Mohawk SSB reception

[AB3FL]

When I listen to SSB on my  Mohawk, I have to move the tuning around.  For USB I can put the VFO right on frequency, but for LSB, I have to lower it about 2kc on 80M band and down 4KC on 40M band.  Is this a normal funtion or a problem with the LSB/USB oscillator in the IF, such as drifted parts?

thanks

Tom - AB3FL

[AB3FL]

thanks!   I actually just found the tuner alignment manual (which I didnt even know existed)   I figured that it wasn't working properly


Tom - AB3FL

[WQ9E]

I agree with HRO that the Mohawk does unfairly get a bad rap and it does have a lot of gain!

I have two Mohawks, one paired with an Apache and KL-1; the other with a Marauder and an HA-10 and the receivers both work well on all modes.  The Mohawk/Marauder station also has the Heath 6 and 2 converters along with a VHF-1 and HX-30/HA-20 combo.

The engineers at Heath were probably "inspired" by the Hallicrafters SX-96/100/101 family of receivers and there are some similarities evident.  The IF gain control on the front of the Mohawk is roughly equivalent to the gain set control found in many receivers; the difference is that the Mohawk has its control on the front panel whereas gain set is normally an alignment step.  If you run the Mohawk with IF gain fully advanced it is not going to work as it should and the best setting for the lower bands is where the noise just registers a bit on the S meter.

Like the Hallicrafters low IF receivers, the selectivity is very good for a non-crystal or mechanical filter receiver but the alignment is critical.  To do it right you need a signal generator that goes down to 50 Khz.

However, before you align the final IF check that both conversion oscillator crystals are on the correct frequency.  The easiest way to do this is to check them by tuning for zero beat in an external receiver with an accurately calibrated digital readout (unless you are careful, a frequency counter connected to the oscillator can easily make a slight change in the frequency).  The proper frequencies are 1632 and 1732 depending upon the sideband selected.  This works with the first IF (1682) to provide the final 50 Khz. IF output.  If one of the crystals is off then following the basic alignment instructions won't work.  There is a workaround if one (or both crystals) are only slightly off frequency.  Say for example the low one is correct at 1632 but the high one is 1734.  The difference between the two is now 102 Khz. (1734-1632) instead of the correct 100 kHz.  If you cannot find a replacement crystal that is on frequency you could instead align the final IF for a 51 Khz. output instead of a 50 Khz. output and retain the proper relationship between sidebands.  The first IF would now be aligned at 1683 but since it is fairly broad this is not a critical alignment.  The BFO must be adjusted for zero beat with the final IF when at zero.

I hope this helps and enjoy the Mohawk.  Like HRO said it sounds very good on AM and if you get into "battle conditions" the selectivity choices and selectable sideband work very well.  The best way to tune on AM is to do so with BFO on and set for zero.  Zero beat the AM signal and then you can select sidebands at will to choose the least interference (once tuned however, turn BFO off).

Rodger WQ9E

[AB3FL]

thank Rodger, that worked.  The crystals are off.  Does anyone have the 1632 and 1732 crystals?   I shifted the IF for now and the lsb/usb works properly.  I also spent several hours today aligning the front end.

Tom - AB3FL

[WQ9E]

Tom,

You are welcome.

If the crystal frequencies didn't require a major offset in the final IF you are probably better off staying with what you have now.  It is quite possible that any old crystals you acquire from a "parts" Mohawk will also have drifted and if you order new you will need to provide the proper crystal loading info to the company who makes them or they will be off frequency.  As long as your "new" final IF frequency is within a couple of Khz. of the original value the transformers and their associated passive components are fine and will work as intended.

Rodger WQ9E

[AB3FL]

Actually crystals were fine (According to my pro 3).  The IF was out of wack.  Everything is really working perfectly now.....thanks everyone for all of the tips...


Tom - AB3FL