Toggle sidebar Toggle sidebar
  • You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
  • Retevis is giving away Radios for the New Year and Every Member is Eligible. Click Here to see the details!

Mirage B1030 quirk

Singularity35

Singularity35

DU7DVE
Jan 16, 2014
425
90
138
Small City, Philippines
I have a mirage B1030 and it has a problem which bothers me no end. It triggers fine on all other frequencies with 5 watts of drive except in the range of 146.800 to 148.200. I need to up my radio to 10 watts drive so it triggers in that frequency range. With 5 watts drive, most of the time, it just makes a buzzing sound like the relay can't trip. Any info will be appreciated. Thanks in advance.
 

Moleculo said:
Maybe one of the capacitors in the keying circuit is going bad?
Click to expand...



Thanks for the reply. I've also discovered that it keys ok with my portable at those frequencies. I'm inclined to say that it's the radio(FT-2900) that I'm using with it, but I don't know a durned thing about these matters. You think it could be the radio or maybe something else?

Edit: The radio(FT-2900) transmits fine at those frequencies without the amp.
 
How are you switching it? RF sense by the sound of it ( the buzzing sound) switch it manually and see what happens.Check your input swr some rigs are more sensitive to higher swr and throttle back reducing the drive , try another patch cable of different length.
 
vkrules said:
How are you switching it? RF sense by the sound of it ( the buzzing sound) switch it manually and see what happens.Check your input swr some rigs are more sensitive to higher swr and throttle back reducing the drive , try another patch cable of different length.
Click to expand...

Indeed try another length. You may have an impedance transformation issue happening causing power roll back from the transmitter. The fact it works without the amp and that another radio works fine points in that direction.
 
Singularity35 said:
Thanks very much for the replies. Is there any length of patch cable I should go for?

Edited: Tried another patch cable I had, it seems to work. Your replies are very much appreciated!!!
Click to expand...

Oh God YES there is a proper length to use. You MUST use a length that actually works. :DBeyond that it's time to put those "proper length of coax" myths from CB-land to rest.
 
Captain Kilowatt said:
Indeed try another length. You may have an impedance transformation issue happening causing power roll back from the transmitter. The fact it works without the amp and that another radio works fine points in that direction.
Click to expand...

If you don't mind, can you please explain that? I'm at the retarded child level though but I'd appreciate knowing a bit more about that so I can act knowledgeable when I explain to the club guys why the fix worked. :)
 
This type of problem typically happens when the input swr presented by the amplifier input is high enough to cause the radio to roll back the output power. You gave two clues that together pointed to this problem: 1. The problem only occurred at a specific frequency range; 2. The problem occurred with one radio but not the other.

When the SWR of a load is not flat (1:1), you will have "standing waves" along the transmission line that can be represented by this image:

swr.jpg


Put simply, the greater the SWR, the bigger those "voltage waves" will be. As you can see by the graph above, the voltage gets higher and lower along the length of the line. By changing the length of coax, you can find the point at which the SWR presented to the transmitter is at its lowest, which is what is meant by using the coax as an "impedance transformer". When the radio sees the SWR that it likes, it delivers full power to the amplifier and then it keys normally, but when it sees an SWR that is hight than it likes, it cuts back the output power. The best solution for this problem is to fix the input impedance of the amplifier, which is normally done by adjusting a variable capacitor (or two) on the board. However, if you've solved the problem by changing the coax length, just use the darn thing and have fun!
 
That's a great explanation! Even I understood that. Thanks for taking the time to explain to me. It is very much appreciated.

Edit: There was also another problem which I didn't realize was a problem. When I turned the amp on, I needed to have it on for a while before keying because if I keyed soon after turning it on, the relay would stick on transmit. That problem is also gone.

Again, your answers to my questions are very much appreciated. I have a trouble free amp now and I absolutely love the signal it gives me during our "dx'ing" sessions. I'm really tickled pink when the receiving stations don't believe that I am as far away as I actually am.

HF next maybe? Hahaha I wish.
 
Last edited:
Singularity35 said:
If you don't mind, can you please explain that? I'm at the retarded child level though but I'd appreciate knowing a bit more about that so I can act knowledgeable when I explain to the club guys why the fix worked. :)
Click to expand...


Sorry I didn't get back to you on this but I was working 12 hour nights and things just don't happen to quick. LOL Moleculo answered your question however. Thanks Tim. (y)

Further to that if the load impedance (antenna or amplifier input etc.) is not a pure 50 ohms then the coax cable between the radio and the load will act as an impedance transformer and will have a different impedance at different points along the cable. By adjusting the length of the cable you can adjust the impedance that the radio see's. This property of coax cable is useful when combining antennas or when an antenna impedance is something other than 50 ohms like in the case of a single quad loop where the impedance is a little over 100 ohms.
 
No worries and thanks for the further elaboration Cap'n. So is what's happening similar to the gamma match on the antenna? Also is there a way to determine at which point on the patch cable the best impedance match occurs?
 
In essence the idea about the gamma match works in as much as it also transforms the feedpoint impedance to 50 ohms but in a different manner. As for a way to determine at which point on the patch cable the best impedance match occurs, well how well do you like math? I don't mean 1+1 math, I mean REAL math. Either that or learn how to use one of these charts. LOL




http://www.digikey.com/en/articles/...cient-graphical-tool-still-vital-in-rf-design

Then there is the ever popular cut-try-check-try again approach.
 

dxChat
Help Users
  • No one is chatting at the moment.


      Top Bottom