Exploring Upgrades and Improvements!
Hey guys (and gals) great news: The JABOM is cranking right along. Yesterday on a band that seemed virtually dead (and using the linear amp @ 600 watts out) I worked Portugal in mid-afternoon. The signal reports are excellent and I couldn't be more pleased. It is a testament to the design and circuit topology. The you tube video documents the receive performance. The on air contacts demonstrate the transmit performance.
While not having all the bells and whistles of commercial rigs the JABOM demonstrates that solid contacts, including DX contacts can be made using homebrew equipment. You only to get off the couch and now that March Madness is over --heat up that iron.
3/26/2018 ~ More work on the front Panel.
The Before C Change:
Changed on 3/25 to a really super large LCD Display ~ No Squinting here!
The After C Change:
That is the advantage of having a CNC Mill -- you can make Escutcheons that hide some of the ugly former installations. The material is a piece of single sided copper PC Board and the plan is to paint it black.
I received a letter of chastisement regarding what is on the display. The top line shows 14.200.000 MHz which has been pointed out to me is incorrect as it really is by convention the following 14.200.000 Hz. It would only be correct if it read 14.200 000 MHz which results if you remove the second decimal point. The person so notifying me stated the second line was correct. So my next iteration of the code will remove the MHz and in its place will be either USB or LSB. The bottom line will be changed to include my call sign.
You have to admit --this has a lot of drool factor!
One of my most successful projects was what I affectionately called JABOM which was the subject of an Article in QRP Quarterly. JABOM was an acronym for Just A Bunch Of Modules. At the time it was built the rig transitioned from a varactor tuned VXO, to one with a variable capacitor VFO to finally to digital VFO sold as a kit from K5BCQ. This kit used a Si570 and a non-backlit, non-standard LCD display. It was difficult to read but a really great digital VFO. I was in tall clover.
BTW just today I worked a station in Hawaii barefoot with this rig. So it speaks right up.!
The beginning of this project was a collaboration with one of QRP Quarterly Editors who suggested a project for a 17M SSB transceiver using a homebrew 4.9152 MHz Crystal Filter. While the thrust was for 17M I added a module that with a three pin jumper on either end of a Band Pass Filter/Mixer stage could make it band switch between 20 and 17 Meters. I even had it so that the LPF was installed outside of the rig inline with the antenna. Thus to change bands: move the two jumper pins and install a different LPF inline.
The K5BCQ kit was cost effective but from my experiments not easily adapted to backlighting. I kept a small flashlight handy so I could read the frequency. In time I bit the bullet and moved up to the AD9850/Arduino Uno and "Cool Blue Display". That is in the rig before today (3/25). For the BFO it had a analog crystal oscillator --not easy to switch sidebands. Thus now it is time to transition to a Si5351 so that we have both the LO and BFO.. Thus that is the next upgrade. OK Scroll down and drool!
But let me tell you about the JABOM basics and the method of construction, as I believe this is what makes this rig so outstanding. I might also add it is of my own design and has some innovative features which are detailed below
- JABOM was specifically designed around modules built inside homebrew Copper Boxes. The idea is that you could upgrade modules and all that was needed when making changes was power and shielded cables --yes shielded cables lots of them. The copper shielded boxes made this bullet proof from unwanted coupling to reduction of possible feedback paths
- This was the first time I tried a "single pass" IF versus the bilateral approach which is so popular today. A sub-set innovation is that on transmit this module has an added adjustable gain stage. The 4.9152 MHz filter was marginal and subsequently replaced with a GQRP 9.0 MHz filter. Because of the 9 MHz IF this mow eliminated 17M as a band of choice. Thus one mod was to now have the rig exclusively on 20 Meters
- There was a method to my madness for having an independent transmit gain stage in the filter module because on receive the output was fed into the W7ZOI Hycas circuit. This Hycas Module has the product detector installed on the same board. I modified the Hycas to include an S Meter which is admirably done with an S Meter from a defunct HW-12 rig. Words can't describe how well the Hycas works in this rig. Disable the Hycas AGC and the sound is loud and distorted. Put on the AGC --all smooth and just the right amount of attack and decay. Yes I did diddle with the time constants in Hayward's design.
- The audio amp is a 2N3904 driving an LM386. The Microphone Amp NE5534 and Balanced Modulator, an SBL-1 is another separate module box.
- The RF chain is the driver stage from EMRFD and the final a 2SCc2166.
- Above is how the rig originally looked with the K5BCQ display and a really "junkie" meter from a Galaxy V rig. Basically it looks crude and the paint and change of display makes it a whole different looking rig. This is definitely not a playboy bunny look or even a "porn star" look --but the "knobs" are large. It was desperately in need of a makeover. It will only get better from here.
- Stay tuned for the next upgrade to the Si5351 and a new LCD.
- 73's Pete, N6QW