Hi all,

I may not wait next winter for a good RX antenna...So I put down my EWE last WE, and I'm thinking of building a half-size K9AY antenna.
A lot of litterature is available on Internet for the original one, but 7.5m high and 10m wide is too big for me.
As this original size is designed for both 160 and 80m, I tried a few simulations to cut its dimensions by 2, given the fact that I'm not active on 160m...

I made a few simulations on both MMANA and 4NEC2 to find the best trade-of between over-all performances, size and resistor values (I'll be posting them soon !)

The K9AY relay box is already made, and in the shack, I've already included the relay control inside my preamp + preselector box.

Here are what I made for further illustration...Of course, highly infuences by the original article from K9AY himslef, and from ON4UN Low-band "bible", HI





Ronan

Hi all

I know, it's been months since I haven't been writing a few words about this homebrew staff....

I finished simulated a filter + pre-selector for 80-40m bands, whose results will be posted here VERY soon.
The next phase will be the construction of it, but based on my experience with the previous filters, it shouldn't be that hard, HI.
Then, I'll try to make this Low-bands box a bit more friendly to use, adding the possibility for variable gain (remember I hae more than 40dB of gain with the exisiting one !)
It will be useful for the day I'll finally put up my FLAG antenna (2meters by 2 meters), which is the next (or parallel) step...I already hae everything to build it, I just need to do it now, HI !!!

Ronan, F8AFC

I decided to update the previous block diagram adding:

- More "simple" description of the TX/RX relay from Ramsey.
- A few LED's that will be helpful when switching ON/OFF such or such block.
- updated DPDT block diagram...

Blue color wires are HF signals.
Red color wires are for power supply signals.

Have fun !

Ronan

Hi all,

I've just finished to test the preamplifier (alone) as indicated in a post.

Waouh, I'm impressed, everything worked very closely to simulation results !!!!!
For all tests, Power supply was a regulated +12V.
Total current consumed is 120 mA.

40m
Gain = 22.7 dB
Output 1dB compression point = +26.0 dBm
Output 3rd order point (OIP3) = +36 dBm

80m
Gain = 21.6 dB
Output 1dB compression point = +26.6 dBm
Output 3rd order point (OIP3) = +37 dBm

A few chart thanks to Excel :




I'll add some pictures of the preamplifier very soon.

Next steps :
- Add the HF filter in front of the HF preamplifier
- Think about a clever way to switch RX/TX when using either a single low-band antenna, or a dedicated receiving antenna...

73
Ronan, F8AFC

So here we are, this is a picture of the "test filter" :























































As you may see, I added 68 pF capacitors in parallel of the 680pF on the 40m filter, this sharpens the bandwidth, while increasing slightly the insertion losses.

Corresponding schematics :(measured capacitors on 40m were around 620 pF;..Adding 68pF brings close results than when using 680 pF capacitors directly )




This is the curve I should obtain:



And this is the curve I obtain :


OK, the image is not that good,
- Vertical scale is 7 dB / cm
- Horizontal scale is 800 KHz / cm.
- Calibrated reference level is -20 dBm

But here is a summary of the results

80m band filter real performances:



Minimum insertion losses @ 3.741 MHz : -1.8 dB
IL @ 3.5 MHz : -14.8 dB (I'm not CW op...)
IL @ 3.6MHz : -7 dB
IL @ 3.7 MHz : -2.3 dB

-3 dB BW : [-145..+250 KHz] referring to 3.741 MHz
-6 dB BW : [-185  +300 KHz]
-12 dB BW [ -250  +365 KHz]
-20 dB BW [ -375  + 465 KHz]
-40 dB BW [[ -920  +780 KHz]


40m band filter real performances:


Minimum insertion losses @ 7.073 MHz : -2.2 dB
IL @ 7.0 MHz : -2.5 dB
IL @ 7.1MHz : -2.3 dB
IL @ 7.2 MHz : -2.9 dB
--> the response is quite flat over the 40m band actually.

-3 dB BW : [-250..+290 KHz] referring to 7.073 MHz
- 6 dB BW : [-370  +385 KHz]
-12 dB BW [ -560  +560 KHz]
-20 dB BW [ -830  + 805 KHz]
-40 dB BW [ -1.88  +1.8 MHz] 

With only the "620 pF" (theoretically 680...), the rejection above the central frequency was less good :
-3 dB BW : [-250..+345 KHz] referring to central frequency.
- 6 dB BW : [-357  +473 KHz]
-12 dB BW [ -560  + 675 KHz]
As a trade-off, IL increased from 1.8 up to 2.2dB...But I thought the slope was not sharp enough on high frequencies for the 40m filter...

Next steps:

- Properly place the component on a adequate board (this was just a demo board for "tuning" !!!!!!!!)
- Start the fabrication of the preamplifier !!!!!!!!!!!!!!!!!!!
With a calculated 21-22 dB gain, this will compensate for the my insertion losses, HI !!!!!

73
Ronan