tuner output power while tuning

[rjvalenta]

so i built this linear loaded SWL antenna, a project i found on the swling website, which involved getting a a NooElec 9:1 balun in the middle of two 15ft pieces of romex bound at the ends in a way that it effectively makes a dipole with 45ft elements.

this balun is not made for any kind of output.

my Grundig 750 can be... finiky... about how well it hears, so as a 'control' i conncted the new SWL antenna to my IC7100 to see how well it would hear. it hears pretty well, i was running around the 20m band, through in a few WWV frequencies... and even with the current Kp being above 7 i was happy with the results.

out of habit i hit the 'Tune' button. while it seemed to tune almost instantly, my concern is: did i just throw power into this tiny circuit board balun and fry it?

i will say that it still seems to be hearing well, especially during this solar storm, and it's now connected to the Grundig 750 which is doing ok with it, in general i'm calling it a win... but i'm worried that i'm not doing as well as i could be.

i put this whole setup on my roof, and it's not the safest activity to go up there, much less sit up there attempting to swap out tiny parts that i built in to an electrical box... so before i buy another balun and go back up there...

does anyone know how much power (if any) a tuner (mine is an MFJ939i) pushes out while tuning?

this antenna is on a section of roof under my new fan dipole with about 20-25ft of space between them, which may have been a great place for reception by itself, but i may end up overloading this tiny balun with FT8 signals anyway... until then, i just wonder if i screwed things up with the tuner.

or... do tuners not put out any power during tuning?

thanks,

Richard
N0TZC

 

[W2SOX]

My IC-7300 transmits a 10 watt carrier signal to see the reflected power. I do not believe the MFJ-939 transmits itself without a transceiver hooked up, if I am correct it will use the carrier signal from a transceiver that does not have a control cable and will match its impedance quickly.

When I was doing a lot of SWL I used a manual tuner and listened for maximum noise. Probably not the most efficient way but it worked for me.

 

[prcguy]

A balun like the NooElec might handle about 1 watt or maybe more for a brief moment. The dipole description is a bit confusing, did you do something like connect a short piece of Romex then short the end so it doubles back towards the balun doubling the wire length? If so that doesn't extend anything from an antenna standpoint. A 9:1 may not be the best to use in the middle of a dipole, its better suited for an end fed with about 40-50ft of wire. Less is worse, more can be better but depends on the frequency range you want.

 

[rjvalenta]

A balun like the NooElec might handle about 1 watt or maybe more for a brief moment. The dipole description is a bit confusing, did you do something like connect a short piece of Romex then short the end so it doubles back towards the balun doubling the wire length? If so that doesn't extend anything from an antenna standpoint. A 9:1 may not be the best to use in the middle of a dipole, its better suited for an end fed with about 40-50ft of wire. Less is worse, more can be better but depends on the frequency range you want.

yes... romex has 3 wires, if A attached to the balun, then i would connect A with B at the far end from the balun, and B with C at the close side - 45ft elements.

here's what i did: How to Build a Simple Linear-Loaded Dipole for Low-Noise Shortwave Radio Listening

the 1w thing i had heard before, that's why i'm worried about what a tuner actually puts out... and on some level if the balun can handle whats being radiated from my actual transmitting antenna.

 

[prcguy]

yes... romex has 3 wires, if A attached to the balun, then i would connect A with B at the far end from the balun, and B with C at the close side - 45ft elements.

here's what i did: How to Build a Simple Linear-Loaded Dipole for Low-Noise Shortwave Radio Listening

the 1w thing i had heard before, that's why i'm worried about what a tuner actually puts out... and on some level if the balun can handle whats being radiated from my actual transmitting antenna.

Linear loading with wires that close together will not really improve anything. If the wires are too short the only effective way to improve things is make them physically longer in the same dimension, folding them back cancels out the effects of the extra wire.

 

[rjvalenta]

ok so for now i'm just wondering when i hit the 'Tune' button on my IC7100 - how much power (if any) is being sent to the antenna?

 

[AK9R]

Does your tuner have a connection to the white 4-pin Molex connector on the IC-7100?

 

[rjvalenta]

Does your tuner have a connection to the white 4-pin Molex connector on the IC-7100?

yes it does.

 

[AK9R]

There are 4 wires in the AH-4 interface: +13 volts, ground, KEY, START

Here's what happens when you press the TUNE button:

1. The radio asserts the START line. That resets the AH-4's microprocessor.
2. When the AH-4 is ready, it asserts the KEY line.
3. The KEY signal causes the radio to transmit a carrier at about 10 watts.
4. The AH-4 verifies that the incoming RF is between 5 and 15 watts. If not, the AH-4 aborts the tuning operation. If the power is OK, the AH-4 starts switching relays on the capacitors and inductors to find a tuning solution.
5. About 250 ms after receiving the KEY signal, the radio removes the START signal.
6. If the tuner finds a match, the AH-4 removes the KEY signal. The microprocessor halts and the relays latch in place. When the radio sees that the KEY signal is removed, the radio stops transmitting.
7. If the AH-4 was unable to find a match, it removes the KEY signal for 20 ms then asserts it again for 200 ms, then removes the KEY signal. When the radio sees this, it indicates a "not tuned" condition.

If your MFJ939I conforms to the Icom AH-4 interface, then the system (radio and tuner) will work using the above sequence. So, to answer your original question, when you pressed the TUNE button on the radio, you sent about 10 watts to the tuner. The tuner would have had to send that power to the antenna in order to find a tuning solution. Of course, there are losses in the coax and the tuner, so the antenna would have seen a little less than 10 watts.