I sure miss the bargains. For 25 years I hunted eBay looking for some real bargains. Guess I got lucky as I found many inoperative radios that in their heyday fetched a hefty sum. Most of the stuff I did find often was acquired for somewhere between $50 and $100.
Once I even got a National NCX-3 and the matching NCX-A supply for $69 total! About $1 fixed it and that was for the S Meter circuit. The power supply had a filter cap, (a new replacement) that was not actually soldered to anything. I even got a couple of SBE-33's for around $45 each -- the Collins Filters (both good) are worth more than that.
But today, when a Heathkit DX-20, which is inoperative, missing parts and is listed for $200, there is something wrong. I would have paid $30 for it but not $200. Junk is being sold for exorbitant prices.
There is a story here and that is forget that high priced junk and build something. There are many great projects out there ranging from some basic instruments like SWR Bridges to Direct Conversion Receivers. These are not toys but real radios and test gear that can be used in the shack.
You also have the You Tube videos that show you just about how to do anything including fixing a water intrusion problem in a 1995 Jeep Wrangler to building Double Balanced Mixers both from N6QW.
30dB T Type Pad with tap points at -10 and -20 dB
Plot of Attenuation across the HF Bands
Club projects (think group grope) offer a chance for peer builds where technical help (some good and some bad) abounds.
Some starter suggestions:
Test Oscillator
RF Probe
QRP Dummy Load ( 10Resistors)
Michigan Mighty Mite Transmitter
Direct Conversion Receiver
Arduino based Signal Generator
QRP SWR Bridge
30dB T Type Attenuation Pad
Our last item in the list is shown with the LT Spice Simulation along with the plots in the two photos above. The T Type Attenuation Pad has many uses in both our homebrew Receivers and Transmitters. Wes W7ZOI has a project like this in SSDRA which he uses as a regular piece of bench test equipment.
As an example you can run an empirical test (that means like just a go no go without details to the 10th decimal point type test). Connect your newly built homebrew receiver to your antenna and using a weak oscillator across the room see if you can pick up the signal.
I try to find a spot in the garage about 10 -15 away. Once you hear the signal then insert the T type Pad between your receiver and the antenna. If you still can detect the signal you know that you can hear signals - 30dB down from your reference point.
Now the nit pickers will say but there is RF floating all around the room and the signal is finding its way into the receiver around the T Type Pad. Well I have answer for that: A steel filing cabinet with an empty drawer. Insert your receiver inside the cabinet and it is like a shielded room.
On transmitters, the T Pad can be inserted between the Driver and Final RF Amp to test how much drive it takes to produce a certain amount of RF. The -10dB and -20dB points are very useful for this test.
Now for the potato head who bought 1/8 watt precision resistors and connects this pad to their IC7300 running 100 watts (it is a dummy load in effect ) will smoke everyone of those resistors. Care must be exercised on how much power you run into the Pad. Above 1 watt will smoke things!
I can see the emails now so where do I find 25.97 and 35.14 ohm resistors. Check Mouser and Digi-Key.
So what happens if you you use 24 Ohms and 36 Ohms -- you bought a resistor mix from Banggood (love that name) and without any care or actual verification of the values simply plugged those into the circuit. Here is the LT-Spice circuit with those values.
The Attenuation is close on -10dB but almost 2dB off at -30dB
So get the precision resistors as you want accurate measurements. Get Pads from W1REX and make it look good just like it works good.
73's
Pete N6QW
Funny but absolutely true story. In the Mid-70's McDonnell Douglas sold commercial aircraft kits to the PRC (Chinese). As a part of the kit sale we provided technical information on aircraft testing. Yes, giving away the family farm. I was a part of a team from the Engineering Laboratories who met with the group from the PRC. One day the subject was static testing of the air-frame and our presenter said the data they took on the test floor was calculated with a slide rule (we didn't have any HP-85's) accurate to two decimal pints..
Suddenly a conversation ensued in Chinese about ignoring slide rule data beyond two decimal points. The gist was that they would not stop at two decimal points but hand calculate things to at least 6 or so decimal points.
Later that day we got a debrief from our CIA who was sort of watching things. The issue was not accuracy but the blame game. If one of their built planes crashed, the Chinese would have to supply test data to their CIA (Chinese Intelligence Agency) that all calculations were carried out to 6 decimal places. Use the precision resistors!