God Bless America!
N1NKM's Hy-Gain adventures!
N1NKM's HAM page 17 |
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Hy-gain Boards |
NOTE to modem users: this page has several 80K+ pictures, which may take a few moments to load. Please be patient.
| N1NKM's HAM page 17 |
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Hy-gain Boards |
NOTE to modem users: this page has several 80K+ pictures, which may take a few moments to load. Please be patient.
This page contains photos of my homebrew adventures with converting "Hy-Gain" CB boards into much more USEFUL devices. ;) I obtained 4 of these from Fair Radio Sales in August of 2006. I suspect that they were the very last ones they had in stock, as they gave me four of them for only $10! Two were physically cracked, one severely. I didn't care, because the worst broken area only affected the transmitter, which I ended up removing from all 4 boards, anyway. (Yes, of COURSE I saved the parts! LOL!)
The most damaged board became a dedicated receiver for 1500Khz AM, the station I used to work for! (WFIF) I built it into a cabinet and gave it to a precious lady in my Church who couldn't hear WFIF because of STRONG interference from WDJZ, only 30 Khz away. This special radio 100% cured that problem, and she can now hear the Christian programming, clearly! :) I LOVE IT when I can turn JUNK into something that brings joy into another's life! \o/
The other damaged board became a 75 meter reciever, tuned via a pot. (It had an oddball PLL chip that required a significant amount of external support circuitry from a special digital microphone unit. The PLL was useless, so out it came.)
Another become a 20 meter receiver, with the PLL system fully intact, to tune in to PSK and SSTV. Since I used a very narrow x-tal filter in this unit, it is better suited to PSK, and it does that exceptionally well! It works "OK" for SSTV, but that stretches the limits of the filter, so the pix aren't quite "right". Still, it's enough to see what's happening. The radio is meant for PSK, so SSTV was just an afterthought, anyway. :)
The 4'th is now a 75meter receiver and an RF exciter for the "B.O.B." transmitter! (The RF exciter portion is still under development.)
BTW, did you know that by grounding pin four, the PLL02A goes to 5khz steps? You know, now! ;)
Details below! (Schematics may or may not be forthcoming... I didn't document this stuff too well, I just BUILT it! Hihi!)
The sensitivity of these converted Hy-Gain boards certainly rivals regular commercial-grade receivers. After all, these WERE commercial-grade CB radios, originally. They really do make pretty decent receivers! A REALLY AMBITIOUS project might be to make one into a QRP transceiver... but I don't really have the motivation to do all of that. Yet. A SSB transceiver would be a far better candidate for THAT. (15 watts SSB vs 4 AM for example.) If there are any SSB CB rigs "out there" with a PLL02a, I'd be interested getting my hands on them! :)
(Click the images for LARGE views. Click the BACK button to return.)
| Here's the PSK/SSTV receiver |
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So far, this unit is my "pride & joy" Hy-Gain project! :)
By switching just one line on the PLL chip (160Khz) I select either 14.070 or 14.230. (How convenient, eh?) Using the IF Shift, I can bring the desired freq range into the filter's passband. This also allows receiving weak signals in the presence of strong ones.
The switch on the RF gain pot serves as the selector. (SSTV thus has the RF gain at max.) The PLL locks the receiver onto the proper frequency, so no clarifier is needed. The IF shift does an excellent job with PSK, but because the filter is so narrow, SSTV is less than ideal. This receiver was intended for PSK, anyway. SSTV was just an easy "bonus".
| Inside the PSK/SSTV receiver |
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The small IF shift osc board was "snipped" from the Hy-Gain board that became the WFIF receiver. (See how BTN can be so practical!? Gotta love this stuff!)
| 75 meter variable-tuned RX |
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This one uses a pot to vary the voltage to the varactor diode of the VCO. Because of the large capacitance needed to move it from 37Mhz down to ~14, the full range of the varactor is only about 35Khz, but that's perfect, as it covers 3860~3890, which is the portion I was interested in covering, anyway. The "TX-offset" x-tal osc doubles as a BFO so that I can also copy SSB when needed. The tune control, itself, serves to clarify the signals. The ceramic filter is about 10Khz wide, so SSB reception has lots of "monkey chatter" above & below, but it works OK as a monitor radio. The real purpose was to listen to the AM Window, anyway. There are still a few GOOD guys there, and they are the ones I enjoy QSO'ing and listening to. The belchers & crude ones are a non-issue, as I tune them right out. (Go get 'em, Riley!)
| Bottom view of 75M board |
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The reason for those "piles of capacitors" is because I did not have any NPO's of large enough value, so i had to parallel the smallers NPO's that I did have. It works OK. If I ever get my hands on some NPO's in the 220pf range, I'll put those in here, instead. The VCO and the VCO buffer cans both needed these caps to move them from 37Mhz to ~14. (~14Mhz - 10.7Mhz IF = 75Meter band) *NOTE: After obtaining some new NPO caps, I've removed that unruly "pile". :)
The pot in the lower-left is the Tuning control. the resistor from the wiper to gnd helped to even-out the tuning range. (It was "bunched-up" at one end, due to how the varactor works.)
| WFIF, 1500Khz receiver board |
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Here's the board that receives WFIF. I replaced the first two RF cans and the 10.7 IF cans with standard AM radio oscillator coils. With a 22ph cap across them, they resonate near 1500. Another is used as the LO. There is a small trim-cap in the ckt where the 10.7 Mhz can used to be. This adjusts the RF feedback here, providing for some Q-multiplication and improved selectivity. This was done to compensate for the removal of the 10Khz ceramic filter. I wanted ~20Khz total bandwidth, which this now provides. The sound is quite good.
| WFIF, 1500Khz receiver |
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Here is the 1500 board inside it's "home"... a cheapo stereo speaker cabinet. :) It really cranks pretty loud, and sounds decent. The board is mounted upside-down to the top of the cabinet with the power/volume control nearby. The small gel cell at the bottom was used only for testing. The antenna is simply 6 turns of wire wound wround the inside of the cabinet. Sensitivity is quite good. Having three TRF stages followed by 3 IF stages helps! :) I later added shielding to the loop and made a few other refinements so that this unit would pick up WFIF's signal within the very powerful near-field of WDJZ, which is only 30Khz above WFIF! I used a UL Listed "Wall Wart" to provide power, and gave this radio to a lady in my Church. She loves it! :)
 It once struck terror into the hearts of LIDS, everywhere... Whatever happened to this instrument of law and order?? |
*** DISCLAIMERS ***
(Keep the lawyers happy.)
This information is presented as educational information only. No guarantee is made as to its fitness for any purpose. All risk is assumed by the person who choses to use this information. While the author's experience indicates that this proceedure was effective, any attempt to build/modify these devices IS AT YOUR OWN RISK. Extreme care must always be excercised, this is at the builder's SOLE RISK.