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Author Topic: Add FM to a boat anchor?  (Read 1871 times)
K7LZR
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Posts: 137




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« Reply #15 on: May 19, 2019, 09:54:20 PM »

I once added FM capability to a Yaesu FT-101 but never tried with any of the Heathkits which I've owned. Best to find a good low cost 10m FM rig instead.
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N8YX
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« Reply #16 on: May 21, 2019, 07:22:28 AM »

I once added FM capability to a Yaesu FT-101 but never tried with any of the Heathkits which I've owned. Best to find a good low cost 10m FM rig instead.
Someone added FM TX to an FL-101 whose VFO I obtained as a spare part. They did so in the VFO itself.

Best way to perform that task would be to modulate the carrier oscillator, and source a mode switch with an extra position which would allow the various circuits to be controlled.

Its companion receiver already has FM capability (assuming you bought the FM accessory board). If I can find the right switch I may try my hand at modding my FL.
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K7MYR
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« Reply #17 on: May 21, 2019, 12:50:03 PM »

I'm still trying to get into my club's weekly nets; none of their repeaters are reachable from my home (at least with an 8W HT).  I was holding out hope for the one 10m repeater that connects -- then realized that my SB-102, which will work 10m, is CW or SSB, while repeaters are FM (even on 10m). 



Howdy,

I would obtain an older Motorola Syntor low band VHF FM radio that will easily do 10 and 6 meters.  Many are 100w output and operate on 12v DC

There's a couple of working examples on ebay right now.

73/Rick
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K9SUL
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Posts: 1




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« Reply #18 on: June 21, 2019, 12:39:02 PM »

This is slightly off topic (not for HF/10m), but might be of interest of some people.

The following is a 1966 article on the 73 Magazine by WA5CJG. You can convert an AM VHF rig to do FM.

https://k9sul.fayoly.net/ham/am_to_fm.png

More modern approach will be to use si5351A or si570 and a microcontroller (e.g. arduino) to generate FM at frequency.
Another possibility is to use a NBFM transmitter from late 1940s. I tried a Hallicrafters HT-18 and it worked well.
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G8HQP
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Posts: 971




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« Reply #19 on: June 28, 2019, 08:22:40 AM »

It is a long time since I studied any optics, so let me ask a question. To get significant diffraction, which of the following is required:
1. a corner with radius of curvature similar to or smaller than the wavelength
2. an obstruction with surface features which are 'unfuzzy' when compared to wavelength i.e. there is a sharp transition between 'wave passes edge' and 'wave blocked' for geometrical optics

These two criteria may seem to be similar, but 1 deals with what the wave 'sees' just after passing the obstruction while 2 deals with paths which just skim the surface.

If 1 is the answer, then presumably a hill would need a sharp summit/ridge to cause knife-edge refraction. If 2 is the answer than the hill would need to be rocky with no vegetation. Note that a knife edge has both properties so the name does not resolve the issue.
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KX4QP
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« Reply #20 on: June 28, 2019, 04:17:29 PM »

It is a long time since I studied any optics, so let me ask a question. To get significant diffraction, which of the following is required:
1. a corner with radius of curvature similar to or smaller than the wavelength
2. an obstruction with surface features which are 'unfuzzy' when compared to wavelength i.e. there is a sharp transition between 'wave passes edge' and 'wave blocked' for geometrical optics

These two criteria may seem to be similar, but 1 deals with what the wave 'sees' just after passing the obstruction while 2 deals with paths which just skim the surface.

If 1 is the answer, then presumably a hill would need a sharp summit/ridge to cause knife-edge refraction. If 2 is the answer than the hill would need to be rocky with no vegetation. Note that a knife edge has both properties so the name does not resolve the issue.

Based on my recollection of pinhole photography and related non-refractive optics (zone plates, for instance), I recall 2 as being primary but 1 also enters into it.  Generally, photographic optics (even non-refractive ones) try to minimize the effects of diffraction because it reduces image sharpness; for this reason, with lenses there's a recommendation to avoid very small apertures (so the diffraction zone as a percentage of the complete aperture area is kept small), and with pinholes, there's a "best sharpness" size even though strict geometric considerations would have the smaller the hole, the better.

Based on the combination, then, the best landform to obtain diffractive contact would be a bare ridge with a relatively narrow ridgeline.
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