40m PSK-Warbler

Unpatiently I was waiting for my PSK-Warbler kit to arrive. Just in time, it did. Building it was very very easy, modifying it was relatively straight forward. Modifying? - you may ask yourself, yes, even a nice rig like the Warbler may be modified.

The Plan

Originally the Warbler is designed for 80m using color burst crystals for TX and RX ladder filters. For reasons of W1AW, the Warbler is using a b.f.o. above the filters' frequencies. Given that the Warblers are supposed to be used for PSK, this is an option, PSK-software can be set to operate on the lower side band. 

The modification described here is supposed to get the Warbler running on 40m, with as few changes as possible. The modified Warbler should also serve as a WSPR transceiver. Actually, this was the main point on doing this mod in the first place.

The Modification

This is what I did (please grab a circuit diagram):

1. the b.f.o. xtal changed to 7.038MHz
2. all filter xtals changed to 7.040MHz
3. C13 -> 47pF
4. L3 -> 10µH
5. C10 -> 100pF
6. C11,C12 -> 470pF
7. L2 -> 1.1µH (17 turns on T37-2)
8. C3 replaced by 2.2µH and a polyvaricon-trimmer in series

Points 1. and 2. are somewhat obvious, I believe. The crystals are available from Rich N4ESS.

Points 3. and 4. change the passband frequency if the C13-L3 series resonance circuit of the receiver to the 40m band.

Point 5. matches the coupling between driver and final to the operation frequency. This part of the mod may have to be revisited. 

Points 6. and 7. bring the low pass filter response to something above the 40m band.

Point 8. allows for variable pull of the b.f.o. to 7038600Hz. I used a combination of a polyvaricon-trimmer (4...18pF, I believe) and a 10pF NP0 capacitor in parallel. This is certainly the part of the modification in which some experimentation is required, since tolerances and different cuts or series capacitances of the b.f.o. crystal play a role in that game.

First Results

As I mentioned before, WSPR is certainly a main point for the little great rig. The first night out, RX only, at a hidden G5RV-jr, the following are among the decoded stations: VK6POP (14190km), VK6BN (14188km), W4PJZ (6781km), NB3N (6137kM), K4YO (5954km). 

I did TX, however, only once for testing, with very low power. For regular WSPRing, an enclosure would be required. Presently, the Warbler is laying open on the table, next to the grabber computer.

Next to WSPR many other modes were detected on the spectra, e.g. several types of PSK and even JT65. I am sure that the 40m Warbler will be a big hit! Dave K1SWL may put more on his webpage, stay tuned!

Warbler on WSPR mod

Spent some views on the Warbler's design again, and came to the conclusion that a single crystal in the either TX and RX filter would probably be OK for WSPR and AFSK-QRSS.
For RX, three crystals are foreseen, assume, we would be using one only, one xtal location could be shorted and the other unused one could be populated by a capacitive trimmer, for tuning the filter's response.
For TX, two crystals are foreseen, however, I believe a single one would do for sideband rejection... w/o any further periphery actually.
Reasons: multi-pole filters are employed to widen the filter's response... at a bandwidth of 200Hz (WSPR) of 300Hz (QRSS+WSPR) there is no reason to bother with widened bandwidth, that's what a single xtal has proven to be able in my sub-harmonic DC-RX already.

Warblers on WSRP II

There is a reason for me t have ordered two kits. The 30m version I did explain in an earlier post.
The Warbler can be equally easy (if not even easier) modified into a 40m WSPR transceiver.

That what needs to be done:

• use 7.040MHz crystals for the filters
• use a 7.038MHz crystal for the oscillator
• pull the oscillator frequency to 7.0386Mhz
• adapt the PA and low pass filter to 40m

DONE!

One could consider using the sound cards audio signal to key the transmitter, there are simple solutions out there. See also Dave's PSK20, which is audio keyed. Documentation on Dave's webpage.

Warblers do WSPR

Dave's Warblers come with color burst crystals, that's good, so we could use those for AFSK QRSS. OK, one tiny mod here, we need to get to the lower side of the crystal filter, but that should be all....

Now, what got that to do with WSPR? Ahhh, well, nothing really.... sorry about that, just another mod.


So, WSPR here it comes, assume we would be inserting 10.140MHz crystals, instead the 3.579545MHz ones. Yes, again we would like the oscillator to do its' thing below the filter frequency...
For the rest, some resonant stuff (behind the buffer) and a bit of front-end need to be recalculated.

I am convinced that the Warbler will do a perfect job as WSPR transceiver and METP/Grabber-RX on 30m, more or less OOB.