Surely, common amateur radio transceiver PAs are not able to provide a constant 50 Ohm output impedance. This of course also affects measurements with external VSWR instruments.

Neither was it a disagreement between two devices nor a topic of miscalibration.?Up to 100Mhz it is absolutly uncritical what type of SOL stuff you gonna use. As long as it matches roughly short, open and 50Ohms...

To be clear, if 2 different TRX see 7060khz as lowest SWR it should be the same for the VA5 in scalar mode. Not 7246khz. Neither a poor SWR circuit nor a misscalibration can lead to that offset.

As I mailed with Jan, he directly raised the ground solder point for the BNC connector on the PCB as the most critical part for such failures and wrong values. (I am the second person to report that issue, so don't worry that your device is also affected)

Guess what:


After I resoldered it, the VA5 now works perfectly fine without any deviation from my two TRX. Pls keep in mind that the heat distribution of the PCB requires a strong 60W+ solder iron to resolder it properly!
As I understand, using wires to bridge somehow the ground point doesn't solve the issue. It is this single point which is important for the accuracy of the FA-VA5.

I checked the connection joints for the BNC connector and they were only partically soldered. So the mechanical bending stress seems to be the root cause. So, if someone is searching for that issues, this might be the solution.

Many thanks to Jan and his promt answers to my mails!

Best 73,

Peer, DL8YF

In the meanwhile Jan send me the data via Email. Many thanks for your support, Jan! And, to keep it straight for readers, the Amphenol BNC CAL Kit sold via box73 and sdr-kits requires -41,66ps for "short" and -113,52ps for "open"...!

On Sat, Nov 12, 2022 at 06:13 AM, Peer DL8YF wrote:

"both values should align at least within some khz"

Hello Peer
I think Wes has already commented on the matter very well, so I am not going to repeat here.
The SWR detection inside amateur radio transceivers is not using an impedance measurement technique. Instead, it uses a relatively simple SWR measurement circuit. Therefore, we cannot expect that "both values should align at least within some khz". Neither can we expect a high SWR measurement accuracy of such in-built devices. Their purpose is related to operational monitoring, especially the detection of antenna faults. We also have to be clear about the nature of the transceiver in-built measurements. Unlike with the FA-VA5, transceiver in-built SWR detection assumes a constant source impedance of 50 Ohms. Surely, common amateur radio transceiver PAs are not able to provide a constant 50 Ohm output impedance. This of course also affects measurements with external VSWR instruments.

A remote diagnosis of possible problems in your FA-VA5 is difficult, if not impossible.
I use the "Master Calibration" (SM50) as described on page 12 of the FA-VA5 manual. The FA-VA5 measurement results then compare well with measurements made with my Agilent 8753 network analyser (boat anchor :).
Unlike the "basic calibration", the "master calibration" is storing SOL calibration values permanently.?

I hope, this helps a little.

73
Dieter, VK3FFB

Hi Wes,

For that measurement shown in the pictues I simply swapped the connector between the Icom and the VA5. In general I would agree that the Icom SWR Bridge will be a bit behind the accuracy of the VA5 bridge. But not more than 150khz. As the VA5 measures the scalar SWR in this setting, both values should align at least within some khz. My TS590s shows the same SWR of 1 at 7060khz? and my Dawia CN901 also confirms that. So 7060+- 20khz is the best SWR for my actual Antenna.?

I do have two calibration kits which should be precise enough up to 100Mhz without editing the delay settings according to the manual. The issue I got in the past is the following:
Whenever I calibrate a larger area, eg. 15mhz +- 5mhz, the VA5 somethimes hangs up/freezes in the last cal step for load. Normally after it has finished that last load cal step the VA5 returns back to main menu. I then have to turn it of and on again to get it working. As the VA5 then loses its actual cal settings, I have to start over. As this procedure takes for 5mhz 5-10min, it is really annoying. But thats more a bit of a side problem. The main issueis that right now the VA5 measures rubbish.

My next approach will be a load once again the firmware. Perhaps that will be the solution.

Best 73, Peer

Hi Peer,

As I see it you have two different issues.

1) Disagreement between two different measuring devices

2) Some operational/calibration issues with the VA5.

Issue 1.? I assume that you are not taking your ICOM into the field so you are measuring at the input to the feeder.? If you are measuring at the same point with the VA5 then the difference is most likely the inaccuracy of the ICOM measurement.? Although I'm not familiar with the circuitry in the ICOM, it is most likely using some kind of directional coupler/bridge.? These have multiple sources of error, including source match and coupler directivity.? OSL calibration determines these errors and removes them using calculation.? This is not an option with our transceivers so we are the mercy of the basic design.

With a calibrated VA5 these errors are removed.? Now if you are actually measuring at the antenna (preferred), then you have removed the effects of the feeder.? This alone will give different results even with the same instrument.

Issue 2.? I'm not sure I understand what is happening and quite frankly I use the VA5 so infrequently it is a relearning exercise when ever I do.? I'm blessed (or perhaps plagued) with too many analyzers; an N2PK, DG8SAQ VNWA, Rig Expert AA-55 Zoom, Elekitsorparts FAA-450, and the FA-VA5.? All of the others are generally friendlier to use, but the VA5 is very accurate, portable and usable outdoors in sunlight.

Perhaps someone more familiar with it can help you out.? It is an excellent device and I wouldn't give up.

Wes? N7WS